In over my head with an unbalanced 14S5P battery

Hi!
Going to preface this post by saying that i'm a total beginner and I don't really understand what i'm doing or how this works so bare with me. :? My 4 month old 14S5P 52v/14.8Ah battery with HG2 cells are having big issues with unbalanced cells, but soon realized that shipping a battery for warranty repairs was a no go where I live so i'm stuck trying to fix this myself..

One cellgroup (7) stays around ~3,6V when the other cells are fully charged even with the battery connected to a 5A-charger for many many hours. I've purchased the pack from a reputable seller but haven't had a very good time trying to get this sorted as email is the only communication combined with a huge time difference, long wait times and common misunderstandings so i'm stuck waiting another day or two to get guidance so i'm hoping I can get some advice here instead.

I have inspected the battery and all the fusible links on the cellgroup looks fine so I was sent a better BMS & a 4.2v/500mA USB-charger (AOKoda) to charge the cellgroup directly via the balance wire. So i've finally managed to disconnect the old BMS without dying and connected the USB to an old ipad-charger with 5V/1A output. How long do you guys think this would take as a guess to charge from 3.6v up to 4-4.2v?

I've had it connected for about 12-14 hours now but it still seems to be charging and i'm not sure if that's normal and that it will take a long time or if the cells are damaged in some other way and it's now working. I'm to afraid to let it charge when i'm sleeping so I only leave it when i'm around so charge times are like 6 + 4 + 4 hours at the moment, hopefully that won't cause any more problems.

I don't have any instruments or knowledge to actually measure if the voltage is going up, i've been relying on the bluetooth-bms app earlier.

find the cause of the inbalance. I rekon you have a dead cell in group 7.
Check for a cell that has some leakage or goo on the top of the cell.

If you dont have a multimeter: buy one. Does not have to be a expensive one

500ma is a tiny charger..it will take long but you need to check progress with a meter.

flippy said:

find the cause of the inbalance. I rekon you have a dead cell in group 7.
Check for a cell that has some leakage or goo on the top of the cell.

If you dont have a multimeter: buy one. Does not have to be a expensive one

500ma is a tiny charger..it will take long but you need to check progress with a meter.

Click to expand...

Can't see any leakage but it's an em3ev-battery so the batteries are sort of "hidden" in the way the batterys are secured and it's hard to inspect properly. I managed to replace the old BMS and get the battery decently balanced with all cellgroups at ~4130-4140 with help of the usb-charger. But from just a few short uses the pack is going off balance again.. Here was after a few short uses and charging the battery back to 90% and then another ~15min ride:

Cell: Before: After:
C5 4093 4061 diff 32 0,8%
C6 4092 4064 diff 28 0,7%
C7 4084 4031 diff 53 1,3%
C14 4085 4054 diff 31 0,7%

Am I stuck with a bad cell you think in C7? C14 also looks unbalanced now but is at least staying level.. Shipping a battery for a refund seems to be close to impossible and shipping a damaged battery seems like a very bad idea..

i think there is a bad cell in 7, it would be the logical explanation.

do you have a "mate" with a spot welder that can weld cells? you might ask em3 for a handful replacement cells so you can replace the whole group if you have warranty.

you can also use a smart bms that you can program to balance way sooner so it gets more time to balance then normal stupid bms's can.

so far the difference is pretty small. once you get beyond a constant 0.15~0.2v difference you need to toss the battery.

I been using Li-Ion 18650 and LiPo batteries since they came out. When a cell goes out of balance there is a few reasons.

1. It has lower capacity.
2. It has higher IR (internal resistance).
3. Bad BMS

When good packs are built, these matched cells (both capacity and IR). Lucky I have equipment to test for both parameters (many RC chargers and the Wayne Giles IR tester).

I would first charge that sub pack to 4.2v (or same as the other cells), then check capacity on the whole pack, carefully watching each sub pack voltage and discontinuing discharging when the first sub pack reaches 20% DOD, then discharge each remaining sub pack to compare balance of all cells. I would then check Ir of each sub pack (after waiting a couple hours to make sure all cells are the same temperature, as IR is temp sensitive). Good luck.

flippy said:

i think there is a bad cell in 7, it would be the logical explanation.

do you have a "mate" with a spot welder that can weld cells? you might ask em3 for a handful replacement cells so you can replace the whole group if you have warranty.

you can also use a smart bms that you can program to balance way sooner so it gets more time to balance then normal stupid bms's can.

so far the difference is pretty small. once you get beyond a constant 0.15~0.2v difference you need to toss the battery.

Click to expand...

