Battery problem

[aamacgregor]

I'm really happy with my Gens Ace batteries, but one of them seems to have developed a problem, the initial symptoms for which I described in the closing paragraph of my opening post in this thread:

http://www.rcheliaddict.co.uk/main-d...tml#post999601

Yesterday, I decided to test my initial setup of the VX1 on my Gaui X5 out the back of where I live and thought I'd use the battery where I was getting the weird behaviour (because it had partial charge and the others were not charged). Anyway the behaviour seemed to get worse. When I was giving it a quick initial hover, about 10 seconds into the flight the head speed started to drop quite rapidly so I landed it - almost as if the LVC had cut in (but a bit slower). At that point I landed it, the head speed had dropped about 40%.

I'm sure it's the battery since the X5 has behaved well with the other batteries.

I figured that one or more cells may have died, but when I connected the battery up to my iCharger 306B a few minutes ago and set it to voltage monitor. The results were not consistent with that theory (at least, not to my understanding):

3.97, 3.95, 3.95
3.95, 3.96, 3.95

Any ideas what might be happening here? Is it potentially fixable? If not, then I guess I'll have to bin it... not sure how to do that though... discharge it to 0 and then take it to the battery recycle bank at the tip??? Just for completeness it's a Gens Ace 30C 6S 4000mah battery.

Thanks,

Andrew

[cjcj1949]

You are missing an important piece of information. You don't know what the battery is doing under load. You can check this with a cheap voltage monitor £2 from HK, or you can measure the internal resistance of each cell with your charger. If the resistance is around 2 miliohms and all the cells are similar then the battery is probably ok. As you know it's the battery I would check your soldering. One of the wires might be only just hanging on, or a dodgy connector.

It is easy to fool yourself with faults and jump to the wrong conclusion. In my experience anyway.

I've looked at your first post and your progress is really annoying.... You must be very young to learn that fast... On the battery front though, it really doesn't sound like a faulty battery unless it is a bad connection. You could practice hovering at about 6 feet and if the motor does cut the heli will just land itself if you keep the pitch constant. It is possible that the battery is causing a problem with the esc, as a bad battery can blow the fets in a esc. The other possibility is that the battery doesn't fully charge to 4.20V on each cell, but that is doubtful as all your cells are balanced. You haven't been flying long, so your connectors should be ok. If you bought the battery from electriflyer I'd have a word with him about it. If you are convinced it's faulty don't throw it away, discharge it to 3.7V a cell and send it to me and I'll have a proper look at it.

[aamacgregor]

Thanks for your reply. I'll check the internal resistence and if that check out i'll take a look at the solder connections.:-)

[aamacgregor]

Right, I have checked the internal resistance on all four of my Gens Ace batteries. The first three (the ones that are functioning fine) have the following internal resistance

5, 4, 5
5, 5, 5

3, 3, 3
3, 3, 3

5, 5, 5
6, 5, 5

But the one that is giving me grief gives a result of:

6, 9, 10
8, 7, 8

Does that mean that there is something potentially wrong with the cells?

All four batteries have had roughly the same number of cycles (+/- 1), so I'm not entirely sure why there is such a variation in internal resistance. I think I have put in around 5 or 6 cycles on each.

Most of the time I have charged them at 1C, but I think I charged them all at 2C once. None of them have been involved in any crashes.

I just don't understand why the ESC only seems to play around with just that one battery... unless it's mere coincidence and the ESC is failing? Based on the above results, do you think I should check the solder connections?

My annoying progress comes from hours of practice in Phoenix and then just going for it with the real thing once I am absolutely confident in the simulator. I must admit, that Gaui X5 is something else - it just does precisely what it is told... I'm not sure I would have tried all that on the 450, since the 450 feels less under control to me and therefore I don't think I would have had as much confidence... but then, it might be something to do with the way I had set the 450 up the last time I flew it (it was a bit too sensitive but I've fixed that now).

I've just fitted my 450 with the BeastX that was in my Gaui, so I'll give it a whirl on Saturday (if the weather is good) and see what it's like.

[cjcj1949]

It looks like you have found the problem. They should be much lower, they were 4000mah cells I think. The other point is that ir varies a lot with temperature and the values I gave, around 2 milliohms for a 4000mah cell was at 20 degrees C. If you wait for the Summer you might be able to use the cell that you have had problems with. I'd strongly advise getting the 1-8S cell alarm. It will give you a warning of low cell volts and aging batteries, excessive 3D, or cold weather before the esc complains. It could be an esc problem, and some extra smoothing on the esc might help. The esc caps across the battery input keep the voltage spikes down. I'm happy to investigate more, but I'm too far away. I don't suppose you fly your batteries for too long???, and in the cold??? I'd get a new battery and check the ir against your old batteries, they might all be on the way out. That is might....lots of possibilities with heli problems. Buying new usually sorts it, sometimes a new heli....

