As a follow-up, I have disassembled a few of these packs down to the single-cell level. The mAh out at a 5A discharge was typically around 1600mAh, some as low as 1500, a few as high as 1800mAh+. Most individual cells did improve (around 2%-6%) after two full cycles (charge @ 2.5A, discharge @ 5A). This was using a Hyperion EOS charger with a dedicated LiFePO4 charge cycle to 3.7V CCCV and Competition Electronics Turbo 35 to discharge. The problem is that after two full cycles of each individual cell in a prior 8P group, the returned capacity at 5A went from a low of 1477mAh to a high of 1830mAh with another group going from 1266mAh to 1725mAh. The very wide variation in actual single-cell capacity means that even with a conservative LVC on the (prior) group, the weak cell could be drawn-down dangerously low. FYI, I did a 25A single-cell load-test with a Competition Electronics Turbo35 with remote voltage sensing and the voltage dropped to 2.68V at the 10-second point and 2.32V at the 60-second point in the discharge, thus I really don't think that anything much more than 30A is at all practical.
Your cells are very degraded so their IR has gone up. Fresh cells are fully capable of 50A continuous. They’ll sag down to 2.6V but will give their full capacity, maybe 10% less at such high discharge rates
@@ericklein5097 This video is about decommissioned hybrid-bus battery packs, so comparing them to "new" cells is meaningless. In any case, this form-factor of cell and specific design is essentially obsolete and would probably be impossible to get "new" in any case.
@@awebuser5914 Yes, I'm aware of where these come from. I have purchased packs of them. There is currently a seller on Ebay selling them for $99 shipped and they are testing quite well. I think they may not be from buses, this module/pack design was also used for other applications, I believe some kind of data backup/storage and this was the backup power. Not sure why you think this design is obsolete or not available for purchase anymore. The ANR26650M1B is still available for sale under the new branding of LithiumWerks. I don't know of any cell that matches the continuous discharge rate of this cell unless you go to a MUCH larger size. There are definitely pouch cells that blow this out of the water in terms of energy density, unsure if those are still made. I've been meaning to buy a YR-1035+ to test the impedance of my cells, based on the DC IR results I'm getting I think they will be pretty close to the new value of 6 mΩ
@@awebuser5914 Also individual cell capacity does not matter. When cells joined in parallel they become one cell. The way I read your first comment is "wide variation in actual single cell capapcity" means you're talking about individual cells in a P group. If you're discussing the parallel groups being different from each other, yes that definitely becomes a problem but the fresh packs I got are so tightly balanced that I'm not using a BMS or a cell balancer outside of just hooking it up to a balance charger once a month due to OCD. Realistically I could run 100 cycles and probably still not need a balance charge. I suspect that changes past 1500 hard run cycles which is what I would guess your cells are at based on the figures you've given and A123/Lithium Werks datasheets showing degradation at a 1.2C/8C charge/discharge cycle.
@@ericklein5097 "When cells joined in parallel they become one cell.", is complete nonsense. The cells within one parallel group can and WILL degrade at different rates and a substantial weakening of a cell in a parallel array can lead to the failure of the cell itself and a cascade deterioration of the parallel array, let alone a voltage imbalance in the discharge capacity of the series grouping, leading to far lower overall pack capacity. Also, I doubt you have ever seen these packs in anything but a hybrid bus use since they were specifically designed by BAE systems for use in a hybrid city bus drivetrain, nothing else. These cells might appear to be sold by Chinese "cloners", but they have little to do with the original design of the A123 cells, they are just knock-offs using generic LiFePO4 technology that China has had decades to optimize to make extremely cheap cells. The performance of these knock-offs is terrible in comparison to what were *real* A123 cells.
Good stuff on the testing mine were fairly close to balanced at nominal voltage and they drift apart depending on the load but I've had them hooked up about a month now and they balance within .009 most of the time I only use them from 3.1 to 3.57 as both ends have small capacity but he middle seems to do well. Also I paralleled 12 packs together which seems to keep them to a more medium voltage. Good Luck on the testing. No Ebay straight from the junk yard is a lot cheaper.
