nothing in life is perfect. simply a matter of perspective. no matter how you set it up, you will eventually want to change something. so just make decisions and move on
I don’t like to modify standard things to fit and I think it’s better to design the host system to accept standard parts. On that premise, I would mount two small bus bars to accept the BMS cables and then run heavier cables from the bus bars to the battery and the breaker.
Leave the poor BMS alone and avoid more problems. Just connect externally to your 16mm cable. Bolt on using the existing lugs or cut off the lugs and do a good soldered splice. The short length of the smaller cable won't be significant. Whatever you do, heat shrink over the connection, preferably two layers. I make one layer 3-5cm longer so it extends past the shorter layer a cm or two on each end.
While soldering would be possible, the easier way would be to extend the cable with a crimp connector. You can get thosemin a similar style as the ring lugs, just a metal tube with hole on both sides and a center indent.
My advice would be to bench test the BMS before changing the wires. Hook it back up to your battery and attach an inverter and draw as many amps as you can then check the temperature of the cables to make sure they don't overheat. I run the same Bms with a 2p16s 560ah battery connected to 4600w of solar and a 4400w inverter and never had the cables even get warm.
Yeah, I did that already in the last test with the JK BMS and charged the vehicle form the battery over 6h or so. The cables did get less than hand warm. In the battery shelf, I will pull 80A max per battery (that's the set trip current for the breaker at least.
@@OffGridGarageAustralia sorry, I remember that video just didn't remember if you tested the temperature of the cables on the bms. If 80a is your max draw you have nothing to worry about with the cables that came with the bms.
Concerning cable lugs problems - we face such problems very often during various progects. And it is not a big problems - we also use files, metal scissors to cut lugs to appropriate dimensions. Also, attention must be paid to flatness of lug'g contact surface. Because some lugs could be produced by press-and-cut machine in such way, that lug would have non-flat surface at the edges. That will prevent its "full-surface" contact with busbar or CB's terminal. We detecting these surface problems by observing lug's edges and fixing it with filing adges to flatten contact surface. Maybe, it is not an issue in yours lugs, but we often observe these defects at our domestic (russian) made lugs, especially at sizes from 35 sq mm to 150 sq mm. So, it is our rule to check flatness of lug's contact surface before mounting it to busbar.
I love little chalenges like the issue with the cable lugs. The feeling of accomplishment is great when it all finally gets together. Wish i had more time for my hobby
Andy, you may want to do a test to insure the Bluetooth signal from the BMS can communicate from inside the aluminum walled shelf. Better to know now if you need to mount the BMS on an external wall for the sake of that signal.
That's not a problem at all. I have done a lot of testing with the electrical cabinet since the MPPTs went into it. No issues at all and minimal loss of signal if the dorr is closed.
Andy, do not change the original wires. The bigger the cross section, the more heat will need to have it soldered. You need in those points a VERY good soldering with very low resistance and high mechanical strengh. You definetivelly will face big dificulties and frustration if try the replacement (and maybe even damage the unit). Also, the tin will enter inside the coper wire due to capilarity and will make the wire hard as iron making imposible to bend near the soldering point. Don´t do that. As solution, cut away the original hole terminals and use a junction sleeve to convert 2x10mm to 1x35mm (or whatever). You can crimp it or solder the junction assembly. As a second issue, the resistance of the balancing leads is not so important. 30 mOhm is really not an isue, since the current through the leads are just a few amps and the looses in that resistance will be part (small portion) of the balancing process. If the diferent lenghts are important or not depends only of the software: if the individual cell voltage is measured without load (before sinking energy to be transfered to other cell) or loaded (during the energy transfer peak). In the first case, since there is not current through the balancing wire, there will not any drop (no matter the lenght). In the second case the current through the wire can make the measurement influenced by the diferent lenghs. Could you take apart the white thermal tape over the transistors and show us what transistors JK is using in both ways? (charge and discharge), Thanks in advance, Jose (Madrid)
If it was me I would just clip off the lugs on the BMS wires and combine them into a single high quality barrel crimp and terminate the other end of the barrel crimp with the single heavier cable but I am guessing you won't be satisfied with that. For my own system I have the BMS terminated on one side with a 150A fuse to the busbar and on the otherside I have it terminated to a single post and then have that post connected to a 5 foot 1/0 AWG 105C cable. Having the separate posts makes it easy to swap the BMS when one potentially dies.
I personally would just solder on new cables, the amount of heat that those components near it are rated for is pretty high, plus they don't appear to be on the same pad directly, so the heat will dissipate through the circuit board vs heating up 1 single component. Just remember the maximum junction temp of the inside of a transistor is something around 150c and the body can withstand heat up to 350c directly.
Hi Andy. You can take a copper tube of the required diameter on one side to insert two thinner wires, and on the other the wire is twice as thick, and crimp the tube.
You’ll always have a solution to this situation . You might can try L ing the single orange wire strip end across the soldering terminals and then out the sides . May the solar be with you .
personally I wouldn't mess with the original soldering. The main concern is if you will be able to solder it as precisely so no connection is done to the case - a tolerance is almost inexistent there.
I’m using a 4 ga crimp barrel splice with the two 7ga in one end, 4 ga in the other. I’m not installing fuses on 26 ga wires. If they ever short, I’ll just install a new BMS and leads. I’m not worried about a fire, my batteries are encased in 1/4” concrete board. No wood, no plexiglass, no plastic sheets.
EE here. 10-20 mOhm is about right for those little fuses. It's the resistance of the tiny little fuse wire that is inside the glass body, compounded by the crappy nickel plated steel wires they use. You'll find the same lead wires on leaded resistors.Try measuring one of those some time. As far as the importance of the resistance, it really only matters if you want the 2nd and 3rd decimal point to be really accurate. If you're balancing to the 3rd decimal point, you need to know the cable resistance, and yeah, the JK has that capability and you should use it. For measuring 0.001V changes, cable resistance can be a big deal. For situations where current is flowing, like this one, it's a fact.
The current through those fuses should be close to zero, though. So the voltage is ~0.02 ohms times 0.001 amps = 20 microvolts. Oh no, we're going to see 3.5V less 20 microvolts...
@@mozismobile Yep, but if the system as a whole is counting to the 3rd decimal point, 125mOhm makes a bigger impact, and yeah, it should be factored for. And since the balancer is working on balancing while measuring current, make that 0.001A into 0.5 or 1 or 2 amps, and all of a sudden it actually matters.
I think the resistance matters. A bit. We are charging the cells to say 3.65V max voltage. If the BMS allows them to charge to 3.7V they will be overcharged already. If we assume a max balance current of 2A at 40mOhm (without fuse) we can have a voltage drop of 80mV. Including the fuse this could be 100mV drop then, so 20mV difference. That could mean the cell is at either 3.65V or 3.67V. There is your bit. Does it really matter? Maybe not as I won't charge them to 3.65V anyway...
@@OffGridGarageAustralia realistically you may have 100mOhms or more from the battery to the BMS. With a 2A balance current all of a sudden it makes a real difference. Your wire, connections, and the terminal block will all add a few mOhms here and there and they add up fast. And remember, a bad crimp can cost you 100mOhm without even blinking.
@@OffGridGarageAustralia I have a feeling the voltage is measured, then the balancer is activated, then the voltage is measured again... which means there is virtually no current flow(no voltage drop) down the wire at the point of a voltage measurement. The input resistance of the IC which measures the voltage will be so high that a voltage drop due to the cable resistance will be negligible. If I am wrong and the voltage is measured whilst the balancing is happening, then maybe there is a way to just correct the voltage reading within the BMS settings? you can just measure the voltage of the cells with a good quality multi-meter?
The BMS PCB looks a little shiny so they might have conformally coated the board after it was assembled. That would make soldering the larger cable a little more difficult (removing the coating as needed). You would need a high wattage soldering iron too. If you are able to heat one connection so it is hot enough, then the other 3 connections would probably melt also. Having these connections on both sides of the board make it even more difficult. I would just use the existing wiring as is and use your thicker wire to connect the existing bms cable lugs to the battery/circuit breaker.
Andy, those fuses are designed for PCB use. They're soldered right onto the board and the excess leads are cut off keeping the resistance of the fuse as low as possible. Also, T-Shirts came in last week. Can't wait to see the expressions when people see the shirt and get that WTF? look. I might even meet someone who watches you here in Canada, who knows?
