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Old Jan 26, 2012, 06:09 AM
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Originally Posted by NitroCharged View Post
I emailed them and ask if it referred to constant current or burst current. They replied its burst current for the minimum amount of time.
Very true
150C = 24 seconds.
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Old Jan 26, 2012, 03:34 PM
ancora imparo
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Which illustrates the problem exactly.

If I was to short circuit one of these small cells and measure the current pulse on an oscilloscope I bet I would see a peak pulse of 43Amps or so.

In that sense the manufacturer can claim a "true C" of 100C "for the minimum amount of time" and is not technically lying. It is of no use whatsoever to the modeler wanting to use it for practical flight. Nitro, I assume you didn't buy one of these, not really because of the shipping costs, but because you know from your extensive experience the "100C" claim is nonsense.

Thanks for your previous post. It would be nice if we could get some input from anyone who has tried the calculated C values against their practical flying experience rather than get diverted by armchair arguments.

John
Quote:
Originally Posted by NitroCharged View Post
Here's another brand that would confuse, excite or mislead the average user. MaxAmps.com are now advertising their new lipo's as "true 100C' and 'true 150C' rating. I emailed them and ask if it referred to constant current or burst current. They replied its burst current for the minimum amount of time.
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Old Jan 26, 2012, 03:58 PM
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No, I didn't My guesstimate on what should be on the pack would be around 35C - 70C Burst (and even that would kill the little thing) if they were to class them like everyone else.

Imagine the poor honest lipo seller who tagged their lipo's with "Constant True 25C performance" - no one would touch them because they can get a 'True 100C' lipo for less... and it's 100C !!!! It says so on the pack!... sheeesh.... it's a mess out there!
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Old Jan 26, 2012, 06:19 PM
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Returning to the armchair discussion which some of us dislike so much...

How do you understand "performance"? If you automatically think about "punch" or "climb rate" I'm with you at the moment.
Cell power loss = 6*capacity is not a straight performance indicator. Of course, it may help to protect battery from overloading and resulting overheating. It is also very important, I know by experience.
However simple limit of voltage drop is much better as an index of performance.
For instance: max amps = 268.3mV / Ri
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Old Jan 26, 2012, 06:56 PM
ancora imparo
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You seem to be playing your usual game of changing the discussion to have it on your own terms.

No one ever claimed this simple technique was about a precise way to measure particular battery performance in flight.

Which part of

"The forums contain a wealth of information about battery performance from respected regular posters who have devoted enormous energy and time to creating a valuable treasure trove of battery data; and if you are serious about battery performance and want to have the best possible understanding of how your cells will perform you need to spend time with the test data."

from the first post didn't you understand?

Put bluntly:
1) The current labelled values of C are largely irrelevant and for people who neither want nor need a lecture in battery characteristics downright misleading. I don't see anyone disputing that.
2) A couple of people with a great deal of experience in practical battery testing and usage have suggested a very simple technique that anyone can use that may be significantly better. If it proves even reasonably accurate it will be extremely valuable.
3) It is just a rule of thumb, and like all such rules may prove inaccurate, or there may be cases where it doesn't work. I thought that would be the case for very small cells but so far I have been surprised by the results. However it wasn't developed in an armchair. It was developed by two people (not me just to be clear) who have spent a great deal of time ACTUALLY LOOKING AT BATTERY BEHAVIOR. If you have similar data to contribute it would be welcome.
4) The only way to find out is if people correlate the predictions it makes with what happens in practice. The very essence of a rule of thumb is that it gives useful predictions of behaviour without needing a detailed analysis of the underlying phenomena. Much of what we take for granted in our lives was developed that way - sometimes giving it an air of precision by calling it a "Factor of Safety".
5) This thread was an attempt to start that process of discussion and debate. I think it was a case fairly put and described and so far what have we had - a bunch of the usual nitpicking questions from you and microwave "Why not this, why not that?" and a stupid discussion about how to write Celcius temperatures - which was an entirely sensible point by HarryD and promptly addressed.
6) So here's a suggestion about how to return to the armchair discussion which you so clearly love.

Go start your own thread entitled "Problems and Issues with the proposed LiPo performance tool."