I've also purchased some of these packs from the same vendor. I've been harvesting and testing the individual cells and have noticed that some of them have low capacity compared to the others. Generally I get about 1.4 to 1.5 Ah per cell but some (maybe 5%) are at .5 to 1.0 Ah. If you leave the pack as-is the higher cell will constantly try to compensate for the lower ones. I still like these cell's even if they don't have a lot of capacity compared to Li-ion since they are related for use at -30 celsius.... which is very good in cold climates like in canada.
@@LeafXpack18650 Correct... configuration would be to keep the area where the batteries are heated to over zero with a heat pad just before the sun comes up if the batteries are at say 80% state of charge, top up the batteries then stop the heat pad when at 100%. Arduinio configuration
With a 12v 100 amp load on one of these that I tested, I was getting a 1v drop (4v across 12v) which is only 12.5 amps per cell. So the 60 amp per cell is either really optimistic or my cells were really worn out. A couple of the cells that were pulled tested at 1156 and 1208 mAh
I think what took so long is you tried balancing before clearing the 3.35-3.40V threshold. Attempting to balance during the flat part of the curve is not actually balancing since voltage only correlates to SOC from 2.5 to 2.8’ish and 3.40 to 3.65. In between that if you’re pulling down the highest cells to the lowest cell that happens to be 3.29 or lower you could be pulling down a 20Ah pack by 4, 5 or 6 Ah as the low cell takes it sweet time in the flat part of the curve. 3.27 could be 70% imcould be 50%. Best to set the pack to 3.45*12 and then see where your highest cell is. Inch it up so your highest cell is at 3.55. At this point decide if you want to take the charge or discharge route. If you have one low outlier individually charge that cell. If you have just one or two high cells then put a load on them and charge the pack at a rate that matches the load. Use light bulbs or power resistors. A 1ohm 100W resistor is $6 and gives you 3.5’ish amps if the voltage is 3.5. A 0.1 ohm resistor gives you 35 amps but that does push the resistor at its max power rating of 100W. Use two in series for a 0.2ohm to get 17 amps and charge the pack at 14 amps so you still get a discharge from your high cell if that suits your fancy. If you have to constantly adjust your set up because you have one or more runner groups you might just want to consider salvaging the cells from the pack but label them all first so you know which came from the problem groups. Then you can rebuild a pack with cells that are already top balanced by doing the long row of cells in parallel trick up to 3.6V method. I’ve just never had much luck with these balancers trying to fix a pack that’s out of whack under 3.30V. It takes forever but if you have an hour or two to kind of keep an eye on it you can charge these cells fast enough to get it done manually.
Actually it is three old HP power supplies for laptop docking stations connected in series. They are 230W, 19.5v, 11.8A so in series that's 58.5v just under the maximum 60v the DPS5015 is able to handle. Same as this one: www.amazon.com/HP-Smart-230W-Adapter-Localization/dp/B00325QTOQ
@@scottetherton9364 It is a DPS5015 which I got from Banggood: www.banggood.com/DP50V15A-DPS5015-Programmable-Supply-Power-Module-With-Integrated-Voltmeter-Ammeter-Color-Display-p-1072236.html?rmmds=search&cur_warehouse=CN
hi. I was wondering if the Dc to Dc converter will stop charging if it reach the desired voltage charged you set it too? I have the same battery module and i wanna charge it like you did, the only diffrence is i have a switching power supply to power that dc-to-dc unit. How long did it take to charge the whole pack? Thanks for yiur time. Awesome content i learned some new things.
The DC to DC will not exceed the voltage set so yes, it will stop charging. Note that once the maximum voltage is reached, the current will gradually decrease and eventually will go down to nothing. The pack only took a few hours to charge.
