LiPo over-voltage

[Chris Bott - Moderator]

Posted by Phil Green on 08/07/2020 10:44:44:

I'd go further than that LHF, I would have hoped that on a public forum, mods would remove dangerous advice.

I'd suggest that this is similar to the club arena where "everyone is a safety officer". If you see something that's unsafe you say or do something about it.

That's exactly what's happened here. Well Wefore any of us mods looked in.

My take, BTW is that I balance every charge to make sure no cell goes over 4.2V. if I watch cell voltages on my charger, balance charging a poor battery, as soon as any cell starts to go over 4.2v it appears to be clamped at 4.2 by the discharger being applied to that cell and the overall charge current is reduced to a level where that load can cope.

I wonder if some chargers are better than others at accurately measuring cell volts. I think it's likely that each tapping point is measured from the 0v connection and some maths done to calculate individual voltages.

I also agree that as current is reduced then connection resistance would have less and less of an effect and the over volts should be spotted. If I saw issues like this I'd be suspicious of either my charger or whatever device I'm checking with afterwards.

[Andy48]

I have two good quality double chargers, and yes one of my cells did overcharge. Fortunately it has the option of displaying individual cell voltages, and when I connected it, one cell looked a little low, about 0.3v which was a little unusual. Thankfully I kept checking the charger whilst it was charging, and it was then I noticed that one cell was now reading over 4.3v. The rest (it was a 5S) we just over 4.0. A poor connection was the problem. I must have used these chargers hundreds of times now without any problem until this event. This particular battery was (and still is) in good condition, and individual cell voltages remain very close to each other during flight and at the end of a flight.

Thankfully (1) I had the charger set to show individual voltages, and (2) I was monitoring it frequently. Otherwise I would almost certainly have had a fire.

For those that think it essential to balance charge every time, I would ask why? There is certainly a danger of having the same problem I had, and the possibility of a fire due to overcharging.

Its simple really, check the cell voltages and if there is a difference of more than a couple of tenths of a volt, then do a balance charge, but check individual voltages regularly, otherwise do a normal charge..

[Chris Bott - Moderator]

I don't understand Andy48. If it was reading over 4.3 on the charger screen then it knew it was going past 4.2 and shouldn't have charged it further.

If a bad connection meant that the reading in the charger was actually 4.2 when the battery was over 4.3 then you'd have seen 4.2. I'm missing something, aren't I?

[Tim Kearsley]

In reply to the final point you make Chris, the charger has been in regular use (usually at least weekly, sometimes much more, for the last 10 years or so) and has NEVER overcharged before. As to how I measure the cell Voltages, I normally use a fairly simple LiPo checker which shows the Voltage on each cell. When I saw the anomalous Voltage I further checked with a digital multimeter, which confirmed the value to within 0.01V. The charger has since been used to balance charge without incident. I did take the precaution of re-seating the balance boards where they plug into the charger, in case a poor or intermittently poor connection was the culprit.

Tim.

[Richard Clark 2]

Posted by Tim Kearsley on 08/07/2020 13:21:17:

Posted by Richard Clark 2 on 06/07/2020 21:10:54:

(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.)

Having just read through some forums and seeing the number of people complaining about the short life of the LiPo in their Chord Mojo I don't think Chord, who might well be "reputable", are a good example of how to charge a LiPo battery!

Tim.

Actually I agree. It wasn't a good example. It also gets extremely hot if you charge and use it at the same time which Chord say is fine to do.

A question:

Do you own a Mojo or did you search specifically to cast doubt on my overall 'argument' without yourself trying non-balanced charging over a long period as I have done?

[Richard Clark 2]

Posted by Wingman on 08/07/2020 10:55:03:

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.

Hardly.

I was one of the earliest UK adopters of Lipos (Thunder Power ones which were the only ones available in the UK) and which didn't have balance leads, and the chargers (Astro Flight) didn't have balance ports.. I have used Lipos ever since, And often the old Astro charger, which will do 9S batteries at 8 amps if required. From a 12 volt source.

So why would I want to discredit them?

Also take Tim's experience. He just balance charged the one he had the problem with and after flying it the cells were still within 0.01 volts of each other. Which is well within typical measurement error.

