I just destroyed $500 worth of batteries by doing nothing.

Barbar0ssa

Solar Enthusiast
I recently purchased 16 cells for a golf cart project and decided to switch from one BMS to 2 in series. I disconnected one batch of 8 and brought them inside they are perfect.
PXL_20210906_155122732.jpg
The batch I left in the garage are completely discharged and destroyed. They had balance leads and 1ft wires but nothing else. Something mist have shorted because I can't imagine them self discharging to that extent.
PXL_20210906_155138553.jpg
I just can't explain how I destroyed them.😭
 

upnorthandpersonal

Administrator
So wait, you had a single pack (with a BMS attached? or just the leads?), nothing else, sit in the garage and they completely discharged? No load or anything? How long were they sitting for? Did it get extremely hot? Any signs on the cells? That much energy doesn't just 'go' anywhere without some signs.
 

Horsefly

Solar Addict
All 8 are that low? LFP have essentially no self discharge, so that's not it. What was on the other end of the balance leads?
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
slow down, put panic on hold.
Charge each cell, one at a time, starting at 3.000V and around 10A and let it slowly take the charge till it cuts off. Rinse repeat for each cell. They should all take it BUT BE GENTLE & POLITE ! Once they all get to 3.000 then parallel the cells and top them in INCREMENTS, I would suggest 0.100V increments. Yes slow, painful, TEDIOUS but if you want to recover them....

They technically can recover IF they were not frozen or cooked while in a state of discharge, if they have, then do one cell at a time and in a safe box in case it pops & leaks. IF you are lucky, they will recover and maybe you've only lost a percentage of capacity. IF they recover to at least 3.400Vpc, I would run at least 3 good cycles through them (charge/discharge) and then capacity test each cell to ensure the packs integrity, because even if One Cell goes wonky, it will affect the whole pack, as the lowest common denominator rules.
 

pierre

Somewhere down South
Normally at this voltage the cell is damaged , I thought. I recently received 28 A grade cells and 8 of those indicated voltages from 0,2v to 1,5v / cell. I paired the cells up in parallel according to matching voltages and recharged the pairs. All eight cells have recovered and are maintaining around 3,28 per cell , no load. I am just letting them sit there for a few days before I start load testing. I suggest you split the pack and recharge them. Holding thumbs.
 

Barbar0ssa

Solar Enthusiast
The negative was left attached to the golf cart main ground through a disconnected BMS. The terminal leads were connected to nothing. The positive was connected to a 1ft wire not touching anything (but in my mind it must have touched something because I have no explanation other than that.

So 8 cells in series that shouldn't have been touching anything in the garage that got to maybe 95Β° for a month.

Maybe the positive touch something and maybe the BMS when it has no power and no connection somehow has the ability for current to flow. It is a relay bms. Damnit, there is a resistor in there always connected isn't there?
 

mrzed001

Voice of reason
The negative was left attached to the golf cart main ground through a disconnected BMS. The terminal leads were connected to nothing. The positive was connected to a 1ft wire not touching anything (but in my mind it must have touched something because I have no explanation other than that.

So 8 cells in series that shouldn't have been touching anything in the garage that got to maybe 95Β° for a month.

Maybe the positive touch something and maybe the BMS when it has no power and no connection somehow has the ability for current to flow. It is a relay bms. Damnit, there is a resistor in there always connected isn't there?
BMS has a self consumption ... but not as much to drain big cells in 1-2 months.
But the relay ... that uses a lot
Also if set correctly passive balancer only discharge higher cell when high battery V state.
 

Professor Farnsworth

π•ƒπ• π•˜π•šπ•”π•’π• β„‚π• π•Ÿπ•€π•–π•’π•¦π•–π•Ÿπ•”π•–
What BMS did you use ? Unattached ? maybe some battery builds (chemistry) can self-discharge?
 
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RCinFLA

Photon Sorcerer
If you have battery negative lead and balance leads from a BMS connected without positive lead connected you can have some significant leakage down the balance leads. Can happen just connecting BMS sense leads to BMS without either supply lead connected.

Just about all IC's have ESD protection diodes from their I/O pins to Vss ground pin and I/O pins to Vcc pin in normal reverse bias configuration. Without the positve Vcc bias the protection diodes can forward bias from a positive voltage on their I/O to Vcc of IC causing leakage and some uncontrolled current drain by some of the IC's.

First thing you should always do when working on battery pack is to pull the BMS sense leads connector out of BMS.
 
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Barbar0ssa

Solar Enthusiast
The BMS was connected to the battery negative and then on to the cart negative but the balance leads were not connected to the bms.

PXL_20210906_171329432.jpg


With that connector on the balance leads, they should not have been able to complete any circuit. I am second guessing what was connected to the positive. If anything was, it would have been the positive lead of this wire with an xtc90. Theoretically I could have had a 1-foot jumper cable to connect to the other 8 cells. I wish I had a pic before touching it.


PXL_20210906_171727838.jpg


It was definitely enough for me to mentally say "that circuit cannot complete." But I think I was wrong.

There is no sign of heat or arcing I can see so I am thinking there was a slow short somewhere (maybe through the resistor in the BMS?)

All 8 cells are down, so it must have been across the main neg and the main pos. They must have both effectively shorted through the frame?

Even a bad cell wouldn't take out the rest in a disconnected string of 8, right? No circuit, no current.
 

Sojourner1

Itinerant
OR.... you have demonic spirits that materialized while you were gone and sucked all the juice from your batteries. It can happen, I saw it on tv. :eek:πŸ‘»
 

MisterSandals

Participation Medalist
The batch I left in the garage are completely discharged and destroyed.
What state of charge were the cells when you "stored" them? Were they all uncompressed?
My understanding is that cells stored fully charged and uncompressed will swell and degrade.
 

Barbar0ssa

Solar Enthusiast
They were exactly the same as the other 8 - 3.32v.

I think 8 really were completely disconnected and were fine and 8 were under magical load and are radically low.
 

A.Justice

Swears he didn't start that fire.
...magical load...
I'm trying to understand everything, but is it possible that the relay was triggered "on", even while it was sitting with the main cable disconnected? Relays can be pretty thirsty, especially over a month.

My BMS (JBD) gets power even with the main cable disconnected, because it can pull power through the first (negative) and last (positive) balance leads. On the flip side, you can disconnect all but one balance lead (main positive) and the BMS still runs (and runs relays). Maybe somehow the BMS was able to get power from the loose positive wire or lead.
 

OM617YOTA

Solar Enthusiast
Maybe recreate the setup, and use a clamp on ammeter to check the various lines for current flow? A month + to drain things, the amp draw might be too small for a clamp on meter to measure.

@Barbar0ssa In your OP, the second photo shows a battery with a different colored vent. Is that a common occurrence, and I'm just too new to know it, or is that battery suspect?
 

Barbar0ssa

Solar Enthusiast
That one is over a volt so might be the least dead. Some of these batteries are wrapped blue under the green and that one has the different color as you pointed out. They are a little weird.

The CATL 280ah cells that were delivered today look much cleaner but they are supposed to be brand new grade a.
 
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