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Jun 09, 2014, 11:09 AM
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How do Manufacturers find out 'C rate' for charge and discharge?


Hi All!

I was hoping your would be able to help me out, I understand the principles behind C rates for charge and discharge and how that equates to amperage.

I am trying to find out how the manufacturers get the C Rate for both charging and discharging, are they measuring internal resistance? are they looking for a delta temperature change? the impact on Cycle Life?

I cannot find a single standard or paper that explains how manufacturers come up with their figures.

If anyone has any ideas or documents that would be great,

My business is dabbling in external batteries and I am looking to charge A123 26650 cells at their highest rate, I know that it says the C rate on the datasheet but I want to know what the manufacturer looks for when testing these cells.

Thanks Again!

Leigh.
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Jun 09, 2014, 11:36 AM
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How do Manufacturers find out 'C rate' for charge and discharge?


Sadly, most rely on their marketing departments rather than their engineering departments to establish 'C' rating.

There are a few exceptions. Notably, SMC and Progressive RC. SMC publishes max current that is based upon internal resistance and Progressive RC publishes IR for most of their packs.

Most other vendors seemingly yank a number out of thin air and hope that the modeler is none the wiser. Larger 'C' ratings allow the vendors to charge more $$ and also sell in larger quantities. It's a win-win for lipoly peddlers!!!

It's for this very reason that John, Wayne, and myself developed this and this.

Mark
Last edited by mrforsyth; Jun 09, 2014 at 11:42 AM.
Jun 09, 2014, 12:42 PM
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Quote:
Originally Posted by mrforsyth
Sadly, most rely on their marketing departments rather than their engineering departments to establish 'C' rating.

There are a few exceptions. Notably, SMC and Progressive RC. SMC publishes max current that is based upon internal resistance and Progressive RC publishes IR for most of their packs.

Most other vendors seemingly yank a number out of thin air and hope that the modeler is none the wiser. Larger 'C' ratings allow the vendors to charge more $$ and also sell in larger quantities. It's a win-win for lipoly peddlers!!!

It's for this very reason that John, Wayne, and myself developed this and this.

Mark
Thanks for that Mark,

Just having a quick look it and it must have taken you all ages to compile.

I am testing the A123 26650 cells at their maximum 4C rate (10amps) and these seem to be operating fine, the estimate is 3,000 cycles to 80% DOD

I am also testing some newer Sony VTC5, they have a claim of 4c charging at 10.4 amps and discharge of 30 amps.

I will be testing them for internal resistance with a FMA PL8 but I wanted to know what effects would there be if I increased the charge rate past the maximum? Would I notice an increase in internal resistance and temperature and a decrease in cycles?

I am looking to push as much power into the A123 as possible, if the main issue with charging at too high a current would be a decrease in cell life, could I put more amperage into it (say 15 amps) or 6C. What do I need to look out for? is there a risk of explosion or does the temperature just increase and I have to make sure it doesn't exceed deltaT?

Thanks

Leigh
Jun 09, 2014, 12:47 PM
Registered User
Leigh,

As it relates to A123 M1 2300mAh cells, Charles (Everydayflyer) is the resident expert and he'll hopefully add links to his extensive experience and testing. 6C charging is a cakewalk for these particular cells.

I have not personally seen any test results on the Sony cells as yet.

Mark
Jun 09, 2014, 12:52 PM
Southern Pride
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Post will my A123 links

https://www.rcgroups.com/forums/show...01&postcount=2


Some charge graphs here with aprox. 25A max and 13A average.

https://www.rcgroups.com/forums/showthread.php?t=747911

My reason for going to a Zip charge was charger of that era were limited to 10A max. I have charged a 3S A123 at 100 amps.once and it continued to function fine in my RC applications.s
Last edited by everydayflyer; Jun 09, 2014 at 09:28 PM.
Jun 10, 2014, 03:32 AM
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Quote:
Originally Posted by everydayflyer
Post will my A123 links

https://www.rcgroups.com/forums/show...01&postcount=2


Some charge graphs here with aprox. 25A max and 13A average.

https://www.rcgroups.com/forums/showthread.php?t=747911

My reason for going to a Zip charge was charger of that era were limited to 10A max. I have charged a 3S A123 at 100 amps.once and it continued to function fine in my RC applications.s

Thanks for that Charles,

There are some amazing results here, is there anything to look out for in the behaviour of the cell when pushing the limits of the charge/discharge cycle?

I wasn't sure is there would be a significant temperature increase or the IR would rise?

Thanks

Leigh
Jun 10, 2014, 07:51 AM
Space Coast USA
hoppy's Avatar
Temperature rise is everything. That's the limitation on how many amps the pack can deliver.
The higher the amp draw the higher the pack temperature will go, the degree depending on the cells IR.
Temps of interest-
Try to keep pack below 120F after a flight.
130F shorter cycle life.
>150F Pack can go into thermal runaway and burn.

https://www.electrochem.org/dl/inter...2_p037_044.pdf


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