As I said, I believe once every ten flights or so is more than adequate but personally I often don't balance charge them even then,

We are all free to do what we want and offer differing opinions, Those differing opinions are a large part of what forums such as this are for.

[Andy48]

Posted by Chris Bott - Moderator on 08/07/2020 18:41:15:

I don't understand Andy48. If it was reading over 4.3 on the charger screen then it knew it was going past 4.2 and shouldn't have charged it further.

If a bad connection meant that the reading in the charger was actually 4.2 when the battery was over 4.3 then you'd have seen 4.2. I'm missing something, aren't I?

It was reading under voltage when it started, however, I think the poor connection corrected itself shortly before I checked the voltages again. I'm not sure I understand either, cCould be I moved the battery, and this corrected the bad connection. I just know it happened, and I will be a lot more circumspect before using balance charge again.

[Tim Kearsley]

Posted by Richard Clark 2 on 08/07/2020 18:56:07:

Posted by Tim Kearsley on 08/07/2020 13:21:17:

Posted by Richard Clark 2 on 06/07/2020 21:10:54:

Actually I agree. It wasn't a good example. It also gets extremely hot if you charge and use it at the same time which Chord say is fine to do.

A question:

Do you own a Mojo or did you search specifically to cast doubt on my overall 'argument' without yourself trying non-balanced charging over a long period as I have done?

No, I don't own a Mojo. I'm open-minded about the pros and cons of balance-charging every charge, but on balance (no pun intended) I shall continue to balance every time. My search was to see what came up in respect of Mojo and the battery it used, and it soon became evident that there was a body of complaint about the short battery life. As you say, it wasn't a good example.

Tim.

[Chris Bott - Moderator]

I agree with Tim and think that charging without balancing has more potential to overcharge a single cell than balance charging. So I'll continue to balance, every charge.

[Richard Clark 2]

Posted by Nigel R on 08/07/2020 11:54:39:

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.

The lipo charge protocol requires that ir is charged at constant current to about 80% charged then switched to constant voltage (normally set at 4.2). As each cell's voltage moves towards 4.2 the current it 'absorbs' will drop off. As will the charging current for all the cells (though it won't be the same for each) as they are connected in series.

So the 'better' cells won't reach 4.2. Thus the cells are limited by the worst one 'naturally'. though some won't have been fully charged. And the worst one (which has the highest internal resistance) can't go over voltage if you have entered the number of cells correctly or less reliably (so check), the charger has detected the number.

That is one reason I say balance charging is not strictly necessary.

[Chris Bott - Moderator]

If the cells are in series, the charge current through each cell will be precisely the same. Without balancing, the charger will only know the pack voltage.

So it will limit the pack volts of e.g. a 4S to 16.8V.

But if 3 cells are only at 4V when one is at 4.2V the pack voltage will be 16.2V and the charger will keep pushing current in to get volts up. By the time it gets to 16.8V they might be at 4.15, 4.15, 4.15, 4.35 - an unbalanced charge causing overcharge of one cell. 

Edited By Chris Bott - Moderator on 08/07/2020 20:40:25

[Richard Clark 2]

Posted by Tim Kearsley on 08/07/2020 19:50:29:

Posted by Richard Clark 2 on 08/07/2020 18:56:07:

Posted by Tim Kearsley on 08/07/2020 13:21:17:

Posted by Richard Clark 2 on 06/07/2020 21:10:54:

Actually I agree. It wasn't a good example. It also gets extremely hot if you charge and use it at the same time which Chord say is fine to do.

A question:

Do you own a Mojo or did you search specifically to cast doubt on my overall 'argument' without yourself trying non-balanced charging over a long period as I have done?

No, I don't own a Mojo. I'm open-minded about the pros and cons of balance-charging every charge, but on balance (no pun intended) I shall continue to balance every time. My search was to see what came up in respect of Mojo and the battery it used, and it soon became evident that there was a body of complaint about the short battery life. As you say, it wasn't a good example.

Tim.

 

I'm open minded about it too. I just can't be bothered most of the time As at the field I usually charge them in place and I can't reach  the balance plug.  But I never charge them out of sight either way. I keep them and any Lithium powered tools in a near valueless shed away from the house.