RIDEN® DP50V15A DPS5015 Programmable Supply Power Module With Integrated Voltmeter Ammeter Color Display Module Board from Electronics on banggood.com banggood.app.link/HmdK1nmR16 RIDEN® DP And DPS Power Supply Housing 2 Kinds Aluminum Housing Constant Voltage Current Casing Digital Control Buck Voltage Converter Only Box Module Board from Electronics on banggood.com banggood.app.link/Bo1lDDrR16
Any luck figuring out how to use the built in bms? These packs look perfect for a student electric go kart im building, but a bms that can handle the peak power we're looking for (16kw, so 400a peek ) would be ridiculously expensive
I'm looking at buying some of these packs and I was wondering if they would be any good for an off grid system charged from solar and wind? could they be used as is or would they have to be modified for that use? I'm in ontario canada as well where about's are you?
Depends on the voltage of your system. These packs are fully charged at 43.2v and fully discharged at 24v (although I wouldn't discharge them below 30v on a regular basis) Unfortunately this is not an ideal voltage for solar/wind systems as most of them are designed to run at 12v, 24v or 48v. These packs would only work in a 36v system which is very rare (if it even exists).
@@LeafXpack18650 thanks for the reply, so I would mod the packs then to 24v or 48v instead of 36. there are some good deals around me for old bus batteries
Yes, this is how I have it connected, but you need to make sure the cells are balanced and your charger will cut off at the appropriate voltage (43.2v ideal, 45v MAX)
On both sides there's a thin plastic that you can peal off. Then you just remove all the screws and remove the plastic on both sides. It's a little tricky but if you are patient you can take it apart without causing any damage to the cells. You could also break it up into three 4s9p packs, equivalent to a 12v lead acid.
I did the same thing as yours but mine only charge and the first 6s. The 2nd group of 6s did not charge at all, only charge to. 3.37volts, while the first 6s charged to 3.6 volts. Any Idea why? Thanks man. Learning a lot from your videos..
If you are charging it from the end terminals then your pack is unbalanced. It probably means your cells that charged to 3.6v are weaker than the cells that only charged to 3.37v.
Leaf Xpack i made an output connection to from - to 6s, then 7s-12s so i can charge them as 6s and balance them while charging, i got them charge and balance to 3.7 volts for the whole group, now when discharge im gonna try to charge them as 12s again and observe if they will still do the same, if not, charging simultaneously is not a problem, ill just charge them as 6S. More convenient if charging as 12S though.
The BMS didn't seem to be doing anything, I don't think it was active at all. I didn't realize I could simply remove it, I did so on the second pack. I took this pack apart and tested each cell individually, capacity ranged from .6 Ah to 1.5 Ah, most were around 1.1 Ah, so yeah, this was a bad pack.
@@thedavesofourlives1 You got a good deal, I paid $200 for 2 packs although my shipping was less as I'm in Canada. At least the second pack was better, hopefully yours will be like my second pack.
@@LeafXpack18650 shipping to alberta, mine came at 3.2v and i'm testing now. Word on the street is that the bms is just a monitor, but mine were perfectly balanced so i suspect it must have some balancing effect, especially all the SMD resistors onboard in parallel.
@@thedavesofourlives1 3.2v is a good storage voltage, you should check if they are balanced when fully charged. I think it is a BMS but it probably needs to be activated externally.
How long did it take to balance the "cells", as you call them? It seems to me that the amount of power you'd need to dissipate with an 8P/2500mAh "cell" would be staggering! Most of those small balancers can only dissipate a few watts, and even a small voltage difference would tax such a small unit! As you've probably found out, any group of paralleled cells is only as good as the weakest cell, and that weak cell(s) can damage the rest in the parallel group. If you have a single parallel group that drops precipitously during discharge in a 12S pack, you have a very real potential for voltage reversal, where the entire parallel grouping is driven negative (or very close to zero volts), and will be permanently damaged. These look like very interesting packs, but the lifespan left in the cells looks to be very questionable. I suspect a lot of buyers don't take the effort to really test the cells (per 8P group) in a methodical way, and would be shocked at how poor they can be!
