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Old 03-22-2012, 04:37 AM   #1
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Default C rating question

Hey Guys, I'm a newbie on this forum and to the world of electric R/C!
so sorry if this is a dumb question!

If you are buying a battery does it matter what C rating you get as long as its over the amp draw of the motor?
for example the motor on my redcat racing draws 80amps and the recommended C rating for it it 20C but does it matter if i go up to 40C if i wanted and what are the advantages of a High C Rating.

Any help would be awesome!

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Old 03-22-2012, 05:41 AM   #2
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The higher the C-rating the higher the higher the pack can draw amp! For sereious racing a 45c pack will do the job while for bashing a 20-25c pack is enough.
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Old 03-22-2012, 05:41 AM   #3
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What class of motor are you running?

There is no standard for measuring the 'C' rating of lipo's so most of it is manufacturer BS.

If you're just bashing it won't matter so much, but if you're racing competitively you might want something a bit more powerfull, but again, it will depend on what class you will be running.
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Old 03-22-2012, 06:58 AM   #4
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Remember that the c rating is a multiplier. The c stands for capacity so a 40c 4000 mah battery is 40 x capacity or 40 x 4000 = 160000mah or 160 amps. a 30c 6000mah battery would be 30 x 6000 = 180000 or 180 amps. In this case the lower c is more powerful. a 60 c 2500mah is 60 x 2500= 150000 or 150 amps. In this case the 60c is less powerful.

In most cases a 40c 5000mah will get the job done. You want to pay attention to these numbers not so much for instant power but for a more stable power source throughout the run. A higher c and mah will be more consistent throughout the whole race where a smaller c and mah may start to fade halfway through the race resulting in lower lap times.
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Old 03-22-2012, 03:11 PM   #5
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Pretty much anything over 40C is bogus advertising propaganda and the current draw would be so high as to melt the solder connections, wires and melt the plastic off the battery connector.

I mostly use 4000mha packs, i have them in 20, 30, 40 and 60C ratings, there is not much difference if any between all of them, they all come out of the car about 37deg, they all give about the same length run time and they all feel about the same response wise with the 40C being slightly punchier at the beginning.
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Old 03-22-2012, 03:44 PM   #6
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Originally Posted by RogerDaShrubber View Post
Pretty much anything over 40C is bogus advertising propaganda and the current draw would be so high as to melt the solder connections, wires and melt the plastic off the battery connector.

I mostly use 4000mha packs, i have them in 20, 30, 40 and 60C ratings, there is not much difference if any between all of them, they all come out of the car about 37deg, they all give about the same length run time and they all feel about the same response wise with the 40C being slightly punchier at the beginning.
You are assuming that the c rating is delivered constantly. It is not. The wire esc and connections can sustain momentary bursts of power with no effect.

You also made the point. you state there is not MUCH difference between packs but when you are racing 0.1 per lap can make the difference in the race. The 40c has more punch because it is capable of delivering the momentary burst of 40c where the other packs can not. I bet the 40c is more consistent throughout the entire run as well. The 60c should feel very similar to the 40c in punch too.
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Old 03-22-2012, 05:34 PM   #7
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You also made the point. you state there is not MUCH difference between packs but when you are racing 0.1 per lap can make the difference in the race.
Not if you drive like me, or, not if you drive like the vast majority of club racers. If you do not have an overall level of consistency in your driving, using a pack that has 0.1 advantage over another is not going to make any difference at all.

Unless the standard deviation on your average lap times is almost equal to the advantage gained by using the 0.1 pack, it will never lead to to improved lap times, because brain fart is greater than the advantage gained.
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Old 03-22-2012, 06:05 PM   #8
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For spec classes or stock, higher C ratings are the way to go. Higher C rating usually mean less internal resistance which will translate to punch. In modified, Massive amounts of punch usually isn't desired. So 30 Cs should be fine.
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Old 03-22-2012, 06:13 PM   #9
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Originally Posted by RogerDaShrubber View Post
Not if you drive like me, or, not if you drive like the vast majority of club racers. If you do not have an overall level of consistency in your driving, using a pack that has 0.1 advantage over another is not going to make any difference at all.

