Make sure that the battery is fully charged b4 checking its impedence for accuracy. Great vid & very important when grouping ur batteries together for balance
I agree with you on most of this, but not all of it. If you are building a battery pack for a high drain application then yes, performing an ESR test can be valuable to keep your cells balanced. But if you are running something really low drain like a powerwall, ESR can be mostly ignored since the drain on each cell is so small to begin with.
Fantastic video! Have same SM8124A and love it. Use it to intermittently check solar battery bank of 8S2P Trojan T-105s (6v) for 48v system. I simply let batteries rest a few hours and test each one. Saved my hide once when a float for one of the cells of my watering system (FLA) got stuck and began to allow plates to become exposed. Also, able to test connection resistance of cables between batteries by subtracting the sum of 2 batts in series from the sum of both batts connected with cabling. Temperature is critical and must be constant among all batts when testing, though. Really love your no-nonsense vid; going to check out your other vids now. Thanks, Nexi Tech.
hum... i would totally concur if i was making a high current type battery back to match IRs, but if I was building a low current drain application pack, i would think the IR wouldnt make a significant difference in pack matching. high current, the high IR batteries will drop voltage very fast and get hotter than the low IR batteries. But for low current drain applications, matching capacity would be more important. and in a perfect world matching IR and capacity would be best.
even if you match used cells capacity with reparkr.com and you get your resistance with in 15mOhms you still have to deal with the fact that you are using different chemistries with different attributes. I think a range of 20mOhms to 30mOhms resistance difference is ok for 30A 6P to 50A 10P battery packs.
It shows different resistance values on the charger because contact surface is different each time you plug in the battery. Try applying small pressure to contacts when you plug in the battery and you will get better readings
Try pushing the negative terminal up with a pencil when you test the cell to apply pressure and a full contact (this should then give you an accurate reading)
Thanx for video. Essential information. Generally speaking,. What values limits do u deem useable for 18650. I am building a ebike pack for the first time. Want a safe and reliable pack. Thanx
Are there BMSs that can discharge more than 100milliamps? I mean are there BMSs that are better at balancing recycled 18650s that might not stay in balance as well as new cells?
Hi and thanks for the video. Lets say I have a simple 2s2p battery pack. Two cells are 1500mAh and 100mOhm and two are 2500mAh 50mOhm. If I take one of each and make a parallel connection won't I end up with a battery pack that is balanced? (two 4000mAh + 33mOhm in series) It would be great to see how much the resistance can deviate within a parallel group. We know that in series it's very important that it's matched but parallel?
If you also know the specs of the cell and what the internal resistance should be from the data sheet. Then you can test the IR and determine if the battery has been abused or has internal shunts in it. In other words if the cell should be 3,000mA capacitor @ 50m Ohms and you measure it at 100 then you will probably find the capacity to be around 50% to 60% or the new cell specs. You can also expect that one to get hatter during charging and discharging. So instead of waisting time charging to see if a cell gets hot I would assume if the internal resistance is 60% or higher then listed in the data sheet it not a gold cell to re-use and you save time on charging and discharging.
Doesn't the state of charge matter for these tests? You have a 20ohm resistor in that meter and its drawing power from the battery, lithium battery has high resistance when full or dead but in the middle can be very low. So your going to get varied results depending on how much power is in each battery. Unless your testing each cell at full and again at empty and see what the difference is, the resistance will vary.
Thanks for the informative video, it was very good. I have a question. It wasn't quite clear from your video about how to use this information. Do I want all the cells in the entire pack to be of very similar resistance, or in each parallel group, or each series group? I'm in the process of collecting cells for a small powerwall (about 4000 cells). Matching resistance will mean a LOT more checking and setting aside a LOT of cells with mismatched resistance. Also, how close should the resistance levels be? 5 or less mili-Ohms, or is a 20+ mili-Ohm difference OK? Thanks.
Hi Eric. Well the best of best is if you can match every cell in every group to get perfect results but in your case you are building power-wall and we talking about 4000 cells so am sure you don't need to match every cell in every group but maybe each cells pack(series) and compare with next cell pack. In your power wall is 4000 cells and am sure your discharging current will not be nearly to much stressing like for example on E-bike battery. Usual DIY Ebike battery made from laptop 18650 battery's has around 120 cells (13S) 48V nominal and around 9 battery in parallel due to lack of space. So you can imagine pulling 40-50A from that battery pack? That's 9 cell in parallel puling 40-50A. That's around 5.5A per cell and most Laptop cells are 2C discharge rate. 2000Mah(2C)= 4A in theory when cell is brand new. And there is a problem. Cells very easy become warm and then hot(plus there is no space and cooling in battery bag on e-bike) and after couple charging/discharging cycles they will go out of balance if resistance is not match and BMS has no chance to balance that battery pack and that pack will degrade and fail in short period of time. So resistance,capacity and voltage match in that application is crucial. So less stress on every cell meaning less to none problems with balancing individual cells group. Am not sure how many cells in serial your 4000 cell pack will have am guessing 24V if you go solar? Or 48V if you going on wind? That´s most common setup, In 48V scenario you will have 300+ cells in every group. If you pulling 100A from that battery pack that will be 0.3A per cell and that is nothing. I don't thing you need to worry to much about resistance in your case even 20 milli-ohm is not a big deal in huge batterypack like yours. But keep in mind if one cell die that can discharge and kill whole cellpack(300cells) every cell that is connected in parallel and dis-balance whole pack. So I would just check every cell for precaution. maybe you find some cell with 400-600mili-ohm resistance? I would not use that cell. Max 200mili-ohm is ''OK' cells for low power drain application. Adding small fuse wire to every cells is good option too or adding voltage tester alarm? Look my video about voltage testers it could be useful to you. There you can see dis-balancing in live :) Regards! ruclips.net/video/VTMQ0Eg8Xhc/видео.html
Thanks very much for your clear and detailed answer. It was very helpful. I'm looking at a solar setup, but still deciding between 24/48 V. Most likely 24V due to availability/price of charge controllers and inverters in my area. Thanks again.
