YOU found the JK BMS fix! It is not broken 🥳
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- Опубликовано: 10 сен 2024
- I show again what exactly happened to the BMS and the strange 0.6V voltage drop across the BMS. I really thought it is broken. Apparently it is not and just a normal behaviour if the Discharge switch is set to off.
I didn't know that and it would have such a consequence . Thanks to the community and my viewers here, I learned something. I'm sure not many people know that, so hence the detailed video with the explanation.
The JK BMS is great again 👍
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If you would check the app screen whenever the jump happens, you can see the 'discharge' kicking in automatically. Should have been a hint :) The BMS enables the discharge MOSFETs once enough current is flowing. It still protects the battery from being discharged because once the current drops, the discharge MOSFETs are disabled again by the BMS.
Yeah, I didn't see that at all. That would have pointed me in the right direction, right. Thanks for all your help with this. Great commenting from you on all the video.
I'm being pedantic, there are NOT separate FETs for the charge and discharge paths.
See my other post.
@@graemezimmer604 I've read your other post. Just not in this BMS or in general?
its just understanding, that. when you use expert mode, but not yet qualified, but it's these small mistakes that teach us all.
keep up teaching us, as you learn.
its the best way for all of us to understand.
Yeah, I know, it is complicated and a bit boring. Just sharing what I found...
There is nothing weird here, completely within expectation for people who know how back-to-back FET battery over-charge/discharge setup works. The two back-to-back FETs in their off-state act like two diodes facing each other, blocking all current. If you turn one FET on, it bypasses one of those two diodes and allows current to flow with one diode drop in one direction. You have to turn on the other FET to make its body-diode voltage drop disappear and the BMS automatically does that once the current is high enough to justify it.
Thank you.
Perfectly explained!
Yes.
But one further point, the FETs are always switched together. It is not possible to switch them independently. See my other post.
@@graemezimmer604 Are you on diy solar forum? I can post some links/diagrams there.
@@upnorthandpersonal I'm not on the forum, but I do read it occasionally. Please post.
Perfection is illusive in this imperfect world. The more determined you are to achieve it the more difficult it becomes to find. and this is where obsession comes in handy.
I'm obsessed with that, no question. But 15.000 others too, it seems 😁
Well done Andy and well done Johthe for solving this issue. We are all learning and benefit from your testing and experiments . Thumbs up again!!!!!
Thanks 👍
Thanks
@@OffGridGarageAustralia selam.videolari izliyorum teskkurler.20s lion batarya icin ustaya jk taktirdim.ayarlarina hic dokunmadim.detayli ayarlariniz goremedim.kullanmadigim zaman desarji kapatmalimiyim ? Ve ayarlarda tavsiyeniz olur mu ? Tesekkurler.
I'm so glad you posted this whole thing. I just had a confused moment of my battery voltage being at 26.3v and the BMS exit terminal being at 25.7v. I had the discharge enabled, but the charge was disabled in the BMS settings. Didn't realize that would cause voltage drop as well. All is working now that I've enabled that.
Thanks for your feedback. That confused me as well a lot and kept me busy for a few days, haha. It makes sense though and people have explained it here perfectly why it is happening.
Thanks Johan :). Greetings from Denmark
Hi Andy, happy the issue is resolved. I'll keep watching before ordering.
Regards from south Africa
It is amazing, really good, BMS and app work a treat! More to come.
The Best is... I have two of this BMS in use and everyone who has bought one is now on the bright side of the BMS world.
Lets go Andy, built the next battery.
Yes, full steam ahead!
Эта BMS, к сожалению, измеряет не точно показания тока. Поэтому и неверные значения ёмкости батареи. Есть у кого какие мысли по этому поводу?
Thank you Andy and to Johan.
Thank you.
I am always happy to see your smile sir 😊
Thank you so much 😀
hab das video noch gar nicht gestartet und hastn LIKE!!! :-) Super wie du dich da reinbeisst
Danke Dir vielmals!
@@OffGridGarageAustralia Welcome, Sir
Look at the BMS phone monitor screen at top for discharge 'OFF' as you raise the charging current. It turns to 'ON.
