Jan 23, 2012, 12:54 AM
ancora imparo
Melbourne, Australia
Joined Jul 2005
7,958 Posts
Some "real life" results

Since the whole purpose of the calculator on Mark Forsyth’s post is to provide practical guidance rather than encourage armchair debate I thought I would try it out that way and see how it stacked up against some reliable independent findings.

Still on the theme of small batteries I contacted nitrocharged (also known as Team 30 EDF ) who is in my opinion Mr Micro-EDF and who probably has more experience wringing the best out of small batteries than anyone around. The micro (30-35mm) fan guys are pushing the envelope (for continuous powered flight) for max power/weight with motor rewinds, custom fans and the best cells they can find.

I asked him what current he pulls from the Thunder Power 325 mAH 65C cells which are his current choice. His response was “I pull around +8 amps continuous from them. Besides a throttle back on the turns, they deliver till the end. Even though they are quite warm after a flight if the weathers in the 20's, they are still rock hard with zero puffing so far. And that is in a closed lipo bay - no cooling”. (thanks, Nitro)

Given the intensity with which these guys fly, and their extensive experience, I think we can assume this is a good “practical” current limit for adequate performance and decent life.

So how does this compare with the predictions of the calculator? I tested a 2S and 3S Thunder Power G6 325mAh 65c and also a 2S Hyperion G3 320mAh 25C which I thought would be their closest top-end equivalent. All three batteries are less than 5 months old, have never been stressed and have less than 10 cycles on them.

I got the results shown in “Table” measured at 23°C after resting overnight at 21°-23°C from a full charge.

So the calculator is predicting a recommended maximum current for the TPs of 7.8A almost exactly what the micro EDF guys use.

I then tested these batteries to see how they performed at the recommended C rating (24C = 7.8A for the TPs and 14 = 4.5A for the Hyperion). I converted everything to cell voltage to make comparison easier.

Results are in the graph “Recommended”. Looks pretty good. All three track almost identically at the recommended currents although the Hyperion runs longer of course because it is at a lower current. Voltage stays at about 3.5 mid –run which is about as low as you would want.

I then pushed the current up by a third to see what happened. See “Two rates”. The TPs are still coping pretty well but the voltage is getting below where I would be happy. The Hyperion is really out of the race IMO at this current with a mid-run voltage of only 3.3V.

None of the batteries got really hot – they were pretty well ventilated unlike inside a small foam jet - but the Hyperion is showing the stress at the higher current. See “Temp Rise”.

Overall, I think the calculator gives a reliable indication of a sensible maximum current. And it also shows why these particular Thunder Power batteries are the top dog at the moment for small EDFs. A FOM of over 1.0 is remarkable for sub-400mAh cells.

John

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Last edited by jj604; Jan 23, 2012 at 04:51 PM.
Jan 23, 2012, 02:23 PM
Registered User
Rugby, UK
Joined Feb 2007
984 Posts
Quote:
 Originally Posted by Alan Hahn I applaud your effort, but one question I have is how are you going to define "C"? The only actual definition I have ever seen was off a Lipo "bible" on the old FMA site. I believe the definition was due to Kokam. Anyway the definition of "C" was the max current draw that would bring the total discharge down to some fraction of the total cell capacity(it was close to 100%, but I don't recall the exact %), and keep the pack (maybe cell) temperature less than ~140 degrees F. The assumption was anything above this temperature will damage the lipo. Other specs gave the ambient starting temperature, and the allowed (if any) air cooling Sorry I don't recall the numbers better, but I did go and look for it, but the info seems to be gone now. Presumably that is what "C" originally meant. Clearly it is related to the cell internal resistance, the temperature coefficient, and size of the cell. Also "damage" has a wide degree of interpretation---immediate damage, decreasing the # charge/discharge cycles......... So to be meaningful, I think you need to get a handle around what we actually mean by "C". Not too sure how you are going to do this, simply because some people expect hundreds of cycles, some seem to be happy with 60. To these people, "C" would have a completely different significance. Anyway, good luck!
Alan,
Hope John doesn't mind me jumping in here; I haven't asked him, but I think I understand what you are saying. We should really separate how the makers specify "C" ratings and how the modeller understands them.
The modeller is told and understands that the C number is the multiplier he can use to determine the max current he can take from his Lipo.
Various ways that makers specify it, and I have read several, all seem designed to avoid anything that can be measured by the user. Equally, they are irrelevant to any practical situation in the field.
The idea of the Mark's calculator is to produce realistic "C" number, as understood by the customer, that he can use to calculate the maximum sensible current he can take from his Lipo, at a reasonable efficiency and without unduly stressing the pack.
Experience has shown that just putting the IR and cell capacity into the calculator will give an answer which is surprisingly accurate over a wide range of lipos and capacities.
The few honest suppliers whose packs really meet the C ratings stated are losing out to the many suppliers who make such wild claims that are patently laughable.

