LIPO - out of balance cells?

[Cardnim]

Hi all,

Im new to lipos and have just received my first charger and 2 batts (one brand new Speed Power, the other an older 2nd hand GM.)

Good practice with NiMH was always to discharge the cells before charging again (to prevent cell capacity memory)

So, plugged in my 2nd hand GM lipo (2 cell, 5400mAH, 45C) and plugged in the balance board that came with my charger.

Set the discharge rate to 1.0A

It went for 73mins but by the end, cell 2 had dropped out of sync with cell 1. Before that, they were much the same.

The charger ended the discharge, with the following spec:
- cell 1 - 3.42V
- cell 2 - 2.80V

I have read that discharging lipos beyond 2.8 is very dangerous, but I am surprised at the difference in voltage - surely the balancer should have prevented this? (or at least stopped discharging cell 2 while continuing to drain cell 1 till it was level)

Can anyone shed any light on this? The Internet is filled with scare mongers who say "my granny once looked at a lipo funny and now she is on fire" - so its hard to filter the fact from fiction.

Thanks as always guys.

[Cardnim]

Argh, this is really confusing and slightly worrying.

Now I have to leave work, and the battery is discharged. More reading has just found some guys talking about how to never leave a Lipo less than 3.4V or it permanently damages it.

I cant really charge it safely till tomorrow as I dont want to leave it unattended.

Is this the right thing to do?

(I hate Lipo's and all they stand for - long live Nickel!!!)

[super__dan]

Get some charge back into it TBH, Lipos are balanced on charge and 99.99% of the time are never run flat so being out of balance at full discharge is not a concern. You need to forget the Nimh things we 'HAD' to do, it's different and all for the better IMHO

[Cardnim]

Thanks Dan,

Ive jsut put the charger on for 5mins before I have to go.
Selected "Lipo BALANCE" at 5 amps

individual cells are now at:
cell 1 - 3.82v
cell 2 - 3.62v

going to have to end it there for tonight.

I hope I havent wrecked the battery.

P.S. if discharge isnt needed on a Lipo, why is it an option on the charger (genuine question, Im not trying to be smart)

[Whiskers]

I think just so that you can discharge it to 7.7v for storage.

[ianhaye]

should never really need to to discharge lipos like that, they are balanced at the end of a charge, touch wood you does loose a cell going that low on 1cell.