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Old Dec 04, 2011, 04:00 AM
ancora imparo
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Melbourne, Australia
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Answer is, you better wait for Wayne to wake up in England and read this.

I'm not sure that would work. If you put 5 in parallel say, it might just be like a 5S pack with 3.2A load per cell and you have to multiply the IR by 5. But lead resistances become an issue. These little Molex connectors have a significant resistance and voltage drop at currents like this.
Quote:
Originally Posted by Aviefly View Post
mmm I think I'll leave that to someone who knows what their doing

Just have some um 1S packs at between 130mah and 200mah. What would happen if I connected them in parallel to the main leads so they could take the 16A and used the probe to take the cell IR?
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Old Dec 04, 2011, 05:59 AM
Supersonic Engineering
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UK, Greater London, Uxbridge
Joined Mar 2001
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Received my Wayne-ohm-eter yesterday, too. I'm sure it'll prove to be a very handy piece of kit. I didn't want it so much for measuring which pack has the lowest reistsnce, but to help me monitor my A123 packs for bad cells. I'm using A123's a lot now in various pack sizes, so this should help a lot.

Aviefly - if you connect extra cells in parallel by their main leads, then you've effectively made a (say) 5P pack and that's what the meter will measure.
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Old Dec 04, 2011, 06:24 AM
Skint since 2000
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Joined Oct 2008
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Turnigy 2200mah 3s 45-90c

does anyone else have any readings from this pack? mine appears to be the same as my regular turnigy 2200mah 3s 20c
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Old Dec 04, 2011, 06:35 AM
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Rugby, UK
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Originally Posted by Aviefly View Post
Thanks Wayne that gives me some ideas.


Does this mean that the suggested FOM doesn't take into account the resistance of any leads and connectors?

Take the Gens Ace 25C 450mah 2S pack number 7 from my photo. I picked this one as it looks to be the worst of the bunch. That would be 29.96+29.16/2 giving 29.56, multiply this by the capacity 29.56*450 giving 13302. Then take the 12000 figure and divide by 13302 giving an FOM of 0.9.

Would it be reasonable to take the same method but use the Pack IR divided by the number of cells to start off with to see how much difference your chosen connectors can make. Taking the same pack would give you 97.5/2=48.75*450=21937.5 then the 12000/21937.5=0.55 giving and FOM difference of 0.9-0.55=0.35

Do the same for Billowy number one pack and although the pack has a worse FOM the difference is a lot smaller. Individual cell FOM would be 0.57 the second figure would be 0.52 giving a difference of only 0.05

On another note I have a couple of my mates Gens Ace 25C 2200 3S packs, I'm going to let them settle next to my Billowy 2250's so that I can compare them tomorrow.
Dan,

FOM does not take connectors into ccount. I have been through your calculation and I don't think it works because it will always vary with the number of cells.
I think you should do it separately; the FOM measures how good a lipo cell is over which you have no control once you have bought it.
If you subtract the cells total from the Pack reading it gives you the resistance of the leads + connector and you have control over this with the ability to change the connector.
Re testing very small cells you need to use a much smaller current pulse as John Julian says. I don't think putting cells in parallel will work because you could have a very good one in parallel with a duff one so the results are meaningless. To measure single cells you also need to feed the control circuitry with an auxilliary voltage from another pack. If you want details on the mods. to measure small single cells send me an e-mail.

Interested in your Gens Ace 25C results - see below as I am about to post a reply to Mark Forsyth.

Wayne
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Old Dec 04, 2011, 07:05 AM
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Rugby, UK
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Originally Posted by mrforsyth View Post
Would be very curious to know how your results compare to my results. My measurements were taken with an iCharger so the raw IR or FOM numbers won't be directly comparable but the deltas sure will be. Need to get me one of Wayne's nifty meters... (hook me up Wayne! )

Mark
Mark,

Looked at those results of yours before and they all tie up with figures I have taken on Gens Ace packs allowing for the low resolution which is getting to be a problem now that lipos are so good (Despite all the stick we give them moaning about various aspects!)

I measured a GensAce 3S220025C before power discharge tests but after low C cycling and obtained an average IR of 2.97m.ohm per cell. Did the same with a 55C pack and got 3.43m.ohm per cell and on test,as expected, the 25C pack outperformed the 55C pack.
I contacted a Gens Ace distributor in UK and he volunteered to take measurements of his GA stock of 25C,30C,40C and 55C 2200 packs if I loaned him a meter and let me publish the results (Man deserves a medal for honesty!)
A copy of the results and conclusions are:-

"Graham has kindly measured 10 cells of each of the different C ratings, ie 25C,30C,40C and 55C.
They were all measured at the same temperature and none of the packs had been charged or cycled which means that his results would be higher than my original, but the important factor is the comparative values.
I have taken an average cell ESR of the 10 cells for each C rating and these are:-
25C - 4.47milliohms---75% = 3.35m.ohm
30C - 4.39milliohms---75% = 3.29m.ohm
40C - 4.54milliohms---75% = 3.40m.ohm
55C - 4.58milliohms---75% = 3.43m.ohm

These are the sort of variations that could easily be manufacturing tolerances; individual cell variations were generally within 10% of the norm.
It seems that the conclusion is that the 25C packs are the best buy and are very good packs, but the higher rated packs are no better unless they last longer, certainly they don't perform any better.
BTW two other testers have come up with the same conclusion, so I don't feel too guilty!"