Thanks Bill. Yeah, I was waiting someone said something about the shirts when I wear them in public. There will me more soon... I'm not too worried about the fuses and overall resistance. The BMS won't measure and balance at the same time.
Hahaaha, I won't touch it. Just wanted to have a look at the quality of their soldering. 😂 The 7AWG cables are actually far too thin for 200A continues load...
@@OffGridGarageAustralia is it silicone insulation on those wires? If it is then I would be much less concerned about running the BMS at its max rated load. The cable current rating is based on much lower melting point insulation and quiet high ambient air temperatures, so silicone insulation has a higher melting point and is less impacted by high ambient temperatures. It’s much safer for wires with silicone insulation to run much hotter, and although alarming when you take temperature measurements of the cable, in fact it is not an issue. You can test this easily by trying to burn the insulation with a cigarette lighter, if true silicone insulation then it will not be affected by the cigarette lighter and will remain intact.
So here's some technical advice for all you people who, like me, love reading the comments. Get the T-shirt, get the Hoodie, that way on those days when the sun doesn't want to come out and play you can wear both, be warm and totally stylish. My ageing 48v SLA battery bank hasn't dropped below 85% SOC since I started wearing them and to top it off I had a record input day with of 20.4 KW/H last Sunday, that's 4.088kWh/kW efficiency. Even my Solar setup gets inspired by Andy.
Why does the resistance (assuming it's small) make any difference? doesn't the BMS measure the voltage with very minimal current so small resistance won't make a difference? Also, I won't touch the BMS. If anything, I'd solder a thicker cable do the blue/black cables a few CM from the BMS (if you don't want to use a stud to connect) - you can even connect 2xblue/black to one very tick orange cables to have less wires all over the place and make the setup cleaner.
The resistance should not make a difference. As you said during the measurement, there is no current flowing and while balancing (2A max) it does not measure the cell voltage of this cell anyway. Points about the cables taken. Thank you.
Closing the case of the BMS (without electronics of course) and than use your conical dril to enlage the cable holes to the desired dimension. go for it.
I agree with the earlier comments but I think you should put the BMS in a new bow, cut the P- and B- cables outside the original case, extend them with your preferred cable inside the new box, with the correct length, drill holes in the new box and pass the extended cables to the breaker and the battery. Just my 2 cents!
It is good idea to replace original cables to 2 x 16 sq mm ones. I think, that BMS and its MOSFETs will not overheated to failure - all BMS PCB will act as a huge heatsink. More likely, BMS PCB must be preheated in busbars zone to allow successful unsoldering existing cables and soldering a new ones. Also, suggest to spread strands of 1/2 of cable's core along busbar at each side to lower soldering's height and to ease soldering of huge amount of fine strands.
I at the point where you have opened up the BMS. My thought is that you could extend the bus bars to outside the case ending with proper lugs. Overall for the effort I think it would be best just to use the existing wires and separate lugs. More straightforward to replace the BMS. Maybe put a vertical stand on the shelf next to the battery. I believe you mentioned previously you wanted to make that area a compartment so it out be a perfect area to mount the BMS to. The voltage test wires should all have the same resistance and length. Adding more resistance with fuses will not matter much for purposes of measuring the voltages of the cells which is relative. If I understood you don't want you have the shelf fronts acrylic because acrylic is combustible. You used it for the shelves... There is also more expensive polycarbonate.
Do not change the wires you will end up with a lot of problems. Just connect the wires to a regular bolt and put shrink tubing ( 2 layers perhaps) around bv it. You should not have any problems. Why would you use the fuses anyway. These are just for balancing. It's not like 18650 cells. Always looking forward to yet an other episode.
I would never mess with the pre-soldered cables. I know my limits.😬 You could solder extensions to the existing cables. I'd like to see how that works. This could be achievable for me as well. As they say: Heat shrink and paint make me the solderer I ain't.😜
I would go with the terminals if I extend the cables of the BMS, not soldering them to thicker cables. That is totally messy and I have not seen a good and clean result. Soldering directly tot he PCB/bus bar of the BMS... I don't have the tools to do that professionally either. It would be ugly...
Bonjour ANDY, dans la continuité des réflexions diverses pour cette armoire ! très intéressant l'évolution de la positon du BMS. bonne journée et dans l'attente de la prochaine vidéo. ;-)
I would like to share my bank with you but unfortunately can not share pictures here. Anyway, instead of soldering large wires inside BMS use the same two wires with one terminal and connect with the terminal block.
Andy, don't mess with re-soldering the BMS leads. They are sized to match the capacity of the BMS. Terminate the ends of the BMS cables on the one stud terminals on each side of the BMS then use whatever size cable from there to the battery and breaker. Realistically, how much will you be pushing the limits of the BMS capacity in real life usage? Probably not often at 48V.
The cables to the BMS are actually undersized. By quite a lot. It's just a 7AWG/10.55mm² cable with a max carrying capacity of ~55a or each cable. The BMS is suitable for 200A continues current though... I personally won't push more than 80A through the BMS, 100A for a short time maybe...
Hammer and anvil will straighten them right out. Compare the 6mm and 8mm -- is the body the same size with a different hole? If so, then stock up only on the smaller hole size. In commercial production you need to just grab the right lugs and go, but for home use I find it effective to stock only the smaller hole size and drill it out when I need a larger. This reduces inventory by a factor of 3 or 4, while also helping to qualify for quantity discounts.
Flip the + and negative on the breaker and move the Bms to the top and mount it to the right and you have tons of room and you can extend the cable on the bottom of the shelf above to the battery.
Just a thumbs up with your stud mounts, if they are the same as I have used, they can be modified to accept 2 x 8mm or 1 x 10mm bolt through the plastic, this my give you a option for cables, you might notice the holes in the plastic already there for these options, the back cover pops off
I think I would cut off the 8mm lugs and extend the cables with the 35mm cable. Use some sort of crimp and solder to make the join. And you could do a test before hand to see what the losses would be. And you can make the tails on the BMS as short as you dare.
I'm actually thinking of cutting the cables even shorter as they are right now. They should have the same length though for equal current distribution onto these bus bars in the BMS itself.
Hi Andy, thanks for showing the inside of the JK BMS. Why not crimp the extension cable to the BMS, saves a lot of soldering which will need a lot of thought not to break the BMS?
I'd definitely extend the existing cables. Don't even need a bus bar. just sandwich the two lugs either side of the extension lug, or cut them off and solder a splice.
A little Flux on the bms and heavy solder on the cable tip. Bms should be just fine. Looks like they used plenty of heat on the one side and it works fine. (#Quitoverthinking it Andy). This build is going to turn out amazing.
Yes do it, connect new wires to it then test it to make sure it works, test it to max power output for 30mins and see how hot it gets. To be honest i think you would be fine soldering the new wire in without any problems
Servus Andy, every clamping point is a source of error. Your project will be a collection of clamping points. You already have 9 clamping points on the load side until you reach the upper copper rail. In my opinion, it is easier to solve with cables than with copper bars. But it looks cool with the rails. Cutting a thread in the copper is not enough. Then you would have to counter with a nut at the back. To loosen the cable or turn the cable lug, you have to open two things. It is easier and safer to drill a normal hole and use press-in nuts. Everything else has already been tested. Best regards from fu**ing foggy austria
I thought about using cables instead of the bus bars. It would have been very messy and confusing, a lot of cables going back and forward. I still would have some bus bars to connect all the cables together anyway, so there is really no benefit with having cables instead of bus bars. The connections are not a problem at all if they are made correctly.
As for your fuses... you just need to snip out a section of the BMS sensing cable that has an equivalent resistance to the fuse that you are adding.... or recalibrate the BMS to allow for it.
I ended up keeping the cables as they were and crimped individual lugs onto the cables. You will see this later when I mounted the JK in the battery shelf.
If the lugs aren't perfectly flat you can rotate the changeable dies in your hydraulic lug crimper upside-down to give a flat surface and use it to flatten the lug perfectly flat ;)
0.053ohm @ 2 amp = 0.106v drop down the cable when there is 2 amps flowing. V = IxR. I'd be interested to see if the resistance affects the current balancing as I assume the discharge transfer is constant current?
Andy, can you run the numbers and explain to those who don't understand, just how much difference those extra milliohms would actually make, and if that is a significance difference to NOT having the fuses in?