Actually, it didn't take that much time to balance, at most, about 24 hours. I've balanced far bigger packs with these units and it could take weeks. The key is to balance the pack while not in use. The problem comes if you have cells with a high self discharge rate. I once built a pack with very old 18650 cells and even with this balancer running for days, the pack kept getting more and more out of balance. You are correct about having weak cells in a pack, which is why it is important to stop discharging when any one cell group gets to a low voltage. Also, any low cell group ends up being strained more and more since it would get continuously discharged down to zero whereas the other cell groups may only be discharged to 20%. As time goes by, the weak cells end up getting weaker... I've purchased several of these packs and only one still had fair capacity remaining. There is a reason why these were removed from service...
As a follow-up, I have disassembled a few of these packs down to the single-cell level. The mAh out at a 5A discharge was typically around 1600mAh, some as low as 1500, a few as high as 1800mAh+. Most individual cells did improve (around 2%-6%) after two full cycles (charge @ 2.5A, discharge @ 5A). This was using a Hyperion EOS charger with a dedicated LiFePO4 charge cycle to 3.7V CCCV and Competition Electronics Turbo 35 to discharge.
The problem is that after two full cycles of each individual cell in a prior 8P group, the returned capacity at 5A went from a low of 1477mAh to a high of 1830mAh with another group going from 1266mAh to 1725mAh. The very wide variation in actual single-cell capacity means that even with a conservative LVC on the (prior) group, the weak cell could be drawn-down dangerously low.
FYI, I did a 25A single-cell load-test with a Competition Electronics Turbo35 with remote voltage sensing and the voltage dropped to 2.68V at the 10-second point and 2.32V at the 60-second point in the discharge, thus I really don't think that anything much more than 30A is at all practical.
Your cells are very degraded so their IR has gone up. Fresh cells are fully capable of 50A continuous. They’ll sag down to 2.6V but will give their full capacity, maybe 10% less at such high discharge rates
@@ericklein5097 This video is about decommissioned hybrid-bus battery packs, so comparing them to "new" cells is meaningless. In any case, this form-factor of cell and specific design is essentially obsolete and would probably be impossible to get "new" in any case.
@@awebuser5914 Yes, I'm aware of where these come from. I have purchased packs of them. There is currently a seller on Ebay selling them for $99 shipped and they are testing quite well. I think they may not be from buses, this module/pack design was also used for other applications, I believe some kind of data backup/storage and this was the backup power.
Not sure why you think this design is obsolete or not available for purchase anymore. The ANR26650M1B is still available for sale under the new branding of LithiumWerks. I don't know of any cell that matches the continuous discharge rate of this cell unless you go to a MUCH larger size. There are definitely pouch cells that blow this out of the water in terms of energy density, unsure if those are still made.
I've been meaning to buy a YR-1035+ to test the impedance of my cells, based on the DC IR results I'm getting I think they will be pretty close to the new value of 6 mΩ
@@awebuser5914 Also individual cell capacity does not matter. When cells joined in parallel they become one cell. The way I read your first comment is "wide variation in actual single cell capapcity" means you're talking about individual cells in a P group. If you're discussing the parallel groups being different from each other, yes that definitely becomes a problem but the fresh packs I got are so tightly balanced that I'm not using a BMS or a cell balancer outside of just hooking it up to a balance charger once a month due to OCD. Realistically I could run 100 cycles and probably still not need a balance charge. I suspect that changes past 1500 hard run cycles which is what I would guess your cells are at based on the figures you've given and A123/Lithium Werks datasheets showing degradation at a 1.2C/8C charge/discharge cycle.
@@ericklein5097 "When cells joined in parallel they become one cell.", is complete nonsense. The cells within one parallel group can and WILL degrade at different rates and a substantial weakening of a cell in a parallel array can lead to the failure of the cell itself and a cascade deterioration of the parallel array, let alone a voltage imbalance in the discharge capacity of the series grouping, leading to far lower overall pack capacity. Also, I doubt you have ever seen these packs in anything but a hybrid bus use since they were specifically designed by BAE systems for use in a hybrid city bus drivetrain, nothing else.
