I've seen some specifications of RC brushless motors and ESC with very high current ratings from small motors having 16A draw to ones with 60 to 70A current draw. The specs also says peak current draws unto 200A are possible on certain motors.

What I'm curious is how can such small motors handle such high currents without damaging itself?

I've seen car starter motors draw hundreds of Amps, but they run only for few seconds and are big enough to dissipate the heat.

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    \$\begingroup\$ An example datasheet might illuminate the answer. \$\endgroup\$ – pjc50 Nov 5 '17 at 19:44
  • \$\begingroup\$ read the footnotes, there will be a duty cycle associate with the high current. at eh end of the day it is a thermal fusing issue. i2t \$\endgroup\$ – JonRB Nov 5 '17 at 19:45
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    \$\begingroup\$ Some of them are intended to operate under large fans. \$\endgroup\$ – Brian Drummond Nov 5 '17 at 19:51
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    \$\begingroup\$ @rahulSalin not quite PWM will produce an average current. I am saying such motors can run at peak load/current for say 10seconds and 10% max current indefinitely. \$\endgroup\$ – JonRB Nov 5 '17 at 19:56
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    \$\begingroup\$ How hard you can drive them also depends on how you arrange them mechanically and how well you can get rid of the heat. If it's for an aircraft propeller, you will have a nice fan on the front, if it's buried inside a plastic box somewhere it will melt... \$\endgroup\$ – Trevor_G Nov 5 '17 at 19:59

There are several factors that interact with each other.

The length and diameter of the wire determines the wire resistance and thus the power dissipated as heat in the motor.

The mass of the motor core, frame and windings determines how long it takes for the wire to reach its maximum safe temperature.

The surface area, shape, enclosure style, air temperature and air flow determine how quickly heat is taken away from the motor.

The insulation type determines how hot it can get before being damaged. Magnet wire insulation materials have historically ranged from 100 to 180 degrees C. There may be newer materials that can operate at even higher temperatures.

The duty cycle, operating vs. cool-down time, influences the maximum temperature.

Te expected lifetime of the insulation is directly related by the time that the insulation is subjected to a given temperature.

Industrial motors are designed to operate 24 hours a day, 365 days per year for many years. Hobby motors have duty cycle limitations and shorter life expectancies. Automobile starter motors have duty cycle limitations.


The high current specs you are seeing are probably only for short times. Look at the datasheet carefully. There will probably be a voltage and current for continuous operation. Some motors may be specified for higher values, but for maximum lengths of time with some minimum time between at lower current.

As always read the datasheet carefully.

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    \$\begingroup\$ +1 And read it BEFORE you let the smoke out, not after. \$\endgroup\$ – Trevor_G Nov 5 '17 at 19:48
  • \$\begingroup\$ @Olin So, the current draw will reduce while running I guess. SO the only time when the current draw is very large is only during the initial start and during the reverse-braking time right? If I emulate this high load current scenario by lets say running the RC car up a hill for like a minute, will it burn up the motor? \$\endgroup\$ – The_Vintage_Collector Nov 5 '17 at 19:56
  • \$\begingroup\$ @Rahul: Read what I wrote, particularly the last sentence. \$\endgroup\$ – Olin Lathrop Nov 5 '17 at 21:51
  • \$\begingroup\$ I'm participating in the radio control hobby, and I can assure you that very few if any manufacturers of hobby parts provide datasheets; these things are sold to consumers, not engineering companies. The only thing that you'll find is a table with some limited set of specifications (often just the velocity constant as "KV", the maximum current, the no-load current at some voltage and the recommended voltage in terms of a lithium ion cell count). Some more helpful manufacturers also provide graphs of voltage vs current with certain different propellers. \$\endgroup\$ – jms Nov 6 '17 at 2:02
  • \$\begingroup\$ @Jms: Then either don't try to push those parts against any limits, or buy parts elsewhere that come with proper specs. \$\endgroup\$ – Olin Lathrop Nov 6 '17 at 11:28

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