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Thread: ===Understanding C ratings===

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Old 10-20-2010, 12:59 PM   #1
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Default ===Understanding C ratings===

So, as of late, we have noticed that ALOT of manufacturers lipos are not holding up to their ratings. It kind of depresses me to see all the lieing. No matter if it is a well known brand, cheap ebay pack, or something from hobby king, seems like alot of todays lipos are severely over rated.


Lately I have seen ratings at 50C, 60C, and even "True 150C". Ratings we have seen first hand in most cases, that are FAR from the truth.



What made me want to post is seeing a well known brand advertise a 6500mah pack @ 150C. This would mean by industry standard, that the pack should be able to take a 975amp load, still retain about 3.4-3.7 volts per cell, AND get 6500mah of runtime.

I have problems with this...

A: Solder begins to un-solder it self @ about 200 amps.
B: No one else in the industry, even claims more than 100amps BURST. And that is with their over rated ratings.
C: This brand shows no proof of this rating.
D: We tested this brand's packs. Their pack didn't even hardly qualify as a 10C cell, but it was rated as a 50C. So how is it they cant get a 50C right, but just straight to 150C? 10C is only 20% of it's ratings. So with that, my educated guess is that this pack is probably only a 30C, which is 20% of 150.

I would love for this brand to prove this, or send a pack to me to test. Because if this IS true... I want. That is some massive power.


The above mentioned brand, does not believe in C ratings because they say that no one will ever use the packs at those loads(guess they haven't raced electric boats) which is 99% true. But this is the only way to test everything across the board the same way under the same conditions. That is no different than saying a Dyno is pointless to rate horse power, because someone will never use all the horse power.

Personally I feel there should be regulations with these ratings for all battery manufacturers. This is simply lieing. There is no other word for it. You are paying for something you will not get. It is wrong.


I will let you guys decide what's fair. I am not here to pick on anyone. Perhaps the above brand has no way of testing, and are taking the factories word for it. I don't know. Either way, lieing is lieing.



So just so those that care, and read this post understand, I am going to briefly explain the C ratings.


C rating:

C is a rating at which your battery can be discharged safely. The higher C the more amps(higher load) the pack can handle.


Example:


1000mah(1 amp hour) pack rated at 20C = 20amps constant. 1 amp hour x 20 = 20 amps.

1500mah(1.5 amp hour) pack rated at 20C = 30 amps constant. 1.5 amp hour x 20 = 30 amps.


How this is tested and what to expect.

The way of testing is pretty simple. You just apply a constant load to a lose lipo cell, and record it's voltage, and how long it runs(runtime/mah). The pack should get at or above 3.4v, at it's constant C rating, and get to within 95% of it's rated mah. Below is a good graph as an example. You can see, as the load(amps) increase, the voltage drops. That is normal. But the capacity(mah) is always really close.




Let me know if you guys have any questions. I would be glad to answer them



Last edited by Chris_The_Battery_Man; 10-20-2010 at 02:05 PM.
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Old 10-20-2010, 01:45 PM   #2
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If it's a 35C 1300mah pack shouldn't you post numbers at the rating it's rated for? 45amps? I see the loose cell was done but it doesn't stay above 3.5V like it's supposed to and when it's in a pack it will drop even more... I don't want to start anything but I'm wondering why yours are rated higher as well?

On a side note I run Hyperion batteries and when they kick the bucket I will be buying some from you after seeing the other graphs you have posted. You have some impressive batteries!
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Old 10-20-2010, 02:08 PM   #3
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I mis-typed. 3.4v is the lowest that it should be. Although I like to see above 3.5 personally. We could say 45amps, but it is just redundant.

The Elite is rated as it is. 1.3 amp hour x 35c = 45.5 amps. We can not do .5 amp increments. So that's why we did 45 amps. Elite is a brand. Not our brand. We are testing their ratings.
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Old 10-20-2010, 02:19 PM   #4
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Ya I know they are a brand but you carry them so I just referred to them as yours lol. Thanks for clearing that up... some typo's bite ya in the ass later lol. So at what point can it start to drop below 3.4V to be acceptable? I also notice at 45 amps the MAh only goes to about 1150 but rated for 1300. Is that within reason? Curious how tight the tolerances are on rating it? Just really trying to learn about a true C rating... I have people hear ask me all the time! Thanks Chris I really enjoy learning about batteries and how they are rated!
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Old 10-20-2010, 03:11 PM   #5
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Well, I don't think it is really a problem to drop that low, but it is more of a performance thing. 1150mah is not really abnormal. Generally, if a pack is over rated, it will tend to get little to no capacity at all at higher loads.


Myself... I like to see at or above the mah rating. But the cells tested to about 1250, so 1150 is not far off for such a high load. That is all within normal expectations as per the norm in this industry. Not to mention we did not heat the cells up when we tested them. That is probably a little to do with it. They tested very well, so we neglected to heat them to aprox. 120 degrees where they like to be. They were in the cold basement @ about 60 degrees, which will hinder some performance.
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Old 10-20-2010, 03:15 PM   #6
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Very interesting! Thanks! What are the odds of showing a graph of warm cells next to cold cells? I'd be curious how much they pick up. And a 3s pack at 45 amps?

Last edited by PipeDreams; 10-20-2010 at 03:19 PM.
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Old 10-20-2010, 03:23 PM   #7
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Well, the pack test is not something I can do at the moment as we are out. I used a pack a buddy bought to do the test. But I can have Mike warm the cell and try it again @ 45 amps.
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Old 10-20-2010, 03:37 PM   #8
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OH ya that would be awesome... how long does a test last... or should I say take?
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Old 10-20-2010, 04:03 PM   #9
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Well, a charge, then about a couple minutes for a test. But It's a matter of finding time to do it
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Old 10-20-2010, 04:07 PM   #10
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Cool.. no worries... Just curious how long it can hold discharging at 45 amps for? I can't imagine very long
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Old 10-29-2010, 11:24 AM   #11
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http://www.rccrawler.com/forum/showt...38#post2712438
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Old 10-29-2010, 03:13 PM   #12
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AWESOME! thanks for the graph! I'll be buying some batteries for sure from you next time! I like the honesty!
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Old 10-31-2010, 03:59 PM   #13
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I'm running the Elite 850mah and 1000mah 11.1v packs, and like I've said for a couple years now, Elite has some of the best cells available currently.
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