These cells might appear to be sold by Chinese "cloners", but they have little to do with the original design of the A123 cells, they are just knock-offs using generic LiFePO4 technology that China has had decades to optimize to make extremely cheap cells. The performance of these knock-offs is terrible in comparison to what were *real* A123 cells.
Good stuff on the testing mine were fairly close to balanced at nominal voltage and they drift apart depending on the load but I've had them hooked up about a month now and they balance within .009 most of the time I only use them from 3.1 to 3.57 as both ends have small capacity but he middle seems to do well. Also I paralleled 12 packs together which seems to keep them to a more medium voltage. Good Luck on the testing. No Ebay straight from the junk yard is a lot cheaper.
I've also purchased some of these packs from the same vendor. I've been harvesting and testing the individual cells and have noticed that some of them have low capacity compared to the others. Generally I get about 1.4 to 1.5 Ah per cell but some (maybe 5%) are at .5 to 1.0 Ah. If you leave the pack as-is the higher cell will constantly try to compensate for the lower ones. I still like these cell's even if they don't have a lot of capacity compared to Li-ion since they are related for use at -30 celsius.... which is very good in cold climates like in canada.
you can discharge them at -30C but you aren't supposed to charge them below freezing.
@@LeafXpack18650 Correct... configuration would be to keep the area where the batteries are heated to over zero with a heat pad just before the sun comes up if the batteries are at say 80% state of charge, top up the batteries then stop the heat pad when at 100%. Arduinio configuration
I have the same battery. using two BATTGO Meters where did you connect the negative wires
With a 12v 100 amp load on one of these that I tested, I was getting a 1v drop (4v across 12v) which is only 12.5 amps per cell. So the 60 amp per cell is either really optimistic or my cells were really worn out. A couple of the cells that were pulled tested at 1156 and 1208 mAh
Yes... the 'good' cells seem to be at around 60%... the 'bad' ones (maybe 5-10%) are lower than 1.0 AH
Those were junk cells...
I think what took so long is you tried balancing before clearing the 3.35-3.40V threshold. Attempting to balance during the flat part of the curve is not actually balancing since voltage only correlates to SOC from 2.5 to 2.8’ish and 3.40 to 3.65. In between that if you’re pulling down the highest cells to the lowest cell that happens to be 3.29 or lower you could be pulling down a 20Ah pack by 4, 5 or 6 Ah as the low cell takes it sweet time in the flat part of the curve. 3.27 could be 70% imcould be 50%.
Best to set the pack to 3.45*12 and then see where your highest cell is. Inch it up so your highest cell is at 3.55. At this point decide if you want to take the charge or discharge route. If you have one low outlier individually charge that cell. If you have just one or two high cells then put a load on them and charge the pack at a rate that matches the load. Use light bulbs or power resistors. A 1ohm 100W resistor is $6 and gives you 3.5’ish amps if the voltage is 3.5. A 0.1 ohm resistor gives you 35 amps but that does push the resistor at its max power rating of 100W. Use two in series for a 0.2ohm to get 17 amps and charge the pack at 14 amps so you still get a discharge from your high cell if that suits your fancy.
If you have to constantly adjust your set up because you have one or more runner groups you might just want to consider salvaging the cells from the pack but label them all first so you know which came from the problem groups. Then you can rebuild a pack with cells that are already top balanced by doing the long row of cells in parallel trick up to 3.6V method.
I’ve just never had much luck with these balancers trying to fix a pack that’s out of whack under 3.30V. It takes forever but if you have an hour or two to kind of keep an eye on it you can charge these cells fast enough to get it done manually.
Like your balance meters and watt meters look good.
As constructed could these packs be modified for 24V ? 8S 12P ? Separated to 4S Groups ? How are they configured as is ?
Not easily no, some people just use 2/3 of the pack in order to get the proper voltage
What make / model is the power supply you are using please?
