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Old Jan 28, 2012, 07:31 PM
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Originally Posted by microwave View Post

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.
Not the point. As I understand it, the OP is about a methodology and perhaps tools for qualitatively assessing battery performance/potential. In other words, regardless of being new, old or used, I am able to determine the condition of the battery. Besides, I am not aware of any LiPo mfgr/seller that lists an expected IR for their batteries.

Michael (if your not fryin, your not tryin!)
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Old Jan 28, 2012, 07:33 PM
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Originally Posted by microwave View Post
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.
I know I would, and have.

I restrict my >1000mAh lipoly purchases to US domestic sources that have a solid reputation and return policy. My standard practice immediately upon receipt of a new lipoly is to perform individual cell voltage and internal resistance checks. If all is good, I install a connector, perform break-in cycling, and then place the lipoly into service. If I spot a problem, I contact the supplier and work it out.

One such story - About 16 months ago I received a new lipoly from a US domestic source and did my usual testing and found two cells that had dramatically higher internal resistance than the third cell and much higher than I expected. Knowing the lipoly could not improve to an acceptable level, I contacted the supplier and he sent a replacement the same day. Needless to say, I have sent a LOT of referrals his way.

When dealing with disreputable or foreign suppliers, you obviously have little recourse and more hoops to jump through. But you get super cheap lipos so pick your poison.

Mark
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Old Jan 28, 2012, 07:41 PM
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Originally Posted by elecfryer View Post
Not the point. As I understand it, the OP is about a methodology and perhaps tools for qualitatively assessing battery performance/potential. In other words, regardless of being new, old or used, I am able to determine the condition of the battery. Besides, I am not aware of any LiPo mfgr/seller that lists an expected IR for their batteries.

Michael (if your not fryin, your not tryin!)
You got it exactly right Michael. Objective internal resistance measurements along with the performance calculation formula are a simple means to effectively understand and manage your lipoly investment for maximum long term performance and get the most 'bang for your buck'.

Incidentally, Hyperion used to list internal resistance measurements on their datasheets for their G3 lipolys when they were introduced several years ago. They have since removed this information.

I'm hoping that internal resistance data will one day become standard for all manufacturers as it is extremely simple to assess and causes zero wear and tear on a lipoly. However, most of the shifty lipoly manufacturers will resist an objective measurement method that can be verified by the consumer as it takes away their most effective marketing tool - the horrible 'C' rating.

Mark
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Old Jan 29, 2012, 12:45 AM
ancora imparo
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Not to pursue this too far but the obvious answer is that this particular Zippy pack size are not very good batteries. And no, I'm not making a statement about Zippys in general.

Obviously if one cell was way out of range compared with the other two that would be important but I wouldn't use such results to make the answer to the poster which was about what chargers and other devices were recommended, not batteries. For the same reason I only showed relevant summary results but your point is a good one. However, the post clearly stated there were TWO batteries in each test and that should have made clear there was not a "bad cell" effect I would think.

Just for the record here are the individual cell measurements as requested. They show the sort of variation I might expect from these low cost batteries.

John
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Why such a difference in Cum IR between mrforsyth 3S Gens ace and your 3S Zippy
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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).
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Old Jan 29, 2012, 07:06 AM
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Not to pursue this too far but the obvious answer is that this particular Zippy pack size are not very good batteries. And no, I'm not making a statement about Zippys in general.

Obviously if one cell was way out of range compared with the other two that would be important but I wouldn't use such results to make the answer to the poster which was about what chargers and other devices were recommended, not batteries. For the same reason I only showed relevant summary results but your point is a good one. However, the post clearly stated there were TWO batteries in each test and that should have made clear there was not a "bad cell" effect I would think.


John
John's looks like another case of the lottery of buying Lipos.
I bought two 2200 25C nanotechs which were very high cell IR; average of 9.2mohm, and ran them through a set of controlled discharges. They were OK at 15C but obviously overstressed at 20C and quite incapable of 25C. Other testers have quoted much lower IR figures, so that I obviously had two (not a single pack) from a poor batch. Looking back at it I came to the conclusion that they were only capable of 15 -18C as a practical max rating.

See: http://www.rcgroups.com/forums/showthread.php?t=1406364

I have just put the IR figures into Mark's Calculator and it comes up with a real C rating of 17.2. QED. I noted at the time that having measured the IR that I did not expect the pack to be capable of their claimed C rating.

