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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> A123Racing Support >> Failure modes
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Failure modes - 5/20/2007 3:54:46 PM   
13BRV3


 

Posts: 235
Joined: 10/14/2006
From: Navarre, FL, USA
Status: offline 		Greetings,

I have a few Dewalt packs that I got off Ebay, and it turns out that one of them is bad. I plugged it into a stock charger, and got the "bad battery" flash code, and the pack had no voltage. Since I didn't know exactly who I bought that pack from, I figured I'd take it apart to see if I could salvage any of the cells.

When I took it apart, it had an obvious manufacturing defect. At least one of the wires from the battery to the electronics module had been pinched and shorted to the module casing. I removed all the electronics, and left the batteries in the trays, minus the spring contacts.

I then tried to charge the whole pack via my new Mastech HY5020E (which I love BTW). I started at 18V, and only 1 amp, then checked the cells. One was low, but the rest were all even. I then proceeded to higher voltages, while keeping the current under a few amps. After every new voltage level charge, I checked the cells.

The good news is that 9 of the cells seem to be perfectly healthy. The one bad one has an odd failure mode though. As soon as I take it off the charge, that cell reads a couple tenths of a volt low. The cell is internally discharging itself though, because the voltage continues to drop slowly until it reaches about .15 volts. While it's discharging itself, the cell is slightly warm.

My question is purely out of curiousity. Is this internal discharging a common failure mode for a bad cell? This is one of several cells that had the paper shell burned in one spot, right down to the can. Maybe it was the cell that originally got shorted, and it overheated internally???

Rusty (should be flying instead of typing)
       Post #: 1

RE: Failure modes - 5/21/2007 1:04:44 AM   
Red Scholefield



Posts: 4780
Joined: 12/8/2001
From: Newberry, FL, USA
Status: offline 		What you are seeing is no doubt one of the failure modes induced by leaving the cell in a shorted condition for some time. There have been so few failures with these cells to date that we really don't have a good handle on the failure modes under normal use.

_____________________________

Red S.
AMA 951 Leader Member

(in reply to 13BRV3)
       Post #: 2

RE: Failure modes - 5/21/2007 2:14:16 AM   
13BRV3


 

Posts: 235
Joined: 10/14/2006
From: Navarre, FL, USA
Status: offline 		Hey, if failures are that rare, maybe I'll get a reward

Rusty

(in reply to Red Scholefield)
       Post #: 3

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