All BMS's do this to avoid overheating with high current whenever charging or discharging is disable. It overrides the disable when the allowed current goes higher to avoid overheating MOSFET with their body diode voltage drop when turned off. It uses current measurement by BMS's shunt resistor to monitor current level and flow direction. It re-enables the discharge 'OFF' setting when charging current drops. Again, this is to avoid too much heating of MOSFET's at higher pass currents.
Bravo Johthe!!!🙌🙌🙌
Hi Andy You are a very good and nice person and your reviews are very useful and informative Thank you very much.
Thanks a lot for your kind words!
Cant say I ever saw the point of concern, but I am glad you’re now reassured
There is a part I of this video...
@@OffGridGarageAustralia yep, didn’t understand it then either. But that’s likely just my limitations
Thanks Andy
Brilliant Andy, I didn't realize you turned off the discharge MOSFET's. I assumed they were 'ON' and had a problem with the trigger voltage of discharge MOSFETS, and why I asked if you checked it with a discharge load.
I didn't realise either until then. It really makes the difference!
Thanks Andy I have just put together my first LifePO4 pack with a JK BMS and had this exact issue! I thought something was broken.
Just the normal behaviour of an open switch. If the discharge an charge function is deactivated, it has to be this way.
Draw the whole circuit with the battery cells, the charger and the bms. Then note the voltage drops across these 3 devices. if the battery is at 57v, the charger at 58v and the BMS is set to charge off & discharge off, you see the remaining 1v as voltage drop across the bms. can also be 13v, if you turn up the charger to 70v (at some point you might damage the bms, so don't try ;))
Just apply Kirchhoffs law.
If you switch on charging AND discharging at the same time, both MOSFET "banks" are switched on and will have close to 0mV voltage drop in total.
So far so good.
It is a litte bit different as soon as you switch on charge or discharge, but only ONE of both functions. Remember, the MOSFETs have an internal body diode. Try to draw the circuit with both these MOSFETS, one is for switching off the charging current, the other one can switch off the discharge current. The two MOSFET (banks) are connected in series, If one MOSFET is switched of, the current can still pass in its body diode - but it will result in the diode forward voltage drop being visible across the bms. This can hurt the MOSFETs really bad at higher currents as it will result in big power dissipation in the body diodes, which will fry the MOSFETs - so the BMS will monitor the current direction, and then close both (!) MOSFETs even though only charging or discharging is enabled. As soon as the charging current goes near zero, it will open the MOSFET corresponding to the deactivated function again.
Great job Andy.. 👍👍👍 always like your video.. very entertaining and educative..thank you..
Thanks a lot!
Another Brain Buster Video! Good Job keeping us all on our toes and thinking, also enjoying the journey, Beers to You! staying tuned.....................
More to come!
Very informative! Thanks Andy
My pleasure!
Its nice when one solves a problem :-)
I found so too. lots of comments and an email. Not much more I can ask for...
So what is happening to clarify any questions someone might have:
The two banks of mosfets are not two paths, they are the same path but in anti-series that means there are two sets of N-channel mosfets, pointing in two opposite directions.
The reason that they are in series is because a mosfet is only a switch in one direction, the other direction it is a diode (called the body diode and is impossible to remove because of how the mosfet is made)
So that is how you can control the direction of current flow, one mosfet is trying to conduct in one direction Drain to Source and the other is acting as a diode Source to Drain.
The reason that he is getting a 0.6v drop when the discharge is off is because he has one set on and the other set in series is off so they are acting as a diode so there is 0.6v drop across.
This voltage only goes away when the current is high enough then the BMS can detect it and protects the body diodes (they make a bad diode which will certainly not handle 200A) so it automatically turns on the discharge fets to drop the voltage across them and current would be able to flow in both directions, but if the BMS sees current in the opposite direction it should turn them back off again.
Hoped this clarified everything a little better.
Thanks heaps for your detailed and great explanation. Much appreciated.
Andy, concerning previous video in its "morning" part - it seems, that one of equipment's fans needs to clean and oil its sleeve-type bearing. As this fan has "humming" sound from its start. This sound is typical for durty and "oil-hungry" fan's sleeve bearings.
That's the e-bike charger. I have to replace the fan with a better quality one. If it fails it will get very hot inside...
thanks for the great explanation by demonstration
You are welcome!
The temptation to buy one is building! Is this the BMS we all need?
Keep up the great work Andy!
