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Old Jun 26, 2005, 09:01 PM
e-flight in 24½th Century
Waldo Pepper's Avatar
Cypress, TX
Joined Jul 2004
525 Posts
Took bad 3 cell lipo and made into a good 2 cell

My very first lipo 3S1P 2200 pack died. I tried charging/discharging and kept getting a FAULT when I got to stage 3 on the AstroFlight 109 charger.

So today, being bored and stupid, I cut the heat shrink off and while looking at its guts noticed that one cell was all spongy. It wasn't swollen but felt like it was filled with jello

So I carefully took it out of the pack, resoldered the wire that went to it to the next cell in line and it's been on the discharger for an hour now and still at it. Can't wait to see what it charges to when it goes on the charger.

What I'm hoping is that I end up with a 2S1P 2200 pack rather than a really messy, hot and stinky fireball

Still have to "kill" the bad cell--but too tired and still stupid to do it tonight. Tomorrow salt water here it comes.

walt
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Old Jun 26, 2005, 09:34 PM
Registered User
Joined Jan 2002
6,587 Posts
walt,

If you're online, take the 2S pack off discharge!

Measure the voltage of each of the cells. If they're both above 3 volts, leave the pack alone until you're rested.

Tomorrow, CHARGE the pack and monitor the voltage of each cell from time to time as the pack charges. When the higher-voltage cell gets to 4.1 volts, stop and charge the lower-voltage cell VERY SLOWLY to match the higher voltage as closely as you can.

Your pack will then be balanced. Monitor the individual cell voltages for several charge-discharge cycles, to see if the pack stays balanced. If it doesn't, you are dealing with mismatched cells, because cells don't always wear out at the same rate in a pack.

- RD
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Last edited by RD Blakeslee; Jun 26, 2005 at 09:45 PM.
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Old Jun 27, 2005, 11:40 AM
Registered User
Florida
Joined Aug 2004
4,108 Posts
Some multicell packs I've opened up do not have solderable interconnects, appear to be welded aluminum connecting bars. How did you solder yours?
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Old Jun 27, 2005, 10:36 PM
e-flight in 24½th Century
Waldo Pepper's Avatar
Cypress, TX
Joined Jul 2004
525 Posts
The mushy cell had the red wire soldered to it. I used a 30W soldering iron to get it off the tab. When I tried to solder it onto the tab of the good cell I had to go to my Weller soldering gun--that's the big one that really puts out the heat. Once I got it hot enough the solder melted and stuck on the tab without a problem.

I did use a heat sink on the tab when I went with the big gun. Wanted to keep the heat away from the cell which seemed to work.

Did get a good discharge (over an hour) and charged right up like the other 2S1P packs I have. Need to get out and fly it! Weather has been high 90's and no change in sight. I love Houston weather in the summer.

walt
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Old Jun 29, 2005, 06:18 AM
who dares wins
like2fly!'s Avatar
London,England
Joined Apr 2005
1,805 Posts
sounds abit dodgy... gotta be carefull with solder iron big time.. probably not a great idea to take packs apart! although i know experience can only be gained by trying..
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