This demonstrates the lipo buying lottery and also that the calculator is a realistic and practical tool that anyone can use to forecast a real C rating.

Mark and John have put a lot of work into this for all the right reasons and yet the usual armchair critics jump in with their obviously destructively intentioned postings aimed at derailing the efforts of other people.
Their problems look suspiciously like a case of the "Not Invented Here" syndome

I do wish that imagined "experts" would avoid sniping when genuine people are trying to offer helpful and properly thought out information.

Wayne
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Old Jan 29, 2012, 11:42 PM
ancora imparo
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Wayne, actually I went back and looked at the numbers in question and would have to say that while I agree about the lottery comments, on this occasion it is probably not the reason and I was too quick with the "obvious" answer.

Microwave was quoting the IR numbers for the 1300mAh Zippy but of course it was the 2200mAh figures that are relevant as that was the size of the Gens Ace that Mark tested. Microwave was asking why the IR of two totally different sized batteries were different. Of course the smaller ones are likely to have a higher IR.

"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"

Mark got 15 and 16 mOhm for the Gens Ace, I had a range of 11-13 mOhm for the various methods on the same size Zippys.

This is not a significant difference and would easily be accounted for by a temperature difference even if both brands had identical IR (which they wouldn't necessarily in any case).. The numbers I quoted were all taken at the same temperature but not necessarily at 73F. From memory it was a fairly warm day and the temperature was a bit higher.


John
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Old Jan 30, 2012, 07:36 AM
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Microwave was asking why the IR of two totally different sized batteries were different. Of course the smaller ones are likely to have a higher IR.
Unless thhere are some really serious problems.

To make it simplier for some to understand perhaps when you parallel two identical LiPolys you double the capacity and half the IR.

Two each 2200s with cell IR of say 5 will become a 4400 with an IR of 2.5.
Capacity is not the only thing that cause IR to change however . That is just because brand X 's 2200 has 5 mOhm IR does not mean their 4400 wil be 2.5 or that their 1100 will be 10 mOhms.

Often modelers make LiPoly choices based on the performance of one size of a brand's LiPoly and often this leads to disapointment. 2200 mAh is a very popular size and is often used as a test standard and sometimes it provides a semi relevant comparison bases but often it does not. Size of the cells as in length,width,thickness,number of layers,type of constuction (how layers are formed) etc. can all come into play.


jj604
You should know without having to be told but if you feel any of my post / comment are distracting from this threads purpose I will happily delete same.

Mark same goes for you.
Charles
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Old Jan 30, 2012, 06:46 PM
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Thanks, Charles.

Another more subtle problem that arises from what you identify is that manufacturers will bring out a range of batteries and label them accordingly. This is perfectly reasonable and reputable suppliers like Thunderpower and Hyperion will have their "65C" or "25C" series which are honestly described for most sizes. What gets overlooked is that the very small batteries in the range sometimes don't have the current capability you would infer from the C rating and capacity. It's a case of one label does not fit all sizes.

Charles, you know your vast experience and wealth of knowledge on the practical use of batteries is exactly the sort of input that we want in this thread. I have tried as straightforwardly as possible to make it clear I would welcome discussion and comment on how well the approach seems to work in practice. This is a rule-of-thumb method that seems sensible in principle and seems to have been verified as reliable over a long time by respected people. The question is how well it correlates in practice over a wider range of users and batteries.

The whole intent was to see if it is a method that would help the modeler who, unless they have good knowledge of testing methods and the interest to do that, has to rely on what are patently unreliable manufacturer specifications.

What I hope will not happen is that we get sidelined by an armchair discussion on the variables and possible mechanisms. Interesting in itself but distracting and eventually destructive to the whole enterprise and I have suggested to those who like that sort of thing they start a separate thread on it. That suggestion was not of course applicable to someone who spends much of their time in providing just the practical test results that are so valuable.

One thing we do need to bear in mind however. Given the very great dependence on temperature of the IR measurements, Mark's emphasis on a standard measurement temperature is critical. Some of the numbers I have quoted in the earlier post comparing different methods were not taken at 72F. Did not matter for that comparison since they were raw IR numbers and all at the same temperature, but would not be valid if I was quoting results from the calculator.

John


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Originally Posted by everydayflyer View Post
Unless thhere are some really serious problems.

To make it simplier for some to understand perhaps when you parallel two identical LiPolys you double the capacity and half the IR.