Is .02v variance between groups a concern on a new pack? Most of mine(14s9p) are 4.05 , but 2 groups are 4.03 , and 2 are 4.04v . I'm not using a bms yet . If these variances are going to lead to a shortend life span, I'll get one asap.

Dak77 said:

Is .02v variance between groups a concern on a new pack? Most of mine(14s9p) are 4.05 , but 2 groups are 4.03 , and 2 are 4.04v . I'm not using a bms yet . If these variances are going to lead to a shortend life span, I'll get one asap.

Click to expand...

for a brand new pack its "concerning". and a (smart) bms can 100% extend the life of a battery.

"A BMS" is a collection of functionality.

As long as you are **sure** you stop discharging before the **lowest** cell/group hits your bottom cutoff voltage, and

**sure** that you terminate charging when the **highest** cell/grouo hits your top voltage stop setpoint

then you are fine.

As they get more out of balance over time, you are just losing some overall capacity, that is set by the weakest cell / group.

But if you are regulating these high- and low- voltage stop points via the overall **pack voltage**,

then you are increasingly certain to cause damage, since you are "flying blind" at the individual per-cell/group voltage level

john61ct said:

"A BMS" is a collection of functionality.

As long as you are **sure** you stop discharging before the **lowest** cell/group hits your bottom cutoff voltage, and

**sure** that you terminate charging when the **highest** cell/grouo hits your top voltage stop setpoint

then you are fine.

As they get more out of balance over time, you are just losing some overall capacity, that is set by the weakest cell / group.

But if you are regulating these high- and low- voltage stop points via the overall **pack voltage**,

then you are increasingly certain to cause damage, since you are "flying blind" at the individual per-cell/group voltage level

Click to expand...

Thanks, once again . Both of you

Thanks for all the advice, it's very appreciated!
I've been speaking to em3ev but they (at least before) believed the battery is fine and that I should just use a 0.3A charger to balance the battery once a month. But this is how the cells looks after three weeks of charging pack to 80% everytime it hits ~50% (about every 3-4th day).



I feel like this is way to off balance to safely use and not constantly monitor voltage via the app and I cant even be close to get the same lifetime as if the pack would have been fully balanced.. I've had no luck trying to find an option of shipping back the battery, can't find anything that's even close to what a new battery would costs even though how pricy these things are..

With how fast and how bad it gets unbalanced would a smartbms be an option or should I just throw this in the trash soon?

edit: I came off a bit to harsh on em3ev on the original post which I didn't mean to. They have been very accomdating and we might still find a way to solve the warranty still. If there's any spotwelders from Sweden hanging around here at the forums reading this send me a pm!

a smart bms would be a viable option. but its still fighting symptoms instead of fixing the base problem.

i would try and see of you can get replacement cells for group 7 and get someone with a spot welder to replace the cells in that group.

You say you got the lower cell groups up to 4.2v? Insure that they are at 4.2v with a full capacity charge; full amount of amp hour. Want to start to view voltages higher than 4.2v insure this. Then if possible disconnect the BMS, to insure that nothing could drain your pack.

Allow your pack to sit for a few days and each day monitor the cell group voltages until they go out of balance, or after a period of stability are satisfied the pack be good.

If a cell group starts dropping voltage then are guaranteed to have a faulty individual cell(s) within a cell group. Or a nickel strap connection issue.

If the voltages remain solid across all cell groups and after a ride they continue to go out of balance perhaps it’s the riding style drawing too high amps? BMS, could be mismatched to the charger and the charger charges too quickly from too high Ah; balance circuitry cannot drain quick enough the highest cell voltage. Effect is when believe charge be finished and start using the battery, when indeed balance circuitry hasn’t completed it’s task. The result an out of balance pack that hits lowest cell voltage rapid.

NB, better if the pack be charged to less than 4.2v. 80% or 4.05v per cell group is proven add significant life cycles to any pack, and less concern about cell over voltage.

The photo above appears fine after a ride almost all the pack is in balance. Amazing feat, really. My packs are always all over the place some up to 200mv. Although after a charge I can get them to balance perfect. To achieve this require an overnight 100ma charge cycle from 10-11Ah capacity.

You may actually have a low capacity cell in group 7. But its NEVER going to balance charging it to 80%. Your bms doesn't work that way. You have to charge to 100% to get the bms working.

I'm not sure how to read that graph, but visually, it looks a lot more balanced than 4.2v vs 3.7v to me. You will have some inbalance on a perfectly good pack after a few rides, if you never let the bms work. I think I see most of the cells at 3.76v and group 7 at 3.6v. That is out of balance, but not dangerously, it just shows time to balance it by charging to 4.2v. Its only .05v off. That is what I call balanced enough for a naked pack with no bms. I balance when its .06 or more out.

