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Old Nov 12, 2013, 12:17 PM
Supersonic Engineering
GordonTarling's Avatar
UK, Greater London, Uxbridge
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I just received two new 4S 2200mAh packs of a reputable brand from a UK supplier. On checking the IR of the cells, they're all pretty much the same at around 16mOhms. I checked an identical pack that's had some use and is over a year old and each cell is around 8mOhms. Can I expect the IR of the new packs to fall with use, or should I reject them now?
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Old Nov 12, 2013, 12:50 PM
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Canton, Michigan USA
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Originally Posted by GordonTarling View Post
I just received two new 4S 2200mAh packs of a reputable brand from a UK supplier. On checking the IR of the cells, they're all pretty much the same at around 16mOhms. I checked an identical pack that's had some use and is over a year old and each cell is around 8mOhms. Can I expect the IR of the new packs to fall with use, or should I reject them now?
Wow, assuming temperature is about the same those cells are not very good. 16 mOhms is like an old, old pack. I had a similar problem with a local hobby shop where I wanted to buy one of their "house brand" lipos. I came in with the ESR meter and tested one pack and the cells were 20-21 mOhms. I tested more and all were in that range. These were simply relabeled new old stock lipos.
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Old Nov 12, 2013, 01:00 PM
Supersonic Engineering
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Prof100 - just as I thought! I'll be having a conversation with the supplier tomorrow!
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Old Nov 12, 2013, 02:48 PM
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Originally Posted by GordonTarling View Post
I just received two new 4S 2200mAh packs of a reputable brand from a UK supplier. On checking the IR of the cells, they're all pretty much the same at around 16mOhms. I checked an identical pack that's had some use and is over a year old and each cell is around 8mOhms. Can I expect the IR of the new packs to fall with use, or should I reject them now?
Gordon,

I have found during testing that new lipos generally, fall in IR values by about 10% after the first cycle or at most the first 3 cycles. The biggest fall I have seen is 25% although that was exceptional. The IR of any lipo then rises steadily throughout its life at a rate dependant on how (badly) you treat them.

Assuming you measured at the same temperature as prof100 said, the other possibility is that they are different cells with a different temperature coefficient of their IR, although that is no defence if the labels are identical.

Wayne
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Old Nov 12, 2013, 02:55 PM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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Gordon, just to complicate matters. There are some modern packs that display fairly high IR and relatively poor performance at normal rates but improve substantially when they are pushed hard. Revolectrix 60C is one that does that. At least mine does. The IR is high at ambient but drops off more rapidly than other similar packs at temperature rises. Essentially the IR vs. Temp. curve crosses over other packs somewhere around 30-50deg C.

Not suggesting that is the case here as most brands do not show this effect, but it is worth being aware of. Waynes comment about the identical labels is spot on however.

John
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Prof100 - just as I thought! I'll be having a conversation with the supplier tomorrow!
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Old Nov 13, 2013, 02:44 AM
Supersonic Engineering
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Thanks for the replies chaps!

Just for the record, these are Gens Ace 4S 2200mAh 25C packs. I've measured identical packs previously at between 6 and 8 millohms when received.

Wayne - I'd read all through this thread and already knew that IR falls by up to 25% in the first few cycles. However, these are now reading approx 15 milliohms per cell at 20C, so There's no way they're likely to fall to under 8 milliohms with use. IMHO, they should be around 6 milliohms at first, then maybe fall to 4 or 5 after a few cycles.

John - These are labelled the same and are identical in every way that I can see to previous packs from the same supplier.

Gordon
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Old Nov 13, 2013, 02:56 AM
ancora imparo
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Gordon, I know you can read a graph () so here's some interesting info. These are 3S 2200/2250 mAh nominal packs

Note how my Gens Ace and Revo 60C packs cross over at about room temp and above that the GensAce has the worst IR of all. Also how the ordinary Turnigy Nano might actually perform better than all the others in cold weather but the Turnigy Nano A-Spec blitzes them all at anything over 18degC.

Usual disclaimer about this is all based on only 1 or 2 packs I happen to have applies.

John
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Old Nov 13, 2013, 09:19 AM
Adam Gibson
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United States, FL, New Port Richey
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jj604, How many charges on each of those batteries? It would be interesting to see the same comparison at 50 charges, 100 charges, 150 charges, and 200 charges. The results might be entirely different.

I have also read that batteries of different sizes from the same manufacturer can be different so the 4000mah Gens Ace 25C might be nothing like the graph you have there.

If temps stay around 40C the regular nano-tech batteries are better than the gens ace by quite a bit just going by that IR graph and are much cheaper. My batteries come down barely warm on my Trex 500 so it appears the GensAce is not a good brand to use when you are not stressing the batteries going strictly by your graph.

An interesting thrust test of nano tech vs gensace... It is only 1 sample from each though so you of course can not come to any conclusion but it conflicts with the graph above as the video shows more power coming from the GensAce.