I've had two of these for over a year now. No issues.
Wait for the next video!
@@OffGridGarageAustralia Provide link when available, thank you for all your effort in everything.
amazing, thanks Andy , happy to have followed your advices , this is better than a engineering degree, ha ha ha
Glad you enjoyed it Thank you.
my head exploded watching this complexity
Ask me editing it 💥
@@OffGridGarageAustralia lol
10:20 I dont see anything wrong.
The voltage you were seeing across P- and B- is exactly the voltage when the BMS is off while connected to a charger.
IF said voltage is zero, then it means ZERO impedance and cells will be subjected to accept charge from a charger.
Simple!!!! You are working with Confused Electrons🤔😩. Or they are Lazy. Keep it up buddy. I enjoy your efforts. Maybe you have found Negative energy. With a diode and relay this could still charge… Alien technology!!!!!!👽
That's the plan, flux-compensator and deflector ion-shield
Heya, oh good it isn't faulty now w can go on testing
Thanks to the community of smart people… we all benefit!👍
Yes, I was close to contact the seller and claim a faulty BMS 😁
So it looks like this be I'm asking separately regulate the charging of the batteries without affecting the load. This is great if you have solar panels connected directly to the DMs and don't want to overcharge the batteries.
It's probably worth mentioning that there are NOT separate charge and discharge paths.
The reason that there are two FETs in series is a little more complicated:
The magic of FETs is that they can conduct equally well in either direction when On.
The problem however is that there's an inherent body diode across the Drain and Source, which means that even when the FETs are Off, they can conduct in one direction (albeit inefficiently).
The answer to this is to connect two FETs in series (but opposing) which prevents the body-source diodes from conducting.
To put it another way, the junction of the two FETs is not available externally, so the path for both Charge and Discharge is via both FETS in series. And both FETs must be switched on for there to be a path.
And lastly, both Gates are connected together, so they cannot be switched individually.
Edit: Have just watched the rest of the video. It seems clear that you have misled yourself by talking about separate Charge and Discharge switches. It is true that the settings in the software allow different current settings for this, but the key point is that THERE IS ONLY ONE SWITCH!. eg the FETs cannot be individuality switched.
"And lastly, both Gates are connected together, so they cannot be switched individually." This is not correct. They can be switched individually (and are), but they only conduct through the parasitic diode at low current. The reason they can be switched individually is to do exactly what the BMS is supposed to do: prevent discharge when discharge is disabled and prevent charge when charge is disabled - from the battery perspective. The BMS will enable both MOSFETs when there is enough current so it guarantees the battery won't get drained (in the case discharge is enabled) and will only enable the charge MOSFETs (if charge is disabled and discharge enabled) if the current flow from the battery increases (so it knows the MPPT is not delivering enough to also charge). It uses the parasitic diode of the MOSFET as a feature to do this.
@@upnorthandpersonal Thanks, but I'm trying to follow your argument..
> prevent discharge when discharge is disabled, and prevent charge when charge is disabled
Why not simply switch off both FETs?
> The BMS will enable both MOSFETs when there is enough current so it guarantees
> the battery won't get drained (in the case discharge is enabled)
If discharge is enabled, then both FETs are already on, so a discharge is possible.
(assuming battery voltage is above cut-off)
I've yet to see a convincing reason to switch the FETs individually.
@@graemezimmer604 This would be easier with a diagram and the ability to post links, but let's try - assume the BMS does not do what it's doing in Andy's case and enable the discharge FET at higher current...
Suppose you want to allow discharge, but not charge, for whatever reason (temperature, whatever). Using two MOSFETs independently means you can turn off charging and guarantee discharge is still allowed because of the body diode in the turned off charge FET. The reverse is also true: you can guarantee charging is enabled, while discharge is absolutely blocked since the discharge FET is off; the charge current flows through the body diode of the turned off discharge FET.
The reason for the BMS to auto switch at higher currents is to prevent the FETs overheating from the current through the diode.
Please search for the following which explains this much better than I can in a YT comment:
"Lithium-Ion Batteries and Applications: A Practical and Comprehensive Guide to Lithium-Ion Batteries and Arrays, from Toys to Towns." This book should be available online. Look at page 363 onward. There are other resources as well that explain this; wish my comments with links weren't auto deleted...
