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Lipo problems - is it me?

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Herri30/08/2012 19:42:34
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I wanted to fly my spitfire the other day and when I arrived at the site my ignition wouldnt work. Back home I found the Lipo (Dualsky 2 cell 1000 mah) was dead.

I tried to charge it but when I connected the balancer it said "battery too low"

I have a Graupner charger.

This is the fourth Lipo in three seasons where this has happened.

On my Jodel I just nosed over and hey presto- Lipo dead- 0V.

Again another 3 cell 3600 just showed 0V one day at the field after it had been normally charged and maintained.

A smaller 1500 3 cell started to play up when I tried to charge it. The charger said "voltage too low" . I charged it a few times without the balancer connected but it has now given up - 0V.

I have just connected the Dualsky 2 cell to the charger and tried to charge it without the balancer connected. It started off at 4.8v, rose rapidly to 7.3v at which point I connected the balancer again and its still on charge.

Whatever happens I really dont trust it.

Question is: is this normal? I dont fly that much, have a decent charger, dont charge at a fast rate.

Do you guys get these dud Lipos or is it just me?

Thanks

Herri

WolstonFlyer30/08/2012 19:47:36
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Are you testing them with a different voltmeter other than the display on your charger?

Perhaps the charger is faulty?

I have about 30 LiPo's and not a single one of them has had a fault and so far they all stay quite well balanced.

Edited By WolstonFlyer on 30/08/2012 19:48:33

malcolm woodcock 130/08/2012 19:49:05
397 forum posts

Both myself and my brother had Graupner chargers that wen bad. I'd check the balance of the batteries after charging on a independant checker or multi-meter. I found that when I used the Graupner it left the batteries seriously out of balance and later the thing packed in altogether, not long after the warranty ran out. I now use a Sigma II EQ and I'm very happy with it But still check the batteries on a watt meter or battery checker.

Chris Bott - Moderator30/08/2012 19:49:23
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Hi Herri

In a word - no, this sounds most unusual.

With so many LiPo problems I would say your problems are something other then the LiPo's themselves.

Taking the 0V ones which seem to be most of your problems, it sounds to me like they are being discharged too low, at which point they give up and fall 0V.

Do you disconnect them completely when not in use? Or do they stay connected to some unit that may be drawing a current, even if it's a very small current?

Tim Mackey30/08/2012 19:54:17
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It sounds to me that you are leaving them connected to "something" after use IE: An ignition module or similar. This will result in a very small current being drawn, and over sufficient time this will drain the cells to a level where they are useless. Unlike other battery chemistry, Li-Po will NOT tolerate low voltage, and a lipo cell is considered empty at around 1.8V or so. Another common problem is in electric flight models where the battery is left connected to the speed controller ( even though everything else is effectively "off". The speedo will consume a tiny amount of residual current which over a few days will drain the battery as above.

Allowing them to fall to 1V or lower usually means they are goosed. SOMETIMES they can be recovered by a "cheat charge" but even if that works, they are unlikely to ever perform as they used to.

Edited By Tim Mackey on 30/08/2012 19:55:12

Tim Mackey30/08/2012 19:56:11
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LOL, Chis was answering as I was "waffling" cheeky

Chris Bott - Moderator30/08/2012 19:58:33
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It's a good waffle though Tim

Looks like we have the two main possibilities covered here already. Over discharge or a faulty charger.

Myron Beaumont30/08/2012 21:47:30
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Apparently it is possible to rejuvenate a lipo at 0V by leaving it on a very small trickle charge for about 3 days until it regains enough whoomf to make a balance charger respond sometimes .

Garbo30/08/2012 22:01:56
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I have given a lipo a dart of power on the nimh setting (30mins) constantly watching for anything strange. And this has taken it to a sufficent voltage for a proper recharge.

The thoughts of a 3 day unattended trickle scare me.

Though I see one supplier is bringing out Lipo charging protective metal boxes.

Mark Powell 231/08/2012 04:24:02
430 forum posts

I was going to say exactly what Garbo said. An NiMh or NiCd setting (or just an NiMh/NiCd charger) works well for me too. Only needs a few minutes and watch it all the time. But I thought I might be stamped on by the 'Elf and Safety nannies. So kept quiet. As Garbo has now blown the gaff, I am just backing up his experience.

It's no less safe, PROVIDED YOU WATCH IT AND ONLY DO IT FOR A FEW MINUTES than  a regular charger. At the beginning of the charge process the NiMh/NiCd and Lipo charging 'regimes' are much the same. Not so long ago , before these things were common, the 'authorities' , including the model magazines, were saying you could charge Lipos on an adjustable 'stabilized power supply', and that was/is true., but again, you have to observe all the time. 

Edited By Mark Powell 2 on 31/08/2012 04:25:33

Edited By Mark Powell 2 on 31/08/2012 04:33:55

Herri31/08/2012 07:51:02
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Thanks for your comments chaps.

I always dissconnect and remove my Lipos from my electric aircraft. Its only since I have been using small Lipos for receiver/ignition in my petrol engined ones that I have left them connected.

The drain theory seems to match my latest problem as it was left connected to the ignition via a kill switch and voltage regulator.

The other Lipo in the plane was connected to the receiver via a Digi switch. This was ok.

The said Lipo showed 4.8 V yesterday so I connected it up to the charger again without the balancer lead until it reached 7.3 V where I re-connected the balancer. It charged ok and I have just checked it this morning and it still shows 8.3V.

I shall put the other bad Lipos down to bad luck and dissconnect all Lipos after flying.

Now all I want is for it to stop raining!