Two each 2200s with cell IR of say 5 will become a 4400 with an IR of 2.5.
Capacity is not the only thing that cause IR to change however . That is just because brand X 's 2200 has 5 mOhm IR does not mean their 4400 wil be 2.5 or that their 1100 will be 10 mOhms.

Often modelers make LiPoly choices based on the performance of one size of a brand's LiPoly and often this leads to disapointment. 2200 mAh is a very popular size and is often used as a test standard and sometimes it provides a semi relevant comparison bases but often it does not. Size of the cells as in length,width,thickness,number of layers,type of constuction (how layers are formed) etc. can all come into play.


jj604
You should know without having to be told but if you feel any of my post / comment are distracting from this threads purpose I will happily delete same.

Mark same goes for you.
Charles
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Old Feb 01, 2012, 04:32 PM
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I bought two 2200 25C nanotechs which were very high cell IR; average of 9.2mohm, and ran them through a set of controlled discharges. They were OK at 15C but obviously overstressed at 20C and quite incapable of 25C. Looking back at it I came to the conclusion that they were only capable of 15 -18C as a practical max rating.Wayne
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Originally Posted by jj604 View Post
Mark got 15 and 16 mOhm for the Gens Ace, I had a range of 11-13 mOhm for the various methods on the same size Zippys.
This is not a significant difference and would easily be accounted for by a temperature difference even if both brands had identical IR (which they wouldn't necessarily in any case).. The numbers I quoted were all taken at the same temperature but not necessarily at 73F. From memory it was a fairly warm day and the temperature was a bit higher. John
The Gens ace were rated at 25C, while those Zippys were rated at 40C. Wayne considers 27.6mOhm Cum IR very high for his 2200 25C nanotech. It would seem 11-12.88mOhm is superior to the Gens ace at 15-16mOhms, but in reality aren’t there are other factors that determine the overall quality of a LiPo pack. According to Wayne a Cum IR of 27.6mOhm (9.2/cell) is only capable of a 15-18C rating. So, do we know for sure that a Zippy with a Cum IR of 12mOhm is capable of a sustaining higher continuous discharge rating than a Gens ace with a Cum IR of 15.5mOhm over the same number of performance cycles assuming identical care and discharge conditions.

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Originally Posted by everydayflyer View Post
To make it simplier for some to understand perhaps when you parallel two identical LiPolys you double the capacity and half the IR.
Two each 2200s with cell IR of say 5 will become a 4400 with an IR of 2.5.
Capacity is not the only thing that cause IR to change however . That is just because brand X 's 2200 has 5 mOhm IR does not mean their 4400 wil be 2.5 or that their 1100 will be 10 mOhms.
Often modelers make LiPoly choices based on the performance of one size of a brand's LiPoly and often this leads to disapointment. 2200 mAh is a very popular size and is often used as a test standard and sometimes it provides a semi relevant comparison bases but often it does not. Size of the cells as in length,width,thickness,number of layers,type of constuction (how layers are formed) etc. can all come into play. Charles
So, you call a supplier and tell him your pack(s) aren’t up to snuff. Isn’t the bottomline that you get what you pay and not to expect a bargain brand to actually have a continuous discharge rating as high as listed on the label. Also, as Charles eludes there are other variables so a supplier may just try to snow you. Which we haven’t seen much of so far this winter.
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Old Feb 01, 2012, 11:07 PM
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There is any relation between cell IR and possible maximum charge rate?
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Old Feb 02, 2012, 07:45 AM
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Yes.


Sorry I just realized I should not have answered that as this thread is about relative discharge performance not charging.
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Old Feb 02, 2012, 12:21 PM
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Originally Posted by everydayflyer View Post
Yes.


Sorry I just realized I should not have answered that as this thread is about relative discharge performance not charging.
Charles,

I saw Vlad's question this morning and thought "I will pass on what little information I have tonight and refer him to Charles"
Come in this evening and you have already scrubbed it; I don't think John is that particular about being slightly off - topic and I think it is relevant.

My little bit of info is that a Lipo retailer has been told by a producer that although their lipos are rated at 5C charging rate, they can in fact be charged at 10C without damage. The purveyor of this info was a technical marketing man rather than an engineer so that must qualify it a bit, but not necessarily disqualify it.
Obviously there must be a connection in that the IR affects the amount of heat generated by charging although the stress is nowhere near that of a discharge.
Now wondering what you said???