All cells were measured at the same temperature which could not be specified, but would be about 20deg.cent, whereas I take all my measurenets at 25deg.cent. Would expect mine to be slightly lower therefore.
The other factor is that I noticed that the first cycle of low C on my GA packs dropped the IR values to 75% of their "As delivered" value so I have added those 75% values to make it a fair comparison.

Two conclusions are that we agree that the GA 2200 25C pack has outstandingly low IR values however we measure them and the higher C rated packs are still very good, but no better than the 25C - more evidence that C ratings are meaningless.

Wayne
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Old Dec 04, 2011, 07:51 AM
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I see what you mean about the parallel idea Wayne, so the 16A load is applied through the probe in cell mode? Also the idea about the connectors, your totally right, amazing how you can miss the obvious at times

I tested the Gens Ace packs and this time got a temperature out in the shed of 12.2C, not bad considering it's snowing outside but noticeably colder than when testing yesterday which shows in the results.

I tested the Billowy 2250 3S and got pack 33.3(Yesterday 31.2) cell 1-10.36(9.64) cell 2-10.2(9.4) cell 3-10.44(9.8) giving an FOM of 0.52

The two Gens Ace 2200 3S had an average cell IR of 7.95 and an FOM of 0.69

Think I'd be warming up the pocket bombs as I call them if I was planning on flying them today

Think I'll crank the heating up in the shed for the rest of the day and test them again. Good excuse to go out there for a snooze while it's warming up
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Old Dec 04, 2011, 08:08 AM
Skint since 2000
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Reading, United Kingdom
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Quote:
Originally Posted by Aviefly View Post
I see what you mean about the parallel idea Wayne, so the 16A load is applied through the probe in cell mode? Also the idea about the connectors, your totally right, amazing how you can miss the obvious at times

I tested the Gens Ace packs and this time got a temperature out in the shed of 12.2C, not bad considering it's snowing outside but noticeably colder than when testing yesterday which shows in the results.

I tested the Billowy 2250 3S and got pack 33.3(Yesterday 31.2) cell 1-10.36(9.64) cell 2-10.2(9.4) cell 3-10.44(9.8) giving an FOM of 0.52

The two Gens Ace 2200 3S had an average cell IR of 7.95 and an FOM of 0.69

Think I'd be warming up the pocket bombs as I call them if I was planning on flying them today

Think I'll crank the heating up in the shed for the rest of the day and test them again. Good excuse to go out there for a snooze while it's warming up
The load is applied through the main discharge leads but in cell mode it measures the voltage drop of just the cell, Because there is no/little current going through it is much more accurate.

Pretty sure thats it but Wayne can confirm
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Old Dec 04, 2011, 10:08 AM
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Originally Posted by ghost2212 View Post
does anyone else have any readings from this pack? mine appears to be the same as my regular turnigy 2200mah 3s 20c
Brett, (Re: 3S220045C Nanotech lipo)

I tested 3S220025C and a 3S220045C packs some time back and the results are at
http://www.rcgroups.com/forums/showthread.php?t=1384403
You can see that the 25C were way high (two packs the same), but they fell to average 9.2m.ohms/cell after initial cycling. The 45C was better at 4.37milliohms.
I then carried on doing full power testing which is at
http://www.rcgroups.com/forums/showthread.php?t=1406364
In the testing I compared them with a standard 25C Turnigy and it well outperformed the 25C Nano and was nearly as good as the 45C.
It was an old pack so I don't know if the cells are now made by the same manufacturer. Lottery stuff!

Wayne
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Old Dec 04, 2011, 10:28 AM
Skint since 2000
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Reading, United Kingdom
Joined Oct 2008
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Quote:
Originally Posted by Wayne Giles View Post
Brett, (Re: 3S220045C Nanotech lipo)

I tested 3S220025C and a 3S220045C packs some time back and the results are at
http://www.rcgroups.com/forums/showthread.php?t=1384403
You can see that the 25C were way high (two packs the same), but they fell to average 9.2m.ohms/cell after initial cycling. The 45C was better at 4.37milliohms.
I then carried on doing full power testing which is at
http://www.rcgroups.com/forums/showthread.php?t=1406364
In the testing I compared them with a standard 25C Turnigy and it well outperformed the 25C Nano and was nearly as good as the 45C.
It was an old pack so I don't know if the cells are now made by the same manufacturer. Lottery stuff!

