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Charge unprotected lipoly with desktop power supply? Answered

I have a few, almost dead 700ma li-polies taken from a macbook battery that would not charge. I have no formal Li-Poly charger, and most commercial charger will refuse to charge these batteries anyway- because most of them are lower than 2.7v right now. I wanted to see if I could revive these, which I have read can be done, using constant voltage and current. 

My problem is how to charge these using a common desktop power supply. My setup right now is a charger set on 3.7v, multimeter in parallel (to measure the cell voltage), and a current of 20ma. So far, nothing dramatic has happened thus far. Thing is, the "shorted" light on my power supply is on, and the voltage says its around 2.8v right now (rising slowly). Is this just due to the battery charging? I mean, is this behavior normal for an unprotected cell charging on a power supply? 

Also, please note that I do know what lipolys can do. I am not just gonna hook this thing up to 20v and leave to go to town. I am monitoring it, and have it in a large, thick plastic box that is 2ft from a door. I will not leave it on unsupervised. 

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frollard
frollard

Best Answer 8 years ago

a 3.7 volt cell needs 4.1-4.2 volts to charge it fully.

If it's at 2.8 it's discharged too far and the cell is likely shot (what the protection circuitry was supposed to be there for).

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astroboy907
astroboy907

Answer 8 years ago

One got to about 2.5 volts (down from 1.3ish), and stayed there at 20ma. Bringing the power up to 40ma seemed to continue charging, but I brought it back down just to be safe. As this is not even 1/10C, do you think it would be fine to charge at 70ma (no more, and always supervised), and see if it takes?

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frollard
frollard

Answer 8 years ago

realistically, so long as they don't get warm you could go for a full 1C, so long as you don't overvolt them.

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astroboy907
astroboy907

Answer 8 years ago

Accidentally left it on for an hour while I was in another room. Didn't do a thing whatsoever. Set it to 4.2 volts at 50ma, came back and the cell was sitting nicely at 3.7 volts..

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astroboy907
astroboy907

Answer 8 years ago

Yeah, it was really weird. I think the battery must of sat for like a year without a charge (I bought it off of ebay). I got it for $25 and it wouldnt charge in the computer. So I thought I'd try to resuscitate the cells, as they were undervoltage...

Seems that some revive, some dont... e.g
http://www.rcgroups.com/forums/showthread.php?t=432292

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iceng
iceng

8 years ago

Don't Ever Leave It Alone !   at 20 VDC !!!

It could out-gas a noxious vapor or start a fire after melting your plastic.

The Li-poly Cell is 3.7 V and a cutoff charging voltage of 4.2 V NO MORE.

A

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astroboy907
astroboy907

Answer 8 years ago

I was kidding about hooking it up to 20v, its set to 3.7v right now...
Seems to be going well so far...

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iceng
iceng

Answer 8 years ago

Yea ...  figured it out  ...   once  thenervesstopped  jangling.

I apologize for going ballistic with a friend.

Best Regards,

A

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astroboy907
astroboy907

Answer 8 years ago

Hehe no problem. I myself have done this a few times to friends- WHAT THE HECK WERE YOU THINKING?!?! Do you WANT to die?!??

Then of course I realized that they were kidding. Oops.. :)