[aamacgregor]

Thank you very much for your response. I live in Scotland, so I have flown them in the cold a few times (the warmest I have flown them is probably 7 degrees centigrade, and the lowest probably -5 degrees centigrade). That said, they have only been in the cold when strapped onto the helicopter, most of the time they have either been in a warm car, or in a warm cabin (Waterfoot Helicopter Club has a nice heater in the cabin) waiting to be used. The maximum I've taken out of them is around 2200mah.

I was concerned about the internal resistance of all of the batteries, so I phoned up Chris at Electriflyer and he was very helpful as always. The first thing I asked him was what he would expect the internal resistance of the cells to be on a Gens Ace 4000mah 30C battery. He told me that when they are new, they tend to come in at around 3 to 5 milliohms, I then told him the readings that I was getting from all four of mine. He said that the first three were absolutely fine, but like you said, he said that the fourth one sounded like it had gone bad. Based on the number of cycles it's had, he suggested that it was a bad one in the batch, which apparently happens from time to time. It would seem that the bad ones are not always obvious from initial checks. He did say that it is possible it could perform a bit better on hot days, but I'm of the mind that I don't want to take the risk.

In the last month I have spent a bit too much money to be considering buying any new batteries right now (a Spartan Vortex a couple of weeks ago and a Futaba 14sg combo on Friday night which should be arriving today). Perhaps towards the end of next month I might invest in some more batteries. I'm very interested in trying out the Haiyin batteries that Electriflyer are now stocking.

[cjcj1949]

They take a while to warm up, a few hours. You can damage them flying in the cold unless you keep a check on the voltage on each cell during flying. The ir is a bit lower just after charging as well. I don't agree with Chris, as the usual fault is one cell, not all 6. You ir values should be much lower. 3 milliohms is the value on a 2200mah cell from him, and the ir value goes down as the capacity goes up. I think there is something wrong in the way you are treating them. Do you store them at storage volts and in a cool place, but not cold? Some people think they should be charged in the warm. How long have you had them?

[aamacgregor]

Hmm, I checked the IR again on the batteries last night and the readings were very different to when I measured them the other day - the readings were about 30% higher! The batteries have been kept in a room that is kept at around 20 degrees centigrade, so there hasn't been any wild temperature variations and I haven't used the batteries since the last time I checked them. I'm beginning to think that the charger is supplying bogus readings. I have a multimeter, so I guess I could check the IR manually... I take it that it is just a case of reading the resistance over the pins of the balance connector (i.e. pins 1&2 for cell 1, pins 2&3 for cell 2, pins 3&4 for cell 3, pins 4&5 for cell 4, pins 5&6 for cell 5 and pins 6&7 for cell 6)?

I'll look into getting a cell alarm, sounds like it could be useful.

[cjcj1949]

No. Don't do that. You can't measure resistance when there's volts there. You might need a new meter if you that. ir is the voltage drop divided by the current change. You can get an idea of it by looking at the change in volts across a cell when the charge current changes. If your cells start at the same volts then they should also be at the same volts when being charged. The m go to elecore the ir the more the change in volts. Charge at 0.1 amps, make a nore of the volts. Increase the charge to say 2.1 amps and make a note of the volts. You have to do this quickly or the cells will charge up. If the change in volts was 50 mv then the ir would be 25millohms. If you go to electrilfyer you'll see a proper ir meter by Wayne Giles. It is expensive, but more accurate than a meter. The ir does change a lot with temperature and Wayne advises keeping the cells at the same volts for a long time, something like 12 to 24 hours.

Your meter will give fairly good results and I'd suspect the cell temperature first. If only the dodgy cell is changing, then it is worse than I thought. It could be as simple as a wiring fault.

When flying in the cold, you may find it better to fly for a minute, allow the internal heat to spread and then continue.

[Dorlingus]

Hi everyone, I just thought I'd share my thoughts on what may have happened here. I think I may have been slightly misunderstood when explaining my thoughts, but understandably so when so many variables are involved.

There are so many variables which can cause a LiPo to fail or on the reverse, last a long time. It is always extremely difficult to pin point reasons when certain batteries fail and others don't, especially when dealing with second hand batteries, too. Deep discharging is one variable, shorting the pack by accident is another, using packs in cold temperatures is bad as the chemistry doesn't work until a lipo is above 15°C, one cell could be defective, etc. The list goes on. It could be a mixture of variables, so it's always hard to tell.

Just to clarify, what I actually said was that the pack may be good enough to be used in a less demanding application. For example, I have some old 3S 2200 packs with nearly 200 cycles with IR measurements reading way above 10 mili ohms, these packs would now be useless in a 450 helicopter but in an FPV glider pulling all of 7 amps, they're ok and still give a flight. Sadly the pack mentioned has gone bad for whatever reason and sadly you'll probably never really know why. Also with the pack being second hand nobody really knows how it was treated before hand. I've had many packs that have gone on for two years and some that have lasted only a few months, yet I've felt that I've treated them the same. One thing that is known for certain is that deep discharging is the most significant contributing factor to shortened battery life. Always stick to 20%+ rule

Always a tricky subject, this one......