Also, if you would turn off both at the same time, you'd disconnect the battery entirely and the charge controller/inverter wouldn't see a battery voltage anymore.
@@upnorthandpersonal Yes, but (I hate "yes, but").
This is pretty much inevitable unless there is a separate wire for the charger/inverter to monitor the battery voltage.
Using the body diode doesn't solve this, especially when the diode is reverse biased.
As far as the charger/inverter is concerned the battery is simply disconnected, something which the charger/inverter needs to be able to deal with.
You should make a wall of Fame for people finding the solution😁
That's a great idea!
Now to check the other end, the low voltage charge/discharge disconnects. Also don't forget what will protect your battery against charge controller failure?
Coming...
Holy Smackimoly !!! :) 🤣😂😁
This is very interesting. I could help diagnosing my issue. I have a similar issue with a JBD bms on a 300ah java energy battery. I am using the xiaoxiang app and when I turn off both the charging and discharge switch I still have about 12.9 volts on the battery when I turn on some light load like my LED lights in my trailer I can see a very small amount of current start to flow. When I turn on more load like my heater blower the charging switch turns itself on and the amperage goes up to 7 or 8 amps also the voltage then increases to the actual battery voltage, in this case 13.4v. I turn off the fan motor the load drops and the charging switch returns itself to the off position and voltage again drops to 12.9 or 12.7 if I have my LED lights on.. I'm trying to figure out if this BMS is bad. Seems similar but reverse of what you are doing here.
This s what Up North and Personal has been saying many times
Tell me about it. Apparently he has found another issue with balancing now. Can't wait to see what that's all about...
It's not a diode this time 😉
@@OffGridGarageAustralia I guess you also meant that stand alone balancer, not the JK integrated one.
@@upnorthandpersonal Yes, the NEEY Active Smart Balancer.
I'm trying to return mine.. Mine does exactly the same. But the minute i put any discharge load on it and actually correct the number of cells. The bms shuts off immediately and then have to unplug the balance cable and set the incorrect number of cells to make it stay on.
Hi can u do test to see if a lead acid battery and lifepo4 batteries can be used by the same inverter. Of course using different charge controllers for each. Would be nice to know if it would work. Thanks.
@Off-grid Garage Have you looked at the Seplos Bms? Love to hear your thoughts, about to venture into a LiFePo4 16s 48v build and pulling together the components👍
Watch this space...
Why this happening with my jk bms all the leads are open bms is off but still its passing full voltage, due to that my cells are over discharging
Morning.
Hi!
My battery 173ah, but bms charge only for 75%, and show 130, and not charge further, what it can be?
Looks like the the charging mode only allows mosfets to turn on when voltage is above batteries. Probably intended to be used with a wall charger that outputs a constant voltage and to limit the power used until it can be charged. Would be interesting if this will toggle automatically when the bms hits a very low voltage.
Hello off grid garage!
I have problem with jkbms it shows "Protection CPUAUX anomaly". Does anyone know what this error? Thank you
Good to know it's fine. However, this situation might occur in an undervoltage situation where the BMS turned off discharging.
But of course, that's not a big issue since it will be out of that state way before you reach maximum voltage on the charger.
That's exactly it - you have to remember that the BMS is a safety device that is supposed to do one thing only: protect the cells. Using these manual features in day to day use is not what this is for. They are intended for diagnosis and trouble shooting if something went really wrong.
As for the negative voltage across to be a mess that would be the forward drop across the mosfets.
Hello, I use jikong BMS, but the charge status always off at the first page at the app.. but at the third page, it's turn on... Why?
And I can't charge the battery, even if at the 3rd page charge turn on..
So, I use emergency button to charge the battery.. can u help me?
Respect i uvazhuha Johany
Dear Sir, your videos are very informative. I got a 2 wheeler supplied by Komaki. As the PassWord is a failure when I try to make minor settings, I need your help. The App opens with 1234. But when I try to change settings, 123456 is a failure. Please help me detect the PW or delete the PW and enter new one,by Forgot PW procedure.
Not certain... but, ~0.6V smells like a PN (diode-like) forward voltage drop...
Of course... 2nd 1/2 of video pretty much confirms my suspicion...