I will be happy to contribute positively and it may well turn out to be really important.
Quote:
Originally Posted by LeszekJ View Post
Returning to the armchair discussion which some of us dislike so much...

How do you understand "performance"? If you automatically think about "punch" or "climb rate" I'm with you at the moment.
Cell power loss = 6*capacity is not a straight performance indicator. Of course, it may help to protect battery from overloading and resulting overheating. It is also very important, I know by experience.
However simple limit of voltage drop is much better as an index of performance.
For instance: max amps = 268.3mV / Ri
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Old Jan 26, 2012, 07:36 PM
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Quote:
Originally Posted by jj604 View Post
5) This thread was an attempt to start that process of discussion and debate.
Now I'm really wondering what "discussion and debate" mean in your language.
Praises?
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Old Jan 26, 2012, 07:43 PM
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You're not helping your cause here. Many of your questions do not appear to be motivated by genuine interest and desire to foster collaborative improvement to the hobby. I suspect that this assessment is more common than not. Time will serve as the truth. I hope this assessment is incorrect.

Mark
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Old Jan 26, 2012, 11:35 PM
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Last statement is bold in first post

Quote:
Please put any discussion and comments here in this thread not the reference site. A reference thread is only useful if it is easy to find things and comments and discussion make that impossible.
Perhaps it should be clearly stated that only discussions of this new rating system merits to be discussed and / or only your experience with such ratings.

Honestly I am not sure I even fully understand myself.

From the other thread
Quote:
The Performance Calculation Tool has been demonstrated to be valid if the cell IR is measured:

1) After 1 hour minimum rest to stabilize charge and pack temperature (or at 1C max charge rate if using FMA charger).

2) At measurement temperature of 72F (22C).

3) Using a reliable IR measurement method. The ESR/IR meter was used for the verification of the method, and it has also been checked with an iCharger 3010B, 306B, and FMA Powerlab PL8.

Which to me sounds like ,we know this works great and our 12C obtained by our means rating of a vendors 40C LiPoly is correct and we just want you to confirm our findings.



Charles
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Old Jan 26, 2012, 11:55 PM
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Yes, you do understand Charles.

There is a very clear difference between a legitimate query motivated by a desire to promote the hobby and contribute to the knowledge base and an obviously considered but thinly-veiled attempt at self-promotion and ego aggrandizement. John and others are merely attempting to steer the discussion toward the former. I consider this to be a noble pursuit.

Mark
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Old Jan 28, 2012, 08:50 AM
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Correlation between measured ESR and discharge graphs

Posted below are measured IR data of my most-used packs (taken two weeks ago) and discharge graphs of the same packs (taken late last night).

Before any data was taken, all packs were connected in parallel and allowed to soak at the same temperature for an extended period of time. I allowed 8 hours to elapse prior to taking the discharge data last night to ensure that all packs were starting from the exact same point (voltage potential and temperature).

I have not had the opportunity to study the data in great detail as yet but it certainly appears as though the internal resistance measurements are a very solid indicator of actual performance for this particular sampling of lipoly packs.

Mark
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Old Jan 28, 2012, 11:05 AM
The 6 P principle works for me
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I am just a small fish in this ocean however, the stated concept appeals to me and seems both practical and accurate.

Question, is there a list of "good" equipment (IR testors or chargers that can also test IR) that those of us that have an interest in this might look to purchase?

Michael (if your not fryin, your not tryin!)
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Old Jan 28, 2012, 03:40 PM
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Great question Michael.

Yes, there are a few chargers that have been determined to be able to produce quite accurate and repeatable internal resistance measurements. As John noted in post #2 of this thread, the iCharger line of chargers as well as the FMA CellPro chargers have demonstrated through quite a bit of testing to be excellent at measuring individual cell internal resistance. I personally use an iCharger 306B and have found the data that I gain from it to be a perfect replication of real world performance. Others have similar experience with the data that they have gained from FMA chargers.

In addition to the iCharger and FMA chargers, Wayne Giles makes a dedicated ESR meter that is exceptionally accurate and has higher resolution than either of the two aforementioned charger brands. The higher resolution is helpful when pack capacity is above about 2500mAh. A thread on Wayne's device can be found here: http://www.rcgroups.com/forums/showthread.php?t=1323465.