The way I learned years ago is that each series cells need to be close to the same internal resistance at the same state of charge. When you have parallel cells, they don't have to match, but they need to add together so each series cells match. Here is an example of a 3p4s battery: P1. P2. P3. Total S1. 65. 85. 25. 14.9 S2. 60. 25. 45. 12.5 S3. 75. 55. 25. 14 S4. 30 45. 80. 14.7 In S1 65milliohm, 85mohm, and 25mohm add up to 14.9mohm when in parallel. See how the totals are all close. Numbers like these are close enough. They don't have to be perfect. Parallel resistance doesn't add together. There is a formula, but I use a parallel resistance calculator on Google.
Hello,i want to ask a question,does resistance matter if i a am building a battery pack out of 15 batteries and the maximum load on the pack will be about 15A. Each cell can output 4A...so if i have about 1A load on each battery is it necessary for the batteries to have the same resistance ? because buying new batteries would be a big expense for my project....thanks for any answer :D
Plazma Plazmitch 15 Batteries in total? 15 bat in serial configuration? 15 bat in parallel configuration? What is the battery pack configuration? Voltage? BMS? Usage? I need more info...
"Hi, I have a question regarding the internal resistance of 18650 battery 1- What is the risk of building a recycled 18650 lithium battery without checking and measuring the internal resistance? 2- How is the battery built after measuring and knowing the internal resistance values of the 18650 batteries, especially if the internal resistance values for each battery differ from the others for 18650 for recycled lithium batteries?"
cells that are were manufactured next to each other years ago and after being used for years will now have different capacities. in my experience, cells from the same old laptop battery can have up to 200mah difference. That means lower capacity batteries will get under voltage while the rest are still draining, in high current draw the lower capacity batteries will heat up more. heat is the biggest enemy
@@daftnord4957 EXCEPT ... when we create a Power Wall Battery, with many cells in parallel and many cells in series, we arrange the cells in parallel groups, such that each parallel group has nearly the SAME Amp-Hour capacity ! This significantly reduces the over-charge & under-charge issue and allows the BMS to tightly BALANCE !
I think those cells have different c rate..how can you factor that in?..after you match these cells carefully with their IR and capacity, how does each cell behaves when discharging with regards to their different C rates?..do they discharge evenly?..thank you..
Thx for an informative video. I'm getting ready to build a 20s3p pack using identical cells but with varying condition. Some have a bit higher resistance and lower capacity. My question is, to achieve as balanced a pack as possible should I focus on capacity or resistance first? Every group of 3 cells in parallel should have similar total resistance and capacity, yes? Can I calculate resulting resistance by using 1/R = 1/R1 + 1/R2 + 1/R3 ? So for example I can mix 30+30+30mOhm in one group and have 20+30+40mOhm in another group and still have balanced groups? Thanks!
Mike H Mike H 1- Yes 2- Yes 3- Yes Also I would suggests that you connect balance connectors on the whole pack, for example 2x7 and 1x6 conector and use 3 of ISDT BC 8S to monitor voltage and live discharge diagram under the load. Using this device you can easily see in live voltage sag under the load of every 3p cell group. It's pretty awesome device that has adjustable High voltage protection as well. Check video here: ruclips.net/video/VTMQ0Eg8Xhc/видео.html
thanks for your video. The closer to zero or the lower the resistance the better for the life of a future battery pack, right ??? On my meter which ohm's option do I choose to make this measurement ???
Well it looks good but the numbers in your resistance meter are all over the place! How do you get consistance in a meter that the reading is all over the place?
That's how device works guys. You have to wait few second to get exactly resistance number. Pressure on your fingers needs to be same and you have to hold few sec to impediance go down to result number. If you do so device will hold results number. I move from one battery to next battery very quickly and you get wrong feeling that numbers are jumping. I should go slower. Sorry guys.
How close an IR do you think the cells need to be? The 85mOhms and 60mOhms in your video that you said can't be in the same cell group but that is only a 0.015 Ohms difference. In that case it appears you are saying that every cell in the whole battery needs to be less that 0.015 Ohms difference? I don't think that is necessary in a 30A to 50A maximum discharge pack that is 6P to 10P made from cells with different chemistry, resistance, and capacity. With different cell resistance you will have different allowable discharge rates. You Sony VCT4s are 13mOhms datasheet and 17mOhms real life. They are 20A high drain cells. So cell Resistance and discharge rate are indirectly proportional -- low resistance == high discharge. So you don't want to be pulling 60A from a 6P battery pack when some of the cells are high resistance and low discharge. So if you have a 6P battery and you use 20A cells like VTC4's and other cells that are 60mOhms and perhaps 5A cells and you draw 60A from the 6P you will harm the 5A cells. So what you need to do in that case is make your maximum draw xP * 5A for 30A maximum. When you are dealing with cells connected in parallel they self-balance when the current draw stops. So when you draw current some cells will have a higher voltage drop due to higher Resistance and during a current draw the higher resistance cells will discharge less energy and when the current draw is removed they will be at different voltages and they will automatically self-balance so that they all have the same voltage. The BMS balancing you discuss is serial balancing as parallel cells self-balance. When it comes to serial balancing it is about having the same capacity in each cell group that is important, way more important that the internal resistance of the cells. With used cells you can use repackr.com for that. But still the internal resistance is important to keep as close as possible because what will happen is the higher resistance cells will loose capacity faster than the lower resistance cells and your cell group capacity will become different and that is why serial balancing with a BMS or balancing charger is required. When you have used cells you have different capacities, different resistance, AND different chemistries the cells are deteriating at different rates. To think that you are going to be able to keep a battery pack balanced made from cells with different capacities, resistance, and chemistries, you are expecting a bit to much. Also for smaller packs like 13S6P 100mA will work to balance, just the balancing bleed will be a bit slow but you can leave it on over night and it will balance it self out. Of course what will happen is the higher resistance cells will loose capacity faster than the lower resistance cells and your cell group capacity will become different. Now 100mA on your bit battery hidden in the corner that is a different story. Also when you want to group your used cells together into same Ah groups you can use repackr.com which works well for used cells.