Unattended laptops are more of a fire problem. I've removed the battery and run it from its charger as it stays in one place and its keyboard and screen are not used,

Edited By Richard Clark 2 on 08/07/2020 20:25:05

[Richard Clark 2]

Posted by Nigel R on 08/07/2020 13:29:55:

I rest my case.

 

 

No case to rest.

It's the excessive heat when using and charging the Mojo at the same time is the problem, though Chord say it is fine to do. Not the lack of balancing.

The two Bosch garden tools I've got won't even start to charge even if the battery is just slightly warm.

Edited By Richard Clark 2 on 08/07/2020 20:36:37

[Allan Bennett]

Posted by Richard Clark 2 on 08/07/2020 20:06:34:

The lipo charge protocol requires that ir is charged at constant current to about 80% charged then switched to constant voltage (normally set at 4.2). As each cell's voltage moves towards 4.2 the current it 'absorbs' will drop off. As will the charging current for all the cells (though it won't be the same for each) as they are connected in series.

So the 'better' cells won't reach 4.2. Thus the cells are limited by the worst one 'naturally'. though some won't have been fully charged. And the worst one (which has the highest internal resistance) can't go over voltage if you have entered the number of cells correctly or less reliably (so check), the charger has detected the number.

That is one reason I say balance charging is not strictly necessary.

There's obviously many different makes/types of chargers being considered here. Mine displays individual cell voltages throughout the charge, and I've never seen any cell go above 4.20v -- if it did, the charger would have stopped and given an 'over voltage' error message. If a pack is out of balance it holds the first cell to reach 4.20v while the other cells catch up. Like Chris, I don't understand how any charger can display a cell voltage over 4.20v and not figure out that something's wrong.

[Tim Kearsley]

Posted by Richard Clark 2 on 08/07/2020 20:06:34:

Posted by Nigel R on 08/07/2020 11:54:39:

Posted by David Hall 9 on 08/07/2020 11:23:12:

As will the charging current for all the cells (though it won't be the same for each) as they are connected in series.

Really? That's the first time I've heard of items in series having different currents through them. Physically impossible I believe.

Tim.

[Andy48]

Posted by Allan Bennett on 08/07/2020 20:37:39:

There's obviously many different makes/types of chargers being considered here. Mine displays individual cell voltages throughout the charge, and I've never seen any cell go above 4.20v -- if it did, the charger would have stopped and given an 'over voltage' error message. If a pack is out of balance it holds the first cell to reach 4.20v while the other cells catch up. Like Chris, I don't understand how any charger can display a cell voltage over 4.20v and not figure out that something's wrong.

Simple, because at the time it does not realise the cell voltage is over 4.2v due to a poor connection.

[Richard Clark 2]

Posted by Tim Kearsley on 08/07/2020 20:40:10:

Posted by Richard Clark 2 on 08/07/2020 20:06:34:

Posted by Nigel R on 08/07/2020 11:54:39:

Posted by David Hall 9 on 08/07/2020 11:23:12:

As will the charging current for all the cells (though it won't be the same for each) as they are connected in series.

Really? That's the first time I've heard of items in series having different currents through them. Physically impossible I believe.

Tim.

You are of course correct. I was wrong.

But I'm still mostly not going to bother. Because as soon as you use it, completing the circuit with the ESC/motor each 'high' cells charges any adjacent low one so it self corrects.

Which is probably why yours measured in near perfect balance after flying it.

[Chris Bott - Moderator]

I'm sorry Richard but that's incorrect again. As soon as the ESC is connected, ALL cells see the same DISCHARGE current which is in the opposite direction to a charge current so all will start going down.

While I agree that most lipos will stay in balance for a number of unbalanced charges and some will for many charges, any that are out of balance are likely to have that imbalance become slightly greater at each charge cycle.

This is why balance charging was invented in the first place. Early lipos had no balance lead, early chargers had no balance facility and people had fires!

I've heard folk complain that balance charging takes too long. Well, if that happens, it's telling you that your packs are being pushed out of balance by your charge cycles. I balance charge every time. It keeps my packs in balance. Very little time is spent in the balance part of the charge so my charges take only as an unbalanced charge.

