LiPo C Ratings
11-15-2011, 05:11 PM
#1
LiPo C Ratings
Hey everybody. Just want to start a thread out and this one pertains to LiPo C ratings. As most of you already know, the C rating of a battery pack refers to the continuous discharge of that pack. Now, the burst rating of that pack could be extensively higher and it usually is depending on how much amp draw an esc can pull. Typical C ratings are around 25C-40C. With higher power LiPo batteries now, C ratings are hitting 70C and above. I was wandering if anyone one of you out there has or know of a battery managing system that can tell us how to monitor the C rating of a battery pack. Typically, I want to know that if I paid for a 70C 6000 mah battery pack that I am getting what I paid for it, and usually it isn't cheap.
11-15-2011, 05:19 PM
#2
Tech Master
iTrader: (3)
Generally speaking ratings above 40c or so are nothing more than marketing spin
Very few are tested correctly to perform at those sort of discharge ratings
The sort of test equipment required to discharge at hundreds of amps is very expensive
Many will swear that their expensive 100c pack outshines the run of the mill 20c pack, usually with little or no real data
If they are happy to fork out big bucks for a fancy sticker more fool them
The IR (Internal Resistance) is the best indicator of a cells quality for the end user
For info ...........
If a 60c pack was discharged at its full rated current the pack would be at LVC (assuming 20% left) in 48 seconds
Assume a 5000mah sized pack, you really think connectors can handle 300 amps ?
Cheers
Very few are tested correctly to perform at those sort of discharge ratings
The sort of test equipment required to discharge at hundreds of amps is very expensive
Many will swear that their expensive 100c pack outshines the run of the mill 20c pack, usually with little or no real data
If they are happy to fork out big bucks for a fancy sticker more fool them
The IR (Internal Resistance) is the best indicator of a cells quality for the end user
For info ...........
If a 60c pack was discharged at its full rated current the pack would be at LVC (assuming 20% left) in 48 seconds
Assume a 5000mah sized pack, you really think connectors can handle 300 amps ?
Cheers
Last edited by crusey_aus; 11-15-2011 at 05:36 PM.
11-15-2011, 05:28 PM
#3
....so which batteries have the lowest IR? Im up in the air between Thunder Power 5300mah 65C and Orion 6500 90C.
11-15-2011, 05:40 PM
#5
Crusey_Aus, that is exactly what I mean. The C ratings in my honest opinion is a marketing scheme. When we all were racing sub C cells, Competition Electronics and some of the higher end chargers gave us the info we needed. The industry could not cheat and you had each cells labeled with all the info. If anyone is in this hobby for a while, they soon realize that batteries and motors are what makes you win.
11-15-2011, 05:59 PM
#6
Tech Master
iTrader: (3)
I'm not a racer so dont care about possibly getting every last watt out of a system
Pretty sure drivers win racers though not batteries
Certainly is getting silly people spending hundreds on packs because they have a sticker on them that says is capable of a silly discharge rate
I bash my Slash 4x4 on 2s - 4s up to 70 mph with motors capable of bursting to 180 amps or so
Gensace 5000mah 40c packs work for me
Cheers
Pretty sure drivers win racers though not batteries
Certainly is getting silly people spending hundreds on packs because they have a sticker on them that says is capable of a silly discharge rate
I bash my Slash 4x4 on 2s - 4s up to 70 mph with motors capable of bursting to 180 amps or so
Gensace 5000mah 40c packs work for me
Cheers
Last edited by crusey_aus; 11-15-2011 at 06:24 PM.
11-15-2011, 10:09 PM
#8
Really good info guys, thanks for starting this thread. I was getting confused with these crazy numbers some companies are claiming.
I remember that with sub-C cells, there were only a handfull of actaul battery manufacturers, but every company had some magic combination, that made their cell THE STUFF in the pits, and I'd bet to guess it's the same with Li-po batts. Which makes these crazy power claims even crazier.
I remember that with sub-C cells, there were only a handfull of actaul battery manufacturers, but every company had some magic combination, that made their cell THE STUFF in the pits, and I'd bet to guess it's the same with Li-po batts. Which makes these crazy power claims even crazier.
11-16-2011, 10:27 PM
#9
Tech Master
iTrader: (2)
I am so glad to have found this thread. I was thinking or trying to find out "how many C's to too much?" what is does not make a difference. From the little that I know, going from a 20C for a 40C can be felt in the form of punch, but can the difference between 40-60 be felt or better yet, can it make a difference?