As you can probably tell by my above posts, I do have discharge equipment that is capable of graphing pack performance. I must say that my equipment gets very little use now since I have empirically determined that the IR data tells me all I need to know about how a lipoly will perform, is much faster to obtain, and does not take any cycle life out of my lipolys.

Mark
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Old Jan 28, 2012, 03:55 PM
ancora imparo
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Michael, I did a fairly comprehensive set of tests with an FMA PL8, iCharger 3020i, Hyperion SuperDuo3 and the ESR/IR meter (there is a separate thread on the meter if you want to know about it here http://www.rcgroups.com/forums/showt...ghlight=esr+ir)

In general I was satisfied that all four gave consistent IR results over a range of tests. The SuperDuo gives very similar results on Charge or Discharge while the PL8 only does IR on Charge. The iCharger measures IR by loading the battery similar to the ESR meter.

They all use different methods and times of measurement and I evaluated this using an oscilloscope and information from the manufacturers.

I came to the conclusion that the ESR meter, PL8 and iCharger3010 gave sufficiently similar readings for the batteries I tested. Mark has done comparison work with his own ESR meter and a different iCharger and may want to post his findings. The SuperDuo seems to give significantly lower readings, despite being a pack-only not cell-measuring device, but I found some inconsistency between different battery sizes that I have not further investigated. For the moment I am not recommending the Hyperion chargers for use with the calculator. This NOT a criticism of the charger by the way.

I did not want to load up the thread with detailed charger info early on as from previous experience I know there are people out there that will jump on it as an excuse to get into a detailed discussion of their favourite charger and why it is better.

The whole purpose of this thread was to see if we can get some good feedback and comments to show if the method actually works for others in practice.

That is, is this crude rule of thumb a practical solution to the C rating nonsense for ordinary folks? It may be that we have just been “lucky” and that the batteries we have tested all happen to work and others won’t. I doubt it but the question is certainly important. That is why this thread was set up and I was hoping we might see some useful contributions from people who actually have credibility in testing and using batteries under carefully controlled conditions. Hence my annoyance with the armchair theorists. I could raise many theoretical objections to this method in an instant. That’s taken as given. Whether they are important or not can only be proven by data and results. That’s how experimental science works.

Here are some typical findings on two battery sizes that I think are typical of what the average park flier might use. They were of batteries purchased at the same time, only a few months old, and with similar unstressed histories. They show that the three methods give different values for IR but that they are fairly close.

Good enough for a simple tool – not what you want if you expect exact results and precise comparisons. I am well aware that we could argue the principles and assumptions for ever but the whole thrust of the calculator was to provide a useful assistant, not prove a scientific point.

Mark and Wayne have done much more extensive testing using this simple calculator than I and have come to the conclusion over the years that it works remarkably well for their batteries. What we need to know is whether it is generally true or there are some categories of battery or usage or environment (eg Temperature) where it simply doesn’t work.

Two identical Zippy 3S 1300mAh 20-30C rating.


Note the iCharger only reports IR to 1mOhm resolution.

Hope this is useful.

John
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Old Jan 28, 2012, 05:45 PM
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Why such a difference in Cum IR between mrforsyth 3S Gens ace and your 3S Zippy
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Old Jan 28, 2012, 05:48 PM
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Quote:
Originally Posted by jj604 View Post
Here are some typical findings on two battery sizes that I think are typical of what the average park flier might use.John
The Cum IR shown by mrforsyth for his 3S 25C rated lipo such as the Gens ace is considerably less at 15-16mOhm(5-6mOhm per cell) than that of your 20C-30C 3S Zippy at 45-51mOhm Cum IR. It might be helpful if you listed each individual cell's mOhm resistance as some packs may have one or more cells that are not within an accepted IR tolerance range for a continuous discharge rating (in this case 20C-30C).

So, is average Joe Parkflyer going to call HK or another hobby supplier of his favorite bargain brand to inform them that he has one of their packs that has one cell or all cells with an IR mOhm reading that is not within the tolerance range recommended by jj604 and others at rcgroups.
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