For anyone to suggest that balance charging is unsafe and that it's safer to charge without balancing (because of one event that was in effect a fault situation) really is dangerous talk and is doing a disservice to beginners reading this forum.

Of course anyone can make their own choices. But balance leads are there for a reason and I will always use them. I also charge in a safe place and carefully monitor my charges too and I use a separate device to check voltages before and after charges and flights.

[Nigel R]

Richard Clark:

"trying non-balanced charging over a long period as I have done?"

I have seen results of this in a professional context. Unbalanced charging does not end with the lithium battery packs magically returning to a state of balanced cells. Quite the opposite, in fact.

" As will the charging current for all the cells (though it won't be the same for each) "

I can assure you they very much will be the same on each cell, a series connection has no other possible outcome.

"Thus the cells are limited by the worst one 'naturally'."

They are not.

"the worst one (which has the highest internal resistance) can't go over voltage if you have entered the number of cells correctly or less reliably (so check), the charger has detected the number."

Chargers (generally, perhaps there are exceptions, but it would be necessity slow the charge process) do not apply the 4.2V target to individual cell readings during the initial fast charge. The high current causes the reading at the cell terminal to be only approximately indicative of a cells state of charge. Age and condition of cell as well as charge current make this worse. It is not something easily compensated for. The charger will not know the age or condition. It will not know how much effect applying charge has.

If the charger misdetects the cell count, then something is badly wrong with your pack, and it needs special attention (the bin, would be my first suggestion, although I have seen suggestions to save packs by stuffing a constant charge in for a few minutes to try and "rescue" a dead cell).

"It's the excessive heat when using and charging the Mojo at the same time is the problem, though Chord say it is fine to do. "

Again, being blunt, Chord are wrong. I would imagine the reason it gets hot is because they do not have a proper mechanism to manage the selection of power input, nor a proper charger. A simple scheme of permanently charging whilst running from a battery just doesn't work on lipo (unless your design goal is to degrade the battery very quickly in order to mandate a frequent replacement cycle).

Laptops (for example) have more sophisticated power management and are quite capable of running from mains whilst the battery is connected, and neither drawing power from the battery nor charging it.

"completing the circuit with the ESC/motor each 'high' cells charges any adjacent low one so it self corrects"

You are, incorrect again. It is impossible for this to happen with a series connection.

I would make the polite request that you stop adding more misinformation to this thread, as your posts seem to demonstrate an incomplete understanding of batteries and electronics.

Allan Bennett: "Like Chris, I don't understand how any charger can display a cell voltage over 4.20v and not figure out that something's wrong."

Cell lifespan effects coupled with high fast charge current will produce a high voltage reading which is at best loosely indicative of the state of charge of a particular cell. The charger does not know what the age effects are and cannot compensate. At best, it can set a maximum limit, but that limit must by necessity be over the 4.20 target if the fast charge is to be effective; when charge current is cut to zero, the cell voltage will gradually drift down over the course of several minutes. Only after that time has passed, with no charging being done, can you get a more accurate reading on each cell.

Chris Bott: "I've heard folk complain that balance charging takes too long. Well, if that happens, it's telling you that your packs are being pushed out of balance by your charge cycles. I balance charge every time. It keeps my packs in balance"

Could not agree more.

Balance every time, do that, and the balance will be quick.

If a particular pack starts taking a long time to balance, that's an early warning on the health of that pack.

[Tim Kearsley]

Posted by Andy48 on 08/07/2020 22:16:10:

Posted by Allan Bennett on 08/07/2020 20:37:39:

There's obviously many different makes/types of chargers being considered here. Mine displays individual cell voltages throughout the charge, and I've never seen any cell go above 4.20v -- if it did, the charger would have stopped and given an 'over voltage' error message. If a pack is out of balance it holds the first cell to reach 4.20v while the other cells catch up. Like Chris, I don't understand how any charger can display a cell voltage over 4.20v and not figure out that something's wrong.

Simple, because at the time it does not realise the cell voltage is over 4.2v due to a poor connection.