Can you show me that voltage drop again? NO NO please don't, I think I've seen it enough Andy.
just rewind
Hello I'm sorry to bother you but I forgot the custom password I set for bms, how can I do a factory reset, thank you in advance for your reply.
I have a problem with poor bluetooth connection with bms, is there a solution to this problem
Andy, do the same experiment on your QUCC with the relay open and closed... Amazingly you will get the same result.
Stupid😁
I'll do the same experiment on the Daly 🍺
@@OffGridGarageAustralia I can already tell you th eDaly does the same. You have 2 PD's and a closed switch.
If you turn off charging will the solar still work to run your loads during the day. ( so you don't have to cycle the batteries and can run them down further)
This is under and over-voltage protection with a buffer on either end.
Which type of JK BMS do you use?
This is the 8s-24s version for my 16s battery B2A24S20P. There is also a pure 8s version available now which does nto need an additional power supply.
Links are here: off-grid-garage.com/battery-management-systems-bms/
@off-grid garage Is there a fix for the issues you found in this video
i'm curious. what would you do when building not a 16sp1 but a 16sp2 battery setup? would you use one or 2 bms'es ?
Congratulations now you know, How many Angels can dance on the head of a pin. The BMS does it's job what we think is now in question.
And wait for the next video 😊
@@OffGridGarageAustralia Yep I watch them all with glee lol. It is tough to think in absolute terms and get it right every time
how many amp. need to bms for 72v 70ah battery with 3000w motor motorcycle
Hey Andy! Do you have a video of setting JK BMS up with the display? Learned we don't need the external start voltage when using the display...
if it 'Breaks'16:23 , discharge is turning on in the top of the app.
Se,, I didn't not pay attention to that. thanks for pointing this out!
Time fir full load and short cicuit test
Just done it! Video is next...
Hi sir can you help me regarding how to reset the password of jk bms i forgot the password almost
Hi,
I just recieved my JKBMS JK-B2A24S15P (150A)
It’s connected to a 12V (4S) 280Ah (Eve) with a 12V -> 24V Booster to power the BMS.
Everything seems fine EXCEPT it’s not very accurate in reading the Current (which potentially is a huge flaw! How can it know how much capacity is left then…!)
I can calibrate the JKBMS Current to a specific number, for example 10A when charging with 10A, all good BUT as soon as Ampere is lower the accuracy goes way off…
(I have a Victron Smart Shunt to compere with and when Victron says the Load is 3.6A the JKBMS says the Load is only 2.1A)
My normal use is charging with 25A and Discharge with 8-10A (use it in a boat for all 12V loads (sonars, gps, stereo etc) except starter/main motor)
Any one else who has this problem?
Any one who can compere and see if yours are more accurate and mine is faulty?
Fantastic, already have the Daly16s 100A, but this looks so much better.
Did it have low temp shut off?
Yes, it does and it works. Video is coming soon.
@@OffGridGarageAustralia
Oh boy, dang now I HAVE to get it , thanks for a thorough job.
Yeah for Hive-Mind :) WooHoo
up to 96S LFP and NMC BMS
YES, I paid money for this headache. mostly for the heater connection which is also a useless overly confusing gimmick because every heat pad already has a thermostat. bummer.
But the thermostat in the heat pad is more for safety purposes if the normal temperature regulation does not turn of the pad.
@@OffGridGarageAustralia I now see the pads thermostat actually comes on way before needed and would be on a lot more than needed. Most likely because it is for heating big tanks an keeping them from freezing.
Andy, are you from Germany?
Great video, what size are the lugs for BMS all leads?
Thanks Peter. They are M8 lugs.
This JK device is a common port BMS where charger and load are connected to the same P- port. How is this different from the other relay based BMS? How does JK work that it can disconnect charger and load separately if they are both on the same port?
"FET" and "diode". (able to control direction of electricity)
relay -> just a switch, when on allows electricity in both directions, or when off neither direction.
OR what i like to call BLACK MAGIC! lol
@@dobrzpe Thanks. Just found the diagram of mosfet internal connection. Basically two banks of mosfets connected in series with body diode in opposite direction, then turning on/off each bank for desired operation.
:-) Bin jetzt durch , das is ja ein Action Film ... irgendwann krieg i an Herzinfakt mit dir :-) Puh, ich glaub Alibaba wollte schon die Türen verammeln damit keiner das BMS zurückgeben kann :-)
Hahahaha, so muss das sein. Die Seifenoper geht weiter, die Lindenstrasse der Solartechnik!