Wayne
 Jan 23, 2012, 02:57 PM Team30 Micro EDF Adelaide, Australia Joined Apr 2004 11,300 Posts Nicely explained Wayne.
 Jan 23, 2012, 03:31 PM Bart Netherlands Joined Oct 2010 289 Posts John, what are you trying to do, don't mentioning the C rating of the hyperion is not very nice. > 2S Hyperion G3 320mAh which I thought would be the closest top-end equivalent How can you call this a equivalent it is a 25C and the TP is a 65C Why ????? DB,
Jan 23, 2012, 03:45 PM
ancora imparo
Melbourne, Australia
Joined Jul 2005
7,958 Posts
Thanks for spotting that oversight. I've added it in the text. It was clearly stated as a 25C in the table.

By "equivalent" I meant it is Hyperion's highest rated 320mAh cell. I thought that was obvious but perhaps I should have been a bit clearer.

I also have made it abundantly clear from the beginning this thread is not about comparing batteries but a tool to manage their use. The point about including the Hyperion was to show that it IS equivalent to the TP for voltage delivery if you use both at the current recommended by the calculator. The TP has a significantly higher C rating however (as you would expect from the label).

There are plenty of other threads where battery fans can slug it out.

John
Quote:
 Originally Posted by dirtyballs John, what are you trying to do, don't mentioning the C rating of the hyperion is not very nice. > 2S Hyperion G3 320mAh which I thought would be the closest top-end equivalent How can you call this a equivalent it is a 25C and the TP is a 65C Why ????? DB,
 Jan 23, 2012, 03:53 PM Since 1952 Canada, AB, Edmonton Joined Oct 2004 1,430 Posts If I may be permitted to nitpick a bit: it would be a Good Thing to distinguish between C (the temperature) and C (the battery parameter). It can get a bit confusing to see things like "25C at 14C". For those who may not know, to enter the degree symbol (°), hold down the key and type 0176 on the numeric keypad. So we get: 25°C at 14C. Or is it 25C at 14°C? I'm following all this good stuff with interest. Thanks, guys. I hope to be able to make some kind of useful contribution, in due course.
Jan 23, 2012, 04:30 PM
ancora imparo
Melbourne, Australia
Joined Jul 2005
7,958 Posts
Thanks, Harry. Good point. I will update in the text and temperature graph. I normally avoid special symbols in emails and the like because of the dumbing down that occurs at some gateways and the habit took over!
UPDATE: The ALTnnnn method doesn't work in the thread for two different keyboards for me. It changes windows and the like. You can get around it by creating the degree symbol in Wordpad with ALT0176 then pasting it in wherever you need it.

John
Quote:
 Originally Posted by Harry D If I may be permitted to nitpick a bit: it would be a Good Thing to distinguish between C (the temperature) and C (the battery parameter). It can get a bit confusing to see things like "25C at 14C". For those who may not know, to enter the degree symbol (°), hold down the key and type 0176 on the numeric keypad. So we get: 25°C at 14C. Or is it 25C at 14°C? I'm following all this good stuff with interest. Thanks, guys. I hope to be able to make some kind of useful contribution, in due course.
Last edited by jj604; Jan 23, 2012 at 04:49 PM.
Jan 23, 2012, 06:05 PM
Registered User
lac superieur - chemin le pointe croix
Joined Apr 2008
159 Posts
Quote:
 Originally Posted by everydayflyer Hard to convince many that proper care and feeding has an awful lot to do with the end results.
A quality charger in good condition and waiting until approx 90% SOC (4.1v) for balance charging is common sense.

Quote:
 Originally Posted by jj604 This is the “Simple LiPo Performance Tool” Discussion thread. This thread is an attempt to provide a forum to discuss an improved way for the average modeller to get a handle on LiPo (or lipoly) performance using a simplified “IR” derived maximum current figure – normally called the C rating - but one which reflects the performance of the battery in practice better than the one on the label.
Quality control, common sense, average and simple are all relative terms. What is "simple," and "common sense" to everydayflyer and jj604 may not be simple and common sense to the “average modeler” and vica versa.

One average modeller that believes he has good common sense may not even need to be all that concerned about minor IR discrepancies even in some of his relatively inexpensive LiPo packs; while another average modeller even without good common sense may not be all that concerned about minor IR discrepancies in some of his expensive LiPo packs. It's your word against the distributor (E-flite, TP, Gens ace, etc.) as to whether or not you mishandled or abused their LiPo pack or whether it was defective from the Get-Go. So there is a simple test any average modeller can do with any new LiPo pack to see if it is questionable from the Get-GO with a few conditioning cycles. Do you really think a supplier (E-flite, CSRC, TP, Gens ace or whatever) is going to refund your money because it is closer to 20C than its label rating of 25C. And how much discrepancy in actual to label C discharge rating before you would return it and expect them to send you another at the label C rating. That doesn't sound like what an "average modeller" would do, and I doubt whether even everydayflyer would want to get a reputation as a nitpickin pest.