But this doesn't make logical sense. If the charger is displaying a Voltage of, say, 4.35V then it "knows" that the offending cell is over-Voltage - how else can it be displaying it? I can understand the similar scenario where some high resistance connection results in the charger "seeing" a falsely low Voltage, but then it would display that false reading wouldn't it?

Tim.

[Nigel R]

As mentioned above, for good reason I doubt many chargers actually use the individual cell voltages to limit the fast charge.

They do, however, all appear to display what they sense.

Edited By Nigel R on 09/07/2020 09:04:57

[EarlyBird]

As a novice the dangers of lipo batteries were emphasised to me and the advice given was :-

1. Always balance charge.
2. Check cell voltages before and after every flight.
3. Remove from the plane and allow to cool before balance charging.
4. Do not go below 3.8 volts per cell (3.8 is my safe target).
5. Return to storage charge once finished flying for the day.

Obviously having been made aware of the danger I complied with my instructor's and manufacturer's advice.

I am stunned to learn that lipos are used in consumer electronics and therefore it is easy to assume that in our situation they must be completely safe.

I think not!

I will continue as I have always done which to me is the safest way.

I now know that when the balance phase takes a long time it is an indication that the internal resistance of cells in the pack is increasing. I have observed that there is also a loss of power which can result in the loss of the model. When the balance charge time increase I buy a new lipo before I am forced to repair or buy a new model.

[Richard Clark 2]

Chis and Nigel,

All I can say is this:

I have used lipos in model planes  since day one, right from the time the Israeli military pure metallic lithium cells could be obtained if you were in the right sort of work (which I was). Long before balancing was thought of,  and have never had a fire except when I deliberately destroy them before getting rid of them, which I do as a matter of course. Because even a nominally 'discharged' one can catch fire if accidentally shorted.

So I DO bear the dangers in mind.

Balancing.

It was a balance charger that caused the problem. A poorly designed one. I mostly use a Thunder Power 1430C which will charge their own batteries at up to 12C rate and 14S. (They don't recommend you charge other makes of battery at such a  high rate)

You have to enter the number of cells, the capacity, the desired charge rate, and a time limit (all this can be stored per battery if you wish).Balancing is an option.

Normal charge end is 4.2 volts by default. This 4.2 value can be altered but if you alter it is not stored. as 'routine'. This is deliberate of course.

Connect the battery and press 'Check'. If all is ok it starts. Every ten seconds or so the charge stops and. everything, balance included, is rechecked automatically. This only increases the charge time by about 8% and there isn't an option to remove it.

If every charger was as well designed as this I would unhesitatingly balance every time. But as many customers appear to be mostly interested in low prices they aren't.

(PS: Many laptops used to have a facility that even when permanently plugged in you could lower the 'stop charging percentage. So the  battery would not  charge beyond, say, 70% full. Unfortunately this is not so common today  and keeping it 100% full all the time greatly reduces the service life.) 

Edited By Richard Clark 2 on 09/07/2020 09:52:16

Edited By Richard Clark 2 on 09/07/2020 10:05:12

Edited By Richard Clark 2 on 09/07/2020 10:07:21

[Tim Kearsley]

If you are referring to the charger I used when I saw the high cell Voltage, it is a Graupner Ultra Duo Plus 60, which was not a cheap charger when I bought it (somewhere around £280) and I don't think is "poorly designed".

As for charging at 12C, well I wouldn't do it even if the manufacturer said it was possible. I'm never in a hurry as I prepare batteries the night before a flying session, so I charge at 1C.

Tim.

[Nigel R]

Richard

The manual for your charger states:

"The balancer can also further ensure that you’ve set the cell count correctly, and as a result
we strongly recommend keeping the balancing turned ON at all times. Please also note that
when balancing is turned ON you MUST connect the balance connector of the battery to the
balance connector adapter board (which must be connected to the balancer/charger) BEFORE
you start the charge process otherwise you’ll encounter a Battery Type Error warning.
However, if you understand the associated risks, accept full responsibility, and choose to charge
LiPo/LiIon/LiFe batteries without balancing/using the built-in balancers, it is possible to turn the
balancing OFF"

Emphasis is as per the manual.

 

Edited By Nigel R on 09/07/2020 10:40:42