It would not make a difference at all I think. The BMS measures and balances at different times so the resistance is not of a concern at all. Older or simpler BMS may handle this differently and it could be of an impact for these system but with the smart BMS, they will be totally fine.
Hiya! I'm guessing the chip doing the voltage measurement in the BMS will have very high input impedance: hundreds of k-ohms at least. The measuring current will be very small and a few milliohms worth of fuses and cables should not have an appreciable effect. (If you can figure out what chip the JK BMS is using, this might be specified in the datasheet.) Good luck!
@@OffGridGarageAustralia Probably the BMS is not measuring the cell voltage when it is balancing 2A. Probably it will measure the voltage "between" 2A balancing cycles.
Even an incorrect bolt/screw tighten (i say incorrect,not "much more" or "much less") will give you more resistance than the fuse. That is why i think it is very important to check connection with ohmmeter
'It's called bended cable'! As my teacher used to say 'You might be sitting at that back making jokes but at least that proves you are paying attention'. Personally I would make the cables from the BMS as short as possible and change the terminals to ones with the correct size holes and then connect them to the single pole bus bars that are then connected to much larger diameter cables. This way you have absolutely minimised voltage drop as much as you can. A short section of undersized cable within a longer section of correctly sized or oversized cable will have little or no effect. You have to calculate the voltage drop over a length based on all the cable used in the circuit. Messing with the solder will be a total disaster in a DIY environment.
Thanks Chris. It's not so much the voltage drop I'm concerned about but more the heat which could be created in this thinner section of the cable. The 7AWG cables are undersized by 50% and should have been 2AWG for a 200A BMS.
@@OffGridGarageAustralia Are you sure about that. 7AWG is 16mm squared cable and basic single core welding cable of that size has a nominal current rating of 110A. You have two cables so combined they are rated for 220A. Yes one size up would be better so going to 20mm but jumping to 2x35mm seems a bit extreme.
@@OffGridGarageAustralia Ooops. just realised 7AWG is actually 10mm cable and so rated for 70A I believe. So you have 2x70A = 140A so yes it is rather undersized for a 200A BMS. Never could get used to AWG sizes compared to mm2!
Servus aus Austria Schönes Projekt Videos und Tests sehr lehrreich. Würde vom Hauptschalter Kupfer Schiene verwenden kurz ,da kann man dann beidseitig das BMS klemmen . Kannst dann ebenso mit deinen einzelklemmen eine zweite kleine Schiene für BMS Eingang und weiter zu den Akkus .Hast dann auch die Möglichkeit Kabel parallel zu verlegen Lg Anton
Hello again What will happen with the BMS when one fuse get damaged ? and it cant messure the voltage of these Cell !!! Will it measure up two times voltage at the next Cell = Cutoff because Cell overvoltage !!! I playing arround with a mounting plate for the BMS with the M3 screws and two Terminals. Still at work, i print it today. In my case with M10 screws.
If you don't mind modifying the BMS case you could eliminate soldering the bigger cable buy removing the smaller cable by cutting them off near solder or de- solder...... Then drill through the BMS board attach a bolt ..... then put a single lug on the new wire and mount..... I would also keep wire length same size on input and output
My suggestion would be that you cut the balancing cables so they are 10-20cm for into the BMS and that you use "regular" cables for electricity (0.75-2.5mm2 so what you have lying at home) up to the poles of the cells that you solder in the fuse. The cables for BMS, I would probably try to put on a 10mm or two 6mm cables and cut them and put them in one that is made for 35mm (becomes 31-34mm2) so it should fit and reduce the losses but I do not think they is so much losses and then you still do not take out as much as 100A but it is barely 50A as max
Many electronic components have connecting wires made out of iron. Check with magnet - should be same with resistors. Teh iron would explain the resistance you measured. You might want to solder wires close to the galss body of the component in order to overcome the problem. In case you want so solder at your BMS please cover all electronics thorougly i.e. with tape. Any small solder splash might destroy your BMS. It is essential to solder those fat wires quickly along a powerful soldering iron in oder to not stress your device too much. Provide a suiting jig that holds the wires in place while they are hot as you might want to cool them down after soldering as soon as possible. Alternative: If you hesitate to stress your BMS you might want to just cut the fat wires at your BMS short and crimp them together with your neu fat welding wire. After crimping you can solder this connection point easily while avoiding too much stress for the BMS itself.
Hallo Andy! Also ich würde das BMS nicht modifizieren. Nachdem du so viel Platz hast, würde ich einen eigenen "BMS Bereich" machen. Also sauber horizontal mit den M3, vielleicht auf einem kleinen Gestell, verschrauben. Die dicken Kabeln des BMS würde ich dann beidseitig über eigene Terminals (die du eingeblendet hast) verlängern. Klar ist, dass du dann wieder mehr "Klemmstellen" hast die man ja vermeiden möchte, aber auf das kommt es auch nicht mehr an. Noch dazu tust du dir viel leichter, falls du das BMS mal tauschen musst. Viele Grüsse
I'd say solder it, just use the 450c setting to melt the solder fast without giving it time to transfer heat. Be sure to have the wire insulation right up to the board to prevent any shorts. The other battery maybe keep all the lengths the same so it balances correctly
@@OffGridGarageAustralia though to mention, it's your choice but the options are -Solder new leads to the bms scrapping the warranty -or have multiple pieces of small connections everywhere. Hard decision I know
I would leave the BMS alone. I would "bug" the connection by using a lugs and machine screw ,nut, washer Place lugs on the BMS wire "Back to Back" to give a more slim profile. Connect the orange cable and lug 180 degrees out (in line) with the BMS wire.Tape and shrink the connection. Add sleving for protection. The connection is very low resistance and can carry high current. Conductor wise the bms is the weakest link.
I agree. The added advantage is that should you ever need to replace the BMS it becomes a plug and play swap and the replacement would not have any warranty concerns caused by opening the casing. Alternatively if you aren't concerned about the warranty I would combine each pair of cables into one larger lug whilst I was extending the cables. Not quite plug and play but makes for a neat connection which is retrofitable later.
"there is no movement" let me tell you NOTHING is rigid and EVERYTHING moves lol, the "triple insulation" is certainly good because hard plastic will not break or cut as easily as soft silicone. So it is certainly a step up.
I don't think short cable is a problem, because BMS in nature is a smart contactor and my battery will always have 3 power terminals : Positive, Negative and Protected Negative by BMS. Negative and Protected Negative terminals are very near from each so short cable is perfect
Do not touch their soldered joints as it might be tricky to solder a bigger cable with heat damage. Maybe shorten and then connect to as large a cable you need connecting to rest of circuit with right size lugs. (Unless you are drawing more Amps than these cables are rated for!). Why extend bms leads, just mount Bms close enough so their power (B-) reaches without e tension, and hopefully BMS leads reach w/o extension. Not sure you need fuses on this BMS leads anyway. If a short occurred in BMS, then the fine leads will fuse anyway. Just route them so the do not sit on and bus bars etc.
Hi Andy. I'm so happy you're using the JK BMS. I have one that I'm going to use on my battery system thanks to your earlier videos (and that one from Lithium RV). Just a comment/thought - you were talking about adding insulation to one of your big cables that was touching a bus bar mount and saying that it shouldn't matter as there is no movement in the system. I've seen cables move on their own when there is a big shock current go through them. This might not be an issue or even happen - but maybe it could? Short loads on the system could cause the cables to move, even ever so slightly (i.e. fractions of a mm at a time), but maybe this might be enough over a long enough period to warrant your concerns about rubbing through? What do you think? Also - the split soldered cables - are they split exactly in half? i.e. what happens if you don't split your 16mm2 cables in half exactly and solder (for example) 1/3 to one side and 2/3 of the cable to the other side??
All cables touching anything inside the shelf will definitely have another layer of protective conduit. I'm not expecting having any movement from 'shock' current. Each battery bank will only supply 80A max. I'm not sold on the soldering of the cables to the busbars. It is an option but.... 🤔
@@OffGridGarageAustralia oh I meant about the P- and B- cables inside the JK BMS. The factory ones are soldered to the copper bus bars inside. You were talking about changing them to the 16mm2 cables you have but noticed the factory 7mm2 cables were split and soldered on each side....
how long are the balancer cables of the JK-BMS? could not find any numbers about it, seeing pictures i would guess something between 600 and 800mm? And maybe 150mm for the 7awg? for the 7awg, would it maybe be possible to solder not 2x 16mm2 to it but something like short busbar-plates to the bms to then have a point to screw usual cables on?
