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Old Mar 21, 2012, 03:46 PM
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Why you don't charge an overdischarged lithium polymer battery.

Well, this was a real eye-opener!

I needed to make a product video for a non-RC customer of ours. It involved essentially a 3s 2100 pack that had been discharged to zero volts placed inside one of our OEM 13x18 LipoSacks. I charged at 3 amps on a lipo setting with a "smart" charger (B8-style) using only the main leads and without balancing lead attached.

At 11.5 volts the battery let go with the classic lipo ignition that we've seen all over the internet at nowhere near full charge! Talk about a disturbing surprise!

NOTE: My usual mode of charging is quite hands on as I use Blinky balancers and also check individual cells during charging. I do not use balancing leads attached to the charger. Would using the balance function have helped? Somehow I doubt it as this was not an out-of-balance issue but a simple charging of an overdischarged lipo battery.

Lesson (at least for me and YMMV): Do NOT charge overdischarged lipos...especially if you have left the battery plugged into the esc overnight.

Comments?

mw (www.LipoSack.com)
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Last edited by Mark Wood; Mar 21, 2012 at 04:00 PM.
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Old Mar 21, 2012, 03:53 PM
Prefectionist
United States, MN, Minneapolis
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I read that wrong, yeah, once you discharge a lipo to 0 volts it's done as in done done. It should be thrown away. Attempting to charge it at all is a risky adventure as you have irreparably harmed the chemicals inside there is a significant chance that it will blow up. A few have tired using 1/10 C rating eg .3 amps for your example. But that battery really really isn't trustworthy.

Old post I thought you had just low discharged to like 3.0 volts:


90% chance that one of the 3 cells got over charged. I bet only one cell let go and the others maybe followed in the heat.

If you low discharge a battery any variance in the cell resistance will become very un-balanced during charging. So yes using the blinky might have stopped it, but blinky might not have been able to shunt enough juice away from the bad cell. Chargers without built in balancers really aren't worth using anymore.
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Old Mar 21, 2012, 03:59 PM
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Yea I found out one of my really old eflight 800mAh 3s is very out of balance with an over discharged cell. It appears pretty bad. Accoring to my lipo feild tester its reading 2.67v, 3.59v, 3.62v.

I know this battery is hazardous but it doesnt appear puffed yet. I have an older style align charger that I may use to see if I can revive the bad cell. Im pretty sure my other computer charger (triton 2 orignal) will refuse to charge it. I will only attempt this outside in a lipobag/sack far enough away from the charger to make sure it doesnt set fire to anything incase it goes off. Bad idea? Maybe this pack need to get thrown out. At least its cheap.
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Old Mar 21, 2012, 04:07 PM
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Problem with your test and was common before balancing chargers is you did not balance charge. You had at least one cell stay really low which drove up the other 1 or 2 cells to >5 volts. I have accidently charged a cell at 4.6x before without heat or fire but who knows, the next cell charged to that may have let go.

Best lesson here is ALWAYS use a balancing charger and if you only use it from time to time ALWAYS use it on an abused pack.

Rick
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Old Mar 21, 2012, 04:13 PM
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I agree with Creapyd that the Blinky balancer would only be capable of sinking a small percentage of the 3A away from any cell so that if one cell was completely dead and refused to accept any charge (very likely) , then the other two cells would have no voltage limit applied to them. This would inevitably lead to the results you saw.
If you had been using a balancing charger the software would have refused to charge the pack or at least refused to overcharge any single cell.

Wayne

PS Rick, hadn't seen your post - agree completely.
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Old Mar 21, 2012, 04:24 PM
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Yea balancing chargers are the only way to go.
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Old Mar 21, 2012, 04:29 PM
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Des Moines IA
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Quote:
Originally Posted by Mark Wood View Post
Well, this was a real eye-opener!

I needed to make a product video for a non-RC customer of ours. It involved essentially a 3s 2100 pack that had been discharged to zero volts placed inside one of our OEM 13x18 LipoSacks. I charged at 3 amps on a lipo setting with a "smart" charger (B8-style) using only the main leads and without balancing lead attached.

At 11.5 volts the battery let go with the classic lipo ignition that we've seen all over the internet at nowhere near full charge! Talk about a disturbing surprise!

NOTE: My usual mode of charging is quite hands on as I use Blinky balancers and also check individual cells during charging. I do not use balancing leads attached to the charger. Would using the balance function have helped? Somehow I doubt it as this was not an out-of-balance issue but a simple charging of an overdischarged lipo battery.

Lesson (at least for me and YMMV): Do NOT charge overdischarged lipos...especially if you have left the battery plugged into the esc overnight.

Comments?

mw (www.LipoSack.com)
My question is why would you try and charge a fully discharged lipo that reads o volts in the first place?

What would you call an overdischarged lipo more than 80% ?

