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Old Apr 12, 2012, 03:43 AM
BrainFart RC-Pilot
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@Wayne

did GensAce send also their new 60C for testing?
Gerd Giese received them, but he is not using your method

The 60C pack Gerd did test had a bit of thin main lead wire and he does label them as real 45C pack.

http://www.elektromodellflug.de/gensace-25c-65c-ii.html
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Old Apr 12, 2012, 04:53 AM
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Originally Posted by TreeDiver View Post
@Wayne

did GensAce send also their new 60C for testing?
Gerd Giese received them, but he is not using your method

The 60C pack Gerd did test had a bit of thin main lead wire and he does label them as real 45C pack.

http://www.elektromodellflug.de/gensace-25c-65c-ii.html
No, they don't send to me. I take my packs at random from a stockist in the UK.
They did send me a second 55C pack after I found the original was no better than the 25C, but it was the same as the original 55C.

I am not clear how Gerd Giese decides on his actual C rating as his load pattern is a fixed 10C load with pulses to 15 and 25C. I am not criticizing and agree that his load pattern is closer to real flying than a fixed load.However, I understand "Continuous Rating" as the max current that the lipo will deliver over a full discharge and therefore a 2600mAh 60C pack should deliver 2.6 x 60 = 156A which it will not.
Rating the pack at 45C suggests that it will deliver 117A continuously which I also very much doubt, looking at the IR figures. Perhaps the 45C figure is a pulse loading limit but it should be specified.
It all adds to the unnecessary fog of C ratings - If the manufacturer does not mean that the customer can take 60C continuous, then he should specify what the user can take and if it is pulse loading, then quantify the pulses.
The claims that makers use unspecified voltages and temperatures to decide on C ratings is disingenuous and a smoke (!!) cloud to hide the truth.

Wayne
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Old Apr 12, 2012, 06:17 AM
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Having found that the gens ace 25C pack, based on its IR using the ESR meter, was a 25C pack it is a shame that other gens ace packs are not what they seem.
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Old Apr 12, 2012, 06:34 AM
BrainFart RC-Pilot
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@Wayne

thanks for your feedback
the 25C packs of GensAce are anyhow, the ones I purchase. The max load I use (static) is 15C. Otherwise the flight time is too short for me.

60C packs should have better voltage under load, but if it is noticeable with a 15C (static) load...that is the question if you have real 25C packs (like the 25C GensAce)

Some users will need higher C rating I guess.
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Old Apr 12, 2012, 06:42 AM
BrainFart RC-Pilot
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Originally Posted by Andy from Sandy View Post
Having found that the gens ace 25C pack, based on its IR using the ESR meter, was a 25C pack it is a shame that other gens ace packs are not what they seem.
yes, it would set a real standard

anyhow, label their 25C packs as 25C and not as 40C... generated allot of buzzzzzz
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Old Apr 12, 2012, 06:53 AM
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Originally Posted by Wayne Giles View Post
I agree Mark. The whole point of the calculator and FOM is to tell the user the truth about the Lipo. The C rating written on the side of the pack is irrelevant as it has generally proven to be fiction.
Surely the user wants to know what the Lipo is really capable of - the calculator and FOM does that and the label does not.

ToBeFrank,
I wouldn't call a 25C Lipo a 'great' battery, but the genuine 25C pack is equal to the 65C marked pack in your example and surely that is what we want to know and makes sense.
This is the 'raison d'Ítre' for the calculator , and for the FOM.

Wayne
I agree that FOM is a good tool to compare similar size batteries to figure what the true C rating is. To have this completely normalized I think you also have to take into account the power application. Not everyone is going for the 1400W edf system. I have a few smaller park flyers <1000mAH and right off the bat they are significianctly lower on FOM to be considered unusable although they are brand new and the lower capcacity gives a higher IR. Normalizition should be key for the FOM or then you would have to disclaim what applcation this is meant for, ie cap and c rating.
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Old Apr 12, 2012, 07:16 AM
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Originally Posted by Wayne Giles View Post
They did send me a second 55C pack after I found the original was no better than the 25C, but it was the same as the original 55C.

I understand "Continuous Rating" as the max current that the lipo will deliver over a full discharge and therefore a 2600mAh 60C pack should deliver 2.6 x 60 = 156A which it will not.

Rating the pack at 45C suggests that it will deliver 117A continuously which I also very much doubt, looking at the IR figures. Perhaps the 45C figure is a pulse loading limit but it should be specified.

It all adds to the unnecessary fog of C ratings - If the manufacturer does not mean that the customer can take 60C continuous, then he should specify what the user can take and if it is pulse loading, then quantify the pulses.

