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Old Apr 12, 2012, 08:57 PM
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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.
I have no idea how you came up with that. In fact, by arguing that a 65C rated battery that is 25C in real life should get a FOM exactly the same as a 25C rated battery that gets 25C, you are the marketer's dream. My argument is that the incorrectly rated 65C battery should have a much worse FOM because you're paying much more money for the 65C rating and it is vastly overrated. That is exactly the opposite of what a marketer would want. The FOM does not live up to its name as it is currently defined.
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Old Apr 12, 2012, 09:09 PM
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Maybe I missed it, but what is the eqn used to calculate "true C rating"?
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Originally Posted by mrforsyth View Post
Additional theory and empirical data basis for the calculator is contained in the data thread. Specifically, post #3 has pertinent information:

http://www.rcgroups.com/forums/showp...85&postcount=3

Mark
Maybe that post is over my head, because I still can't find an equation in it.

Can you please simply report the equation used to calculate true C? I'd examine it in the XLS file but the sheet is locked... I'd just like to understand the fundamentals behind it better.
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Old Apr 12, 2012, 09:24 PM
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Max_Sustained_Current = SQRT(6 * Cell_Capacity / Cell_IR)

where capacity is in mAh and IR is in mOhms
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Old Apr 12, 2012, 09:52 PM
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Originally Posted by ToBeFrank View Post
I have no idea how you came up with that. In fact, by arguing that a 65C rated battery that is 25C in real life should get a FOM exactly the same as a 25C rated battery that gets 25C, you are the marketer's dream. My argument is that the incorrectly rated 65C battery should have a much worse FOM because you're paying much more money for the 65C rating and it is vastly overrated. That is exactly the opposite of what a marketer would want. The FOM does not live up to its name as it is currently defined.
That is not the point of the lipo performance tool, it's so you can gauge every battery against each other... the FOM is accurate, the C rating on the battery is not. It's pretty easy to understand that when you run the calculator, if the battery is rated as a 25C with a FOM of 1 and its suppose to be 65C, then isn't it obvious that the battery is overrated? The user needs to realize that when they use the tool in the first place. The FOM just tells you what its rated at, it's not partial to a label with a C rating attached to it lol

A 25C battery is a 25C battery, introducing a FOM score that judges based of what a battery manufacture labels its batteries only adds to the confusion and accomplishes nothing at all in my opinion.
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Old Apr 12, 2012, 09:56 PM
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Can someone help me with battery selection? It seems that most everyone is out of 3S 2100-2200mah 25-45C batteries and I want to buy some more batteries for my Mini Ultra Stick with eflite park 450. What other choices do I have, can I go higher in mah with a lower C rating?
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Old Apr 12, 2012, 10:01 PM
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a 65C rated battery that is 25C in real life should get a FOM exactly the same as a 25C rated battery that gets 25C,
This is absolutely true. Two packs that measure the same should have the same rating.

It has just become clear to me that your desired definition of FOM and Wayne Giles' stated (and oft repeated) definition of FOM are in stark contrast, and hence our disconnect.

As I can clearly gather from your past postings that you possess vast intellectual capacity, a brief review will undoubtedly bring agreement.

FOM is nothing more than a figure that represents capacity normalized internal resistance. It wholesale ignores manufacturer stated C rating. More detail can be found in Wayne's FOM thread here: http://www.rcgroups.com/forums/showthread.php?t=1392662. A review of post #1 should aid in achieving consensus.

Mark
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Old Apr 12, 2012, 10:03 PM
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The FOM just tells you what its rated at
Exactly! It's just another way to say the true C rating. It is not a figure of merit (figure of worth) at all.
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Old Apr 12, 2012, 10:07 PM
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A 25C battery is a 25C battery, introducing a FOM score that judges based of what a battery manufacture labels its batteries only adds to the confusion and accomplishes nothing at all in my opinion.
Bingo!

FOM wholesale ignores manufacturer rating, levels the playing field, and helps the end consumer determine which batteries perform better, regardless of manufacturer C rating.