If your BMS can maintain the same voltage across the Parallel Cell Groups then your Power Wall is OK. It all depends upon: a) How fast you charge; b) how fast you discharge; c) How many many milliamps your BMS can dissipate. There is NO such rule that +/- 15 milliohms difference is bad ...
@@MrSummitville while higher Resistance cells will cycle more Watts in sag and heat loss a 15mΩ difference between cells it not an issue. If you using high discharge cells like VTC6 cells that are around 20mΩ then you shouldn't mix 85mΩ cells with those.
@@bobmutchseo After 3 years this still has become an issue. How many YEARS did it take before Internal Resistance became an issue with your power wall?
@@MrSummitville I don't have a power wall. again I think trying to get the IR of the cell you us in a battery pack with in 15mΩ your going to almost have to use new cells.
Franco Pieruccini Faria That will mostly depend on the quality and capabilities of the bms that you select for them... Generally speaking, most (Chinese) bms manufacturers recommend that the cells used be matched well, so each cell paired up match each other at least to voltage ≦0.05V, IR≦15 mΩ,capacity≦30mAh. Doing this will help the longevity and reliability of the assembled battery pack.
Franco Pieruccini Faria Yes, those are the variance figures I generally rely on when matching cells for constructing packs. Obv when building packs, for best consistency it's best if the cells used are new and of the same type and generally when using new (quality) cells, people don't bother checking their resistance and capacity, but imo one should anyway, because even if only one cell is not to spec, the "chain will only be as strong as its weakest link."
it's ok to have different resistance, that just means you have a cell that will have a lower discharge rate, as long as your discharge per cell is below the maximum dischange of your weakest cell you are ok. Of course what will happen is the higher resistance cells will loose capacity faster than the lower resistance cells and your cell group capacity will become different.
@@bobmutchseo so what’s best to check for battery capacity when doing a pack ? I have a problem with a pack I made they are from the same 1c rating 2000mah each and I made a 6s1p pack and my charger has “balanced them and fully charged them “ all show same voltages when charged but I have noticed since I don’t have a bms that in the over all24v output cables I get after a load of .5A draw a lower voltage on cell1/2 . I have the 6s balance leads cables to connect to the smart charger . Yet resistance of cell 1 is 46.9milliohms same on 2nd 3rd is 50,4th48.2,5th47.8,6th43.9 after fully charge same was when plugged in when discharged and charge but then again I have done a capacity test and that I don’t know how to do?
So a charger with a capacity of 300 mA balance is better then one with 100 mA balance? Can you detail please? The diff between cells must be maximum 100mA ? or why?
The closest the better. If you can not close match resistance in one cell groups then split those higher resistance cells in other cell packs as well. And when you chech each parallel cell group they should be the same or very close resistance. Then connect those parallel cell packs in series. By doing this your battery will be more balanced and it will last longer.
so there you are hiding your battery packs!hmmm...Nice info there.What is a max number for 18650 internal resistance to use it to a battery pack?for example 150? can be used?And something last as more internal resistance has a battery means is used more so it drains faster?
With the YR 1035 milliometer tester I measured the internal resistance and voltage of numerous rechargeable batteries that I had finished recharging. I wanted these conditions to see the parameters at full charge of all the batteries. I noticed that some of the same make and model have almost the same voltage (varies by a few millivolts) but different values of internal resistance (sometimes even double and triple). This is because some batteries are old, others partially new and others new (an older battery has a higher internal resistance). So the data I have are: internal resistance and voltage at full charge but without load connected to the battery. With these data with which calculation is it possible to know the real charge in Ampere available to the battery? To give an example: two identical batteries measure like this: batt1: 1,2806 volt and 0,0227 Ohm (or 22,7 mOhm) batt 2: 1.3204 volt and 0.0216 (or 21.6 mOhm) How many amps does one and the other battery have inside? Thank you
Say I want to build a 6S 4P and I have different old cells with different capacity groups off laptops, which ones do I add for the series groups and which ones for the parallel groups ? Meaning is it more important that the capacity is closer in the series groups or in the parallel groups?
Niko Niko You need to have close capacity in every parallel group or in all 6 cells group (6S) You don't have to have equal number of cells but you need to have equal total capacity in each group or you will have unbalanced battery directy after first discharging/charging cycle. Also try to get resistance of every cells group(1-6) close as possible.
@@NexiTech How far of can the resistance be from each parallel group? I understand that the capacity of every parallel group needs to be close. Are you saying that even if the batteries in parallel are a bit of, it does not matter as long as the next parallel group is close to the same?
