Getting a grip on Lipo C ratings. It is insane.
10-07-2009, 04:13 PM
#46
Tech Adept
I used a 1-amp current regulator and digital meter that reads millivolts to measure voltage drop under modest regulated load, but the error of the meter in the millivolt range increases as the value goes toward zero.
10-07-2009, 04:35 PM
#47
Tech Adept
Sorry, I didn't elaborate. I was referring to the method of testing a cell with the intent of determining the discharge C-rate. You start with a low enough C rate discharge that you know the cell will pass, and then you keep ramping up from there until the cell fails (usually temp, voltage cutoff or capacity). For example, you would start somewhere around 10C and go up in 2C increments. You gotta start low. There are "20C" labeled cells that can't handle 15C.
"time of discharge was used to calculate a C-rating" - no I think you are confusing C-rating with capacity, which ROAR does record for every pack that it tests.
A. maximum pack temperature (what is the failure temperature?)
B. minimum pack voltage (what is the failure cutoff voltage?)
C. discharge time (failure time calculated from C rating and current C-rate)
Repeat this test in 2C increments until the pack goes into overtemperature, or hits the minimum cutoff voltage before reaching the rated discharge time.
This gives a process by which published C-rates would be valid comparables based on testing with the same temperature and cutoff voltage limits, no?
10-09-2009, 07:51 PM
#48
This is more to the point. "C" rating doesn't matter, voltage under load and punch/rip on the track does. While in general Higher C ratings indicate lower IR it doesn't guarantee better performance when racing rc cars that draw a fraction of the 40C the battery may be capable of.
After all this time using Lipo's you think someone would have done some good unbaised testing of the top brands, but no!
SMC say that their 6000 28C is a better performing battery than their 5200 40C in stock racing. What does that say about C ratings versus performance?
I have done discharge curves on quite a few different Lipo's and so far the Thunder Power/Fantom Pro Race 40C are the best. They are also the most highly regarded batteries on the track.
After all this time using Lipo's you think someone would have done some good unbaised testing of the top brands, but no!
SMC say that their 6000 28C is a better performing battery than their 5200 40C in stock racing. What does that say about C ratings versus performance?
I have done discharge curves on quite a few different Lipo's and so far the Thunder Power/Fantom Pro Race 40C are the best. They are also the most highly regarded batteries on the track.
i wish rctvlive would get off their butts and do one finally.
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