Actually it is three old HP power supplies for laptop docking stations connected in series. They are 230W, 19.5v, 11.8A so in series that's 58.5v just under the maximum 60v the DPS5015 is able to handle. Same as this one: www.amazon.com/HP-Smart-230W-Adapter-Localization/dp/B00325QTOQ
@@LeafXpack18650 Thanks so much for the speedy reply. I meant the adjustable power supply you are using to charge this battery? Cheers.
@@scottetherton9364 It is a DPS5015 which I got from Banggood: www.banggood.com/DP50V15A-DPS5015-Programmable-Supply-Power-Module-With-Integrated-Voltmeter-Ammeter-Color-Display-p-1072236.html?rmmds=search&cur_warehouse=CN
@@LeafXpack18650 Awesome - thanks. Gonna get me one :-)
What do you use as a power source to your Riden? I see you have close to 60 volts input?
I use three large laptop power supplies in series.
hi. I was wondering if the Dc to Dc converter will stop charging if it reach the desired voltage charged you set it too? I have the same battery module and i wanna charge it like you did, the only diffrence is i have a switching power supply to power that dc-to-dc unit.
How long did it take to charge the whole pack?
Thanks for yiur time. Awesome content i learned some new things.
The DC to DC will not exceed the voltage set so yes, it will stop charging. Note that once the maximum voltage is reached, the current will gradually decrease and eventually will go down to nothing. The pack only took a few hours to charge.
Leaf Xpack thank you...
What's that dc to dc converter called i would like to buy one. WOuld perhaps you have a link to it. TKS
RIDEN® DP50V15A DPS5015 Programmable Supply Power Module With Integrated Voltmeter Ammeter Color Display Module Board from Electronics on banggood.com
banggood.app.link/HmdK1nmR16
RIDEN® DP And DPS Power Supply Housing 2 Kinds Aluminum Housing Constant Voltage Current Casing Digital Control Buck Voltage Converter Only Box Module Board from Electronics on banggood.com
banggood.app.link/Bo1lDDrR16
Any luck figuring out how to use the built in bms? These packs look perfect for a student electric go kart im building, but a bms that can handle the peak power we're looking for (16kw, so 400a peek ) would be ridiculously expensive
Unfortunately no, but you don't need to run the power to your controler though the BMS, you can use the BMS to run a separate contactor (relay).
Yeah those are from 2012 and older. Mine from 2018 and newer are mint 92% capacity 2300mah per cell
where did you get your charger
I'm looking at buying some of these packs and I was wondering if they would be any good for an off grid system charged from solar and wind? could they be used as is or would they have to be modified for that use? I'm in ontario canada as well where about's are you?
Depends on the voltage of your system. These packs are fully charged at 43.2v and fully discharged at 24v (although I wouldn't discharge them below 30v on a regular basis) Unfortunately this is not an ideal voltage for solar/wind systems as most of them are designed to run at 12v, 24v or 48v. These packs would only work in a 36v system which is very rare (if it even exists).
@@LeafXpack18650 thanks for the reply, so I would mod the packs then to 24v or 48v instead of 36. there are some good deals around me for old bus batteries
@@jasona.neverforgetfukushim647 where are you located?
@@LeafXpack18650 Wasaga beach ontario
@@jasona.neverforgetfukushim647 Where are you able to get the batteries?
Where would you connect a charger to. I have a 42v lifepo4 Charger. Can it be charged from the end terminals ?
Yes, this is how I have it connected, but you need to make sure the cells are balanced and your charger will cut off at the appropriate voltage (43.2v ideal, 45v MAX)
where can i buy this bms charger ?
What equipment do you use to balance and charge?
Balance: ISDT BG-8S
Charger: RUIDENG DP50V15A DPS5015
Got one of these. Any advice on opening the enclosure up leaving it as intact as possible?
On both sides there's a thin plastic that you can peal off. Then you just remove all the screws and remove the plastic on both sides. It's a little tricky but if you are patient you can take it apart without causing any damage to the cells. You could also break it up into three 4s9p packs, equivalent to a 12v lead acid.