If I was a LiPo manufacturer/distributor and knew that everydayflyer (Charles) had requested a few of my packs for some extensive IR C rated continuous discharge and burst testing I would certainly see that he didn't receive any below par packs(if possible) that were possibly overrated.
Last edited by microwave; Jan 23, 2012 at 07:16 PM.
Jan 25, 2012, 08:18 AM
Registered User
lac superieur - chemin le pointe croix
Joined Apr 2008
159 Posts
Quote:
 Originally Posted by everydayflyer Whould those who are very knowledgeable about such please explain the following to me? Perhaps I sould mention the Preset I am using is a custom one where no balancing takes place until 4.1V per cell. What I find most confusing is that my sample (yes could be a ringer but I highly doubt it) has been what I consider rather abused and still has IRs less than 1/2 of other's posted IRs. I have read post that SOC (state of charge) does not have much effect in cell IRs also have read that 10% difference between cells is normal . Is there a normal difference for same cells at difference states of charge?
Charles,

You, I and other average modellers might agree that there are slight cell IR differences and that is perhaps the primary reason why some of us don't balance charge until approx 90% into the SOC (on avg 4.1v per cell).

Have you ever noticed that there is a difference in the IR ("still has IRs less than 1/2 of other's posted IRs") when comparing charge rates of say, 1/2 C as compared to charging the same lipo at 2C or even 5C. One reason could be that any IR differences between cells is less noticeable at a charge rate of 1/2C compared to a higher charge rate as you sometimes use a charge rate of 5C with a LiPo that hasn't been mishandled or abused.

This might be something that jj604 and other average modellers might like to know ... Does the charge rate as well as the discharge rate influence the amount of IR? In other words does a continuous discharge rate of 15C result in a higher IR than a charge rate of 1/2C or even 5C OR are any differences in IR insignificant whether charging at 1/2C or 2C or discharging at 15C or 20C with a 25C LiPo that hasn't been mishandled or abused and is able to withstand a continuous discharge of 20C.
Last edited by microwave; Jan 25, 2012 at 08:28 AM.
 Jan 25, 2012, 08:57 AM Southern Pride Haralson County GA. USA Joined Oct 2004 34,852 Posts Wouldn't it be easier to just use F or Cel or some combo such as a Red C or a Red F. As the recomended IR testing range if 72Fn which is 22 C and I have never seen a LiPoly listed as having a 22C discharg rating are there any likely C discharge ratings which would match the C recommend range for taking IR reading?
 Jan 25, 2012, 09:57 AM Registered User lac superieur - chemin le pointe croix Joined Apr 2008 159 Posts Charles, It's your call whether your preference is Red F or Red C or both. Perhaps, you believe there may be a significant IR temp difference between a charge rate of 1/2C and 5C or you wouldn't have so posted. Your earlier posting query had to do with the IR during the SOC. I assumed your earlier post concern had more to do with IR during charging. So, being that you are now adding temperature into the equation during SOC you must feel it is an important factor worth considering in this thread. Where you live it can get uncomfortably warm so that may figure into the amount of IR when charging outside at a field. You, jj604, Wayne are certainly qualified to provide your expertise on this thread as to any significance that temperature plays (being you may believe that is a factor that needs to be considered) when charging at a higher charge rate under significant changes in temperature as well as flying. Most average modellers are possibly aware that IR temp at a charge rate of 1/2C is lower than a charge rate of 5C. Average modellers might all agree that there are slight cell IR differences and that is perhaps the primary reason why you and others don't balance charge until approx 90% into the SOC (on avg 4.1v per cell).
 Jan 25, 2012, 09:59 AM Registered User Poland Joined Nov 2010 462 Posts Would not be easier just to write degree or deg. before C or F for temperatures? Assuming that numeric keypad is always broken or turned-off
 Jan 25, 2012, 10:07 AM Registered User lac superieur - chemin le pointe croix Joined Apr 2008 159 Posts Agree! Why complicate matters any more than necessary. Not sure if Charles was serious or just adding a little humor with his Red F, Red C suggestion.
 Jan 25, 2012, 04:14 PM Team30 Micro EDF Adelaide, Australia Joined Apr 2004 11,300 Posts Before this thread derails on a trivial matter may I suggest a listing of specs? Temp = 23°C IR = 33mΩ Max amps = 8A True C = 24C
 Jan 26, 2012, 05:22 AM Team30 Micro EDF Adelaide, Australia Joined Apr 2004 11,300 Posts 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. It would be interesting to apply this tool to see what the Real C of the lipo is. Unfortunately, the lipo is only 15 bucks but shipping is 30 to me, so it won't be me testing it out.