Any battery, no matter its chemistry, which, if being tested, shows a drop of its original capacity (in mAh) equal or more than 20%, or in other words if you get only the 80% of its original capacity, it's considered as worn out. From that condition onwards, it will not last any longer if you intend to keep using it. Talking about Lithium batteries specifically, no balancer will work perfectly in this condition. The deviation between the cells will always get bigger and growing. When a new lithium battery measures 20mOhm, the rule of thumb is "reject it if it measures the double internal resistance", I.e. 40mOhm. If you'll measure its capacity you will easily understand why is that true. Therefore the best info this instrument can give you, is when to reject worn out batteries, instead of trying to match old ones, at the end of their operational life. Any rechargeable battery with high internal resistance consumes (in fact wastes) energy during both, charging and discharging. Through its internal resistance, in both processes, it transforms this energy in heat, which is nothing but loss of energy. This simply means that a worn out battery can never be fully charged (referenced to its nominal capacitance), while it gets much more quickly discharged if put in service, (because its internal resistance adds to its external load)...Matching worn out cells is practically meaningless and is, in any case and among others, waste of time.
@@MrSummitville If you refer to my comment, the answer is: it depends on what you mean "operational", in reference to what is theoretically accepted on the topic, as I described it above. All the necessary details are there. Nothing more, nothing less...
@@ΠάριςΑζής You stated, " ... From that condition onwards, it will not last any longer if you intend to keep using it ..." I consider another 3 - 4 years, so far, as a very long time ...
@@MrSummitville Yes, perhaps it will last 10 years more, but AT WHAT CAPACITY? You seem to neglect this...detail, but this is the crucial thing. A worn out battery takes much more time (than that it was taking when it was new), and discharges at a much shorter time (than that it was ordinarily lasting) on a given load. And this effect worsens with time. You need to charge the set very frequently, while it cannot support your load for long time any longer. This is because the losses (in form of heat) within the worn cells are getting bigger and bigger with time, no matter if you charge or discharge the battery. And the internal resistances of worn out cells change very fast as well. In other words, when playing with worn out cells, their matching of, say, today, will reveal much of deviation after relatively few cycles of operation. At least this is not to be trusted in terms of reliability, especially if you need to support crucial loads. For playing and having fan, this is another story, and one can build as many power walls he needs. In any case one must distinguish between serious professional applications and hobbyist playing...
@@ΠάριςΑζής I have found Power Walls with *USED* 18650 Cells that have been in-use for 5 years. Who cares if the capacity drops 10%, after another 5 years? Families are actually living Off-Grid with 18650 Power Walls. It appears that you have nothing but complaints and excuses, with no real-world experience of living off-grid ...
With the YR 1035 milliometer tester I measured the internal resistance and voltage of numerous rechargeable batteries that I had finished recharging. I wanted these conditions to see the parameters at full charge of all the batteries. I noticed that some of the same make and model have almost the same voltage (varies by a few millivolts) but different values of internal resistance (sometimes even double and triple). This is because some batteries are old, others partially new and others new (an older battery has a higher internal resistance). So the data I have are: internal resistance and voltage at full charge but without load connected to the battery. With these data with which calculation is it possible to know the real charge in Ampere available to the battery? To give an example: two identical batteries measure like this: batt1: 1,2806 volt and 0,0227 Ohm (or 22,7 mOhm) batt 2: 1.3204 volt and 0.0216 (or 21.6 mOhm) How many amps does one and the other battery have inside? Thank you
There are different type of batteries. Some with HIGH discharge rate and other with Low discharge rate (High discharge rate used for power tools - e.g.: screwdrivers, drills, etc. LOW discharge rate for computers, flashlights, etc) High discharge rate battery has a MUCH lower internal resistance (around 20~50 mOhms) Low Discharge rate battery has higher (80~150 mOhms)
Make sure that the battery is fully charged b4 checking its impedence for accuracy. Great vid & very important when grouping ur batteries together for balance
I agree with you on most of this, but not all of it.
If you are building a battery pack for a high drain application then yes, performing an ESR test can be valuable to keep your cells balanced. But if you are running something really low drain like a powerwall, ESR can be mostly ignored since the drain on each cell is so small to begin with.
The discharge on 18650s is Around 2% to 3% a month .
@@MasterYota1 Who cares if self-discharge is 2% or 3% ever month ... When the cells are top-balanced nearly every day !
Fantastic video! Have same SM8124A and love it. Use it to intermittently check solar battery bank of 8S2P Trojan T-105s (6v) for 48v system. I simply let batteries rest a few hours and test each one. Saved my hide once when a float for one of the cells of my watering system (FLA) got stuck and began to allow plates to become exposed. Also, able to test connection resistance of cables between batteries by subtracting the sum of 2 batts in series from the sum of both batts connected with cabling. Temperature is critical and must be constant among all batts when testing, though. Really love your no-nonsense vid; going to check out your other vids now. Thanks, Nexi Tech.
Hi, Nice to see your comment, do you have a table that shows resistance of cables for current and distance and volt?
hum... i would totally concur if i was making a high current type battery back to match IRs, but if I was building a low current drain application pack, i would think the IR wouldnt make a significant difference in pack matching. high current, the high IR batteries will drop voltage very fast and get hotter than the low IR batteries. But for low current drain applications, matching capacity would be more important. and in a perfect world matching IR and capacity would be best.
even if you match used cells capacity with reparkr.com and you get your resistance with in 15mOhms you still have to deal with the fact that you are using different chemistries with different attributes. I think a range of 20mOhms to 30mOhms resistance difference is ok for 30A 6P to 50A 10P battery packs.