Remove wires and add better bus bars on PCB. Or. Remove ring connectors from existing wires and combine them into one 6mm ring connector. I am the one that asked for interior look while back. Thanks for doing that. Wiring part of design of the JKBMS is not that great. Reason for such a high pressure on wires from enclosure is because they want to eliminate possible de lamination of copper from PCB while wires are being moved around. Missed opportunity on JKBMS part to truly make a good BMS.
Why are you using only red cable for the power distribution and not red for + and black for - ? Using the same colour is asking for an accidental mix-up if you aks me.
Carroll or Cabac lugs are better i have found, the narva are kind of in between cheap lug thickness and good lug thickness. Put them away as spares for another project you will be surprised how many things use 8mm lugs. I myself have about $500 of lugs in all sizes in stock at all times in my inventory and i find i use them all so it pays to have a mix handy.
Thanks you. I was really disappointed about these lugs. I will order the heave duty one from Blue Bar Industries again. They are perfect and I can double crimp them.
Good day. Thank you for the awesome channel, please could you see if you could do a video on the rs485/comm on the JK BMS. I'm sure you did say you would connect the comm cable to your Victron inverter and I would love to see how you do that and how well it works. I would also love to see a bench test and review of the new LiFePO4 Blade Battery Cells Again thank you for the informative channel I love it and I'm so close to building my own battery 🔋 with your channels help.
I am slightly confused and in a similar pickle. If I use the standard wires and I use a bus bar as you suggested. Wouldn't the pieces that are the smaller wires/cables still heat up during continuous discharge and charging, even though after the busbar we have better wires? Would that be a potential risk/problem/factor?
It all depends on how many amps you will draw through these cables. As they are 7AWG/10.55mm² they can carry around 60-70A max each. In my understanding the cables are not right in their dimensions if the BMS can support 200A continues current, even 350A for a few seconds. That should be at least 2x 3AWG/25mm². As I'm not intending to pull more than 100A form each battery ever (that's the rated circuit breaker trip current). And yes, you're absolutely right, the thinner wires from the busbar to the BMS may get warm during normal operation due to the above fact.
Andy. Many comments here that there is probably no current flowing in the balance leads when the BMS is measuring the cell voltage, and therefore the additional resistance of the fuse (which is very small anyway) will have no impact. HOWEVER, many BMS stress that the balance leads should be the same length. If balance lead resistance is not a factor, then why the precaution on lead length by the BMS manufacturer (and in so many forums)? Mmmm ... Since there does not seem to be any consistency in "common knowledge" I think the only solution is for a test in your garage. 4S configuration with a BMS that has a higher current active balancer, and where two of the balance leads have a higher resistance. Does it make a difference to the final balance numbers? Only your garage experiment will tell us ...
Exactly John. I guess, this was coming from the years, when balancing worked differently and the BMS measured and balanced at the same time. These days with all the mirco controllers we have a total different setup and approach to that. Look at the JK-BMS and its capability to calibrate each single resistance of the balance system. Outstanding!
@@mausball I think, If the soldering ob the Board can take ist, than a good soldering with wrappig can take it also. But i would prefer the wago. We are using the bigger ones at Work with upto 800Amps. And we open and close them several times a day. Works perfect
@@svens.5588 Soldering cable to cable is never as good as a quality crimp, which is a cold weld. A connector like a giant Wago is 3rd place in that ranking.
Actually their is movement under high loads. I hit 150 amps at 60v setup and the wires begin to vibrate and you can hear it. So yes wires do infact vibrate 8n small fast movements.
Would it be possible to put the BMS wires into the top of the breakers to make it fit better for you? That would also bring the harness out the bottom of the BMS.
I'm flexible with that. The breakers are non-directional so can operate in any direction. I'll have another look and se if this would give us some new options.
LOL Didn't read my comment about buying all 6mm and then drilling the to the exact size needed. The lugs are all the same size, so a quick drill and you get the perfect size. So fed up with loads of 10s and 12s left over when I need a bloody 6. Also, I seem to get a better fit if I drill them. Bonus. These lugs are the same ones I get off ebay, very nice. Narva 35mm x 6mm. The others are cheap crap and dangerous. I pulled one of my factory cables apart. Scary they'd use cheap crap lugs.
Have a go ya mug. ;) What's the worst that could happen? All the heat will be sucked up the copper cables. Spread them on the bars on the board. It will look heaps better with right length cables on it with no joins. You know you want to. Hahaha. Good luck.
Hello from Canada! I’ve just stumbled upon your channel because I just bought the 100a version of this and I went thru the same thing you did with the BMS not turning on! Thanks for your help with that! Now my question to you and to anyone else reading this, is are you concerned at all about the cell voltages jumping around so much while balancing? I’ve hooked mine up and it tends to jump around along even when not charging?
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nothing in life is perfect. simply a matter of perspective. no matter how you set it up, you will eventually want to change something. so just make decisions and move on
Yes!
I don’t like to modify standard things to fit and I think it’s better to design the host system to accept standard parts. On that premise, I would mount two small bus bars to accept the BMS cables and then run heavier cables from the bus bars to the battery and the breaker.
Thanks for your feedback.
Leave the poor BMS alone and avoid more problems. Just connect externally to your 16mm cable. Bolt on using the existing lugs or cut off the lugs and do a good soldered splice. The short length of the smaller cable won't be significant. Whatever you do, heat shrink over the connection, preferably two layers. I make one layer 3-5cm longer so it extends past the shorter layer a cm or two on each end.
Thank you. Good thinking.
Agreed. Overdoing it. You're going to scream and cry when you see what I'm doing...
While soldering would be possible, the easier way would be to extend the cable with a crimp connector.
You can get thosemin a similar style as the ring lugs, just a metal tube with hole on both sides and a center indent.
I don't know if such a crimp connector is the easier way than soldering and a bit of heatshrink. It's just a different method, I guess...
My advice would be to bench test the BMS before changing the wires. Hook it back up to your battery and attach an inverter and draw as many amps as you can then check the temperature of the cables to make sure they don't overheat. I run the same Bms with a 2p16s 560ah battery connected to 4600w of solar and a 4400w inverter and never had the cables even get warm.
Yeah, I did that already in the last test with the JK BMS and charged the vehicle form the battery over 6h or so. The cables did get less than hand warm. In the battery shelf, I will pull 80A max per battery (that's the set trip current for the breaker at least.
@@OffGridGarageAustralia sorry, I remember that video just didn't remember if you tested the temperature of the cables on the bms. If 80a is your max draw you have nothing to worry about with the cables that came with the bms.
Concerning cable lugs problems - we face such problems very often during various progects. And it is not a big problems - we also use files, metal scissors to cut lugs to appropriate dimensions. Also, attention must be paid to flatness of lug'g contact surface. Because some lugs could be produced by press-and-cut machine in such way, that lug would have non-flat surface at the edges. That will prevent its "full-surface" contact with busbar or CB's terminal. We detecting these surface problems by observing lug's edges and fixing it with filing adges to flatten contact surface. Maybe, it is not an issue in yours lugs, but we often observe these defects at our domestic (russian) made lugs, especially at sizes from 35 sq mm to 150 sq mm. So, it is our rule to check flatness of lug's contact surface before mounting it to busbar.
Thanks for sharing, Sergey. I'm checking every lug on the corner of a flat piece of metal and see if light gets through.
I love little chalenges like the issue with the cable lugs. The feeling of accomplishment is great when it all finally gets together. Wish i had more time for my hobby
Yes, it is very rewarding to finish these challenges along the way. And not having enough time is my problem as well... I could do so much more.
To solve the hole size in lugs, I buy lugs with the smallest hole size and use a step drill bit to expand hole to the bolt size I need.
Andy, you may want to do a test to insure the Bluetooth signal from the BMS can communicate from inside the aluminum walled shelf. Better to know now if you need to mount the BMS on an external wall for the sake of that signal.
That's not a problem at all. I have done a lot of testing with the electrical cabinet since the MPPTs went into it. No issues at all and minimal loss of signal if the dorr is closed.
@@OffGridGarageAustralia Good to Know, thanks.