Mark
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Old Apr 12, 2012, 10:24 PM
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Originally Posted by mustangherb View Post
Can someone help me with battery selection? It seems that most everyone is out of 3S 2100-2200mah 25-45C batteries and I want to buy some more batteries for my Mini Ultra Stick with eflite park 450. What other choices do I have, can I go higher in mah with a lower C rating?
Off topic for this particular thread subject but you might check here:
http://www.haiyinstore.com/compares....=176+&PID=177+

Welcome to RCGroups!

Mark
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Old Apr 12, 2012, 10:33 PM
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First, a big "thank you" to everyone involved with this effort. After a couple of hours of happy measuring and labeling, all my lipos now sport written descriptors of their current "true C", FOM, and max current. (I'll be pasting those data on the "results" thread shortly.)

Re the FOM debate, I find the statistic useful in its current form because I'm interested in comparing batteries against each other irrespective of their manufacturer's quoted stats. The fact that a bunch of "40C" batteries may be more like 22C in reality is a somewhat unpleasant discovery, and one which I'll certainly be taking into account the next time I buy, but in terms of flying it's still first and foremost a 22C battery - that's the important number when deciding which pack to grab from a bag of charged ones, as opposed to whether or not the "40C" manufacturer ripped me off more than his "30C/50C" counterpart.

Another layer could be added on top - FOV (Figure of Veracity) - defined as the "true" C-rating over the manufacturer's own number. By itself, FOV would be useless in terms of deciding which battery to bung into the >1000W FunJet, but it would perhaps be an interesting way to track each manufacturer's tendency towards stretching the truth.

Over time, given enough data, we'd be able to look up an "Average FOV" for a particular line of batteries or even their manufacturer. "When buying XYZ brand batteries from the RST line, multiply the stated C-ratings by 0.71 to get the projected 'true C'".
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Old Apr 13, 2012, 12:10 AM
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mer·it/ˈmerit/
Noun:
The quality of being particularly good or worthy, esp. so as to deserve praise or reward.

Figure of merit
From Wikipedia, the free encyclopedia
A figure of merit is a quantity used to characterize the performance of a device, system or method, relative to its alternatives. In engineering, figures of merit are often defined for particular materials or devices in order to determine their relative utility for an application. In commerce, such figures are often used as a marketing tool to convince consumers to choose a particular brand.

And from another dictionary site:
figure of merit
Definition
Numerical value representing a measure of effectiveness, efficiency, performance or other important factor, and ascertained or approximated from analysis, appraisal, or estimation techniques.
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Old Apr 13, 2012, 01:04 AM
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Really appreciate the positive reinforcement and constructive feedback gentlemen.

We all knew full well that we would potentially be dog paddling in a sea of derision and ridicule for having the audacity to publicly challenge and offer an objective alternative to the kooky and arbitrary 'C' rating system. However, we were fed up to the point of bursting and felt that an objective measurement tool that was supported by a healthy dose of independent testing would be warmly received by at least some modelers who were like-minded and desired to have an objective and simple means of predicting, cataloging, and comparing lipoly performance.

It has been clearly stated from the outset that this tool is a 'practical rule of thumb' to arm the modeler with data that will predict lipoly performance and provide solid guidelines on how to maximize his lipoly investment. By no means do we make any claim that it is perfect but believe that it can be quite beneficial to the average modeler and certainly more informative than ratings that are printed on the side of a pack. Best of all, it's simple, repeatable, and provides an easy to understand basis for comparison. We consequently agreed that the potential scorn was well worth the effort and are encouraged that some find it helpful.

Regards,
Mark
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Old Apr 13, 2012, 07:26 AM
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>> we would potentially be dog paddling in a sea of derision and ridicule for having the audacity to publicly challenge
that is correct as some vendors are lying right to your face and there's nothing you can do about it. Well, there is, buy quality products from a reputable company, for example.

Let's be honest. Vendor X advertises substantially better performance at a substantially lower price. Most people have learned long since: If it sounds too good to be true, it's not true...
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Old Apr 13, 2012, 08:48 AM
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Gens ace appeared to buck the trend with the lauch of their 25C packs. Unfortunately this couldn't be maintained with the launch of their 50C packs.
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Old Apr 13, 2012, 08:51 AM
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Surely even the most determined axe grinders can see that some of us do find this work useful, even if they don't. If others want a value-for-money or vendor veracity measure then could they start another thread for the purpose - please!
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