Plus how did you get your charger to charge it as most quality lipo chargers will refuse to charge a lipo reading o volts
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Old Mar 21, 2012, 08:28 PM
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OK this has not happened to me in years and thousands of flights but I lost one in the fog Wed, morning and when my wife and I found it 6 hours later it was perched 90 feet up in a rather large Popular tree approximately 1200 feet from the center off the runway where I was standing. Great Planes Electro Stik 52.5" WS.

LiPoly a Thunder Power Pro Power 40 3S 3250 placed ij service 9-18-2010 and it had 186 flights on it. When retrived after wind blew it out into a much smaller tree which I cut down ,six days later the LiPoly read 0.295 volts total. Charged in Ni mode to 9V at 300 mA rate then charged to Storage (3.86 per cell) as a LiPoly ,no balancing but closely monitored. Left set for 24 hours and all cells still 3.85. Charged to 4.2 per cell 1,517 mAh added IRs @79F 3.3 / 2.9 / 2.7. It is every so slightly puffy,not as firm as it was but not thta bad either.

It will now get discharged back to Storage and someday soon I will charge it back up and do some discharge test on it.

Quote:
My question is why would you try and charge a fully discharged lipo that reads o volts in the first place?
This question was not directed at me but my reason is to gather first hand data . I revived a TP ProLite 3S 13c 1300 years ago that was 2.X volts total and it last over another hundred flights in a flat plate foamie 3D plane.

Charles
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Old Mar 21, 2012, 09:22 PM
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LOL @ Charles. I need to fly in places that have fog. Fog in AZ? Pfff. I can't blame anything buy lockout or thumbs... JK

I have charged so many over-discharged lipos over the past 5 years I can't count them. One thing I will note and I know Charles knows this, is they will never recover fully. Sure, they will work if they recover like Charles' did but they sometimes start out puffed, some tend to stay puffed, some get sorta hard again, some puff easily at max C constant, some lose capacity or, once in a great while, seem to work about as good as before. Never have I seen one "works as good as new". Impossible but if only used at 10C the user may not notice any difference.

Most of the time they give up the ghost in about 3 months or less; usually less. As a result I don't even bother anymore when as low as Charles' was today. If less than 1v per cell I just salvage wires/connectors and toss in garbage. Same goes for a cell with a puncture but that is another story for another day..
Never have I had a mishap with one of these but I take just about every precaution possible when recovering a pack and I always put a mark on the pack reminding me that this is damaged merch so I don't push them too hard.

I think it will be good to get Charles' IR on these cells if he has a recent benchmark.

Oh, I suggest that the OP should contact the LipoSack people, I heard they sometimes help the person out that lost their OEM sack to a fire.

Rick
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Old Mar 21, 2012, 09:52 PM
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I didn't know they had lipos 1300 years ago.
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Old Mar 21, 2012, 11:04 PM
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I didn't know they had lipos 1300 years ago.
I read the article in National Geographic where they found a couple of puffed packs in a Hopi Indian archeology dig among some pottery fragments. They apparently were the first to store LiPo's in pottery for fire protection.

-= Dave
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Old Mar 22, 2012, 12:54 AM
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Originally Posted by eckace1 View Post
My question is why would you try and charge a fully discharged lipo that reads o volts in the first place?
Second sentence of the OP.

Quote:
What would you call an overdischarged lipo more than 80% ?
Huh?

Quote:
Plus how did you get your charger to charge it as most quality lipo chargers will refuse to charge a lipo reading o volts


Bottom line is that I wasn't trying to charge the battery for use. The intent was to ignite it for a customer's product video as requested. That it lit off at less than storage charge was a bit of a wonder to me. That is all.

mw
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Old Mar 22, 2012, 02:34 AM
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-overdischarge at high current (standard load by motor) may destroy lipo CELL at once, it is possible that it will start selfdischarge or some kind of short circuit. Problem may come from difference between cells and attempt to charge without good balancer (safe, that will not let any cell overcharge even if another cell keeps very low voltage).

- slowly overdischarged lipo is often "resurrectable", I mean that if no cell did baloon YET, we may try to charge it slowly until it reach nominal voltage (3.6V or little more, EACH CELL measured separately). The time of how long it was discharged deep, do matter.

-Most of balancers are capable of very low balancing current. There is no reason to force balancer to recover e.g. 400mAh difference in such case, by its maximum current of 75mA - it would take 6 hours even if the charger would not destroy some cells by overcharge(voltage above 4.20) in the meantime.
Just charge each cell separately, connecting the charger directly to one cell through balance connector and charge leads like this:
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Old Mar 22, 2012, 07:49 AM
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I interpret Mark's post as saying, "How Lipo cells may react under various circumstances is sometimes unpredictable and charging in a firesafe location is always recommended. You never know when the unexpected might happen."
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Old Mar 22, 2012, 09:36 AM
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You got it, Hoppy.
I'm pretty sure that two cells went then the third. What really startled me was the amount of energy that the battery let go of at only 11.5 volts. I heard the telltale pop, checked the charger and then hit the go button on the camera. Fifteen seconds later the pack ignited.
I've burned a lot of old and new packs in the development of our products but this was a new one on me.

mw
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