It shows different resistance values on the charger because contact surface is different each time you plug in the battery. Try applying small pressure to contacts when you plug in the battery and you will get better readings
Try pushing the negative terminal up with a pencil when you test the cell to apply pressure and a full contact (this should then give you an accurate reading)
This worked. Got the same reading every time.
Thanx for video. Essential information. Generally speaking,. What values limits do u deem useable for 18650. I am building a ebike pack for the first time. Want a safe and reliable pack. Thanx
Are there BMSs that can discharge more than 100milliamps? I mean are there BMSs that are better at balancing recycled 18650s that might not stay in balance as well as new cells?
Hi and thanks for the video. Lets say I have a simple 2s2p battery pack. Two cells are 1500mAh and 100mOhm and two are 2500mAh 50mOhm. If I take one of each and make a parallel connection won't I end up with a battery pack that is balanced? (two 4000mAh + 33mOhm in series) It would be great to see how much the resistance can deviate within a parallel group. We know that in series it's very important that it's matched but parallel?
I am curious what is the maximum variation of IR acceptable?
If you also know the specs of the cell and what the internal resistance should be from the data sheet. Then you can test the IR and determine if the battery has been abused or has internal shunts in it. In other words if the cell should be 3,000mA capacitor @ 50m Ohms and you measure it at 100 then you will probably find the capacity to be around 50% to 60% or the new cell specs. You can also expect that one to get hatter during charging and discharging. So instead of waisting time charging to see if a cell gets hot I would assume if the internal resistance is 60% or higher then listed in the data sheet it not a gold cell to re-use and you save time on charging and discharging.
Doesn't the state of charge matter for these tests? You have a 20ohm resistor in that meter and its drawing power from the battery, lithium battery has high resistance when full or dead but in the middle can be very low. So your going to get varied results depending on how much power is in each battery. Unless your testing each cell at full and again at empty and see what the difference is, the resistance will vary.
I guess I'm kind of off topic but do anyone know a good website to watch new series online ?
Thanks for the informative video, it was very good.
I have a question. It wasn't quite clear from your video about how to use this information. Do I want all the cells in the entire pack to be of very similar resistance, or in each parallel group, or each series group? I'm in the process of collecting cells for a small powerwall (about 4000 cells). Matching resistance will mean a LOT more checking and setting aside a LOT of cells with mismatched resistance.
Also, how close should the resistance levels be? 5 or less mili-Ohms, or is a 20+ mili-Ohm difference OK?
Thanks.
Hi Eric. Well the best of best is if you can match every cell in every group to get perfect results but in your case you are building power-wall and we talking about 4000 cells so am sure you don't need to match every cell in every group but maybe each cells pack(series) and compare with next cell pack. In your power wall is 4000 cells and am sure your discharging current will not be nearly to much stressing like for example on E-bike battery. Usual DIY Ebike battery made from laptop 18650 battery's has around 120 cells (13S) 48V nominal and around 9 battery in parallel due to lack of space. So you can imagine pulling 40-50A from that battery pack? That's 9 cell in parallel puling 40-50A. That's around 5.5A per cell and most Laptop cells are 2C discharge rate. 2000Mah(2C)= 4A in theory when cell is brand new. And there is a problem. Cells very easy become warm and then hot(plus there is no space and cooling in battery bag on e-bike) and after couple charging/discharging cycles they will go out of balance if resistance is not match and BMS has no chance to balance that battery pack and that pack will degrade and fail in short period of time. So resistance,capacity and voltage match in that application is crucial. So less stress on every cell meaning less to none problems with balancing individual cells group. Am not sure how many cells in serial your 4000 cell pack will have am guessing 24V if you go solar? Or 48V if you going on wind? That´s most common setup, In 48V scenario you will have 300+ cells in every group. If you pulling 100A from that battery pack that will be 0.3A per cell and that is nothing. I don't thing you need to worry to much about resistance in your case even 20 milli-ohm is not a big deal in huge batterypack like yours. But keep in mind if one cell die that can discharge and kill whole cellpack(300cells) every cell that is connected in parallel and dis-balance whole pack. So I would just check every cell for precaution. maybe you find some cell with 400-600mili-ohm resistance? I would not use that cell. Max 200mili-ohm is ''OK' cells for low power drain application. Adding small fuse wire to every cells is good option too or adding voltage tester alarm? Look my video about voltage testers it could be useful to you. There you can see dis-balancing in live :) Regards! ruclips.net/video/VTMQ0Eg8Xhc/видео.html
Thanks very much for your clear and detailed answer. It was very helpful. I'm looking at a solar setup, but still deciding between 24/48 V. Most likely 24V due to availability/price of charge controllers and inverters in my area.
Thanks again.
The way I learned years ago is that each series cells need to be close to the same internal resistance at the same state of charge. When you have parallel cells, they don't have to match, but they need to add together so each series cells match.
Here is an example of a 3p4s battery:
P1. P2. P3. Total
S1. 65. 85. 25. 14.9
S2. 60. 25. 45. 12.5
S3. 75. 55. 25. 14
S4. 30 45. 80. 14.7
In S1 65milliohm, 85mohm, and 25mohm add up to 14.9mohm when in parallel. See how the totals are all close. Numbers like these are close enough. They don't have to be perfect. Parallel resistance doesn't add together. There is a formula, but I use a parallel resistance calculator on Google.
