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Old Jul 04, 2014, 06:08 AM
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Overdischarged 3s battery

Hi all, i overdischarged my 1000mah 3s lipo battery while flying my heli to 10.6v. After balance charging it, each cell voltage differs by a lot. 4.2v,4.17v,4.23v respectively. Is my battery damaged? Can i still use it?
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Old Jul 04, 2014, 06:35 AM
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You did not damage battery.. unless u took it down past 3.00 volts a cell.. my math says 3.533 volts a cell .. sounds..

I would still use battery
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Old Jul 04, 2014, 08:29 AM
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As noted above, 10.6v is not over discharged at all. You would have to be down around 9v to be in genuine over-discharge short term damage territory.

For the cell voltages, how are you checking them? If you are using one of those little voltage checkers then they are not accurate and often report slightly incorrect voltage. On the other hand if you are 100% sure that the voltages are correct then you need to look at your charger, are you sure it was set to balance charge?
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Old Jul 04, 2014, 09:07 AM
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Yes i used the small voltage checker to check the voltage. I am positive i chose balance charge when charging. So meaning to say i can still use the battery? It'll be used to fly my fms mini p51.
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Old Jul 04, 2014, 09:08 AM
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Yes, there is nothing to indicate that there is anything wrong with it at all... So go fly!
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Old Jul 04, 2014, 09:12 AM
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Thats good news. Thank you very much. Im still in the process of learning in the rc world
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Old Jul 04, 2014, 10:47 AM
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Originally Posted by syaf View Post
Yes i used the small voltage checker to check the voltage. I am positive i chose balance charge when charging. So meaning to say i can still use the battery? It'll be used to fly my fms mini p51.
Since the total pack voltage is 12.6V, that would strongly suggest that the balance mode was not used and the charger was only looking at the pack voltage, not cell voltages.
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Old Jul 04, 2014, 11:15 AM
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Unless the OP checked all cells in the discharged state, 10.6 volts after discharge may be an overdischarge that could affect pack integrity. Few lipolys are comprised of cells that are capacity matched and 10.6 volts aggregate for a 3S pack is well into the 'danger zone' where voltage drops off very rapidly and should be avoided. If the pack is not well matched, it certainly may have had a cell that went below 3.0 volts.

Alas, we'll never know and I'd personally advise against letting the pack go this low on a repeated basis. I'd keep an eye on it. I'd also seek out a better charger that is more accurately calibrated and does not chronically overcharge beyond 4.20 volts.

Mark
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Old Jul 04, 2014, 11:23 AM
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Mark,

If that were the case (sub 3v cell) then the charger should have gone into error when he hooked it up in balance mode.

While running down to 10.6v is not good for the battery if you do it on a regular basis and therefore not recommended, personally I've accidentally run LiPos down lower than that very many times and no single cell has even approached 3.0v, let alone gone below.

I think it's scaremongering to suggest that the battery might be damaged. Agreed on not charging above 4.2v but there really isn't any evidence that that is the case. Those cell checkers cant be trusted when it comes to accuracy down to hundredth of a volt.
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Old Jul 04, 2014, 11:57 AM
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If that were the case (sub 3v cell) then the charger should have gone into error when he hooked it up in balance mode.
Yes, I agree that it should. However, there have been several reports that the cheaper chargers allow such.

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While running down to 10.6v is not good for the battery if you do it on a regular basis and therefore not recommended, personally I've accidentally run LiPos down lower than that very many times and no single cell has even approached 3.0v, let alone gone below.
As have I. It's obviously wise to avoid this, not only for the sake of the battery but, more importantly, for the sake of the plane and property given that there's precious little energy left at such low levels.

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I think it's scaremongering to suggest that the battery might be damaged. Agreed on not charging above 4.2v but there really isn't any evidence that that is the case. Those cell checkers cant be trusted when it comes to accuracy down to hundredth of a volt.
My deep apologies if my post came off as such. I merely wanted to convey that there's a chance that the pack may have been mildly compromised and that it'd be prudent to keep an eye on it for the next several cycles. I'd also get a decent quality DMM and get a true read on the accuracy of the charger and calibrate it (if possible) to avoid potential accelerated degradation and future woes.
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Old Jul 04, 2014, 02:14 PM
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I knew what you meant but when words like 'dangerzone' are mentioned beginners might panic.

When you think about it, if the battery is at 10.6v then for any one cell to be down to 3v would mean that the other two were at 3.8v average (i.e. the other two were only around half depleted). That couldn't realistically happen to a healthy battery.
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Old Jul 05, 2014, 03:47 AM
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I am positive i chose balance charge when charging.
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Old Jul 05, 2014, 08:49 AM
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The battery voltages say something different.

One way to find out.
Charge it in balance mode and see what you get. If they again are 4.17, 4.2 and 4.23V than you need a new charger.

A charger connected in the straight charge mode will charge the battery until the pack reaches 12.6V no matter what the individual cell voltages end up to be. They could end up as 3.5V, 4.2V, 4.9V = 12.6V.
In the balance mode, the charger will not let any one cell go above 4.2V and will keep charging until each cell is at 4.2V.
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Old Jul 05, 2014, 11:03 AM
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Hi guys i have charged the battery after my flying session. My charger displays 4.2v per cell after balance charge. My small battery voltage checker says otherwise. It displayed 4.18,4,17,4.25. I guess the fault lies in the battery checker. Thank you for helping me understand more about lipos, really appreciate it!!
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Old Jul 05, 2014, 11:24 AM
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Agree that you likely have an inaccurate voltage checker. To better understand charger accuracy and whether your charger may be placing your packs at risk, I highly recommend that you purchase or borrow a DMM of reasonable quality and fabricate a .100" spacing probe and check each cell via the balance tap.

Here's how: http://www.rcgroups.com/forums/showp...4&postcount=29

Mark
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