I will start racing again, so I think there is much to learn for me on the subject.
Additionally, I would also think that having the most capacity (for instance 5000mah) with a good C rate would make for a good combination. Which brings me to another question, what mah are people running in Blinki, touring and RCGT ?
I will start racing again, so I think there is much to learn for me on the subject.
Additionally, I would also think that having the most capacity (for instance 5000mah) with a good C rate would make for a good combination. Which brings me to another question, what mah are people running in Blinki, touring and RCGT ?
01-10-2012, 08:45 PM
#10
Tech Adept
How I determine my real "C" rating for modern LiPo batteries:
C = 0.08 * 3.7 / (Q * IR)
where:
Q - cell capacity (Ah)
IR - average cell internal resistance (Om)
It's very important to measure IR at stable battery temperature 22-25C (72-77F).
for battery TP 4S 5200mAh 50C/100C and average cell IR=1,7mOm
C = 0,08 * 3,7 / (5.200 * 0.0017) = 33.5C or ~30C
Most reliable results for measuring cell IR can be obtained by ESR Meter
http://www.rcgroups.com/forums/showthread.php?t=1323465
or with FMA Direct chargers Cell Pro 10 / CP10XP, Power Lab 8 and Power Lab 6.
C = 0.08 * 3.7 / (Q * IR)
where:
Q - cell capacity (Ah)
IR - average cell internal resistance (Om)
It's very important to measure IR at stable battery temperature 22-25C (72-77F).
for battery TP 4S 5200mAh 50C/100C and average cell IR=1,7mOm
C = 0,08 * 3,7 / (5.200 * 0.0017) = 33.5C or ~30C
Most reliable results for measuring cell IR can be obtained by ESR Meter
http://www.rcgroups.com/forums/showthread.php?t=1323465
or with FMA Direct chargers Cell Pro 10 / CP10XP, Power Lab 8 and Power Lab 6.
07-17-2012, 04:40 PM
#12
How I determine my real "C" rating for modern LiPo batteries:
C = 0.08 * 3.7 / (Q * IR)
where:
Q - cell capacity (Ah)
IR - average cell internal resistance (Om)
It's very important to measure IR at stable battery temperature 22-25C (72-77F).
for battery TP 4S 5200mAh 50C/100C and average cell IR=1,7mOm
C = 0,08 * 3,7 / (5.200 * 0.0017) = 33.5C or ~30C
Most reliable results for measuring cell IR can be obtained by ESR Meter
http://www.rcgroups.com/forums/showthread.php?t=1323465
or with FMA Direct chargers Cell Pro 10 / CP10XP, Power Lab 8 and Power Lab 6.
C = 0.08 * 3.7 / (Q * IR)
where:
Q - cell capacity (Ah)
IR - average cell internal resistance (Om)
It's very important to measure IR at stable battery temperature 22-25C (72-77F).
for battery TP 4S 5200mAh 50C/100C and average cell IR=1,7mOm
C = 0,08 * 3,7 / (5.200 * 0.0017) = 33.5C or ~30C
Most reliable results for measuring cell IR can be obtained by ESR Meter
http://www.rcgroups.com/forums/showthread.php?t=1323465
or with FMA Direct chargers Cell Pro 10 / CP10XP, Power Lab 8 and Power Lab 6.
07-17-2012, 10:04 PM
#13
Tech Adept
07-18-2012, 01:35 AM
#14
For racing, the C rating is not the most useful piece of information. With all the high capacity LiPo in the market now, the voltage of the pack during high current discharge (i.e during acceleration) is more important. The voltage is what determine the max rpm produced by a given motor. Higher voltage = higher motor rpm = higher speed.
The C rating only tells you how much current is available, but it doesn't tell you the voltage at a given current draw. After all, what we really want to know is how much speed, not how much current the battery can provide.
A better way to check battery performance is check the voltage during max discharge or check max motor rpm (while the car is running). This can be done with MT4, M12, or any other device with power / rpm logging function.
The C rating only tells you how much current is available, but it doesn't tell you the voltage at a given current draw. After all, what we really want to know is how much speed, not how much current the battery can provide.
A better way to check battery performance is check the voltage during max discharge or check max motor rpm (while the car is running). This can be done with MT4, M12, or any other device with power / rpm logging function.
07-18-2012, 02:53 AM
#15
Straight from Orion's site:
the Carbon Pro LiPo can now withstand discharge rates of up to 90C.
99% of people just look at the sticker and assume what they want. They are too lazy to do a little research and find out what they are buying. Orion is counting on this.