Hello,i want to ask a question,does resistance matter if i a am building a battery pack out of 15 batteries and the maximum load on the pack will be about 15A. Each cell can output 4A...so if i have about 1A load on each battery is it necessary for the batteries to have the same resistance ? because buying new batteries would be a big expense for my project....thanks for any answer :D
Plazma Plazmitch 15 Batteries in total? 15 bat in serial configuration? 15 bat in parallel configuration? What is the battery pack configuration? Voltage? BMS? Usage? I need more info...
Thanks for the video. But what about battery capacity, do we not need also the match those as close as possible?
Yes you need to match capacity as well.
"Hi, I have a question regarding the internal resistance of 18650 battery
1- What is the risk of building a recycled 18650 lithium battery without checking and measuring the internal resistance?
2- How is the battery built after measuring and knowing the internal resistance values of the 18650 batteries, especially if the internal resistance values for each battery differ from the others for 18650 for recycled lithium batteries?"
cells that are were manufactured next to each other years ago and after being used for years will now have different capacities. in my experience, cells from the same old laptop battery can have up to 200mah difference. That means lower capacity batteries will get under voltage while the rest are still draining, in high current draw the lower capacity batteries will heat up more. heat is the biggest enemy
@@daftnord4957 EXCEPT ... when we create a Power Wall Battery, with many cells in parallel and many cells in series, we arrange the cells in parallel groups, such that each parallel group has nearly the SAME Amp-Hour capacity ! This significantly reduces the over-charge & under-charge issue and allows the BMS to tightly BALANCE !
I think those cells have different c rate..how can you factor that in?..after you match these cells carefully with their IR and capacity, how does each cell behaves when discharging with regards to their different C rates?..do they discharge evenly?..thank you..
Thx for an informative video. I'm getting ready to build a 20s3p pack using identical cells but with varying condition. Some have a bit higher resistance and lower capacity. My question is, to achieve as balanced a pack as possible should I focus on capacity or resistance first? Every group of 3 cells in parallel should have similar total resistance and capacity, yes? Can I calculate resulting resistance by using 1/R = 1/R1 + 1/R2 + 1/R3 ? So for example I can mix 30+30+30mOhm in one group and have 20+30+40mOhm in another group and still have balanced groups? Thanks!
Mike H Mike H
1- Yes
2- Yes
3- Yes
Also I would suggests that you connect balance connectors on the whole pack, for example 2x7 and 1x6 conector and use 3 of ISDT BC 8S to monitor voltage and live discharge diagram under the load. Using this device you can easily see in live voltage sag under the load of every 3p cell group.
It's pretty awesome device that has adjustable High voltage protection as well.
Check video here: ruclips.net/video/VTMQ0Eg8Xhc/видео.html
Always use cell level fusing when creating large packs like the one by the wall.
More about the Anet A6, pls.
Great video BTW. Love yourvids
Iván Expósito Coming in max 24h :)
Done :)
Do capacity matter to cell?
If one cell had 2600mah and another brand 2000mah and both have same resistent will this be ok for battery bank
@@khalilkh7389 Yes it will be ok but you need to match all cells group to have the same capacity.
@@NexiTech thanks 👍
Which is best for internal resistance
Higher or Lower?
Thanks
The lower the number the better battery.
@@NexiTech Thankyou
thanks for your video. The closer to zero or the lower the resistance the better for the life of a future battery pack, right ??? On my meter which ohm's option do I choose to make this measurement ???
No, do not us a DMM, use an Internal Resistance Meter ...
Well it looks good but the numbers in your resistance meter are all over the place! How do you get consistance in a meter that the reading is all over the place?
santiago vindell glad that you are saying that i watched the video and he didn’t get a solid number, The numbers keeped deleting by one numeral
That's how device works guys. You have to wait few second to get exactly resistance number. Pressure on your fingers needs to be same and you have to hold few sec to impediance go down to result number. If you do so device will hold results number. I move from one battery to next battery very quickly and you get wrong feeling that numbers are jumping. I should go slower. Sorry guys.
Nexi Tech Ok good to know.. Thanks.
Wow 260 cells in that pack he had behind the foam wall lol
How close an IR do you think the cells need to be? The 85mOhms and 60mOhms in your video that you said can't be in the same cell group but that is only a 0.015 Ohms difference.
In that case it appears you are saying that every cell in the whole battery needs to be less that 0.015 Ohms difference? I don't think that is necessary in a 30A to 50A maximum discharge pack that is 6P to 10P made from cells with different chemistry, resistance, and capacity.
With different cell resistance you will have different allowable discharge rates. You Sony VCT4s are 13mOhms datasheet and 17mOhms real life. They are 20A high drain cells. So cell Resistance and discharge rate are indirectly proportional -- low resistance == high discharge. So you don't want to be pulling 60A from a 6P battery pack when some of the cells are high resistance and low discharge. So if you have a 6P battery and you use 20A cells like VTC4's and other cells that are 60mOhms and perhaps 5A cells and you draw 60A from the 6P you will harm the 5A cells. So what you need to do in that case is make your maximum draw xP * 5A for 30A maximum.
When you are dealing with cells connected in parallel they self-balance when the current draw stops. So when you draw current some cells will have a higher voltage drop due to higher Resistance and during a current draw the higher resistance cells will discharge less energy and when the current draw is removed they will be at different voltages and they will automatically self-balance so that they all have the same voltage.
The BMS balancing you discuss is serial balancing as parallel cells self-balance. When it comes to serial balancing it is about having the same capacity in each cell group that is important, way more important that the internal resistance of the cells. With used cells you can use repackr.com for that. But still the internal resistance is important to keep as close as possible because what will happen is the higher resistance cells will loose capacity faster than the lower resistance cells and your cell group capacity will become different and that is why serial balancing with a BMS or balancing charger is required.
