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-   -   Discharged Li-Po (https://www.rcuniverse.com/forum/e-flight-power-sources-126/2997465-discharged-li-po.html)

Gullwing72 05-21-2005 05:57 PM

Discharged Li-Po
 
I bought a 11.1v 4200mah Thunder Power battery with only 10 cycles on it from a hobby shop buddy a couple of weeks ago. Knowing that this guy knows his stuff when it comes to electric flight. When he said he would take $50 for it I jumped at it(he was having money problems and was selling most of his personal stock). First question: It has been setting in a drawer for I know for 2 weeks and don't know how long before then. Well it has discharged below the limit. Has it setting there done that? And question #2 can I revive it somehow? Thanks for any help...

Matt Kirsch 05-23-2005 07:55 AM

RE: Discharged Li-Po
 
Do you know what the voltage was BEFORE you put it in the drawer? LiPolys normally discharge veeeery slowly just sitting around. Two weeks, you shouldn't even be able to tell the difference in voltage...

If it dropped from a full charge down below the limit in two weeks, something is seriously wrong with the pack. It's a judgement call on your part, but I would ask for a different pack or my money back...

Now if your friend just ran it down to the limit, and left it sit discharged for a few months, that's different. What voltage is it at right now?

Bringing a pack back up needs to be done CAREFULLY. With a 3S LiPoly pack, the best way to go is to connect it to the transmitter side of a transmitter/receiver wall wart charger, then watch it with a voltmeter until it comes up above 9.0 Volts.

Gullwing72 05-23-2005 06:35 PM

RE: Discharged Li-Po
 
I don't know what the voltage was before. I think he just ran it down. The pack looks to be in very good shape physically (not swollen or dinged up) The pack is at 5.21 volts now. I have a charger that will charge ni bats and lipoly down to .10, will that work as well? It would be easier than trying to connect it to the tx/rx charger. If not I will find a way to connect it to the wall charger... Let me know what you think Matt.....Thanks

Matt Kirsch 05-23-2005 09:14 PM

RE: Discharged Li-Po
 
5.21 Volts? There's not much hope of reviving that pack. Once you get below 7.5 Volts on a 3S pack, the writing is pretty much on the wall. I would also suspect that the cells in the pack are now horrendously out of balance, if one cell isn't dead outright. Trying to charge the pack, even slowly with a wall wart, is potentially dangerous at this point.

Gullwing72 05-23-2005 09:33 PM

RE: Discharged Li-Po
 
Alright Matt, thank you for your help. My hobby shop bubby and I are going to have a talk tomorrow. I guess I learned that same old lesson.....If is sounds to good to be true than it is.......Thanks agian..............CDP

supi7 05-23-2005 11:58 PM

RE: Discharged Li-Po
 
7.5V per 3 cell pack is no way safely rechargable. a 3 cell pack should not be dropped below 8.25V and even at this point most auto chargers will not pick it up.


I reccomend that you take it back. This pack is too far gone to risk recovery.


Best Wishes,

Dan
TrueRC


Matt Kirsch 05-24-2005 05:37 AM

RE: Discharged Li-Po
 
Hmm, original "conventional wisdom" on LiPoly packs was a 2.5 Volt per cell cutoff. That eventually became the "drop dead" point, and that's not to say that the pack would recover with 100% of its capacity and capability after being drawn down that far.

I agree, most automatic chargers won't even touch packs that are below 9.0 Volts, let alone 8.25 Volts.

Gullwing72 05-24-2005 05:38 PM

RE: Discharged Li-Po
 
Hobby shop buddy was not there today.(out sick) I will catch him. I am thinking of cutting the shrink wrap off and seeing if I can get one or two cells salvaged out of it, that is if he tells me to kiss off. Don't want it to be a total loss.....


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