# Am I screwed, sort of screwed, or maybe okay?



## taken by aliens (May 26, 2011)

I think you can bring your battery pack back to life. Sounds like you've taken the right steps to bring it back... trickle charge then when the pack seems to hold a solid low voltage charge switch to a constant voltage or constant current charger to finish charging the LFP bats. LFP should bounce back even from a total drain, but they might not bounce back to 100 percent, maybe like 70 to 80 percent. I also believe there are some burst chargers designed specifically to bring a LFP back from total drain.


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## frodus (Apr 12, 2008)

hope you have a BMS or are monitoring cells. Some cells won't come back neccessarily. There's nothing telling that charger if one cell isn't charging. You may have one pop up to 4V and another to 1V, or stay at 0V, and the charger would never know.

I'd get a single cell charger, or an adjustable power supply and bring them up, one by one. Watch voltage and heat.


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## rmay635703 (Oct 23, 2008)

Personally in these situations I use my diode powered lightbulb battery charger. I can set the charge current to 1/100 of an amp or whatever I want.

Using this you can charge so slowly that the inevitable issues won't cause explosions or even damage and this charger can charge any single cell or combination.

Cheers
Ryan


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## frodus (Apr 12, 2008)

rmay635703 said:


> Personally in these situations I use my diode powered lightbulb battery charger.


Can you elaborate on what a "diode powered lightbulb battery charger" is?


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## dtbaker (Jan 5, 2008)

yikes... yeah I would not use your regular charger at first. I would take'em out, wire in parallel and set target voltage on a power supply. This way if one is completely dead, you won't fry the others.


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## taken by aliens (May 26, 2011)

diode battery charger with light bulb im guessing is a zener diode with a break down voltage just under your cells max voltage, and the light bulb is probably to shunt the current when the zener break down voltage is reached.
............................__
(-)______|\|______/.. \___________
...........| |/|......... \__/ PR2 lamp.. |
...........| 3.5v Zener diode... __..... |
...........|___|\|___________/. \____|__ (+)
.................|/|................ \__/


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## ElectriCar (Jun 15, 2008)

taken by aliens said:


> diode battery charger with light bulb im guessing is a zener diode with a break down voltage just under your cells max voltage, and the light bulb is probably to shunt the current when the zener break down voltage is reached.
> ............................__
> (-)______|\|______/.. \___________
> ...........| |/|......... \__/ PR2 lamp.. |
> ...


I was thinking today about using a zener and resistor to balance cells. Just clip it on and let it drain, rinse and repeat until finished.


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## mora (Nov 11, 2009)

How did cell revival go? Half a year ago I got a pack of 31 cells where lots of cells read about 0.1V. Some were at 0.01V or lower and didn't hold charge at all. I guess cells get shorted internally if voltage gets too low. I got 22 very usable cells out of that pack though. I believe their internal resistance went up but available capacity at 1C discharge rate remained very same (90Ah cells).


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## Beemer (Jun 2, 2011)

mora said:


> How did cell revival go? Half a year ago I got a pack of 31 cells where lots of cells read about 0.1V. Some were at 0.01V or lower and didn't hold charge at all. I guess cells get shorted internally if voltage gets too low. I got 22 very usable cells out of that pack though. I believe their internal resistance went up but available capacity at 1C discharge rate remained very same (90Ah cells).


You are thinking of them like lead acid cells. They don't short internally, ever. Instead the lithium comes out of the electrolyte solution and plates the anode/cathode (depending whether over charging or over discharging).
It's irreversible but if the other cells are good. i.e. the BMS hasn't drained them to death then they will carry on performing.

Normally Lithium cells have no self discharge if nothing is connected across them and they stay clean and dry.


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## gte718p (Jul 30, 2009)

It's been a while, but I finally moved into a house with a garage. The batteries charged up fine. Pack is holding 41 volts. I road about ten miles the other day. The bike did well. This week I will see if I can still get 30 miles out of a charge. It seems to have lost some low end torque and gained some top end speed. I probably need to go in and look at the controller settings.


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