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LiPo over-voltage

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Tim Kearsley06/07/2020 18:47:09
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I've just finished charging a 4-cell, 1800 mAh LiPo. I always check cell voltages after charging and I was most surprised to see one cell at 4.34V. Now I've always reckoned a fully charged LiPo cell to be, at max, 4.20V. I should add that I always balance charge and always store batteries at around 3.85V per cell.

There's no sign of the pack puffing or any other outward sign of problem.

Is it safe to use do you think?

Tim.

Richard Wills 206/07/2020 18:59:22
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chances are you have a bad contact on the balance connection for that cell causing the charger to overcharge it. As for safe to use, if you discharge it immediately and there is no sign of damage, maybe. But is the value of a 4s 1800 worth the risk of burning your house down if there is damage you cant see.

Tim Kearsley06/07/2020 19:44:22
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Thanks Richard. I hadn't thought of the possibility of a bad connection on the balance connector. I'm discharging the pack as I write, so we'll see how things progress.

Tim.

Andy4806/07/2020 19:46:02
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I posted about the danger of this just 2-3 weeks ago. It only happens with balance charging, due to a bad connection somewhere between the balance plug and the charger.

For this reason it seems far better to NOT balance charge unless the cells actually need it, and then do a normal charge followed by a balance charge, watching the individual cell voltage frequently.

As for your overcharged battery, as Richard says, I'd also be inclined to discharge it and then send it for recycling. Better safe than sorry, for what such a battery costs.

Richard Clark 206/07/2020 21:10:54
416 forum posts
Posted by Tim Kearsley on 06/07/2020 19:44:22:

Thanks Richard. I hadn't thought of the possibility of a bad connection on the balance connector. I'm discharging the pack as I write, so we'll see how things progress.

Tim.

A bad contact is always a danger with balancing chargers.

Bear in mind balancing doesn't need to be done every time. Balancing one in every ten charges is more than adequate. I've got two 3S 2200 25C batteries used several times a week in summer, never balanced them at all in three years and they are still fine.

Much depends on how well the individual cells were matched before the pack was assembled. Inherently lithium batteries need no more balancing than lead acid, nicads, or nimh and nobody ever balances them. Its just the potential danger of over charging lithium cells that is the problem.

(I recently replaced the 2 cell 1600 lipo inside a British made £400 Chord Mojo portable digital to analog 'hi-fi' converter. It's intended to be charged from near enough any USB charger (I mostly use the Apple iPhone charger) and it's not got any facility for balancing at all, so Chord, which is a very reputable company, think it's safe enough.)

Tim Kearsley07/07/2020 16:46:41
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I just read your post from a while ago Andy. Yes, indeed it does seem to be a potential hazard in balance-charging. I've always, in my ignorance, balance-charged, every single time, because I didn't see any disadvantage. But this puts a new perspective on it.

In my own case, I partially discharged the over-charged battery and then balanced it and finally re-charged. I have to say that it seems absolutely fine and in fact powered a model for a decent flight this morning. I checked the cell Voltages after the flight and all were within 0.01V of each other.

Tim.

Richard Wills 207/07/2020 17:14:09
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Can you measure the cell internal resistance with your charger? If they are all similar I would be inclined to think the pack is OK to continue using

Tim Kearsley07/07/2020 18:10:32
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Posted by Richard Wills 2 on 07/07/2020 17:14:09:

Can you measure the cell internal resistance with your charger? If they are all similar I would be inclined to think the pack is OK to continue using

Unfortunately I only get a measure of the total pack IR, not individual cells. The pack IR is very similar to two other packs which are of the same capacity, cell count and manufacturer, and which have had similar use, as I always use the three packs in the same session.

Tim.

Lima Hotel Foxtrot08/07/2020 10:26:15
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I can not believe* that people on this forum are recommending not balance charging lipos. Given that most chargers now will not charge without the balance lead being connected, this "advice" is both outdated and dangerous.

If you're charging a lipo, why would you not balance? It extends the life of the cells. It's safer. Are you just going to bung it on a NiMH or Pb setting and hope for the best?

I happen to have in front of me the instructions from an Overlander battery (7.4 450mah FYI):

"Always charge batteries with a balancer or use a charger with balance function. Overcharging may occur to the unbalanced cell of the pack if you use a series charger, or series charge programme, and it may shorten battery life, and may even cause fire."

It's up to you... But, hey, it's your house you may or may not burn down.

*On balance, yes I can.

Nigel R08/07/2020 10:38:09
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"it's not got any facility for balancing at all, so Chord, which is a very reputable company, think it's safe enough"

I work with lithium batteries. Not balancing them has never, ever, been a consideration, as both my work and the client highly values reliability and longevity of battery units. And my place has done a lot of lengthy and very expensive work studying the effects of cell degradation and battery performance.

So I'm afraid I have a very different assessment of Chord's approach. Which is, to be blunt, that it is cobblers.

Given that the first google result for 'chord mojo' is 'chord mojo battery replacement' which seems to be a £100 service on a £400 unit, I'm inclined to think there may be a cynical commercial component to their decision to avoid bothering with balance charging, too.

As for other chemistries. If you trickle charge nimh/nicd/lead (or your charger performs a fast charge then drops back to a trickle) you are balancing them.