Andy, do not change the original wires. The bigger the cross section, the more heat will need to have it soldered. You need in those points a VERY good soldering with very low resistance and high mechanical strengh. You definetivelly will face big dificulties and frustration if try the replacement (and maybe even damage the unit). Also, the tin will enter inside the coper wire due to capilarity and will make the wire hard as iron making imposible to bend near the soldering point. Don´t do that.
As solution, cut away the original hole terminals and use a junction sleeve to convert 2x10mm to 1x35mm (or whatever). You can crimp it or solder the junction assembly.
As a second issue, the resistance of the balancing leads is not so important. 30 mOhm is really not an isue, since the current through the leads are just a few amps and the looses in that resistance will be part (small portion) of the balancing process. If the diferent lenghts are important or not depends only of the software: if the individual cell voltage is measured without load (before sinking energy to be transfered to other cell) or loaded (during the energy transfer peak). In the first case, since there is not current through the balancing wire, there will not any drop (no matter the lenght). In the second case the current through the wire can make the measurement influenced by the diferent lenghs.
Could you take apart the white thermal tape over the transistors and show us what transistors JK is using in both ways? (charge and discharge), Thanks in advance,
Jose (Madrid)
Thanks Jose. Appreciate your feedback.
If it was me I would just clip off the lugs on the BMS wires and combine them into a single high quality barrel crimp and terminate the other end of the barrel crimp with the single heavier cable but I am guessing you won't be satisfied with that. For my own system I have the BMS terminated on one side with a 150A fuse to the busbar and on the otherside I have it terminated to a single post and then have that post connected to a 5 foot 1/0 AWG 105C cable. Having the separate posts makes it easy to swap the BMS when one potentially dies.
I could do the crimping, sure. I probably will go ahead with the single stud bus bars though...
Just have a beer, and truly enjoy all you have done and how much information you have passed on.
Great work Andy.
Thank you kindly, Marc!
Re balance lead resistance, if you increase resistance the cell voltage will bounce more when balancing. Use big wire and big fuses.
I don't think the BMS will measure and balance at the same time...
I personally would just solder on new cables, the amount of heat that those components near it are rated for is pretty high, plus they don't appear to be on the same pad directly, so the heat will dissipate through the circuit board vs heating up 1 single component. Just remember the maximum junction temp of the inside of a transistor is something around 150c and the body can withstand heat up to 350c directly.
OK, great...
Hi Andy. You can take a copper tube of the required diameter on one side to insert two thinner wires, and on the other the wire is twice as thick, and crimp the tube.
Cool, thanks
You’ll always have a solution to this situation . You might can try L ing the single orange wire strip end across the soldering terminals and then out the sides . May the solar be with you .
Thank you.
personally I wouldn't mess with the original soldering. The main concern is if you will be able to solder it as precisely so no connection is done to the case - a tolerance is almost inexistent there.
Yes, I made the decision, to not go ahead with the cable upgrades and use the existing 2 cables of the BMS. It's too risky.
I’m using a 4 ga crimp barrel splice with the two 7ga in one end, 4 ga in the other. I’m not installing fuses on 26 ga wires. If they ever short, I’ll just install a new BMS and leads. I’m not worried about a fire, my batteries are encased in 1/4” concrete board. No wood, no plexiglass, no plastic sheets.
Yeah, right... I'm not worries about a fire either, it's just cables have fuses, so why make an exception with these ones...
EE here. 10-20 mOhm is about right for those little fuses. It's the resistance of the tiny little fuse wire that is inside the glass body, compounded by the crappy nickel plated steel wires they use. You'll find the same lead wires on leaded resistors.Try measuring one of those some time. As far as the importance of the resistance, it really only matters if you want the 2nd and 3rd decimal point to be really accurate. If you're balancing to the 3rd decimal point, you need to know the cable resistance, and yeah, the JK has that capability and you should use it. For measuring 0.001V changes, cable resistance can be a big deal. For situations where current is flowing, like this one, it's a fact.
The current through those fuses should be close to zero, though. So the voltage is ~0.02 ohms times 0.001 amps = 20 microvolts. Oh no, we're going to see 3.5V less 20 microvolts...
@@mozismobile Yep, but if the system as a whole is counting to the 3rd decimal point, 125mOhm makes a bigger impact, and yeah, it should be factored for. And since the balancer is working on balancing while measuring current, make that 0.001A into 0.5 or 1 or 2 amps, and all of a sudden it actually matters.
I think the resistance matters. A bit. We are charging the cells to say 3.65V max voltage. If the BMS allows them to charge to 3.7V they will be overcharged already.
If we assume a max balance current of 2A at 40mOhm (without fuse) we can have a voltage drop of 80mV. Including the fuse this could be 100mV drop then, so 20mV difference. That could mean the cell is at either 3.65V or 3.67V. There is your bit. Does it really matter? Maybe not as I won't charge them to 3.65V anyway...
@@OffGridGarageAustralia realistically you may have 100mOhms or more from the battery to the BMS. With a 2A balance current all of a sudden it makes a real difference. Your wire, connections, and the terminal block will all add a few mOhms here and there and they add up fast. And remember, a bad crimp can cost you 100mOhm without even blinking.
@@OffGridGarageAustralia I have a feeling the voltage is measured, then the balancer is activated, then the voltage is measured again... which means there is virtually no current flow(no voltage drop) down the wire at the point of a voltage measurement. The input resistance of the IC which measures the voltage will be so high that a voltage drop due to the cable resistance will be negligible. If I am wrong and the voltage is measured whilst the balancing is happening, then maybe there is a way to just correct the voltage reading within the BMS settings? you can just measure the voltage of the cells with a good quality multi-meter?
Do the cables! Finally you opened it😁
The BMS PCB looks a little shiny so they might have conformally coated the board after it was assembled. That would make soldering the larger cable a little more difficult (removing the coating as needed). You would need a high wattage soldering iron too. If you are able to heat one connection so it is hot enough, then the other 3 connections would probably melt also. Having these connections on both sides of the board make it even more difficult. I would just use the existing wiring as is and use your thicker wire to connect the existing bms cable lugs to the battery/circuit breaker.
The bus bars inside are not coated but I definitely would need a larger soldering iron for this job.
Andy, those fuses are designed for PCB use. They're soldered right onto the board and the excess leads are cut off keeping the resistance of the fuse as low as possible. Also, T-Shirts came in last week. Can't wait to see the expressions when people see the shirt and get that WTF? look. I might even meet someone who watches you here in Canada, who knows?
Thanks Bill. Yeah, I was waiting someone said something about the shirts when I wear them in public. There will me more soon...
I'm not too worried about the fuses and overall resistance. The BMS won't measure and balance at the same time.
No!!!! Agh!!! Why? It works & like my father used to say “if it isn’t broken then don’t fix it.”
Hahaaha, I won't touch it. Just wanted to have a look at the quality of their soldering. 😂
The 7AWG cables are actually far too thin for 200A continues load...
@@OffGridGarageAustralia is it silicone insulation on those wires? If it is then I would be much less concerned about running the BMS at its max rated load. The cable current rating is based on much lower melting point insulation and quiet high ambient air temperatures, so silicone insulation has a higher melting point and is less impacted by high ambient temperatures. It’s much safer for wires with silicone insulation to run much hotter, and although alarming when you take temperature measurements of the cable, in fact it is not an issue. You can test this easily by trying to burn the insulation with a cigarette lighter, if true silicone insulation then it will not be affected by the cigarette lighter and will remain intact.
you should use flux to minimize the time to heat the BMS busbars, and pre tin the splitted wire to solder faster.
So here's some technical advice for all you people who, like me, love reading the comments.
Get the T-shirt, get the Hoodie, that way on those days when the sun doesn't want to come out and play you can wear both, be warm and totally stylish.
My ageing 48v SLA battery bank hasn't dropped below 85% SOC since I started wearing them and to top it off I had a record input day with of 20.4 KW/H last Sunday, that's 4.088kWh/kW efficiency.
Even my Solar setup gets inspired by Andy.
Thanks Capt K. This is good advice 😂
Why does the resistance (assuming it's small) make any difference? doesn't the BMS measure the voltage with very minimal current so small resistance won't make a difference?
Also, I won't touch the BMS. If anything, I'd solder a thicker cable do the blue/black cables a few CM from the BMS (if you don't want to use a stud to connect) - you can even connect 2xblue/black to one very tick orange cables to have less wires all over the place and make the setup cleaner.
