Batteries!!

[gazza131]

l have problems understanding batts, coz of my memory problems, but as a good freind of mine pointed out to me, if i buy the cheapy hobby king ones (£24.79 6s 3000mAH and they last for lets say 30/50 cycles then when i replace them again with cheapy ones they still work out a lot cheaper than buying a good one and it only doing 60/80 cycles (hope that made sense) lol

[bolders]

No idea beyond the obvious one that only the better packs are capable of giving the 550 everything it wants, the lack of punch you describe is the zippy battery just not giving it up as fast as you demand where the Voltz and FP are able to give you all you ask for and hence feel more punchy so they are being stressed more than the zippy.

Without knowing what the 550 is actually drawing it is not easy to comment further.

Are the packs on the 550 coming down noticeably warm or hot?

A bloke at my club has a 550 with an Ice 100 fitted. He says that he is within the 100amp rating of the ice but his son (who is a much more aggressive flyer) can hit well over 100Amps. I think he said somewhere around 130A.

Regardless, if a 5000mAh 50C pack cant hold its own on a 550 then there is something very screwy with their C ratings. This pack should theoretically be able to deliver 250A continuous - even without flight logs you can be pretty sure a 550 is not going to pull anywhere near this level of current

[cjcj1949]

I think you misunderstand what C rating means. It is not a level that the batteries can be used at and give a useful life. It is about how much current you can take out of a battery with a specified amount of cooling. Without cooling the batteries can reach any temperature they feel like. Good batteries are warm at the end of a flight and batteries that start getting hot will just get hotter until they puff. The C ratings are just marketing unless defined.(A clear test procedure with numbers) The manufacturers show no intention of defining them. I use 25C batteries at 10C and they seem happy. But some 25C batteries run cooler than others and have different values of IR. If the specs meant anything then we would get identical IR values from batteries of the same C rating and capacity.

[bolders]

I think you misunderstand what C rating means. It is not a level that the batteries can be used at and give a useful life. It is about how much current you can take out of a battery with a specified amount of cooling. Without cooling the batteries can reach any temperature they feel like. Good batteries are warm at the end of a flight and batteries that start getting hot will just get hotter until they puff. The C ratings are just marketing unless defined.(A clear test procedure with numbers) The manufacturers show no intention of defining them. I use 25C batteries at 10C and they seem happy. But some 25C batteries run cooler than others and have different values of IR. If the specs meant anything then we would get identical IR values from batteries of the same C rating and capacity.

I do understand what C rating is and I do think it is (or should be) an indicator of a batteries useful life else as you say it is just marketing and a totally useless metric.
I do see what you are saying about clearly defined test parameters and I do agree but lets be honest If this lipo is not able to survive for any length of time running at a current that is half what the C rating indicates then there is obviously a problem with the lipo or the C rating the manufacturer has applied to the pack and this is really what I was trying to point out.

I know you can say "well the C rating is for a single cell tested under forced cooling and not a complete pack" etc but if this is the case for FP (im not suggesting it is or isn't) then we as the customers need to know as it is the only metric that we have to judge a lipos performance before buying it. I could except this behaviour (to some degree) from cheaper brands such as turnigy but not from premium brands that are charging over twice what the cheaper brands cost.

[J-S-Q]

No idea beyond the obvious one that only the better packs are capable of giving the 550 everything it wants, the lack of punch you describe is the zippy battery just not giving it up as fast as you demand where the Voltz and FP are able to give you all you ask for and hence feel more punchy so they are being stressed more than the zippy.

So you seem to be saying that the FP/Voltz batteries are so good that they can't handle there own power and hence they become puffed where as the Zippy's aren't strong enough to cause any damage to themselves? That doesn't sound very convincing to me.

Regardless of how C ratings should be interpreted, the fact is that in this case the far more expensive, higher C batteries have not lasted as well as the cheap Zippies when seemingly used under the exact same conditions.

