Battery not charging

[billadie]

I have a problem with a battery. Yesterday (seriously bad day) I ran the battery flat. Now when I connect to charger the chrger light remains green. If I press the test button on the battery no lights are shown I have swopped the fuse with that on my spare battery, made no difference. Charger works fine with the spare battery. The faulty battery is a BMS 37v/15Ah Li-ion, about 15 months old. It has not had any previous problems.

Any help, advice, appreciated.

Thanks in advance

Bill

 

[Deleted member 4366]

Did you check that your charger is giving 42v at the connector? If not, do that first.

With no LEDs lighting, the most likely cause is that the BMS has shut down because one cell is below the charging threshold. Start by measuring the voltage on the battery terminals and then the charge socket. Report the results here. If both results are below 20v, you'll have to open the battery to measure the individual cell voltages. It's not difficult to fix batteries when the BMS has shut down. You have to probe around with a meter and do a bit of temporary wiring to charge the low cells. It's a good chance to learn something about your battery, but if you feel you're really not up to it, you can send it to me to fix, which will cost about £7 each way by Collect Plus.

 

[billadie]

Did you check that your charger is giving 42v at the connector? If not, do that first.

Thanks Dave. haven't checked charger voltage. Will do so on Monday as Multmeter at work. Will then think about opening battery. Shouldn't be beyond me but most things seem to be over last few days!

Cheers

Bill

 

[billadie]

Well, I can't explain this, but if anyone has got a few hours spare, they might give it a try.

Connected the charger to the main battery, which had been flattened, light remained green, no charging. Tested charger voltage. Zero, not a flicker on the meter. Connected charger to spare battery, light turns red, charges battery til full - all lights on battery - then turns off, as it should.

Concerned about the Zero reading I bought a new charger. Tested this - 42 Volt. Connected to main battery fine, charged as expected. Returned from work today and out of curiosity connected old charger to main battery. It is now happily charging the main battery again.

Now, the main battery was flat, flat, flat (approx 8.5 V) and I can possibly understand that the old charger was not up to charging it, but I can't see where the Zero volts came from - I got a colleague to check it, unless there is some protection circuit.

Anyway, I now have a spare charger and two working batteries.

Thanks for the advice D8veh.

 

[Deleted member 4366]

When the BMS shuts off, the battery isn't zero volts. It's about 31v, but you see much lower on the connector because the cells are blocked by the MOSFETs. With the BMS switched off, you can still get some charge on the terminals. Your meter might show ov, 31v or anything in between, but as soon as you connect anything that draws current, it'll go to zero.

It seems that your new charger was able to kick the BMS back on again to allow normal charging. No damage will have been done.

This situation demonstrates why running batteries right down should be avoided if you can , and you should never leave a battery run down.

You don't have to panic about running your battery to empty, but don't do it unnecessarily.