The resistance should not make a difference. As you said during the measurement, there is no current flowing and while balancing (2A max) it does not measure the cell voltage of this cell anyway.
Points about the cables taken. Thank you.
@@OffGridGarageAustralia Doesn't it send a current down the balance cable to do the balancing?
@@ViewerWatch2194 yes, that is correct. But it does not measure the voltage at the same time.
Closing the case of the BMS (without electronics of course) and than use your conical dril to enlage the cable holes to the desired dimension. go for it.
I would prefer a round file for that job. It's casted aluminium, so will file like butter.
I agree with the earlier comments but I think you should put the BMS in a new bow, cut the P- and B- cables outside the original case, extend them with your preferred cable inside the new box, with the correct length, drill holes in the new box and pass the extended cables to the breaker and the battery. Just my 2 cents!
That's an option...
It is good idea to replace original cables to 2 x 16 sq mm ones. I think, that BMS and its MOSFETs will not overheated to failure - all BMS PCB will act as a huge heatsink. More likely, BMS PCB must be preheated in busbars zone to allow successful unsoldering existing cables and soldering a new ones. Also, suggest to spread strands of 1/2 of cable's core along busbar at each side to lower soldering's height and to ease soldering of huge amount of fine strands.
Thank you. I'm not sold on soldering new cables to this busbar...
I at the point where you have opened up the BMS. My thought is that you could extend the bus bars to outside the case ending with proper lugs. Overall for the effort I think it would be best just to use the existing wires and separate lugs. More straightforward to replace the BMS. Maybe put a vertical stand on the shelf next to the battery. I believe you mentioned previously you wanted to make that area a compartment so it out be a perfect area to mount the BMS to. The voltage test wires should all have the same resistance and length. Adding more resistance with fuses will not matter much for purposes of measuring the voltages of the cells which is relative.
If I understood you don't want you have the shelf fronts acrylic because acrylic is combustible. You used it for the shelves... There is also more expensive polycarbonate.
I now have the proper solder equipment and could have extended them. But they work just fine since I connected them to my battery.
Apply cold spray for the parts you don't want to heat up, i do it all the time when soldering on logicboards.
Thanks for the tip.
Do not change the wires you will end up with a lot of problems. Just connect the wires to a regular bolt and put shrink tubing ( 2 layers perhaps) around bv it. You should not have any problems. Why would you use the fuses anyway. These are just for balancing. It's not like 18650 cells. Always looking forward to yet an other episode.
Well you make all the balance leads and then cut the fuses to different lengths to balance all the balance leads 😄 NOW that’s an adventure!
Hahaha, THAT would be one. Glad I can just calibrate this all in the app...
Thanks Andy for your energetic videos. I have learned quite a lot and will follow you all the way.
Regards,
Peter
I would never mess with the pre-soldered cables. I know my limits.😬
You could solder extensions to the existing cables. I'd like to see how that works.
This could be achievable for me as well. As they say: Heat shrink and paint make me the solderer I ain't.😜
I would go with the terminals if I extend the cables of the BMS, not soldering them to thicker cables. That is totally messy and I have not seen a good and clean result.
Soldering directly tot he PCB/bus bar of the BMS... I don't have the tools to do that professionally either. It would be ugly...
Bonjour ANDY, dans la continuité des réflexions diverses pour cette armoire ! très intéressant l'évolution de la positon du BMS. bonne journée et dans l'attente de la prochaine vidéo. ;-)
I would like to share my bank with you but unfortunately can not share pictures here.
Anyway, instead of soldering large wires inside BMS use the same two wires with one terminal and connect with the terminal block.
Thanks for your tip and suggestion.
Andy, don't mess with re-soldering the BMS leads. They are sized to match the capacity of the BMS. Terminate the ends of the BMS cables on the one stud terminals on each side of the BMS then use whatever size cable from there to the battery and breaker. Realistically, how much will you be pushing the limits of the BMS capacity in real life usage? Probably not often at 48V.
The cables to the BMS are actually undersized. By quite a lot. It's just a 7AWG/10.55mm² cable with a max carrying capacity of ~55a or each cable. The BMS is suitable for 200A continues current though...
I personally won't push more than 80A through the BMS, 100A for a short time maybe...
Hammer and anvil will straighten them right out.
Compare the 6mm and 8mm -- is the body the same size with a different hole? If so, then stock up only on the smaller hole size. In commercial production you need to just grab the right lugs and go, but for home use I find it effective to stock only the smaller hole size and drill it out when I need a larger. This reduces inventory by a factor of 3 or 4, while also helping to qualify for quantity discounts.
That's a good question... not sure if the 6mm and 8mm lugs have the same footprint...
Flip the + and negative on the breaker and move the Bms to the top and mount it to the right and you have tons of room and you can extend the cable on the bottom of the shelf above to the battery.
Just a thumbs up with your stud mounts, if they are the same as I have used, they can be modified to accept 2 x 8mm or 1 x 10mm bolt through the plastic, this my give you a option for cables, you might notice the holes in the plastic already there for these options, the back cover pops off
Ah, I was wondering what the two extra holes are for... Thanks for the tip!
AHH yes. The reverse Midas touch. I've had days like that 😀
I think I would cut off the 8mm lugs and extend the cables with the 35mm cable. Use some sort of crimp and solder to make the join. And you could do a test before hand to see what the losses would be. And you can make the tails on the BMS as short as you dare.
I'm actually thinking of cutting the cables even shorter as they are right now. They should have the same length though for equal current distribution onto these bus bars in the BMS itself.
Hi Andy, thanks for showing the inside of the JK BMS. Why not crimp the extension cable to the BMS, saves a lot of soldering which will need a lot of thought not to break the BMS?
I'd just extend the cables that are there, using the single pin bus bar you mentioned.
I'd definitely extend the existing cables. Don't even need a bus bar. just sandwich the two lugs either side of the extension lug, or cut them off and solder a splice.
The two busbars will have the benefit that I don't need to mount the BMS anywhere. It will just sit in between these two studs.
A little Flux on the bms and heavy solder on the cable tip. Bms should be just fine. Looks like they used plenty of heat on the one side and it works fine. (#Quitoverthinking it Andy). This build is going to turn out amazing.
Yes 👍 ⚡
Go for it Andy. Your viewers wants to know and I bet you do to.
I'm still on the fence with this soldering...
Andy this happens to me all the time but just file it square it will work perfect
Yes do it, connect new wires to it then test it to make sure it works, test it to max power output for 30mins and see how hot it gets.
To be honest i think you would be fine soldering the new wire in without any problems
Servus Andy, every clamping point is a source of error. Your project will be a collection of clamping points. You already have 9 clamping points on the load side until you reach the upper copper rail. In my opinion, it is easier to solve with cables than with copper bars. But it looks cool with the rails.
Cutting a thread in the copper is not enough. Then you would have to counter with a nut at the back. To loosen the cable or turn the cable lug, you have to open two things. It is easier and safer to drill a normal hole and use press-in nuts. Everything else has already been tested.
Best regards from fu**ing foggy austria
I thought about using cables instead of the bus bars. It would have been very messy and confusing, a lot of cables going back and forward. I still would have some bus bars to connect all the cables together anyway, so there is really no benefit with having cables instead of bus bars. The connections are not a problem at all if they are made correctly.
As for your fuses... you just need to snip out a section of the BMS sensing cable that has an equivalent resistance to the fuse that you are adding.... or recalibrate the BMS to allow for it.
Great video. Just bought 2 of these. What size lug did you end up with the the 7awg, 10 or 16 mm2? Thanks. Sorry if this was asked before.
I ended up keeping the cables as they were and crimped individual lugs onto the cables. You will see this later when I mounted the JK in the battery shelf.
If u have to solder anything ....go with battery bus bars...few cooper leaf's ....
All in all more direct lines less problems....
If the lugs aren't perfectly flat you can rotate the changeable dies in your hydraulic lug crimper upside-down to give a flat surface and use it to flatten the lug perfectly flat ;)
Good idea!
0.053ohm @ 2 amp = 0.106v drop down the cable when there is 2 amps flowing. V = IxR. I'd be interested to see if the resistance affects the current balancing as I assume the discharge transfer is constant current?