Cheers,

Chris

[cjcj1949]

My point was that I thought Electriflyer were being over generous in saying that the battery pack was faulty or below standard. I've only seen single cells go bad, the chance of six going at the same time seems very small. The most likely explanation, I thought, was misuse. I wasn't aware of earlier usage, I was trying to explain a dead pack after only a few flights.

[aamacgregor]

Hi everyone, I just thought I'd share my thoughts on what may have happened here. I think I may have been slightly misunderstood when explaining my thoughts, but understandably so when so many variables are involved...

Thank you for your response .Sorry if I misunderstood and/or misrepresented what you were saying - it wasn't intentional. I remember you saying that the battery may still be useful in a lower power application. I also thought I remembered you saying that lipo's function better when it's warmer, although looking back, because it directly followed your statement of using it in a lower power application, I think you were making a general comment and not saying that I should try the "bad one" in the X5 on a warm day.

I must admit, I'm not convinced that the iCharger is reading the internal resistance properly, since it's readings are far from consistent when measuring the IR on the same battery over the two times I've checked - this is true for all 4 batteries. Therefore, it might be that all four packs are fine, and it is just coincidence that the two times that the ESC has been playing around it has been with the same battery twice in a row... I guess it is possible that something else is at fault although the battery is looking to be the likely candidate. I need to do more investigation.

My point was that I thought Electriflyer were being over generous in saying that the battery pack was faulty or below standard. I've only seen single cells go bad, the chance of six going at the same time seems very small. The most likely explanation, I thought, was misuse. I wasn't aware of earlier usage, I was trying to explain a dead pack after only a few flights.

To be fair to Chris, when I was speaking to him on the phone he straight away suggested that the most likely cause to a pack failure would either be deep discharging, shorting the pack by accident or using it in cold temperatures. When I said

Based on the number of cycles it's had, he [Chris] suggested that it was a bad one in the batch, which apparently happens from time to time

I think I have unintentionally misrepresented what he said. As mentioned, his first port of call was to detail the most likely causes of failure, at which point, I was saying that I hadn't deep discharged any of the packs, I'd never shorted them and although I'd used them in the cold, I'd always tried to keep them warm when not on the helicopter, plus they've all been treated the same (or so I'd remembered at the time). So, on the one hand, Chris was saying that "one or more of these are the most likely cause", and on the otherhand I was pretty much saying "but none of them apply". Chris, then also made the comment that we don't know how they were treated before I got them. Now, I did buy the packs off someone on this forum, who said they'd just had a few cycles on them before selling them on (change of project direction and therefore no further use for them), but I bought them in the summer time, and that person is pretty experienced, so I don't expect they would have treated them badly or had opportunity to expose them to the cold. So, with that in mind, my opinion was that I was pretty sure that the packs wouldnt't have been abused before I got them and that I hadn't abused them. This left Chris in the position where I'd removed all of the likely possibilities and therefore the only remaining possibility was that the pack may have been a bad pack (I can't remember, but he may have also mentioned that it's usually only one cell that is bad in such a case).

I think at the time, I was pretty certain that neither I nor the previous owner of the packs had caused damage in any way. However, now I'm gaining a better understanding, I think the fact is that the evidence suggests that the pack has most likely been treated badly at some point in its life. So, I've been really trying to think back. Part of the problem is, up until I read Chris' post, I think I've had a wrong definition of cold - I've been thinking cold is a few degress, but now that I've read that "the chemistry doesn't work until a lipo is above 15°C", I think I might have a possible cause. The first time that I flew the X5 at Waterfoot, it was on a really cold day (minus something). On that day I think I may have ended up having a pack on the helicopter for slightly longer than it should have been in the cold before using it. That day, I moved the helicopter with one pack installed on it, from my warm car into the portacabin (the three remaining packs were in pockets in my ruck sack that I also transferred from the car to the portacabin at the same time). The portacabin at Waterfoot has a really nice heater in it, so the cabin was heating up quite the thing, but the heater then went out for a while until it was relit and so the temperature in the portacabin was probably around 7 degrees (or slightly less) for an hour or so - outside it was really cold. It is most likely that I therefore flew one of the batteries when it was well below 15°C. I then had a break for a couple of hours, to allow others to fly and also so that I could have a chat with the others there and keep warm. Meanwhile the portacabin had heated up really nicely and stayed pretty warm for the last hour and three quarters. The other 3 packs had been in the warm cabin for that time and were therefore probably warm themselves before I used them. So perhaps that did it to that one battery???

Anyway, because I've been getting inconsistent results, I think I need to do some proper testing on the packs to the point of obtaining consistent results. At that point I'll post my findings.

Thanks both of you to your replies, they've been very helpful. Again apologies to Chris for any misrepresentation of what he said, it wasn't intentional and the last thing I'd want to do is blacken his name or the reputation of Electriflyer - I have always been very impressed with Chris' knowledge, willingness to help and the service that I have received.