# Better Performance when Warm?



## Hollie Maea (Dec 9, 2009)

I'm guessing your batteries were also warmer. Now that does make a difference.


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## dougingraham (Jul 26, 2011)

Warmer motor should not improve performance. You get more copper losses as the temperature rises. I too suspect warm batteries is the answer. Or you are just getting better at shifting (assuming you have a transmission).

The only thing motor related I can think of would be getting the brushes seated and the bearing grease thinning. Top speed is going to be a function of HP and that is going to be a function of battery voltage when at full throttle.


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## major (Apr 4, 2008)

Hi Frank,

Plenty of things change with temperature, inside the motor and out. The viscosity of lubricants in the motor bearings and also in the entire drive line. With heat, the circular steel parts expand giving a small increase in clearance for bearings. This also can increase the motor air gap ever so slightly which would act similar to field weakening. The carbon and graphite in the motor brushes have a negative temperature coefficient of resistivity. The friction of the brushes on the commutator surface might be a bit less when warm.

I would say there is a difference in motor performance when warm. At light loads it may run a bit faster and actually be a percent or two more efficient. But at heavy loads the motor will undoubtedly be less efficient due to the increased copper loss. 

major


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## Frank (Dec 6, 2008)

Thanks for the comments. The reason I don't think it's batteries is that they're 100/100C cells; 9AH running at about 400A i.e. they're only at 50% of continuous rating and well above the motor voltage limit.

I'll keep an eye on this. Specifically, my last run was .010 second quicker but 2 mph faster. 

Thanks again


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## dougingraham (Jul 26, 2011)

Frank said:


> Thanks for the comments. The reason I don't think it's batteries is that they're 100/100C cells; 9AH running at about 400A i.e. they're only at 50% of continuous rating and well above the motor voltage limit.
> 
> I'll keep an eye on this. Specifically, my last run was .010 second quicker but 2 mph faster.


I would not trust a manufacturer C rating of 100. That smells of advertising exaggeration. There are no industry standards for C ratings. Your 400 amps with a 9 ah battery is 44.4 C. You should log battery voltage, current and temp in the middle of the pack to see what is really going on. Battery current should be less than the motor current up to the point of max power at which point you should shift up. Motor current will be the 400A after the tires lock up until you reach the point where the back emf from the motor approaches the pack voltage. A small increase in pack voltage will delay the shift point and increase max HP.


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