It won't affect anything as the BMS does not measures the voltage and balances at the same time. So the resistance is negligible.
Andy, can you run the numbers and explain to those who don't understand, just how much difference those extra milliohms would actually make, and if that is a significance difference to NOT having the fuses in?
It would not make a difference at all I think. The BMS measures and balances at different times so the resistance is not of a concern at all. Older or simpler BMS may handle this differently and it could be of an impact for these system but with the smart BMS, they will be totally fine.
MOSFETS can handle heat.
Good MOSFETs can get so hot they melt the solder and fall off the board, and they'll still be good.
I've done it.
Yeah, I had this situation as well...
Hiya!
I'm guessing the chip doing the voltage measurement in the BMS will have very high input impedance: hundreds of k-ohms at least. The measuring current will be very small and a few milliohms worth of fuses and cables should not have an appreciable effect. (If you can figure out what chip the JK BMS is using, this might be specified in the datasheet.) Good luck!
I agree with you. Even Andy could try to measure that current, uA? nA ? So the voltage drop across cable+fuses will be very very low.
It's more about the balance current of 2A going through these cables as well.
@@OffGridGarageAustralia Probably the BMS is not measuring the cell voltage when it is balancing 2A. Probably it will measure the voltage "between" 2A balancing cycles.
Even an incorrect bolt/screw tighten (i say incorrect,not "much more" or "much less") will give you more resistance than the fuse. That is why i think it is very important to check connection with ohmmeter
'It's called bended cable'! As my teacher used to say 'You might be sitting at that back making jokes but at least that proves you are paying attention'.
Personally I would make the cables from the BMS as short as possible and change the terminals to ones with the correct size holes and then connect them to the single pole bus bars that are then connected to much larger diameter cables. This way you have absolutely minimised voltage drop as much as you can. A short section of undersized cable within a longer section of correctly sized or oversized cable will have little or no effect. You have to calculate the voltage drop over a length based on all the cable used in the circuit. Messing with the solder will be a total disaster in a DIY environment.
Thanks Chris. It's not so much the voltage drop I'm concerned about but more the heat which could be created in this thinner section of the cable. The 7AWG cables are undersized by 50% and should have been 2AWG for a 200A BMS.
@@OffGridGarageAustralia Are you sure about that. 7AWG is 16mm squared cable and basic single core welding cable of that size has a nominal current rating of 110A. You have two cables so combined they are rated for 220A. Yes one size up would be better so going to 20mm but jumping to 2x35mm seems a bit extreme.
@@OffGridGarageAustralia Ooops. just realised 7AWG is actually 10mm cable and so rated for 70A I believe. So you have 2x70A = 140A so yes it is rather undersized for a 200A BMS. Never could get used to AWG sizes compared to mm2!
Servus aus Austria
Schönes Projekt Videos und Tests sehr lehrreich.
Würde vom Hauptschalter Kupfer Schiene verwenden kurz ,da kann man dann beidseitig das BMS klemmen .
Kannst dann ebenso mit deinen einzelklemmen eine zweite kleine Schiene für BMS Eingang und weiter zu den Akkus .Hast dann auch die Möglichkeit Kabel parallel zu verlegen
Lg
Anton
Danke Dir, Anton.
Hello again
What will happen with the BMS when one fuse get damaged ? and it cant messure the voltage of these Cell !!! Will it measure up two times voltage at the next Cell = Cutoff because Cell overvoltage !!!
I playing arround with a mounting plate for the BMS with the M3 screws and two Terminals. Still at work, i print it today.
In my case with M10 screws.
The measured voltage will be 0 and it may turn off discharging as the voltage is under the low voltage disconnect set in the BMS (2.5V for example).
@@OffGridGarageAustralia Thats the best case :)
If you don't mind modifying the BMS case you could eliminate soldering the bigger cable buy removing the smaller cable by cutting them off near solder or de- solder...... Then drill through the BMS board attach a bolt ..... then put a single lug on the new wire and mount..... I would also keep wire length same size on input and output
My suggestion would be that you cut the balancing cables so they are 10-20cm for into the BMS and that you use "regular" cables for electricity (0.75-2.5mm2 so what you have lying at home) up to the poles of the cells that you solder in the fuse. The cables for BMS, I would probably try to put on a 10mm or two 6mm cables and cut them and put them in one that is made for 35mm (becomes 31-34mm2) so it should fit and reduce the losses but I do not think they is so much losses and then you still do not take out as much as 100A but it is barely 50A as max
Heya, yes put some ticker cables on it. it's already open so don't think off warranty lol
Many electronic components have connecting wires made out of iron. Check with magnet - should be same with resistors. Teh iron would explain the resistance you measured. You might want to solder wires close to the galss body of the component in order to overcome the problem.
In case you want so solder at your BMS please cover all electronics thorougly i.e. with tape. Any small solder splash might destroy your BMS.
It is essential to solder those fat wires quickly along a powerful soldering iron in oder to not stress your device too much. Provide a suiting jig that holds the wires in place while they are hot as you might want to cool them down after soldering as soon as possible.
Alternative: If you hesitate to stress your BMS you might want to just cut the fat wires at your BMS short and crimp them together with your neu fat welding wire. After crimping you can solder this connection point easily while avoiding too much stress for the BMS itself.
Is there enough height between the PCB and the aluminium enclosure to house the thicker cable-end and solder without shorting?
Yes, there would be enough space
Lithium solar tested wires that were soldered together and found that resistance was less than non cut cable. Maybe cause diameter increased!
Yeah, contact area is increasing and diameter as you said...
Hallo Andy!
Also ich würde das BMS nicht modifizieren.
Nachdem du so viel Platz hast, würde ich einen eigenen "BMS Bereich" machen.
Also sauber horizontal mit den M3, vielleicht auf einem kleinen Gestell, verschrauben.
Die dicken Kabeln des BMS würde ich dann beidseitig über eigene Terminals (die du eingeblendet hast) verlängern.
Klar ist, dass du dann wieder mehr "Klemmstellen" hast die man ja vermeiden möchte, aber auf das kommt es auch nicht mehr an.
Noch dazu tust du dir viel leichter, falls du das BMS mal tauschen musst.
Viele Grüsse
Yup, danke Dir!
Go for it it will work
I decided against it. The risk is too high.
I would like for you to add a tab to your website where subscribers could upload their photos to share their great ideas on how they did things.
How about you make this website and I upload all my stuff to it 😂
Hehe, just make sure to have a powerful solder iron (atleast 150W) so you don need to heat up for a long time, then it "should" be fine :)
We will see...
I'd say solder it, just use the 450c setting to melt the solder fast without giving it time to transfer heat.
Be sure to have the wire insulation right up to the board to prevent any shorts.
The other battery maybe keep all the lengths the same so it balances correctly
I would need a bigger soldering iron for this job.
@@OffGridGarageAustralia though to mention, it's your choice but the options are
-Solder new leads to the bms scrapping the warranty
-or have multiple pieces of small connections everywhere.
Hard decision I know
Are you going to shrink wrap the lug to cable joins? With OCD comes great consternation!
I would leave the BMS alone. I would "bug" the connection by using a lugs and machine screw ,nut, washer Place lugs on the BMS wire "Back to Back" to give a more slim profile.
Connect the orange cable and lug 180 degrees out (in line) with the BMS wire.Tape and shrink the connection. Add sleving for protection. The connection is very low resistance and can carry high current. Conductor wise the bms is the weakest link.
I agree. The added advantage is that should you ever need to replace the BMS it becomes a plug and play swap and the replacement would not have any warranty concerns caused by opening the casing. Alternatively if you aren't concerned about the warranty I would combine each pair of cables into one larger lug whilst I was extending the cables. Not quite plug and play but makes for a neat connection which is retrofitable later.
"there is no movement" let me tell you NOTHING is rigid and EVERYTHING moves lol, the "triple insulation" is certainly good because hard plastic will not break or cut as easily as soft silicone. So it is certainly a step up.
Thank you.
I don't think short cable is a problem, because BMS in nature is a smart contactor and my battery will always have 3 power terminals : Positive, Negative and Protected Negative by BMS.
Negative and Protected Negative terminals are very near from each so short cable is perfect
Do not touch their soldered joints as it might be tricky to solder a bigger cable with heat damage. Maybe shorten and then connect to as large a cable you need connecting to rest of circuit with right size lugs. (Unless you are drawing more Amps than these cables are rated for!).