The claims that makers use unspecified voltages and temperatures to decide on C ratings is disingenuous and a smoke (!!) cloud to hide the truth.
If and when you've ever confronted your favorite LHS or the actual distributor/manufacturer on how Li-Poly manufacturers arrive at what certainly appears to be a "disingenuous smoke (!!) cloud" ... what kind of an explanation could one possibly except that might possibly explain their rationale for a 45C, 55C or 60C continuous discharge label rating.
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Old Apr 12, 2012, 07:50 AM
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So hows this: If you use Power=IV=I^2R. you always use I^2R with losses. if you use the nominal voltage of the lipo to be 3.7 volts and the amps to be CAP*C rating and measure the IR you can use this eff equation:

eff% (Power-Power Loss)/Power

so for example I have a 2200 3s 25C with a average IR of 4.36mohms per cell

Power=2.2*3.7*25=203.5 watts
Power Loss=(2.2*25)^2*.00436= 13.189 watts

note the FOM of this battery 1

(203.5-13.189)/203.5= .9351 => 93.5%

so since we know you can never have a 100% eff battery the key would be comming up with an agreed battery eff so lets say 93.5%

so 93.5/93.5 would give a corrected FOM = 1

now lets look at another battery

2200 3s 25C with a average IR of 15mohms per cell

Power=2.2*3.7*25=203.5 watts
Power Loss=(2.2*25)^2*.015= 45.375 watts

eff= 77.7% with corrected FOM= 77.77/93.5 = 0.83

So to make sure that this does not favor large CAP 25C batteries only, here is my brand new 2s 370mah 20C battery:

by using the IR calculator this battery should have a calculated IR of 40.54mohms. Now the Power loss calculations with should be a FOM of 1 but is reads 0.80 so so here is the eff:

Power=.370*3.7*20=27.38 watts
Power Loss=(.370*20)^2*.04054= 2.219watts

eff= 91.892%

now my reader for this brand new battery said it has an IR of 51 mohms

Power Loss=(.370*20)^2*.051= 2.792watts

eff=89.8% corrected FOM = 0.97723

So your perfect battery should have an IR as calculated on the IR calculator here:
http://www.jj604.com/LiPoTool/
will give you the max eff of the battery. by figuring your own IR and can get a corrected FOM this you are not looking at specifically for a 22C or 25C which is what this calculator seems to be meant for. realize this is all thumbs rules, using linear approx for non-linear systems and computed averages. But then again most engineering is like that.
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Old Apr 12, 2012, 07:56 AM
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I am currently looking to define a scale for the corrected FOM for desired power application ie EDF, park, heli. I am trying actual systems now
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Old Apr 12, 2012, 09:11 AM
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Quote:
Originally Posted by TreeDiver View Post
60C packs should have better voltage under load, but if it is noticeable with a 15C (static) load...that is the question if you have real 25C packs (like the 25C GensAce)

Some users will need higher C rating I guess.
Very true that a 60C lipoly pack should have better voltage under load than a 25C pack, especially if these packs are from the same manufacturer. However, as Wayne's earlier testing of Gens Ace 55C concluded, this is not always the case as his 55C sample actually tested worse than his 25C sample.

I must say that I was disappointed when I saw that Gens Ace was releasing a line of 60C packs. It seems that they have now fallen into the same C-rating BS scheme that so many other manufacturers hide behind. Apparently their marketing department is more powerful than their engineering department.

The fact of the matter is that there are currently no 60C lipolys available. Anywhere. From anyone. A 60C pack should be able to repeatedly sustain a 1 minute discharge to 100% DOD without damage and hold a usable voltage while doing so. I have yet to see any testing that substantiates this. Matter of fact I don't think that I have ever seen any packs that could repeatedly sustain a 30C discharge to 100% DOD without damage. Some contend that pack manufacturers rate cells, not packs. Well fine. I find this shady but I still have yet to see a lipoly cell that can repeatedly sustain over 40C discharge without suffering irreparable damage due to extreme temperature rise.

Eager to see some test results of the Gens Ace 60C packs with Wayne's meter. They might be better than the 25C but likely not by much, and certainly not enough to warrant a 60C rating.

Mark
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Old Apr 12, 2012, 12:45 PM
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Originally Posted by Wayne Giles View Post
but the genuine 25C pack is equal to the 65C marked pack in your example and surely that is what we want to know and makes sense.
I don't agree. I would bet that when most people go looking for batteries (myself included), they are mainly thinking of two things: 1) does this battery meet my power needs? and 2) is this battery worth the money? 1) is answered by the effective C number. The FOM implies by it's name (the synonym for "merit" is "worth") that it answers 2), but it does not. In a larger battery, the 65C rated battery will cost significantly more than the 25C rated one, but the FOM indicates their worth is exactly the same.

IMO, the FOM is not a figure of merit at all. It is simply another way to represent the C rating where 22C has arbitrarily been picked as the line between good and bad.
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Old Apr 12, 2012, 01:19 PM
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Originally Posted by ToBeFrank View Post
In a larger battery, the 65C rated battery will cost significantly more than the 25C rated one, but the FOM indicates their worth is exactly the same.

IMO, the FOM is not a figure of merit at all.
If battery A and battery B test exactly the same but have different labels (one says 25C and the other says 65C), you indicate that the test results should be discarded and the number printed on the label should be trusted? You are a lipoly marketer's dream customer.

