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-   -   Failed cell LiPo's and use - instead of bin ! (http://www.Wattflyer.com/forums/showthread.php?t=73820)

solentlife 05-31-2014 09:09 AM

Failed cell LiPo's and use - instead of bin !
 
OK ... I have a few 3S and 4S packs that have a dud cell ... but the other cells seem to hold and provide good power ... I agree that it's only a matter if time before they go west also .... but ....

There are times when a model is poorly designed / made that CoG is a problem and often requires weight up front.

Given that a 4S pack of similar capacity weighs significantly more than a similar 3S pack ... if the 4S is dud on one cell ... (I know you lose 1/4 mAh) ... maybe it can be used in that 3S model that needs nose weight.

Similarly the 3S with a dud cell in a 2S model.

I've looked at the packs with idea to cut out the dud cell ... but the foil tabs and soldering is welded or Hard soldered - not Soft soldered. I'm a bit reluctant to play about with cells and trust them to stay connected etc.

How many people modify or use such packs ? So far I use them for bench testing ... but thinking to use in less demanding models.

Nigel

fhhuber 05-31-2014 01:45 PM

Can't fly with a daed cell because the dead cell has internal resistance and robs power plus you are carrying the excess weight.

And its not safe to be passing current through a dead cell.

Its generally not worth the effort to cut the bad cell out because the other cells in the pack are the same age and have the same use history as the bad one. You can expect them to fail pretty soon.

So I just drive a nail through the pack and toss it in a safe place for it to burn. Then I put the remains in the trash.

tobydogs 05-31-2014 02:08 PM

ditto fh,i can't stand batts that have defects. the one's i hate the most is a broken red or black lead. i have tried to reheat existing solder on the wire but it never holds.

i no longer pop/burn packs to the open air and pollute my neighbors air. i use a 3 prong garden rake to poke a hole,wait for the smoke to start and plop it in a small bucket of water to boil away. after a few minutes it threat is done. i leave it in the bucket till i get around to tossing it.

having only flown electrics I've smoked enough batteries to no longer need to see the deadly smoke[popcorn].

this reminds me to pop 2 batts in the storage cabinet that just aren't safe anymore.

JetPlaneFlyer 05-31-2014 02:10 PM

Yep, it would only be safe to do this if you bypassed the bad cell by re-soldering the output wires, or removed the cell completely. Otherwise you are still passing full current through the damaged cell which is likely to end badly. To be honest really not worth the hassle.

CHELLIE 06-01-2014 01:10 AM

The old Align lipos you could solder them because they had a soldered tab, but the newer lipos are fuse welded and you cant do any thing with them, best to just toss them out.

Walt Thyng 06-01-2014 02:19 PM

Re-wiring LiPos
 
I guess I haven't run into those "hard soldered" or "fuse soldered" cells. A lot of guys in my club fly 5,6,7,8,10 cell packs. When they lose a cell or two, the packs come to me (I'm the club scrounge). I use WD40 and an old business card to separate the cells. Next I snip off the metal connector tabs on the bad cells. I use those salvaged tabs to make new connections. I still have a hammer head iron from NiCad days and use it when resoldering. I like to have a lot of heat that can be applied quickly before the cell heats up.
Walt


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