I have 10s3p battery from BKB that went dead after I left my board on for too long. It won’t charge anymore when I plug in the official 42V5amp charger. When I plug it in, the charger led flickers on and off from red to green. The board only has like 300 miles on it. I’m assuming it went under voltage and now won’t charge because of the BMS. Any ideas on what I can try?
First of all, you need to know the actual voltage of the battery.
Knowing the individual voltage of each p group would also be advantageous.
Without these bits of information, I would advise that you don’t try anything further.
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Its possible to revive by effectively bypassing the BMS and using a very slow charger to get back to normal voltage, but you need to know what you’re doing.
If the cells are unhealthy, or have internal damage from being undervolted, you could start a fire. Is the entire board, or worse your house going up in flames worth the purchase price on a new pack? The risk is obviously very small, but not as small as you’d hope.
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Thumbnail says it all
I just want to highlight the important parts here.
You can burn your home down.
Don’t do anything unless you know exactly what you’re doing. Even discarding it requires care.
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Unknown cells, 5P pack with 10Ah in total… So 2Ah per cell. Thos can only be crappy cells. I would avoid that pack far away.
Always use known and tested cells with a good reputation. As far as 18650s go I recommend Molicel P26A, Molicel P28A, Samsung 30Q and Sony VTC6. As far as 21700s go Samsung 40T, Samsung 50S, Molicel P42A, Molicel P45B cells are all solid choices. If I recall it correctly the BKB used 18650
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Unknown cells in unknown condition? Big risk-taking there.
A battery pack is the worst thing to buy based on price IMO. The quality of the pack is critical not only for the ride experience you’ll have every day but for your safety too.
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Just checked and voltage is at 29.8 V
At that voltage most chargers should have no problem charging, that’s strange. That’s an acceptable voltage. So long as the pack is balanced, in other words if all the cells have the same voltage, the pack is fine.
This might be the important part.
The total pack voltage might seem okay but one or more p-groups might be at too low a voltage and the BMS is preventing charging.
Or the charger is broken. @JohnnyDog, do you have another charger you can try?
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I do not have another charger. I don’t want to open the pack to check individual groups yet.
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Sounds like we’re at a standstill then.
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You need to do this. If the pack is way out of balance, connecting it to a charger could overvolt some of the p groups. That’s not a fire risk 2 years down the line, that’s an instant bonfire right then and there.
Option 2 is to charge it outside on a concrete block, downwind of anything that breathes air.
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I have used 2 dead/revived battery packs and for both of them I quickly decided they should be replaced with a new pack.
Revived packs are shit. They don’t have the same capacity so you’ll get less range, and they have balancing issues.
Don’t mess with reviving it. Just replace it, don’t kill the new one.
If it’s still in balance then it should be around 3V per cell which is no problem. Only worth “reviving” it if it’s still balanced though.
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I respectfully disagree.
Cells naturally go out of balance when down at near 3.0V, and lower, due to the inevitable cell-to-cell differences. Especially over time.
As long as no cell has spent any time below 2.5V or so, and is otherwise not damaged internally, there’s no reason IMO why that pack can’t be charged normally.
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Sorry I phrased that wrong, yeah some imbalance is totally fine. If all cells are above 2.5V than some imbalance is fine.
100% agree, that’s why I put the reviving in quotation marks.
Also I want to add that my 10S chargers only blink red/green when the battery is below 26.5-27V. I’ve only seen chargers blinking red/green when hooking them up to a too low voltage battery, and all of my chargers have this same behaviour - I find it strange that OP’s charger does this already at 30V, that’s pretty high. That’s my usual hard cutoff on 10S batteries… Also I don’t think the BMS is cutting the charger off, because if that were the case then the charger should light up green in my experience
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So I fixed the battery pack… or more like it fixed itself?
Turns out I had my multimeter in the wrong setting, so it actually was reading much lower at 21 V. I was about to buy a 36 V charger to try and jump start it, but then I stopped. I decided to try again with the original 42 V charger and I noticed that the Voltage was actually rising slowly but surely. During 21-34V the charger still would blink from red and green. Then after it got to 34V the charger started charging like normal.
The battery charged all the way to 42 V and I watched it the whole time to make sure nothing went wrong. This morning I connected it to the esc and ran the motors just fine, monitored it via Bluetooth. I finally took it for a spin, nothing unusual as of now. Speed and range acting like usual, no heat spikes, and charges normal when plugged back in.