Unless the standard deviation on your average lap times is almost equal to the advantage gained by using the 0.1 pack, it will never lead to to improved lap times, because brain fart is greater than the advantage gained.
Brain Fart reduction is the best Hop up yet!!!
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Old 03-22-2012, 06:28 PM   #10
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Originally Posted by RogerDaShrubber View Post
Not if you drive like me, or, not if you drive like the vast majority of club racers. If you do not have an overall level of consistency in your driving, using a pack that has 0.1 advantage over another is not going to make any difference at all.

Unless the standard deviation on your average lap times is almost equal to the advantage gained by using the 0.1 pack, it will never lead to to improved lap times, because brain fart is greater than the advantage gained.
You do have a point. Our vta class has 5 or 6 drivers that can run a 0.2 or 0.3 standard deviation over a 8 minute race with 7 to 10 cars on the track so every tenth helps. Tenths add up into seconds so why not go ahead and get a good battery now instead of buying another one later. You don't need your equipment losing time for you that's what driving is for. Its a progression. as long as your equipment is capable of doing more than the driving is then you can concentrate on driving better. If the equipment is lacking you have to learn to drive the car upgrade it learn to drive it again and so on and so on.
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Old 03-22-2012, 06:33 PM   #11
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Quote:
Originally Posted by RogerDaShrubber View Post
Unless the standard deviation on your average lap times is almost equal to the advantage gained by using the 0.1 pack, it will never lead to to improved lap times, because brain fart is greater than the advantage gained.
However, could it not be argued that a pack that is a tenth faster may still be a tenth faster if the lap is slow, compared to a comparable slow lap with the "slower" pack? I'm just hypothesizing. I mean, an inconsistant driver may drive a 13.5 car faster than a 17.5 car, just not cleanly.
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Old 03-22-2012, 06:46 PM   #12
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However, could it not be argued that a pack that is a tenth faster may still be a tenth faster if the lap is slow, compared to a comparable slow lap with the "slower" pack? I'm just hypothesizing. I mean, an inconsistant driver may drive a 13.5 car faster than a 17.5 car, just not cleanly.
I would agree. Yes we are playing a game of tenths but it all adds up. Would you ignore other things on the car to gain speed? What if changing shock oil was a tenth then changing springs was a tenth and decreasing toe was a tenth and lowering ride height was a tenth and the battery was a tenth? Now you have lost a half a second a lap. It may not be much alone but it all adds up.
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Old 03-22-2012, 07:41 PM   #13
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Quote:
Originally Posted by 6376vette View Post
You are assuming that the c rating is delivered constantly. It is not. The wire esc and connections can sustain momentary bursts of power with no effect.
For most packs, the C rating is the continuous discharge rating. The "burst" current rating is generally 2x the continuous rating. Thus a 40C rated pack can produce 80C for short periods of time (like 10 seconds or less).

Also, the manufacturers' ratings are taken directly at the tabs on the cell, *not* through the wire and connector.

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For spec classes or stock, higher C ratings are the way to go.
Not necessarily true. Two years ago, stock TC was won with a 28C sport pack. The theory is that the lower C rated packs heat up more internally, which generates higher voltage.
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Old 03-22-2012, 08:29 PM   #14
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For most packs, the C rating is the continuous discharge rating. The "burst" current rating is generally 2x the continuous rating. Thus a 40C rated pack can produce 80C for short periods of time (like 10 seconds or less).

Also, the manufacturers' ratings are taken directly at the tabs on the cell, *not* through the wire and connector.



Not necessarily true. Two years ago, stock TC was won with a 28C sport pack. The theory is that the lower C rated packs heat up more internally, which generates higher voltage.
Maybe a 40c can burst to 80c but we are still not constantly discharging at 40c.

I have heard that theory and I don't buy into it. I was visually slower on a 25c vs a 40c and the lap times came down even more with a 65c.

Heat cannot generate more voltage. It MAY be able to release voltage and amperage faster but voltage can't be generated. I still don't buy it though.
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Old 03-22-2012, 09:01 PM   #15
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Originally Posted by 6376vette View Post
Heat cannot generate more voltage.
Never heard of a thermocouple I guess
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