Expensive and painful Li-Po lesson! - Page 3 - RC Groups
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Feb 22, 2004, 09:51 PM
Registered User
Headless, many people have reported having very briefly shorted their LiPos and suffered no ill effects. Center taps allow you to check the balance of the cells. But that's really not necessary to see if a pack is holding a charge. Just put them on the charger, give them a full charge and measure the pack voltage an hour after they come off the charger. If pack voltage is normal, you should be fine.

Daveoner, an 8 second short is probably long enough to do damage. Any puffiness is a bad sign. In this case it would be best to contact the vendor who sold you the pack and ask for advice before doing anything else.

LiPos are less tolerant of mistakes than other cells, so you have to be extra careful with them. But we're all human and make mistakes even when we're being extra careful. So no one should ever go into LiPos thinking "it can't happen to me."
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Feb 22, 2004, 09:55 PM
Does anyone hear a cat?
headless's Avatar
Heya Dave; thanks for the input

All of my lipo's drop voltage an hour after a full charge... should it only matter if they continually drop voltage until the pack is maybe 2 volts or something lower, or should i be worried if they drop a third of a volt or some such? it seems that even my new tp860 packs drop from 12.54 to 12.3 or so volts a little while after charging...
Feb 22, 2004, 10:03 PM
Registered User
I don't think it's unusual for voltage to fall like that in the first hour or so after a charge. They should not, however, continue to fall off at that rate. Lithium cells really have a low self-discharge rate. So once they stabilize after a charge, they should lose voltage very slowly over a period of weeks and months.
Feb 22, 2004, 10:12 PM
Registered User
Dave, thanx for the input. I can not contact the vendor, it was a flybynight ebay outfit. The cells worked fine when new, I am nervous to use them now. Even nervous to store in the house. I left them outside and will check them again 2moro. My other post about my "Y" harness is confusing. To elaborate: I took two female battery plugs and connected them + to - on BOTH. Then I connected them BOTH to a male connector. I should have only connected + to - and then the remaining - & + would have been connected, but somehow in a "wire" configuration (rather than terminals) I got confused and made a nice little complete circuit "Y" harness.
Feb 22, 2004, 10:15 PM
Registered User
I have made all my lipo packs, 2s and 3s, and had no problem until a hard crash which was followed by smoke rising from the ejected 3s pack. Fortunately it was on the grass and I watched, fascinated, as $30 of 1200mah lipo was converted into a worthless mass. I learned after it cooled that the short was caused by deformation of the pack, bringing two terminals together. I now use hot glue to cover the tabs, and feel much better about their safety. Covering the top surface of the joined tabs still allows access with voltmeter probes at the bottom surface to check cell balance periodically.
Oct 12, 2006, 11:25 AM
Registered User
Man, that is serious. When I was connecting the tabs for the 109 charger and the li-po batteries for my trex 450 I never thought about what could happened as I was doing it inside the house. I was at the flea market and purchased one of those ammo containers typically used by our Armed Forces. I drilled holes for vent and an old brick inside. Thanks for your update. I could imagine you running like crazy inside the house with the flame going on.
Take care,
racer59
Oct 12, 2006, 01:38 PM
so i rewired it...
xorbe's Avatar
I shorted one of my cells through a fused balancer lead, and it popped the fuse with no cell damage. $5 though for another fused lead... but worth it!