[Mark_T]

So you seem to be saying that the FP/Voltz batteries are so good that they can't handle there own power and hence they become puffed where as the Zippy's aren't strong enough to cause any damage to themselves? That doesn't sound very convincing to me.

No, that's not where I'm heading with this, it is entirely possible that there is a problem with the packs, but we don't know that yet.

I do think you can damage these packs more easily though as they tend to have low IR values and will respond to demands with more power and crucially will hold voltage higher, longer and recover faster, that is why I was asking about the percentage remaining figures.

If you calculate that by looking at what you put back in to the packs then all is good, but if you use one of these little pack checkers you are most likely seeing incorrect information as all they do is compare a voltage to a table and give you the answer. The better the pack the more wrong the answer to the point where you may be dropping well below 20% without realizing it.

[J-S-Q]

No, that's not where I'm heading with this, it is entirely possible that there is a problem with the packs, but we don't know that yet.

I do think you can damage these packs more easily though as they tend to have low IR values and will respond to demands with more power and crucially will hold voltage higher, longer and recover faster, that is why I was asking about the percentage remaining figures.

If you calculate that by looking at what you put back in to the packs then all is good, but if you use one of these little pack checkers you are most likely seeing incorrect information as all they do is compare a voltage to a table and give you the answer. The better the pack the more wrong the answer to the point where you may be dropping well below 20% without realizing it.

Certainly a good point about the fallibility of lipo checkers. I can't help thinking that the world of high end lipos is still a bit of a lottery though. It's only a week ago that someone else was complaining about 3 new Flightpower Nano's puffing up:

http://www.rcheliaddict.co.uk/main-d...cking-all.html

At the prices they are charging I just think it's unacceptable and I'd be thoroughly p***ed off if it happened to me. They claim 500+ cycles, high C charge rates, massively high C discharge rates with price tags to match etc etc. and yet we still have to discuss whether they're ok to run in a TRex 550?

[Mark_T]

At the prices they are charging I just think it's unacceptable and I'd be thoroughly p***ed off if it happened to me. They claim 500+ cycles, high C charge rates, massively high C discharge rates with price tags to match etc etc. and yet we still have to discuss whether they're ok to run in a TRex 550?

I don't disagree with you at all and it is interesting, but perhaps not surprising that the problems are mostly showing up on 6S configurations.

A quick hunt around the web shows people logging 200A+ spikes on the 550 but the packs should be able to take that, so why are 6S configurations proving to be so challenging?

One thing I'll say though, people have commented that they are not stressing them as they don't do a lot of 3D. I'm the last one to comment on anyone's flying skills so don't take this the wrong way, but the more highly skilled pilots with better collective control will be able to fly using less amps than someone using raw power to overcome poor collective control and the better packs will allow you to draw amps the weaker ones will not.

I don't know quite where we head with this though, unless there is something in my comments earlier about accidentally running too low, it does seem that 6S is proving to be a challenge for a number of the better packs as this doesn't seem to be limited to any particular brand.

I wonder how the Opti packs are going to do on these 6S configurations in the long run? It will be interesting to see if they too suffer once in the hands of consumers or if they survive. I think Pete has a couple now so that is one to watch.

[cjcj1949]

I do understand what C rating is and I do think it is (or should be) an indicator of a batteries useful life else as you say it is just marketing and a totally useless metric.
I do see what you are saying about clearly defined test parameters and I do agree but lets be honest If this lipo is not able to survive for any length of time running at a current that is half what the C rating indicates then there is obviously a problem with the lipo or the C rating the manufacturer has applied to the pack and this is really what I was trying to point out.

I know you can say "well the C rating is for a single cell tested under forced cooling and not a complete pack" etc but if this is the case for FP (im not suggesting it is or isn't) then we as the customers need to know as it is the only metric that we have to judge a lipos performance before buying it. I could except this behaviour (to some degree) from cheaper brands such as turnigy but not from premium brands that are charging over twice what the cheaper brands cost.