Cheers

Herri

Mark Powell 231/08/2012 08:31:11
430 forum posts

Herri,

You MUST have an on/off regular 'physical' switch beteen the battery and anything else whatsover. A voltage regulator still has a leakage, and even a 'digital' switch, such as the PowerBox ones, has a leakage (which renders it rather pointless if you have a regular switch before it). All semiconductor devices have a leakage, small, but it is there..

Otherwise you must disconnect the battery.

Dave Bran31/08/2012 08:40:12
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Glad that is sorted.........adding my 5p.........

1. Discharge below min LiPo voltage is easily done, usually by forgetting that a small current drain can occur on "non flight power" uses (done it myself on an Rx feed where the switch was the wrong side of the regulator, forgetting the quiescent drain of the regulator).

2. Never EVER leave LiPos on charge unattended, trickle, bagged, cased or not. You want to argue this point, come and talk to my friend who's house burned down four months back starting with a bagged LiPo on charge in his garage he'd left to make a cup of tea!!

3. Graupner chargers seem particularly sensitive to refusing to charge batteries due to voltage below their expectation, threads exist on other forums on this. They also have a tendency to stop charging at the end on "over voltage" rather than a normal charge end. Does not mean they are faulty beyond use, just over sensitive.

4. OUTSIDE and AWAY from any building that matters (!!) an overdischarged LiPo can be placed on NIMH charge of up to about a half the charge "C" rating AND CONSTANTLY MONITORED such that you remove that charge AS SOON as the voltage on the pack reaches 3v per cell. (2S=6v, 3S =9v, etc)

Then immediately change back to a 1C charge rate LiPo charge and keep under observation for the full charge.

I have yet to fail to bring one back that way as long as the recovery was soon after the over discharge.

After that, marked as "suspect", the first subsequent charge is also done "super secure", and after that, usual charge security is I feel sufficient for the risk. Most have returned to a fully acceptable capacity, too.

PS - Had another friend that used a strong metal ex-army ammo box thinking it was safer during charging, but he left ALL his cells in there with the one being charged................DOH!!!!

Peter Beeney31/08/2012 15:23:17
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Actually I think Myron may well be fairly accurate in his assessment of the flat lipo battery. Strictly speaking, trickle charging is simply a low value just to make up the self-discharge losses of a particular battery over time, and for a lipo that’s very tiny. However, let’s assume we have a charging rate of one three hundredth C, or 1/300C. Therefore any pack would take 300 hours to charge, or 12.5 days. Even at 1/100C it’s still 4 days. And if you are using a constant voltage charger, which you should always do, and always repeat always here, then it will never come to to any harm anyway. Unfortunately, the great big fly in the ointment here is the fact that most probably very few modellers have the right kit to be able to do this. Armed with just a standard charger the choices are probably very limited.

But from experience, a low rate, longer time charge will always prove if a battery is up to scratch or not. Inasmuch that at least you always get the best possible charge.

I have to say that if I thought for one second that lipos were seriously that dangerous, that they can just spontaneously burst into flames whilst being charged correctly for no good reason, I don’t think that I would ever consider using them under any circumstances. But as far as I’m aware the various incidents have always been caused by people using an incorrect charging arrangement, such as a nickel constant current standard instead of the lipo’s vital constant voltage requirement. Fortunately it would also seem as though most other folk have also come to this conclusion, other wise I think lithium batteries in general would never have gone into general use in the first instance.
There was the occasion, some years back, with the Nokia phones, they tended to go on fire whilst being used, not charging. The investigation proved they were all fake batteries that had slipped through the net. This is always going to be another aspect to consider.

My charger is more or less permanently in use in the back go my car, simply because I have a 12 volt field battery paralleled with the starter battery, so I’ve got plenty of poke for the charger. I’m always fiddling with someone’s packs. I left a lipo on charge for a month once, and then later, just to prove the point, I did it again. It won’t come to any harm, the voltage simply stays at 4.2V/cell. Basically it’s just connected to the charger, there will be no current flowing into the pack, other than the very small amount of self-discharge current. But I always go the extra second to make sure I have got it right first time; also my charger is pretty good, luckily for me, it won’t accept any cross connections either.

With regard to the semiconductor devices and leakage current, if a voltage regulator is connected to a supply it’s always switched on and it’s always keeping it’s output to 5 volts, even if it’s not going anywhere. To do this certain parts of it are working all the time, and thus consuming some current to do so. For instance, the output transistor is switched on, there is a feedback loop from here to enable it to monitor it’s output voltage, and this eventually returns to 0V. Lets say the total current used is 10 milliamps, and it’s connect to a 1,000 mAh battery. So 1,000 divided by 10, in 100 hours this would discharge 1 ampere hour. 100 hours makes up 4 days. If we consider a diode, or perhaps a transistor that’s switched off, then the leakage current is far less. Lets say for a typical silicon diode the reversed biased leakage current is typically 5uA, that 5 micro amps, or 5 one millionth’s of an amp. Now it would take 1,000,000 divided by 5, that 200,000 hours to discharge our 1ampere hour. 200,000 hours equals nearly 23 years. At my age I’m afraid I’ve not got time to wait that long. I once saw a ‘economical’ circuit for a flashing led from an AA cell, and the author said it would have to be his great great grand children to say whether it worked or not!

Although I would consider lithium charging to be the most simple and easiest of all the battery types, there still seems to be lots of issues surrounding it all in some respects. But I guess lithium technology is not going to go away for some time, so now it’s simply a case that everyone treats it how they think is the best way.

PB

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