Turnigy Nano tech vs Gens ace Lipo test done the proper way! (6 min 15 sec)
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Old Nov 14, 2013, 03:36 AM
ancora imparo
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Well, this just raises all the issues about how difficult it is to make reliable comparisons!

One of the reasons I am reluctant to make public my IR vs/ temp readings is that it is too easy to read into them conclusions that are invalid.

I particularly don't want people to draw the conclusion that one brand is "better" than another from them.

One of the things Mark, Wayne and I have emphasised is that IR is a useful "quick and dirty" measure of LiPo performance. The LiPo tool is only ever claimed to be a "rule of thumb" based on extensive experience. It still remains in my view far and away the best non-destructive really quick way to establish likely pack performance and is particularly useful to keep track of LiPo life cycle behaviour but I cannot emphasise enough:

IR is a derived number from voltage drop under load that is a measure of likely pack performance - it is NOT an intrinsic property of the pack. People who talk about "reducing the IR to improve pack performance" misunderstand this. There is a lot more to pack performance than just IR - but it does remain one of the most useful single parameters we have.

The only real controlled test of a pack is its voltage and temperature trace under varying loads. Comparison of real life discharges such as Joe (MSGUY) has recently done is equivalent and for most practical users is more convincing provided all the variables are tightly controlled. The "I use Brand X and Brand Y and Brand X gives me more punch" do not fall into this category unless we can be sure all tests were made under identical conditions.

The thrust test in the video is unconvincing unless it is continued to LVC. It shows initial thrust to be higher but that may be due to an initial high voltage retention under load. For example I have found my initially superior Turnigy A-Spec drop off more rapidly at a 35C rate than my Revolectric packs which hold a more constant voltage and actually deliver higher Watt hours.

The number of variables is substantial:
1) Temperature affects voltage and current delivery
2) Temperature varies with discharge rate and during the discharge and depends on the physical cooling arrangements
3) Consequently so does pack voltage and current
4) Pack history affects performance and capacity - most of us fly for fun and testing packs for 50,100, 200 cycles is not fun.
5) Pack chemistry is largely a mystery and so we get anomalous behaviours. Different size cells may be different chemistries. Different production batches may have different cells. Voltage vs. time curves have different shapes.
6) Developments in packs may change the results. I just tested a Revo 70C at approx. 35C rate and it shows different initial voltage curve to a Revo 60C. Yet to find out what it does at high rates.

and so on and so on

Bottom line is, I posted the IR vs. Temp curves to make the point that the response of different packs is quite different as temperature changes and this will affect your judgment of what is "best". A pack with relatively low IR below 25deg C if only used at moderate rates may produce excellent power and low temperature rise with consequent long life. A pack with higher IR at room temperature, but which has an IR that drops off rapidly with heating, may perform well at high rates where the internal heating kicks in and lowers the IR.

These packs were my ordinary flight packs and while most were relatively new a couple had some milage under their belt. They were included deliberately to show the difference that can arise between different packs. Specifically my Gens Ace 25C packs have not lived up to the perormance some other people have seen and it is entirely possible that are from a different manufacturing batch. My three Turnigy A-Specs on the other hand have been consistently superior performers with low temperature rise at high current rates - BUT they are significantly lower capacity than claimed on the label.

It's all a bit of a lottery really.

John
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Old Nov 14, 2013, 08:59 AM
Adam Gibson
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United States, FL, New Port Richey
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I hope you didn't take what I said as a complaint or anything negative. I appreciate all the info you have given throughout the years on this subject. Your name has been popping up for along time on this subject as I have been reading a lot about it over the years on this forum (I usually don't post as I couldn't add anything useful to it).

I definitely think you should keep posting data even if it is not something we can draw direct comparisons or conclusions from. It is still useful and very interesting data to me and others too I am sure.

For me I think the best use of IR is to mainly test my own battery packs and monitor them over time to see how they are doing and compare them to the other packs I personally have... but honestly you can feel the difference in flight when they start getting older on a Heli so I guess we really don't need some test to verify what we already know . I can see that people that need the maximum performance for competitions might want to make sure they only use the LiPos they own that are at the top level of performance so it would be beneficial to them.

With that said though I am always drawn to threads on this subject and absorb everything I can on it for some reason. My eyes get big every time I stumble onto a new graph with IR, voltage, or current testing of LiPos. I am just glad I don't have a CBA to test with or I would probably never get out of my house to fly.

I try to log battery stats of every flight I do. I have done this for years but I have had long periods where I stopped flying. I have always sold off my previous helis before getting anything useful out of the data though (flight counts low on the batteries). I am currently logging GensAce 4000mah 6s1p 25C batteries that I originally used in series for my 700 heli but now I use in my Trex 500 and Trex 550. I almost always charge and do IR tests at 77f to 78f degrees in my house. Keep in mind the IR values are from older hyperion charger firmware before they updated their IR testing algorithm. Any future IR tests might be lower because I am now running firmware 5.91 which they brought more in-line with the IR meter that someone made on this forum and other chargers.
https://docs.google.com/spreadsheet/...Xc&usp=sharing
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Old Nov 17, 2013, 04:57 AM
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I received my meter from Wayne yesterday - a great piece of kit. Thanks to Gordon Tarling for the recommendation.