I was getting annoyed with C ratings rather than your knowledge. By understanding C ratings I meant exactly what I went on to explain. It is something that sounds good, leads us to reasonable expectations which later we find are unjustified. I know you know that C rating means the continuous current etc, but as with a lot of things when you look in detail at what it means we often find that there's not much useful information there.

I've been looking at LiFe batteries recently and they do give useful and exact info. Possibly because they have reliable performance and are developed for a professional market. Our lipos are very much a hobby product with little critical comment. They can be made to work reliably in 450s at least.

It sounds to me that as we scale up to larger models that the whole system becomes more critical and perhaps the performance isn't quite there yet. The energy held in these packs will increase with the cube of their size whereas the cooling ability with the surface area or square. It may be worse for multiple packs in series as the heat management or lack of it clearly gets worse.

If the C ratings are derived from single pack tests then that would explain why multiple packs give more problems. Perhaps we need to engineer some of these installations.

[Mark_T]

It may be worse for multiple packs in series as the heat management or lack of it clearly gets worse.

Fortunately though the current drawn is halved when you go from 6S to 12S and that is why I think we are not seeing the same issues on 12S.

If the C ratings are derived from single pack tests then that would explain why multiple packs give more problems. Perhaps we need to engineer some of these installations.

Not sure I follow this one; the C ratings are mostly derived from single cell tests I believe not pack tests and I'm not seeing more problems with multiple pack configurations, quite the opposite.

Perhaps I've misunderstood something?

[J-S-Q]

The Flightpower spec sheets claim "40C Continuous 80C Burst (3 sec)". 80C on a 5,000 Lipo is 400 Amps. That's 200 Amps CONTINUOUS and FOUR HUNDRED AMPS burst!! Aaah but of course, as pointed out in this thread, perhaps this is under laboratory conditions probably with a single cell, with a cooling system etc. so in other words it is of little value to us in the real world. Which begs the question why are they putting this stuff on their spec sheets?

I would be interested to know if the OP or the guy in the other thread I linked to are able to get replacement packs under warranty?

[Mark_T]

Which begs the question why are they putting this stuff on their spec sheets?

Because all the other manufacturers do the same ...

It isn't much of an answer I know and you should read the comments from Andy at Opti on this as they came close to not putting any C rating on the cells for pretty much this reason.

This is something we seem to have inadvertently brought on ourselves through buying behaviour as we insist on treating a 50C pack as automatically better than a 30C pack so as long as manufacturers use single cell C ratings on the packs it is hard for any of them to break free. OptiPower have taken the first step but it remains to be seen if it will work or not.

Right now I'd guess the majority of consumers have no idea there is more than one way to present a C rating so absolute numbers remain king ...

I would be interested to know if the OP or the guy in the other thread I linked to are able to get replacement packs under warranty?

No idea on these specific cases or about the Voltz packs, but Flightpower have replaced packs where there have been problems in a couple of cases that I know of.

[J-S-Q]

Because all the other manufacturers do the same ...

It isn't much of an answer I know and you should read the comments from Andy at Opti on this as they came close to not putting any C rating on the cells for pretty much this reason.

Yes, I read Andy's comments. They kind of confirmed what I (and probably most of us) already suspected!

[gazza131]

wow this is really interesting stuff,, just wish i understood any of it lol !!!!!!!!

[cjcj1949]

Fortunately though the current drawn is halved when you go from 6S to 12S and that is why I think we are not seeing the same issues on 12S.



Not sure I follow this one; the C ratings are mostly derived from single cell tests I believe not pack tests and I'm not seeing more problems with multiple pack configurations, quite the opposite.

Perhaps I've misunderstood something?

Yes. My fault I used the wrong words. I was thinking of packs made from multiple cells. The more cells are assembled together, the lower the surafce area and the higher the temperature that will be reached inside a cell, inside a pack. Reducing the current by increasing the volts will also help if the losses are mainly I**2R as halving the current by doubling the voltage will reduce power losses by a factor of 4.