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Jan 04, 2004, 08:20 PM
Registered User

Balloned Lipo


I made up a 3S1P Tech from Aircraftworld some 3 months back,
put it together, charged up and left untouched since. On Sat
I was loaning it to a mate when I noticed 1 cell was balloned up.
While look at it I drop the pack..straight away the cell was deflated...and I panic abit thinking it would catch fire...nothing
happened, from the outside it looks ok but the pack was dead.
I took it apart and find crystalised white and yellow slim all
over...all 3 cells still measure 3.9 volts each.

That puncture cell must be no good...anyone with similar
experience. This is my 2nd pack that balloned on me..
next time I will buy ready made pack...they balance it
better.
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Jan 05, 2004, 03:37 PM
Registered User
Did you just build the pack with the cells as they came and then charged the whole pack?

I assume the cells were not balanced initially, and when you charged them in series one cell went over 4.25 Volts.

Let's assume the cells were at 3.6, 3.6, and 3.9 Volts when you got them. Charging them to 12.6 Volts in series would yield approx. 4.1V / 4.1V / 4.4V. The cell that was charged to 4.4V is the one that is now damaged.

The chemistry of these cells is only stable within the 2.5 - 4.25 V range.

Always charge each cell individually with the SAME charger and at the SAME charging rate before building a pack.

I am surprised that all three cells still measure 3.9 Volts, though.
Jan 05, 2004, 05:16 PM
Registered User
I charged them individually then solder together. I think it is
better to have a balancer. I will not buy loose cell until I get
hold of a ballancer.
Jan 05, 2004, 10:57 PM
Registered User
I had the same exact problem with Aircraft World ETech cells that I built up. Now I only buy ready made packs.

Victor
Jan 06, 2004, 05:51 AM
Registered User
when i buid packs i don't use a pcb as diy builders tend to put to much heat through the tabs and the copper on the pcb can act as a heat sink holding the heat and you tend to use a lot of solder to make a 'good' joint, and the heat tends to track back down the tab damaging the seal. i use the full lenght of the tad put them together , fold over 1/4" then solder the folded tip. then dip in water to quench, dry fully. then fold back and tape joint. you will find to much heat will damage the seal around the tab. i have thought of putting a drop of thin cyno on the seal just in case when i have finnished. might try it on my next pack

t.n


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