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I'm looking at the data sheet for a DC motor that states:

Current consumption at nominal torque (mA): 380

I have a power supply that can deliver 500 mA. Can I take the above statement to indicate that the motor will never draw more than 380 mA, or does it mean that it usually uses 380 mA, and that I should probably choose a different power supply?

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Nominal torque is usually on some nominal rotation speed, which should be mentioned too.

Maximal torque is usually on zero speed (or even more if you force it to rotate backwards). And the maximal current is usually a lot higher than the nominal on nominal speed and torque.

So it says, that if your motor is running at nominal, it would take the 380mA. You can safely assume, that at many occassions, even in normal usage, the current will be temporary a lot higher.

Power supplies usually state how much current they can provide for a long time (nominal current); good power supplies also state maximal current and how long it can provide it (might also be called surge current).

I personally would consider the 500mA highly underrated for full usage of the motor, but if the power supply is over-current resistant (be it by detection and sophisticated construction, or be it just "weak" source with high inside resistance), then it may work well enough, just sometimes the motor would seem "weak" as the voltage would need to drop in order to keep step with current provided by source. And low voltage means low current means low torque there. On some application it dos not matter, it would just move slower, on other applications that may be a critical flaw - it is you, who decides, what is acceptable and what not.

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  • $\begingroup$ Ok, based on what you're saying, I will up the power supply to a higher rated one. Thanks! $\endgroup$ – Troels Larsen May 5 '17 at 12:05
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You should compare the torque will your application require with the nominal torque specified in the datasheet. You should also check the instantaneous current the motor can require (can be higher when powering up -- also known as the stall current) and also if the power supply can deliver 500mA continuously or only instantaneously. Be sure that the maximum current time for the power supply is larger than the required by the motor.

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  • $\begingroup$ All good points, I will try to do so with my limited knowledge - and learn something in the process, thanks! $\endgroup$ – Troels Larsen May 5 '17 at 12:06

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