When you have used cells you have different capacities, different resistance, AND different chemistries the cells are deteriating at different rates. To think that you are going to be able to keep a battery pack balanced made from cells with different capacities, resistance, and chemistries, you are expecting a bit to much. Also for smaller packs like 13S6P 100mA will work to balance, just the balancing bleed will be a bit slow but you can leave it on over night and it will balance it self out.
Of course what will happen is the higher resistance cells will loose capacity faster than the lower resistance cells and your cell group capacity will become different.
Now 100mA on your bit battery hidden in the corner that is a different story.
Also when you want to group your used cells together into same Ah groups you can use repackr.com which works well for used cells.
If your BMS can maintain the same voltage across the Parallel Cell Groups then your Power Wall is OK. It all depends upon: a) How fast you charge; b) how fast you discharge; c) How many many milliamps your BMS can dissipate. There is NO such rule that +/- 15 milliohms difference is bad ...
@@MrSummitville while higher Resistance cells will cycle more Watts in sag and heat loss a 15mΩ difference between cells it not an issue. If you using high discharge cells like VTC6 cells that are around 20mΩ then you shouldn't mix 85mΩ cells with those.
@@bobmutchseo After 3 years this still has become an issue. How many YEARS did it take before Internal Resistance became an issue with your power wall?
@@MrSummitville I don't have a power wall. again I think trying to get the IR of the cell you us in a battery pack with in 15mΩ your going to almost have to use new cells.
Hi, In your opinion what would be the tolerance value of capacity and internal resistance values to match 2 or more 18650 cells?
Franco Pieruccini Faria That will mostly depend on the quality and capabilities of the bms that you select for them...
Generally speaking, most (Chinese) bms manufacturers recommend that the cells used be matched well, so each cell paired up match each other at least to voltage ≦0.05V, IR≦15 mΩ,capacity≦30mAh.
Doing this will help the longevity and reliability of the assembled battery pack.
ABritInNY Very good explanation and well consistent. Have you made many pack with these limits mentioned and worked out as intended?? Many thanks
Franco Pieruccini Faria Yes, those are the variance figures I generally rely on when matching cells for constructing packs. Obv when building packs, for best consistency it's best if the cells used are new and of the same type and generally when using new (quality) cells, people don't bother checking their resistance and capacity, but imo one should anyway, because even if only one cell is not to spec, the "chain will only be as strong as its weakest link."
Will that tester work with lipo cells? So I can test my drone batteries ?
Rowan Ballinger Yes it will.
Nexi Tech one more question do you match cell resistance in series or parallel ?
Do the "10 min Resistance/Capacity Hack for Opus BT C3100" to correct the resistance reading.
Thanks for the info! I will for sure do it. Have a great day.
can you please please please make a video on how to hook up a anet a8 to a pc ! :) :)
subscribed/liked...right up my alley!
U Do It Thanks :)
Could we add resistance to a cell to balance it with another?
it's ok to have different resistance, that just means you have a cell that will have a lower discharge rate, as long as your discharge per cell is below the maximum dischange of your weakest cell you are ok. Of course what will happen is the higher resistance cells will loose capacity faster than the lower resistance cells and your cell group capacity will become different.
@@bobmutchseo so what’s best to check for battery capacity when doing a pack ? I have a problem with a pack I made they are from the same 1c rating 2000mah each and I made a 6s1p pack and my charger has “balanced them and fully charged them “ all show same voltages when charged but I have noticed since I don’t have a bms that in the over all24v output cables I get after a load of .5A draw a lower voltage on cell1/2 . I have the 6s balance leads cables to connect to the smart charger . Yet resistance of cell 1 is 46.9milliohms same on 2nd 3rd is 50,4th48.2,5th47.8,6th43.9 after fully charge same was when plugged in when discharged and charge but then again I have done a capacity test and that I don’t know how to do?
So a charger with a capacity of 300 mA balance is better then one with 100 mA balance? Can you detail please? The diff between cells must be maximum 100mA ? or why?
I'm confused now can't you just check resistance within normal multimeter
No you can not test Lithium battery resistanse with multimeter.
How close should the resistance be to each other?
The closest the better. If you can not close match resistance in one cell groups then split those higher resistance cells in other cell packs as well. And when you chech each parallel cell group they should be the same or very close resistance. Then connect those parallel cell packs in series. By doing this your battery will be more balanced and it will last longer.
@@NexiTech Ok awesome. I was wondering about if the match up should be in parallel or series and you answered that as well. Thank you!
@@NexiTech One last question. What if they are matched in resistance and capacity but not discharge rate? Say some cells are 15a and others are 10a?
Not a problem if you have many cells in the battery pack. They will share the load.
@@NexiTech Thank you so much! I just bought 50lbs of drill and tool batteries and that was definitely my concern. 🙏🤘
hello, can NI-MH resistance be measured?
NICOLAI COTUR Yes it can
@@NexiTech thanks
so there you are hiding your battery packs!hmmm...Nice info there.What is a max number for 18650 internal resistance to use it to a battery pack?for example 150? can be used?And something last as more internal resistance has a battery means is used more so it drains faster?
With the YR 1035 milliometer tester I measured the internal resistance and voltage of numerous rechargeable batteries that I had finished recharging. I wanted these conditions to see the parameters at full charge of all the batteries. I noticed that some of the same make and model have almost the same voltage (varies by a few millivolts) but different values of internal resistance (sometimes even double and triple). This is because some batteries are old, others partially new and others new (an older battery has a higher internal resistance).
