Feb 15, 2013, 04:22 PM Registered User Joined Feb 2006 23 Posts Can someone explain how higher Mah batteries make a car faster? I am pretty well versed in electricity, so it intrigues me how increasing battery mah affects anything other then run time. Increasing voltage would increase output (until failure), but the motor draws whatever current it draws. How does the batteries milliamp capacity affect performance?
 Feb 15, 2013, 04:28 PM Rocket Programmer United States, CO, Golden Joined Jul 2007 22,472 Posts It reduces the voltage drop under load. The C rating is actually defined as the maximum current you can pull without suffering a significant voltage drop. It is an actual number, but it's expressed as a factor of the capacity, so when the capacity goes up, so does the C rating, not the factor, the actual number. So, a 30C 1000mah has a C rating of 30 amps, but the 30C 2000mah has a C rating of 60 amps. So your 30 amp car will cause a significant voltage drop on the small battery, but not on the big one. Same c factor, different c rating.
 Feb 15, 2013, 06:28 PM Registered User Canada, ON, Markham Joined Aug 2008 8,242 Posts ^^ What he said. Voltage drop under load at close to the packs happy limit will be pretty bad, so having more amperage available will greatly reduce the voltage drop.
 Feb 15, 2013, 09:04 PM Rocket Programmer United States, CO, Golden Joined Jul 2007 22,472 Posts There is a point of diminishing return... Say you have a 30-amp truck and you're running a 5000mAh 35C battery, like I run in my 1/10th truck. That battery won't experience a significant voltage drop until you pull around 175 amps, so my truck isn't even stressing that battery at all. If I put a 10,000 mAh battery, all that will happen is I will add weight, and the truck will go slower. So, it's only true if your truck is currently being limited by the battery you're running. If that is not the case, then yes, a bigger battery will slow you down. That's why racing is so much fun... so many trade offs to shave those seconds
Feb 18, 2013, 05:43 PM
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United States, NY, Albany
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Quote:
 Originally Posted by dma251 I am pretty well versed in electricity, so it intrigues me how increasing battery mah affects anything other then run time. Increasing voltage would increase output (until failure), but the motor draws whatever current it draws. How does the batteries milliamp capacity affect performance?
RC batteries are generally rated by Ah (mAh) and "C". "C" is a horrible rating since it's really just a relative discarge rate and what is more important is Ah*C which computes the amp rating of the pack. Pulling more amps than Ah*"C" on a continious basis will cause strain on the pack, premature aging, voltage sag, and limit the total capacity you can safely extract from the pack.

If your battery Ah*C is higher than the amps that your ESC/Motor can pull then going with a bigger battery will probably not produce any differences. There would be a tiny difference in voltage drop over time which would probably have a minimal effect in overall speed.

If your battery Ah*C isn't high enough you can get more amps in two ways, go with a higher C rating or a larger Ah, both will allow you to safely pull more amps.
 Feb 18, 2013, 06:31 PM Rocket Programmer United States, CO, Golden Joined Jul 2007 22,472 Posts Brontide, that's why i made it clear that the C rating is the actual number of amps, not the factor. That's just how it's expressed, so the C rating is 40 amps or whatever, it's not the number before the C.
Feb 19, 2013, 02:16 AM
Did you check the FAQ already?
The Netherlands
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Quote:
 Originally Posted by jasmine2501 It reduces the voltage drop under load. The C rating is actually defined as the maximum current you can pull without suffering a significant voltage drop. It is an actual number, but it's expressed as a factor of the capacity, so when the capacity goes up, so does the C rating, not the factor, the actual number. So, a 30C 1000mah has a C rating of 30 amps, but the 30C 2000mah has a C rating of 60 amps. So your 30 amp car will cause a significant voltage drop on the small battery, but not on the big one. Same c factor, different c rating.
Quote:
 Originally Posted by jasmine2501 Brontide, that's why i made it clear that the C rating is the actual number of amps, not the factor. That's just how it's expressed, so the C rating is 40 amps or whatever, it's not the number before the C.
I understand you are trying to make it easier to grasp, but talking about a seperate C-rating and C-Factor isn't helping, I think, it just makes it more confusing. A C-rating is not in Amps, it's just a number. The C number is simply what you need to multiply the battery's capacity with to get the current this battery can deliver without it's voltage collapsing and/or the battery overheating.

You can't simplify that, the only way to determine how much current a battery can deliver is by simple math, a single calcucation. The outcome of that calculation is what matters. C-rating without taking into consideration the capacity of the battery means nothing, and capacity alone means nothing either. As brontide explained, it's a relative number, and as such, you can be tricked thinking into just looking at the C-number. But it is as it is, and once you know how it works, it's easy to compare batteries.
 Feb 19, 2013, 09:39 AM Registered User Canada, ON, Markham Joined Aug 2008 8,242 Posts In reality, the C rating is a representation of the internal resistance of the cells. Lower resistance means higher C rating.