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Safe Discharge Dodgy Lipo

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Tony Smith 713/02/2016 13:45:27
812 forum posts
28 photos

Hi,

I've done nothing with my models for quite some time, and today trying to get one of them airworthy again I find I have a dodgy LIPO. It's a bit puffed up, and squishier than the other one, and one cell reads almost flat compared to the others. At the moment, after an abortive flight resulting in loss of power, the cells read 4.08/4.08/2.92.

What's the best and safest way to run it right down so it can be safely disposed of? It's only a 1300mAh, but I still want to get rid of the energy stored in those two good cells.

If I set a trickle discharge from the main connector would that run down all cells, or would the dud cell prevent that?

Thanks,

Tony S

Terry Walters13/02/2016 13:49:27
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1829 forum posts
1068 photos

Tony - I use a 12v bulb (if it's a 3 cell) to drain the lipo then puncture the lipo covering skin and drop it into a half filled bucket of salt water.

Terry

Edited By Terry Walters on 13/02/2016 13:50:00

gangster13/02/2016 14:06:35
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985 forum posts
17 photos

Probably simpler to chuck straight into the salt water and leave for a day or two it will discharge

Essjay13/02/2016 14:43:28
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578 forum posts
1 photos
Posted by gangster on 13/02/2016 14:06:35:

Probably simpler to chuck straight into the salt water and leave for a day or two it will discharge

I've seen a Youtube video of a lipo that was just chucked into salt water without discharging first, and the problem is oxidisation forming on the cell terminals and cable ends which prevents the cells discharging. Far better to discharge using Terry's method first, then dunk in the salt water.

Steve

Dave Hopkin13/02/2016 14:43:57
3672 forum posts
294 photos

+1 for the lightbulb & Salt Water

John Lee13/02/2016 14:50:57
686 forum posts
52 photos

Tony

Check if your charger has a 'discard' function (usually on a system or sub menu so not obvious) . This uses the balance lead to ensure that all the cells are brought to zero. Otherwise +1 for lightbulb.

Edited By John Lee on 13/02/2016 14:52:25

Tony Smith 713/02/2016 16:28:43
812 forum posts
28 photos

Thanks. I think I'll rig up a bulb of some sort. I take it from that recommendation, that you'd expect this to fully discharge, even though the cells are not balanced. My charger doesn't seem to have a "Discard" function, only Storage or Discharge, Discharge wants to take everything down to 3.0 per cell, but bombs out with an error presumably due to my dud cell.

MattyB13/02/2016 16:45:12
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1999 forum posts
30 photos

Please, can we knock this salt water bunkem on the head once and for all?! It is just a bad method - the contacts on the battery will oxidise long before it is fully discharged, and piercing cells is never a good idea; there's always a risk of fire unless the cell voltages are absolutely zero, and polluting lithium salts will be released as it degrades. The solution is simple - just discharge the battery to 0V with the appropriate load (12v bulbs in series or parallel to match the pack voltage are good), cut the contacts off, tie them together and dispose of at the local tip in the battery disposal bin. Simple, non polluting and completely safe.

MattyB13/02/2016 16:49:45
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1999 forum posts
30 photos

BMFA leaflet on battery safety - it also concludes the salt bath method is a bad idea.

John Privett13/02/2016 16:52:54
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6015 forum posts
239 photos

I had a few to dispose of a while ago, so soldered this together using a car bulb and an XT60 connector.

imag0147 1.jpg

gangster13/02/2016 17:29:59
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985 forum posts
17 photos

Ok I stand corrected on the salt water business. Don't do it

I must admit to discharging mine using methods that I would not even mention on open forum in these safety conscious days.

Tony Smith 713/02/2016 18:00:04
812 forum posts
28 photos
Posted by John Privett on 13/02/2016 16:52:54:

I had a few to dispose of a while ago, so soldered this together using a car bulb and an XT60 connector.


Neat. I was away to copy that, but I don't have the right connector so I've just wedged the leads in for now.

Essjay13/02/2016 18:09:45
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578 forum posts
1 photos

That's a neat idea John. What I would also do is use some heatshrink on the XT60 and some insulating tape around the bulb contacts...........just in case wink

Steve

Wingman13/02/2016 18:26:58
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1125 forum posts
405 photos

I just take them out in the garden and put the garden fork through them - loads of smokedevil

MattyB13/02/2016 18:54:11
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1999 forum posts
30 photos

Darwin would be proud of you... wink 2

Tony Smith 713/02/2016 18:54:23
812 forum posts
28 photos

Not a good day for batteries, the transmitter pack looks dead as well. Just as well the flight was cut short by sudden lack of power.

Delta Foxtrot13/02/2016 18:58:12
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566 forum posts
91 photos
Posted by MattyB on 13/02/2016 16:45:12:

Please, can we knock this salt water bunkem on the head once and for all?! It is just a bad method - the contacts on the battery will oxidise long before it is fully discharged, and piercing cells is never a good idea; there's always a risk of fire unless the cell voltages are absolutely zero, and polluting lithium salts will be released as it degrades. The solution is simple - just discharge the battery to 0V with the appropriate load (12v bulbs in series or parallel to match the pack voltage are good), cut the contacts off, tie them together and dispose of at the local tip in the battery disposal bin. Simple, non polluting and completely safe.

I completely agree with you on this Matt.

PatMc13/02/2016 19:51:40
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4290 forum posts
524 photos

Not sure that I'd be happy discharging this particular battery through a car bulb, at least not as a whole series battery. The bad cell is so far down that there will come a point when the other two cells are reverse charging it. It depends on what the discharge current level is when the bad cell reaches 0v as to whether or this might cause it to overheat.
I'd cut the ballance leads & fit them to a block connector then discharge the two good cells, in series, through the bulb first. Then either connect the lot as a single series battery or the bad cell on it's own to the bulb.
Of course I might just be being a touch over-cautious.

Tony Smith 713/02/2016 20:02:16
812 forum posts
28 photos

I'm using a very small bulb, so it's discharging at around 200mA, no sign of it getting even remotely warm and the bad cell got down to 0v quite quickly.

Don Fry13/02/2016 20:03:52
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4385 forum posts
52 photos

Darwin, who is he, the garden fork system is good for the soul.

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