@@LeafXpack18650 thanks!
@@HansHenderson See my new video: th-cam.com/video/XJ1DjQJDISw/w-d-xo.html
I did the same thing as yours but mine only charge and the first 6s. The 2nd group of 6s did not charge at all, only charge to. 3.37volts, while the first 6s charged to 3.6 volts. Any Idea why? Thanks man. Learning a lot from your videos..
If you are charging it from the end terminals then your pack is unbalanced. It probably means your cells that charged to 3.6v are weaker than the cells that only charged to 3.37v.
Leaf Xpack i made an output connection to from - to 6s, then 7s-12s so i can charge them as 6s and balance them while charging, i got them charge and balance to 3.7 volts for the whole group, now when discharge im gonna try to charge them as 12s again and observe if they will still do the same, if not, charging simultaneously is not a problem, ill just charge them as 6S. More convenient if charging as 12S though.
@@electric_rider2044 That's what I would have done. Once the cells are balanced, you shouldn't need to charge them as 6s anymore.
wouldn't the integrated BMS be limiting the charge? why not disconnect the board and then charge up to 4.2 with your pair of little bms'?
The BMS didn't seem to be doing anything, I don't think it was active at all. I didn't realize I could simply remove it, I did so on the second pack. I took this pack apart and tested each cell individually, capacity ranged from .6 Ah to 1.5 Ah, most were around 1.1 Ah, so yeah, this was a bad pack.
@@LeafXpack18650 well i'm now regretting having just bought 2 packs for $125 +$100 US shipping.
@@thedavesofourlives1 You got a good deal, I paid $200 for 2 packs although my shipping was less as I'm in Canada. At least the second pack was better, hopefully yours will be like my second pack.
@@LeafXpack18650 shipping to alberta, mine came at 3.2v and i'm testing now. Word on the street is that the bms is just a monitor, but mine were perfectly balanced so i suspect it must have some balancing effect, especially all the SMD resistors onboard in parallel.
@@thedavesofourlives1 3.2v is a good storage voltage, you should check if they are balanced when fully charged. I think it is a BMS but it probably needs to be activated externally.
How long did it take to balance the "cells", as you call them? It seems to me that the amount of power you'd need to dissipate with an 8P/2500mAh "cell" would be staggering! Most of those small balancers can only dissipate a few watts, and even a small voltage difference would tax such a small unit!
As you've probably found out, any group of paralleled cells is only as good as the weakest cell, and that weak cell(s) can damage the rest in the parallel group. If you have a single parallel group that drops precipitously during discharge in a 12S pack, you have a very real potential for voltage reversal, where the entire parallel grouping is driven negative (or very close to zero volts), and will be permanently damaged.
These look like very interesting packs, but the lifespan left in the cells looks to be very questionable. I suspect a lot of buyers don't take the effort to really test the cells (per 8P group) in a methodical way, and would be shocked at how poor they can be!
Actually, it didn't take that much time to balance, at most, about 24 hours. I've balanced far bigger packs with these units and it could take weeks. The key is to balance the pack while not in use. The problem comes if you have cells with a high self discharge rate. I once built a pack with very old 18650 cells and even with this balancer running for days, the pack kept getting more and more out of balance.
You are correct about having weak cells in a pack, which is why it is important to stop discharging when any one cell group gets to a low voltage. Also, any low cell group ends up being strained more and more since it would get continuously discharged down to zero whereas the other cell groups may only be discharged to 20%. As time goes by, the weak cells end up getting weaker...
I've purchased several of these packs and only one still had fair capacity remaining. There is a reason why these were removed from service...
It's too bad nobody sat down and looked at the pinout on the BMS.
My results are very similar. Looks like a teardown
more photos here of same units: www.eevblog.com/forum/buysellwanted/a123-anr26650m1a-lifepo4-battery-modules-12s8p-39-6v/
Same units but different use, the one I bought came from a bus (as per the ebay listing)
@@LeafXpack18650 they must have really abused the buses, as these are supposed to last 1000 cycles +