@@OffGridGarageAustralia cool ich hoffe du bist noch lange dabei, ich torkel auch grad erste Schritte :-) ... wanns scheehe macht ... hahaha
Love to see some test's on the ant bms are they any good ??????
Normally you would not twitch the CHARGE and DISCHARGE wires together.
I suspect bad things could happen at higher currents.
There are no separate charge and discharge wires.
@@upnorthandpersonal Have a look again @ 16:50
@@shanesummerhayes7101 There are two sets of wires on each side (blue and black). The two blue ones are connected together on the PCB, and the two black ones as well. They're just to increase the total gauge of the connecting wire.
This is not the optimal behaviour/design. Not for us tinkers that like to play with the charge and discharge switches.
Keeping in mind that the two MOSFETs are connected in series (Not parallel which might be the more intuitive assumption.) then both MOSFETSs are required to be on for charging and both are required to be on for discharging. So it would be a bit confusing to label one MOSFET as charge and the other as discharge. We could instead label them based of whether their body diode points in to the battery or out of the battery.
The optimal behaviour is:
Charge on and discharge on = both MOSFETs on.
Charge off and discharge off = both MOSFETs off.
Charge on and discharge off = out facing MOSFET on and in facing MOSFET controlled as an ideal diode (in facing diode prevents discharge)
Charge off and discharge on = in facing MOSFET on and out facing MOSFET controlled as an ideal diode (out facing diode prevents charging)
When controlled as an ideal diode there should be only 10 or 20 mV drop. Not 600 mV. We see the BMS is already actively turning on the discharge switch when charge current is "high enough". All they need to do is replace whatever detection they are using with a more sensitive 10 mV detection. I guess they they don't because it would cost a few $ more.
The body diode in the MOSFET that is used for this is essentially parasitic, and therefor far from ideal.
Is there anything like this BMS for those of us who are stuck with 12-volt systems?
We can use this BMS with a DC to DC booster and undervoltage protection if needed. Wait for upcoming video here to confirm. Then there may be other options more suitable and cost effective depending on the what you need and use it for.
@@johthe I am building a 12v system with 8 280AH cells. No high current draws.
The charge goes through mosfetts in the BMS which are semi conducts and therefor not perfect conductors - they have a small onward resistance - Its why they heat up and are fixed to heat sinks - this small resistance account for the small difference in charge voltage going into the BMS and voltage of the battery, this difference will go up in proportion to the charge current.
Sorry, but completely wrong. The reason that FETs are used is that they have exceedingly low resistance when on. The point of the discussion however is that when Andy is seeing the voltage drop, the FETs are NOT on.
Do you ever wish you hadn't gone down this rabbit hole?
Yes, I had seme moments and thought about gardening... 😅
All mosfets have a ON resistance or RDSon this is voltage you are looking at .
It is proportion to the current through the BMS be that charging or discharge .
More coulombs = bigger voltage drop & more heat …....
If the BMS is OFF you see the voltage difference across it .
So the pack voltage minus the power supply voltage .
Body diode & software …. LOL
Be glad the Chinese translators who wrote the most excellent manual, didn't vote to use Roman numerals for all the phone displays. (Sigh)
Time to buy us a 🍻🍻.
Especially @Johthe 😊
🎉🎊🎉🎊🎉🎊🎉
🥳🥳🍺🍺
That actually looks like a safety protocol. When the discharge function is turned off. That way the voltage can never go to high, when the discharge function turned off.
I use 4 different type bms's-They have no ability to adjust anything-The US military batteries and other brain dead bms's will pop up to battery readings on p+/p- once you start to draw a minimum amount of current. It is normal
china revenge
It's not a feature, you were measuring two completely different power sources at different voltages just with a common ground.
smell too much a fake community event yay around not real problem. i dislike buzzing like this
A fake community event?
* First, Following
Hello! Do you think it can be good idea for the noob as myself perhaps to get the screenshots of the « perfect » configuration of the BMS? After this next time you come to south of France we can take a beer!
I will have them on my website soon. Working on this project for a while now.
Also thanks a lot for your 🍺 donation! Much appreciate it.