Wayne
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Old Feb 02, 2012, 01:49 PM
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Originally Posted by Wayne Giles View Post
... a Lipo retailer has been told by a producer that although their lipos are rated at 5C charging rate, they can in fact be charged at 10C without damage. The purveyor of this info was a technical marketing man rather than an engineer so that must qualify it a bit, but not necessarily disqualify it. Wayne
Is it not TRUE that charging at 10C as opposed to 5C or even 1C will possibly diminish the number of performance cycles? So, the tradeoff seems to be which is more important to the average parkflyer: (1) Not getting the optimum performance cycles from a less expensive pack(than say TP) or (2) Being able to recharge as quickly as possible at 10C with practically none or insufficient resting period between discharge and recharging. Would it not be to a suppliers advantage to suggest a 10C charge without immediate damage if it means he sells more LiPos as the actual number of performance cycles is diminished.

OK, back to discharge topic ....

So, we know with some reliance that John’s 3S 2200mAh 40C Zippy #1 with an avg. Cum IR of 11.44mOhm is capable of sustaining a higher continuous discharge rating than Mark’s 3S 2200mAh 25C Gens ace #1 with a Cum IR of 15.00mOhm over the same number of performance cycles assuming identical care and a more appropriate discharge rate of each pack based on their extensive testing recommendation as to a more realistic continuous discharge C rating. The Zippy should stand up just as well as the Gens ace and vica versa, but there is no certainty because of other factor variables.

An average parkflyer following this thread so far (as well as a LiPo supplier) could conclude that even if this particular 40C Zippy #1 were continuously discharged at its more appropriate discharge rating that it’s still possible that this particular Gens ace #1 continuously discharged similarily at its more appropriate discharge rating may still outlive the Zippy.

Conversely it’s possible, that John’s Zippy #2 could outlive Mark’s Gens ace #2 assuming identical care and appropriate discharge rates for the Gens ace #2 and the Zippy #2. As Charles has eluded there are other factors and variables that could be brought into play by a supplier to confuse an average parkflyer that calls to complain that two of his relatively new packs actually have a much higher IR that results in a continuous discharge rating around 15C-18C instead of the manufacturers label rating of 25C.

One factor possibly favoring Mark’s Gens ace #1 is its equally matched cell IRs of 5.0mOhm; whereas, we don’t know if John’s Zippy #1 (Cum IR range of 11.00mOhm to 11.68mOhm) has equally matched cell IRs, or instead could have avg. cell IRs of say, 3.70mOhm, 4.10mOhm, 3.64mOhm. This disparity could become even more noticeable with successive continuous discharge performance cycle bench testing (after 10 performance cycles, after 25 cycles, after 50 cycles and after 100 performance cycles assuming they both live that long). This is all assuming the bench testing is under the same conditions, temperature, discharging method, rest period before recharging, identical charging rate, identical equipment, etc, etc, etc to eliminate as many variables as possible.
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Old Feb 02, 2012, 01:56 PM
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A post of mine this morning along these lines.

http://www.rcgroups.com/forums/showp...43&postcount=8

I have often observed that even during a 5C charge right after a discharge which takes cells to between 120 and 140F that the cells continue to cool down nearly as fast as they would if not being charged.

I have asked some manufactures for test data which supports their advise to always let cells cool to <100F before charging but non have ever supplied such.

Most LiPoly cells are not designed for our use and some just happen to work for us but no manufactur is going to spend tens of thousands of dollars doing suitable of use test for us.

Charles
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Old Feb 02, 2012, 02:36 PM
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LiPolys are very complex little critters and most who use them just want their RC craft to perform and really do not care to understand what is going on or why. The debates over all Lipolys being the same is a no win one much the same as trying to explain why there are at least three different mechanical ways the layers in LiPolys are formed. Charles
AMEN!

So, there is the possibility that not even John, Mark or Wayne will reply to my back to the discharge further relevant topic thread discussion as there are other variables to consider that are possibly beyond the time restraints and interest of your average parkflyer. It may just be too technical with too many variables for an average parkflyer to even take the time to attempt to deterimine what may be a more realistic continuous discharge rating than that shown on the pack label.

What percent of average parkflyers even take the time to condition cycle their new LiPolys with some basic bench testing under more ideal conditions to eliminate as many variables as possible to arrive to the point of using a simple tool to calculate a more realistic continuous discharge rating based on the pack's Cum IR of their new less expensive bargain pack?
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