Why extend bms leads, just mount Bms close enough so their power (B-) reaches without e tension, and hopefully BMS leads reach w/o extension.
Not sure you need fuses on this BMS leads anyway. If a short occurred in BMS, then the fine leads will fuse anyway. Just route them so the do not sit on and bus bars etc.
Thanks Ian, good comment and thoughts.
Hi Andy. I'm so happy you're using the JK BMS. I have one that I'm going to use on my battery system thanks to your earlier videos (and that one from Lithium RV).
Just a comment/thought - you were talking about adding insulation to one of your big cables that was touching a bus bar mount and saying that it shouldn't matter as there is no movement in the system.
I've seen cables move on their own when there is a big shock current go through them.
This might not be an issue or even happen - but maybe it could? Short loads on the system could cause the cables to move, even ever so slightly (i.e. fractions of a mm at a time), but maybe this might be enough over a long enough period to warrant your concerns about rubbing through?
What do you think?
Also - the split soldered cables - are they split exactly in half? i.e. what happens if you don't split your 16mm2 cables in half exactly and solder (for example) 1/3 to one side and 2/3 of the cable to the other side??
All cables touching anything inside the shelf will definitely have another layer of protective conduit. I'm not expecting having any movement from 'shock' current. Each battery bank will only supply 80A max.
I'm not sold on the soldering of the cables to the busbars. It is an option but.... 🤔
@@OffGridGarageAustralia oh I meant about the P- and B- cables inside the JK BMS. The factory ones are soldered to the copper bus bars inside. You were talking about changing them to the 16mm2 cables you have but noticed the factory 7mm2 cables were split and soldered on each side....
how long are the balancer cables of the JK-BMS? could not find any numbers about it, seeing pictures i would guess something between 600 and 800mm? And maybe 150mm for the 7awg?
for the 7awg, would it maybe be possible to solder not 2x 16mm2 to it but something like short busbar-plates to the bms to then have a point to screw usual cables on?
Maybe you could increase the length of the fuse cable for shorter BMS cables to make them all the same resistance despite being different lengths.
That's a lot of work. I can simply calibrate the cables later in the app if necessary.
Remove wires and add better bus bars on PCB. Or. Remove ring connectors from existing wires and combine them into one 6mm ring connector. I am the one that asked for interior look while back. Thanks for doing that. Wiring part of design of the JKBMS is not that great. Reason for such a high pressure on wires from enclosure is because they want to eliminate possible de lamination of copper from PCB while wires are being moved around. Missed opportunity on JKBMS part to truly make a good BMS.
Why are you using only red cable for the power distribution and not red for + and black for - ? Using the same colour is asking for an accidental mix-up if you aks me.
Like in an EV, all DC cables are orange. The connections will have different colours of heat shrink to distinguish.
Carroll or Cabac lugs are better i have found, the narva are kind of in between cheap lug thickness and good lug thickness. Put them away as spares for another project you will be surprised how many things use 8mm lugs. I myself have about $500 of lugs in all sizes in stock at all times in my inventory and i find i use them all so it pays to have a mix handy.
Thanks you. I was really disappointed about these lugs. I will order the heave duty one from Blue Bar Industries again. They are perfect and I can double crimp them.
I really like the flexibility of your double insulated wires. What type/brand are you using?
These are locally sourced here in AU. Link is on my website: off-grid-garage.com/cables-and-connectors/
Good day. Thank you for the awesome channel, please could you see if you could do a video on the rs485/comm on the JK BMS. I'm sure you did say you would connect the comm cable to your Victron inverter and I would love to see how you do that and how well it works. I would also love to see a bench test and review of the new LiFePO4 Blade Battery Cells
Again thank you for the informative channel I love it and I'm so close to building my own battery 🔋 with your channels help.
I am slightly confused and in a similar pickle. If I use the standard wires and I use a bus bar as you suggested. Wouldn't the pieces that are the smaller wires/cables still heat up during continuous discharge and charging, even though after the busbar we have better wires? Would that be a potential risk/problem/factor?
It all depends on how many amps you will draw through these cables. As they are 7AWG/10.55mm² they can carry around 60-70A max each. In my understanding the cables are not right in their dimensions if the BMS can support 200A continues current, even 350A for a few seconds. That should be at least 2x 3AWG/25mm². As I'm not intending to pull more than 100A form each battery ever (that's the rated circuit breaker trip current).
And yes, you're absolutely right, the thinner wires from the busbar to the BMS may get warm during normal operation due to the above fact.
Andy. Many comments here that there is probably no current flowing in the balance leads when the BMS is measuring the cell voltage, and therefore the additional resistance of the fuse (which is very small anyway) will have no impact. HOWEVER, many BMS stress that the balance leads should be the same length. If balance lead resistance is not a factor, then why the precaution on lead length by the BMS manufacturer (and in so many forums)?
Mmmm ... Since there does not seem to be any consistency in "common knowledge" I think the only solution is for a test in your garage. 4S configuration with a BMS that has a higher current active balancer, and where two of the balance leads have a higher resistance. Does it make a difference to the final balance numbers? Only your garage experiment will tell us ...
Exactly John. I guess, this was coming from the years, when balancing worked differently and the BMS measured and balanced at the same time. These days with all the mirco controllers we have a total different setup and approach to that. Look at the JK-BMS and its capability to calibrate each single resistance of the balance system. Outstanding!
Did you considered the breaking capability of these small glas fuses? Imaging the short circuit current of the balancing cables of such a battery!
I would assume the measurements are made between balance bursts at zero(ish) current. The balance cable resistance shouldn’t matter in that case.
I think you are correct. I have a JK-BMS balancer-only device (no protection functions) and I observed similar behavior.
Yes, that should be correct.
Why dont you solder the 35mm to the end of the two Cables? I woldnt mess with the Board. Or take a look at wago 285-139
It would be better to crimp. The BMS carries the full discharge current of the pack, and solder has a high chance of melting.
@@mausball I think, If the soldering ob the Board can take ist, than a good soldering with wrappig can take it also. But i would prefer the wago. We are using the bigger ones at Work with upto 800Amps. And we open and close them several times a day. Works perfect
@@svens.5588 Soldering cable to cable is never as good as a quality crimp, which is a cold weld. A connector like a giant Wago is 3rd place in that ranking.
$65 per terminal is a very high price! Wow...
@@OffGridGarageAustralia Oops, in Germany i found 7,1€ per piece at Pollin electronics for example. Part Number 285-135
Actually their is movement under high loads. I hit 150 amps at 60v setup and the wires begin to vibrate and you can hear it. So yes wires do infact vibrate 8n small fast movements.
Would it be possible to put the BMS wires into the top of the breakers to make it fit better for you? That would also bring the harness out the bottom of the BMS.
I'm flexible with that. The breakers are non-directional so can operate in any direction. I'll have another look and se if this would give us some new options.
Damn...That would be the JK Overkill BMS....
why not a table for the BMS to sit on at the same height as breaker & battery? if cables still a bit short, move battery closer. just a thought.
I highly doubt you are going to melt the mosfets by soldering to the bussbar, they were soldered on there somehow so they can take a bit of heat.
What's the resistance of the lugs, I wonder? Nice BMS! Thumbs up and subscribed!
LOL Didn't read my comment about buying all 6mm and then drilling the to the exact size needed. The lugs are all the same size, so a quick drill and you get the perfect size. So fed up with loads of 10s and 12s left over when I need a bloody 6. Also, I seem to get a better fit if I drill them. Bonus. These lugs are the same ones I get off ebay, very nice. Narva 35mm x 6mm. The others are cheap crap and dangerous. I pulled one of my factory cables apart. Scary they'd use cheap crap lugs.
Have a go ya mug. ;) What's the worst that could happen? All the heat will be sucked up the copper cables. Spread them on the bars on the board. It will look heaps better with right length cables on it with no joins. You know you want to. Hahaha. Good luck.
Yeah, nah, I'm not going ahead with that... The risk is too high.
Hello from Canada! I’ve just stumbled upon your channel because I just bought the 100a version of this and I went thru the same thing you did with the BMS not turning on! Thanks for your help with that! Now my question to you and to anyone else reading this, is are you concerned at all about the cell voltages jumping around so much while balancing? I’ve hooked mine up and it tends to jump around along even when not charging?