So the data I have are: internal resistance and voltage at full charge but without load connected to the battery. With these data with which calculation is it possible to know the real charge in Ampere available to the battery? To give an example: two identical batteries measure like this:
batt1: 1,2806 volt and 0,0227 Ohm (or 22,7 mOhm)
batt 2: 1.3204 volt and 0.0216 (or 21.6 mOhm)
How many amps does one and the other battery have inside? Thank you
Say I want to build a 6S 4P and I have different old cells with different capacity groups off laptops, which ones do I add for the series groups and which ones for the parallel groups ? Meaning is it more important that the capacity is closer in the series groups or in the parallel groups?
Niko Niko You need to have close capacity in every parallel group or in all 6 cells group (6S) You don't have to have equal number of cells but you need to have equal total capacity in each group or you will have unbalanced battery directy after first discharging/charging cycle. Also try to get resistance of every cells group(1-6) close as possible.
@@NexiTech How far of can the resistance be from each parallel group? I understand that the capacity of every parallel group needs to be close. Are you saying that even if the batteries in parallel are a bit of, it does not matter as long as the next parallel group is close to the same?
fiy: cheap lipo chargers like the isdt nano can measure internal resistance as well as charge up to 6 li-ion cells
I don't really care about internal resistance .. capacity matching is more important for me ...
Yep i looked at all of your batteries and i suggest that you throw them away because it's a load of crap. :-))
Any battery, no matter its chemistry, which, if being tested, shows a drop of its original capacity (in mAh) equal or more than 20%, or in other words if you get only the 80% of its original capacity, it's considered as worn out.
From that condition onwards, it will not last any longer if you intend to keep using it.
Talking about Lithium batteries specifically, no balancer will work perfectly in this condition. The deviation between the cells will always get bigger and growing.
When a new lithium battery measures 20mOhm, the rule of thumb is "reject it if it measures the double internal resistance", I.e. 40mOhm. If you'll measure its capacity you will easily understand why is that true.
Therefore the best info this instrument can give you, is when to reject worn out batteries, instead of trying to match old ones, at the end of their operational life.
Any rechargeable battery with high internal resistance consumes (in fact wastes) energy during both, charging and discharging. Through its internal resistance, in both processes, it transforms this energy in heat, which is nothing but loss of energy. This simply means that a worn out battery can never be fully charged (referenced to its nominal capacitance), while it gets much more quickly discharged if put in service, (because its internal resistance adds to its external load)...Matching worn out cells is practically meaningless and is, in any case and among others, waste of time.
Then how do explain that dozens, upon dozens of Power Walls, made from *USED* 18650 cells, are still operational after 3 - 4 years?
@@MrSummitville If you refer to my comment, the answer is: it depends on what you mean "operational", in reference to what is theoretically accepted on the topic, as I described it above. All the necessary details are there. Nothing more, nothing less...
@@ΠάριςΑζής You stated, " ... From that condition onwards, it will not last any longer if you intend to keep using it ..." I consider another 3 - 4 years, so far, as a very long time ...
@@MrSummitville Yes, perhaps it will last 10 years more, but AT WHAT CAPACITY? You seem to neglect this...detail, but this is the crucial thing.
A worn out battery takes much more time (than that it was taking when it was new), and discharges at a much shorter time (than that it was ordinarily lasting) on a given load.
And this effect worsens with time. You need to charge the set very frequently, while it cannot support your load for long time any longer.
This is because the losses (in form of heat) within the worn cells are getting bigger and bigger with time, no matter if you charge or discharge the battery.
And the internal resistances of worn out cells change very fast as well.
In other words, when playing with worn out cells, their matching of, say, today, will reveal much of deviation after relatively few cycles of operation. At least this is not to be trusted in terms of reliability, especially if you need to support crucial loads.
For playing and having fan, this is another story, and one can build as many power walls he needs.
In any case one must distinguish between serious professional applications and hobbyist playing...
@@ΠάριςΑζής I have found Power Walls with *USED* 18650 Cells that have been in-use for 5 years. Who cares if the capacity drops 10%, after another 5 years? Families are actually living Off-Grid with 18650 Power Walls. It appears that you have nothing but complaints and excuses, with no real-world experience of living off-grid ...
Sorry but i don’t think your testing device is any good!!!
The numbers are all over the place even in the new battery!!!!
With the YR 1035 milliometer tester I measured the internal resistance and voltage of numerous rechargeable batteries that I had finished recharging. I wanted these conditions to see the parameters at full charge of all the batteries. I noticed that some of the same make and model have almost the same voltage (varies by a few millivolts) but different values of internal resistance (sometimes even double and triple). This is because some batteries are old, others partially new and others new (an older battery has a higher internal resistance).
So the data I have are: internal resistance and voltage at full charge but without load connected to the battery. With these data with which calculation is it possible to know the real charge in Ampere available to the battery? To give an example: two identical batteries measure like this:
batt1: 1,2806 volt and 0,0227 Ohm (or 22,7 mOhm)
batt 2: 1.3204 volt and 0.0216 (or 21.6 mOhm)
How many amps does one and the other battery have inside? Thank you
There are different type of batteries. Some with HIGH discharge rate and other with Low discharge rate (High discharge rate used for power tools - e.g.: screwdrivers, drills, etc. LOW discharge rate for computers, flashlights, etc)
High discharge rate battery has a MUCH lower internal resistance (around 20~50 mOhms)
Low Discharge rate battery has higher (80~150 mOhms)