Got a bit of a shock with my cheap Zippy 2700 3S packs that seem to perform fine in a couple of sport models and a small quad ... the cell IRs (checked at about 19 degrees C I think) were:

39, 19, 39
16, 14, 15
38, 16, 17

A physically identical Overlander 2700 pack was 10, 11, 11. But the other three I had puffed in (careful) use, hence the Zippys!

In contrast the Zippy 8000s I use in my hexacopter seem OK ... most cells around 4 milliohms with not too much variation. Same for my Turnigy 5800s. But I'll certainly be keeping an eye on them from now on in terms of watching for deterioration of individual cells - the reason for getting the meter in the first place.
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Old Nov 17, 2013, 06:02 AM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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Not at all!

It's just that the more I learn about the performance of LiPos the more I see how complex it is. And I worry about some folks taking IR as a "simple minded" fundamental predictor of performance. The variation of composition of electrolytes and cathode/anode materials plus the physical construction including plate thickness all appear to have a significant affect on performance. IR is a measure of those affects - not the cause of them. And like most things it is not a simple linear gain. What you win in some areas you trade off in others. Nor is it something amenable to causal-effect prediction by the armchair theorists. LiPos are very complicated little beasts.

I remain impressed by how the LiPo rule that Mark and Wayne created continues to be such a reliable and straightforward predictor of a reasonable maximum current under almost all conditions. I use my ESR meters daily and rely on the LiPo Tool for practical guidance. But when you start pushing packs beyond that LiPo Tool recommendation to their limits things get a bit unpredictable.

Just one cautionary tale.
One of my three Turnigy A-Spec Packs, referred to in my earlier post a couple of days ago, has been the best performer of my 3S 2200 size packs under increasing current and had significantly lower temperature rise than any other similar pack. It had consistently lower IR across the whole temperature range 0-50degC than any other similar sized pack I own. It had also performed well at 78 Amps which is about 40C based on true capacity, which is a rate higher than most packs can deliver and stay in good shape. This pack is rated by HobbyKing at 65C continuous 130C burst on the label. So I tested it at 124Amps which is 65C for this pack based on actual capacity or about 56C based on label capacity.

It could just keep 10.1-10.2V (3.4V/cell) which is well above the 3V/cell used by some manufacturers, although it showed a marked voltage dip, produced significant amounts of fumes and smoke and had a surface temperature of 105degC and rising when I finished the test and dumped it in a pail of sand. I have no idea how hot it eventually got internally but I'm guessing 120-130deg C minimum. It is puffed like a pregnant pig and, although it will recharge, for all practical purposes is as dead as a dodo. It went in the trash tonight.

John

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I hope you didn't take what I said as a complaint or anything negative.
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Old Jun 03, 2014, 03:28 PM
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So jj, what should I take from my brand new Rhino 3S packs just received 2 Fridays ago, never used with readings like this ?
I have gotten packs with 3s and 2s even 4s but this is insane for a brand new pack never used at least not by me. My other pack is the same thing in the 20s.
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Old Jun 03, 2014, 05:34 PM
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Originally Posted by 91-ZULU View Post
So jj, what should I take from my brand new Rhino 3S packs just received 2 Fridays ago, never used with readings like this ?
I have gotten packs with 3s and 2s even 4s but this is insane for a brand new pack never used at least not by me. My other pack is the same thing in the 20s.
You have not specified temperature of measurement which is most important.
If you go back to John's post 517 and look at the graph, you can see how important it is. The highest plot shows an increase in IR of 30% when the temperature is decreased from 20*C to 15*C.
Also the IR of a cell is inversely proportional to the cell capacity and the pack looks like a 1350mah one. The value also falls by up to 10% after the first few cycles.
All these factors may help to explain why your results look high.

Wayne
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Old Jun 03, 2014, 06:00 PM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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The only other comments I would add to what Wayne said are:

1) I assume this same charger has given consistent lower IR readings on similar size packs in the past - just to eliminate the measuring instrument as the source of error.

2) Your "this is insane for a brand new pack never used at least not by me." struck me as odd. Do you have a suspicion this pack was somehow a used or abused one?

3) Do you get the same values after a couple of cycles?

If the readings are reliable and the temperature is close to 22C/72F then this IR is high for a 1350mAh pack. I would expect a bit better from a "30C" pack but not a huge amount better. My rule of thumb is to halve the published C rating of budget HobbyKing LiPos.

The LiPo tool would suggest it is good for about 17 Amps maximum based on the highest cell IR. That's about 13C. Still perfectly usable for non-demanding use and not unusual for a small budget pack.

John
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