Here is how I force a bms pack to balance. Same thing I told thousands of Ebikekit.com customers when I worked customer service for them.

Charge till the green light goes on. Unplug from the charger, wait 30 min, and plug back in. If its still needing a lot more balancing, it will start to charge again, briefly. If it won't start, ride around the block, and then recharge. Repeat till the battery holds most of its charge voltage after the green light goes on, whether connected to the charger or not. ( not connected to the bike though) Even a new pack with great cells will not always hold the full voltage, but if you have a cell a full volt low, you can see that on the total pack voltage. As it balances up, filling group 7 completely, it should start to show a higher voltage when full and the green light is on.

Once you unplug, and get your full charged voltage right after charging, it may drop a volt or two very quick, and still have great cells. But if it continues to drop some every hour after you unplug, then you have a shorted out, bad cell in there. It will just keep discharging group 7 all night. If it does not do that, your battery is NOT defective. ( likely the original bms was the problem) But it can have a weaker group than the others, without being a warranty situation. EM3ev has done the right thing, sent you another charger and bms, because that could be the problem. Every pack has one group that is not quite the same capacity as the others, and that could get very far out of balance if there was a problem with bms or charger. See how it goes with full charging each cycle, before you start thinking there is a bad cell in group 7.

But if that group 7 just sits there discharging itself day after day while it just sits on the shelf disconnected from everything, then you have a situation where they owe you something.

Let me rephrase this simpler.

If you were charging to only 80% for a long time, you may have just drove that group 7 out of balance. In fact, your group 7 could be the strong group, NOT the weak one!! It could be low voltage because it has more capacity, not less. This is part of what makes this shit tricky.

If you want to run that kind of charge, to make the battery last, then you need to manually balance it from time to time. But you really cannot get good readings at 80%, because voltage and capacity don't correlate very good at 30-80% state of charge. Once in a while, you just have to charge it to 100% to get the bms to balance it properly.

To minimize the effect of a full charge, ride it a mile or two immediately after you get it full and balanced. Then you can resume that 80% charging routine for a while. 100% charge is not that damaging. Its is damaging to let it sit at 100% a long time in a hot garage. So charge it up, get balanced, then ride a mile.

To best check your cells for balance when charging to 80%, you might try riding down to nearly empty, and then look for the cell group with the least voltage. If group 7 is actually the high capacity group, it would then show more voltage then.

--Oz-- said:

I would first charge that sub pack to 4.2v (or same as the other cells), then check capacity on the whole pack, carefully watching each sub pack voltage and discontinuing discharging when the first sub pack reaches 20% DOD, then discharge each remaining sub pack to compare balance of all cells.

Click to expand...

I agree with this.

dogman dan said:

Let me rephrase this simpler.

If you were charging to only 80% for a long time, you may have just drove that group 7 out of balance. In fact, your group 7 could be the strong group, NOT the weak one!! It could be low voltage because it has more capacity, not less. This is part of what makes this shit tricky.

If you want to run that kind of charge, to make the battery last, then you need to manually balance it from time to time. But you really cannot get good readings at 80%, because voltage and capacity don't correlate very good at 30-80% state of charge. Once in a while, you just have to charge it to 100% to get the bms to balance it properly.

To minimize the effect of a full charge, ride it a mile or two immediately after you get it full and balanced. Then you can resume that 80% charging routine for a while. 100% charge is not that damaging. Its is damaging to let it sit at 100% a long time in a hot garage. So charge it up, get balanced, then ride a mile.

To best check your cells for balance when charging to 80%, you might try riding down to nearly empty, and then look for the cell group with the least voltage. If group 7 is actually the high capacity group, it would then show more voltage then.

Click to expand...

Tricky indeed, thanks for the advice. After I managed to get the battery balanced at 4,2v by charging the low cellgroup via the BMS-wire I've only charged it 3-4 times to 100% the last three weeks and currently the cell ares differing over 200mV. I woulnd't say i'm riding aggressively and never go throttle only, not sure how accurate it is but I seldom even go over 3-500W usage so I dont think that should be causing it at least.

However when i've tried charging the pack to 100% with a 0,3A replacement charger from 50-60% the end result was the same, the other cellgroups got to 4,2v and 7 ended at 4,028v so still around that 0,2v difference i'm seeing.

Check all connections carefully.

Consider a dedicated specialist balancer with a low starting setpoint and high balancing current.