FOM is a figure that takes empirically measured performance data and normalizes to specified capacity. As such, it is absolutely a figure of merit. Conversely, numbers printed on labels that have no basis in reality or any objectively measurable performance parameter are rubbish.

If a 65C label has more value to you than a 25C label, then go ahead and spend more for the 65C label. Understand however, that the lipoly with 65C label won't fly your airplane with any better performance than the lipoly that measures identically yet has a 25C label.

Mark
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Old Apr 12, 2012, 01:51 PM
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Originally Posted by ToBeFrank View Post
I don't agree. I would bet that when most people go looking for batteries (myself included), they are mainly thinking of two things: 1) does this battery meet my power needs? and 2) is this battery worth the money? 1) is answered by the effective C number. The FOM implies by it's name (the synonym for "merit" is "worth") that it answers 2), but it does not. In a larger battery, the 65C rated battery will cost significantly more than the 25C rated one, but the FOM indicates their worth is exactly the same.

IMO, the FOM is not a figure of merit at all. It is simply another way to represent the C rating where 22C has arbitrarily been picked as the line between good and bad.
Pretty much my sentiment and I imagine that of many other RC enthusiasts.

As much as I'm impressed by FOM calculations, efficiency and overall thread diligence it does seem like this thread is in some ways hitting its proverbial head against the wall. Yes, it's interesting to a point, but common sense still prevails. It's doubtful this thread is going to result in Lipo manufacturers being more accurate when labeling a pack's true continuous discharge rating: (1) Especially, when more and more RC enthusiasts are using much higher charging rates, which does diminish the number of performance cycles; (2) Many are more interested in less expensive packs whose ratings and consistent quality is still questionable; and (3) Many are not all that concerned about TLC and helping to achieve close to their pack's potential number of performance cycles.

Much of this impressive calculated thread is telling most of us what we already suspected/knew: (1) BuyerBeware that continuous discharge labeling is overrated, (2) Buy packs that have a greater continuous discharge rating then you actually need as a safety buffer to get the most bang for your buck, and (3) Lipo cell swelling results from a pack being stressed.

The vast majority of RC enthusiasts couldn't care less about FOM, a pack's efficiency or power calculations like the following:

Quote:
Originally Posted by MIDNCOCO View Post
I have a 2200 3s 25C with a average IR of 4.36mohms per cell
Power=2.2*3.7*25=203.5 watts
Power Loss=(2.2*25)^2*.00436= 13.189 watts

Note: The FOM of this battery = 1
(203.5-13.189)/203.5= .9351 => 93.5%
So since we know you can never have a 100% eff battery the key would be coming up with
an agreed battery eff so lets say 93.5% … so 93.5/93.5 would give a corrected FOM = 1 ...
Too much ado about what knowledgeable RC enthusiasts already know and compensate for by buying better quality packs, using common sense and not abusing their packs. The few obsessive compulsive RC wingnuts and most likely the vase majority of average RC parkflyers and modellers will never own an ESR meter, even if they were offered one for free.
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Old Apr 12, 2012, 02:04 PM
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>> which does diminish the number of performance cycles
BTW, some manufacturers claim nowadays that it doesn't.

At least the two packs in my 450 heli get charged at the max. permitted rate every time, and don't seem to mind.

>> couldn't care less... or power calculations like the following
neither do I, as it misses the point.

The presented idea of discharging a 2200 mAh "25C" labeled pack at 55 amps in actual flight seems rather absurd to me. I demand (and get) that level of performance from expensive premium packs which are labeled at almost twice the C rating.

PS for a real wacko performance "metric", check out consumer audio. Nothing wrong with it, it makes people happy to know they have 700 W in that flimsy little plastic box on top of their monitor. The 72 kg 18 inch subwoofer I'm occasionally lugging around with my band and that's capable of knocking over trees and leveling small buildings is rated at 800...
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Old Apr 12, 2012, 03:05 PM
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>> which does diminish the number of performance cycles
BTW, some manufacturers claim nowadays that it doesn't.
"some manufacturers claim" >> sounds familiar , but then as they say, FDL, but LCF.

Seriously, it's VERY possible/probable that most all of TPs G6 Pro Lite 25C lipos will get just as many or even more performance cycles charged at TPs recommended maximum charge rate of 5C when compared to yesterdays ParkZone packs or today's cheaper bargain brands charged at 1C.

As far as TPs G6 Pro Performance 45C (8C) and G6 Pro Power 65C (12C) there is little to compare performance cycles to when it comes to yesterday's lack of similarily rated continuous discharge packs charged at 1C. Today's Li-Poly technology advances certainly support "some manufacturers claim" that today's quality 25C lipo packs charged at 5C will provide even more performance cycles than yesterdays 25C lipo packs charged at 1C (and yesterday's quality packs were just as expensive or even more expensive). Another reason for an increase in performance cycles at a higher charge rate is the improvements made in lipo chargers/balancers compared to some of those cheap charger/balancers provided with RTF planes.
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