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Voltage low on 1 cell, x 2 batteries!

Coincidence?

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Ross Clarkson12/07/2015 18:43:41
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1438 forum posts
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So, i've just been flying. Charged 2 x 3S batteries which didn't need much charge before flying and then had two flights each of about 8mins which is less than normal if anything.

No signs of any problems and flights as expected, if not very windy. The batteries are identical batteries bought at the same time and used the same amount of times.

On trying to re-charge them now, both won't balance charge and the middle cell on both is showing about 1.25v.

What's caused this and is there a fix??

Martin Harris12/07/2015 18:51:31
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8478 forum posts
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I don't suppose you happened to check the cell voltages when they came off charge? It might be that your charger has developed a fault - I'd charge another 3S battery (if you have one) from discharged and monitor the cell voltages as it charges to see that they stay balanced while charging.

Although the correct advice is to discard the packs, if the charger has gone faulty, you might be able to recover them by charging the individual duff cells via the balance leads using a NiXX programme at a low rate to bring the cell up above 3V but this is a fairly long shot.  Conventional wisdom is that the low cells will have been ruined but I have recovered a pack which was discharged to 0V by being left (connected) up a tree for 2 weeks and although not perfect, was useable. Please don't decide to try this unless you are confident that you understand the risks and can do it in a safe environment.

Edited By Martin Harris on 12/07/2015 19:00:06

Ross Clarkson12/07/2015 19:24:28
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1438 forum posts
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They charged fine and I checked the voltage on all cells before taking them off charge. All were 4.19v.

Simon Chaddock12/07/2015 19:42:32
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The fact that apparently two LiPo have simultaneously developed the same fault is a concern and does raise a question over the charger.

What charger is it? and is the 1.25V reading shown on it? Could you confirm that cell voltage via a voltmeter?

It the 1.25V is confirmed then that cell will be damaged. It may well recharge again but it will not regain the full capacity so each time it is used to anything like its original performance it will get discharged more than the other cells and the situation will just get progressively worse.

It is time to buy some new LiPO. wink 2

If you charger displays the individual cell voltages during charge it is worth checking them several times during the charge process. If one cell is consistently below the others, even by as little as 1/10 of a volt, it is an indication that the cell is a bit weaker..

Regular balance charging can reduce the likely hood of one cell 'falling behind' the others.

Ross Clarkson12/07/2015 20:39:46
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1438 forum posts
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I have always balance charged them and they haven't been used relatively much at all.

When I charge I have my charger set up so it displays each cell and all was fine. Just a bit miffed both have gone exactly at the same time.

So, is it the charger or my batteries? Suppose i will have to get a voltmeter.

PatMc12/07/2015 20:58:32
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It's probably your charger. There's no guarantee that the voltages displayed for the individual cells are calibrated the same. The result can be that a displayed well balanced battery has actually been charged out of balance possibly sufficiently to permanently goose one or more cells. I once binned a charger for this very reason.

You need to compare the displayed voltages with readings on a decent voltmeter.

BTW the little voltage checking gizmos are also inaccurate in this repect. They're OK for a quick field check that your about to use a fresh battery but not that's all.

Mike Blandford12/07/2015 21:58:44
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497 forum posts
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If your charger will do a non-balance charge, you could try a quick test before you get a multimeter (if you fly electric you really should have one anyway).

Start a charge on each battery, at a low current setting, and see what voltage your charger shows for the battery.

If one cell is at 1.25V, then the total battery voltage will likely only be just over 9 volts, instead of at least 10.5 to 11 volts. If the charger will also do a discharge, again try each battery with a low discharge current. See if the battery voltage is 10.5 to 11, at least, or around 9 or less.

These should tell if the charger is mis-reading the middle cell. My suspicion is you have a charger fault, rather than two batteries failing at the same time in the same way.

Mike.

Frank Skilbeck13/07/2015 10:12:07
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4358 forum posts
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They aren't Gens Ace cells are they, I had this happen to 2 Gens Ace Lipos I had, and also a same with another club member, they were great for a while and then all of a sudden one cell died on each pack. Note both of my batteries failed within a very short period of time (less than a couple of weeks).

Does you charger work fine on your other Lipos.

Bob Cotsford13/07/2015 10:54:43
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7788 forum posts
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If the charger turns out ok and it really is the batteries at fault, were they hot when you took them out of the model? It seems to me that if the outer cells are hot then there is a fair chance that the centre cell will be cooked to a greater extent and more likely to fail.

Ross Clarkson13/07/2015 11:19:17
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1438 forum posts
106 photos

They charger when first started says 11.55v which is as normal as i worked out this was the safe amount to work with given the time I was airborne.

No, they weren't hot, just slightly warm to touch as per normal.

No Frank, they are Turnigy.

I'm swaying to a charger fault. Will do some testing and get back to you.

Thanks.

Edited By Ross Clarkson on 13/07/2015 11:20:32

Ross Clarkson17/07/2015 11:52:36
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1438 forum posts
106 photos

Bought a voltmeter and have discovered that it is indeed a faulty charger, batteries and cells are all fine and within 0.02v of each other.

Off to purchase new charger!!

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