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Should your motor have less Amp draw than your ESC or more, and should your ESC have more or less Amp draw than your battery can supply?

Thanks!

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The batteries should be rated for the same or higher (continuous) current than the ESC, which should in turn be rated for a significantly higher current than the motor.

The rule of thumb is: Never draw any more current than whatever you're drawing it from can supply.

Also, motors can draw more current than they should. Therefore it's important to include a wide safety margin. Failing to do so could destroy the ESC and/or make the batteries explode or burn. Lithium batteries can be pretty dangerous when abused.

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Both the ESC and battery should be rated for higher Amps than the actual current the motor draws in your application. It may draw up to ~5 times higher current at startup or when a load is initially applied, but ESCs are usually rated to handle these momentary current surges.

The ESC should always be rated to handle whatever current the motor draws at full throttle (100% PWM). You can lower the throttle to reduce battery current if necessary, but the motor current will then be higher - in inverse proportion to the PWM ratio. For example at half throttle (50% PWM) the motor current will be double the battery current.

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  • \$\begingroup\$ Are you sure about the inverse current to PWM ratio? If the load required constant power aka needed more torque at lower speeds I could see the motor pulling more Amps at half throttle, but that's not the case with most loads using hobby components (ie propellors and wheels) \$\endgroup\$ Commented Aug 3, 2019 at 16:24
  • \$\begingroup\$ With a propeller as load the current will decrease as throttle is reduced, but the ratio of battery current to motor current will increase. So if eg. the ESC was rated for 10A but the motor drew 15A at full throttle, limiting maximum throttle to 67% might drop battery current to 8A but motor current would be 12A, still over the ESC's rating. Also the higher switching frequency, higher peak current, and recirculation through body diodes when PWM is applied causes higher loss (most ESCs get hottest at around 75% throttle, even though current is lower than at full throttle). \$\endgroup\$ Commented Aug 3, 2019 at 23:23
  • \$\begingroup\$ That should be 'ratio of motor current to battery current will increase' \$\endgroup\$ Commented Aug 3, 2019 at 23:31

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