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Old May 15, 2012, 06:57 AM
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MRGTX's Avatar
United States, CT
Joined Aug 2005
1,937 Posts
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Is a motor's tolerance for power output strictly limited by energy wasted as heat?

As I understand it, a given motor has a certain efficiency rate. The delta between the input power and the output power is absorbed by the motor as heat...and assuming a certain level of cooling airflow, for a given motor mass, a certain wattage as waste heat will be tolerated.

So assuming that the waste heat wattage is kept the same, is there any reason that one wouldn't be able to go up in voltage? Or stated another way, is it possible to run motors at higher voltage levels, assuming the amps are kept sufficiently low?

Thanks for any information on this!
Mike
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Old May 15, 2012, 11:23 AM
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peterangus's Avatar
Blackpool, Great Britain (UK)
Joined Dec 2003
1,342 Posts
Yes.

eg:
When set-up to operate continuously at 80% efficiency, the power output will be 4 times the cooling power. Regardless of the operating voltage.

And there seems to be little change in peak efficiency as voltage is increased,

So the cooling provision effectively limits the usable power.
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Old May 15, 2012, 11:31 AM
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snoopy_schulz's Avatar
Germany, lake of constance
Joined Oct 2010
407 Posts
Hi MRGTX

You can run a dc motor at higher voltage levels, assuming the amps are kept within motor current limit.
The power loss of a dc motor is given in first order by I^2 *R. I is the motor current, R is the motor resistance.

Running a dc-motor with higher voltage at same motor current (prop with less diameter/pitch) means a higher shaft speed. Thus check max allowed speed of motor and max rpm of ESC. Also ESC/BEC must be able to handle higher voltage.

Best regards
Micha
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Old May 15, 2012, 07:53 PM
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Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
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Quote:
Originally Posted by MRGTX View Post
is it possible to run motors at higher voltage levels, assuming the amps are kept sufficiently low?
Yes, up to a point. At very high rpm the bearings may fail or the rotor may fly apart. Cheap outrunners with unbalanced rotors may suffer excessive vibration. The ESC may not be able to commutate fast enough (some controllers are limited to 21,000rpm or less with a 14 pole motor).

I^2*R is not the only loss. Magnetic losses also get worse as rpm increases. At some point the total loss will become excessive even at low current. High rpm motors usually have fewer magnets and thinner laminations to reduce magnetic losses, and often include a fan to help keep them cool.
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