Wayne
Interesting data there Wayne, I'm not sure on the amount of cycles that these batterys have had unfortunately. I started logging on my 20c one but gave up because i'm lazy.

Once I get my 450 fixed up I will try and do an identical flight on both packs and see how the ripple voltage logged on the Castle ICE speed controller differs.
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Old Dec 04, 2011, 10:47 AM
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Repeated the earlier tests at 18.6C

Billowy 2250 3S, pack 27, cell1 8.04, cell2 8, cell3 8.12, FOM 0.66

Gens Ace 2200 3S pack1, pack 24.6, cell1 6.96, cell2 7.08, cell3 6.72, FOM 0.98
Pack2, pack 21.3, cell1 6.16, cell2 5.4, cell3 5.52, FOM 0.96
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Old Dec 04, 2011, 10:52 AM
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Originally Posted by jj604 View Post
Certainly these three methods are all different. My understanding is the SuperDuo measures the voltage between the charge/discharge period and the relatively long rest period which occurs frequently. In the PL8 the current is turned off for 300uS and the at-rest battery voltage is compared to the charging battery voltage on a cell by cell level. Both are measuring the IR based on the difference between the set charge/discharge current (which will vary depending on battery capacity and charge rate) and no load. The PL8 measures only during charge. The Waynemeter measures discharge IR at a standard 16A vs no load.

Note: The Thunderpower 325mAh battery was tested at 1.6A not 16A.

All testing done over a 3 1/2 hour period at about 23C.
The idea of using a 16A pulse for 15mS is based on trying to subject the lipo to the same sort of load that we do in practical use and seeing how much the voltage falls which is why I call it "Effective Series Resistance"; it is the effect of having that resistance in series with a perfect cell ie one which will supply infinite current with no voltage drop (If only!!)
If you look at the link
http://static.rcgroups.net/forums/at...eter%20015.jpg
You will see how the cell voltage responds to the 16A load in a 2250 lipo cell. Timebase is 2milliseconds/division and you can see at 15ms which is where the meter takes the on-load reading, that the voltage is virtually settled. The speed of voltage settling and recovery varies in different lipos and at different temperatures, generally being slower with poor lipos and lower temperatures.
Ideally I would like to use longer than 15mS, but the poor powerfet has to dump 400W for 15mS when a 6S lipo is measured so 15mS is max to keep within the Fet rating. Looking at the start of voltage fall, it is obvious that a shorter pulse would give a lower voltage drop and a lower IR figure. This may be why the PL8 system produces lower fgures.
Wayne
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Old Dec 04, 2011, 10:57 AM
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Rugby, UK
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Quote:
Originally Posted by Aviefly View Post
Repeated the earlier tests at 18.6C

Billowy 2250 3S, pack 27, cell1 8.04, cell2 8, cell3 8.12, FOM 0.66

Gens Ace 2200 3S pack1, pack 24.6, cell1 6.96, cell2 7.08, cell3 6.72, FOM 0.98
Pack2, pack 21.3, cell1 6.16, cell2 5.4, cell3 5.52, FOM 0.96
Dan,

That's more like it. The difference now is just temperature and demonstrates how important it is to warm your lipos in winter.
Even so a FOM of nearly 1 in a temp of only 18.6C is pretty impressive.

BTW How do you get the temperature in Aviemore up to 18C- a blowlamp?

Wayne
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Old Dec 04, 2011, 01:13 PM
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LOL

Small shed and lots of insulation. Perk of working for a builders merchant, gona have to get the window double glazed though. Got a load of profile tin sheeting for the roof but never got round to fitting it before the snow came. Just gona have to keep an eye on it and keep brushing the snow off it if it starts to build up.
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Old Dec 04, 2011, 02:17 PM
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Originally Posted by ghost2212 View Post
The load is applied through the main discharge leads but in cell mode it measures the voltage drop of just the cell, Because there is no/little current going through it is much more accurate.

Pretty sure thats it but Wayne can confirm
Bret,

That's exactly correct. Only the power leads to the pack pass the 16A current; the search lead to the balance connector only passes a few micro-amps so that there is no voltage drop and the meter reads the exact voltage at the cell

Wayne
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Old Dec 05, 2011, 07:48 PM
ProgressiveRC
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Seattle, WA
Joined Dec 2006
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For small packs (1S 160-250mAh) we used the same test parameters as the ESR meter, but with a lower 2.0A load conducted with a CBA to complete the results for our Spyder batteries here. Additional test parameters are detailed in the footnotes of the chart.

All other measurements were taken at 70F with an ESR meter, averaging three tests on three packs for each.

- David
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