Nigel R08/07/2020 10:42:32
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Posted by Tim Kearsley on 07/07/2020 16:46:41:

In my own case, I partially discharged the over-charged battery and then balanced it and finally re-charged. I have to say that it seems absolutely fine and in fact powered a model for a decent flight this morning. I checked the cell Voltages after the flight and all were within 0.01V of each other.

I've always, in my ignorance, balance-charged, every single time, because I didn't see any disadvantage.

Your pack is most likely perfectly ok.

Cell damage is a function of both time, and amount of overcharge (or discharge). So if you get in there quick and bring it back to normal levels any damage will be minimal.

Posted by Tim Kearsley on 07/07/2020 16:46:41:

I've always, in my ignorance, balance-charged, every single time, because I didn't see any disadvantage.

You were doing it right. Lifespan and performance is maximised with balancing.

I would suggest, charge somewhere "fire safe", just in case.

If the charger starts making mistakes with the packs, either fix or replace it.

Phil Green08/07/2020 10:44:44
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I'd go further than that LHF, I would have hoped that on a public forum, mods would remove dangerous advice.
Precise equality of cell voltages isnt important but balance charging keeps each cell between two critical voltages, one of which concerns the life of the cell, and the other the life of the owner.

Wingman08/07/2020 10:55:03
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Yep BALANCE CHARGE AT ALL TIMES - No ifs no buts no maybes - anyone who says otherwise is talking out of their proverbial or is willfully attempting to discredit LiPo use.

Tim Kearsley08/07/2020 11:12:02
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Whoa, I didn't intend to start any arguments!

I don't dispute the necessity to keep the cells in a LiPo pack balanced, and indeed, as I said, that's what I always do. But can you not see the danger that Andy pointed out a couple of weeks ago, and which I encountered? If you have a poor connection somewhere in the chain of connections between the charger balancing circuit and the connections to the LiPo battery, resulting in the balancing circuit seeing a falsely low Voltage on a cell, then it will potentially overcharge that cell. It's the only explanation I have for my own circumstance, where a cell ended up at 4.34V. The charger (a Graupner Ultra Duo Plus 60) has performed faultlessly since.

For what it's worth, my own view is that I will continue to balance charge every time, but having seen with my own eyes that overcharging can happen I will be even more cautious!

Tim.

 

Edited By Tim Kearsley on 08/07/2020 11:17:13

David Hall 908/07/2020 11:23:12
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Please excuse my ignorance, but doesn't a LiPo battery charge to it's limit as determined by its chemistry, then generates heat rather than excess charge?

I'm puzzled how this LiPo battery charged to 4.34v and then appeared to hold that charge.

Phil Green08/07/2020 11:23:13
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Posted by Tim Kearsley on 08/07/2020 11:12:02:

... a cell ended up at 4.34V. The charger (a Graupner Ultra Duo Plus 60)

Just an observation, thats the LiHv terminal voltage. I dont know that charger, could it have been set wrongly?

Edit: sorry I just checked, that charger doesnt do LiHv. 

 

Edited By Phil Green on 08/07/2020 11:30:05

Allan Bennett08/07/2020 11:27:16
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I've been following this thread, and wondering how a balance-charger could let one cell get so far beyond 4.20v. I understand that a bad connection in the balance lead could perhaps fool a cheap charger, but surely the added resistance would have less effect on the cell voltage seen by the charger when it gets to the reduced-current CV stage of the charge? In fact, if one were able to read the voltage without drawing any current, the voltage should be the same with or without extra resistance in the connection. Modern electronics should be almost able to achieve that, in which case the charger should have been able to do something about it -- either an error message and charging stopped, or discharging the cell to balance with the others.

I know that my PL-8 charger is quite annoying at times for stopping the charge within a minute or so of starting, if it detects any fault in the connections. I shall continue to balance-charge every time.

Tim Kearsley08/07/2020 11:28:08
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Posted by Phil Green on 08/07/2020 11:23:13:
Posted by Tim Kearsley on 08/07/2020 11:12:02:

... a cell ended up at 4.34V. The charger (a Graupner Ultra Duo Plus 60)

Thats the LiHv terminal voltage. Is it possible the charger have been set wrongly?

No, Phil, I can 100% guarantee that the charger was set correctly. I use a set of preset values of battery chemistry, no. of cells and capacity (mAh) stored in the charger's memories. Additionally, I do always check that the values are correct before I hit the button to start charging.

Tim.

Tim Kearsley08/07/2020 11:41:17
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I should add, out of interest, that when I tried to use the same Graupner charger to either balance or discharge the pack it refused because of the high cell Voltage! The only way I could proceed was to partially discharge it by connecting ONLY the main power leads (no balance lead connection) and then balance and finally charge as normal.

Tim.

P.S. - The pack, by the way, is a Turnigy Graphene 4S, 1800 mAh 65C.

Nigel R08/07/2020 11:54:39
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Posted by David Hall 9 on 08/07/2020 11:23:12:

Please excuse my ignorance, but doesn't a LiPo battery charge to it's limit as determined by its chemistry, then generates heat rather than excess charge?

No, they just keep on going. Hence why you never trickle charge lithium.

The limit is a level applied by the charger.

The limit itself is a trade off between desired cell life and total energy stored for a single charge cycle.

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