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How to use an external power supply instead of batteries with ESC and brushless motor? Answered

Hello, everybody, this is my first question here !

Recently I have made a remote controlling system for my friend's RC plane, the problem is we want to test it on the ground without batteries..
So, I told him we can use an external power supply that gives 12V, but we can't calculate the needed amperage(? A) ...
We'll be using EMax 18A brushless motor + Emax 30A ESC , all of these are using 11.1V, so what and how can I calculate the needed specifications of the required power supply ?

I wish you could help me, and thanx :)


Your ESC expects to be controlled by a 5 volt signal from your rx or a servo tester.

Make sure it is.

The current isn't an issue from the point of view of too much being available. Too little however may prevent things working.

your motor needs 18 amps. The rest is insignificant in comparison.

I always bench test using the battery system i will use in the aircraft. This way your testing everything and no risk of over volts.

Thank you very much, but I want you to confirm what I understood, that it's not matter the current comming from the power supply even it's more or less then the current needed by the ESC & the motor, and I can use a regular computer or laptop power supply for the job, and the servo tester will be powered with the BEC comming from the ESC which is 5V ?

That sound OK Make sure the BEC can cope with 12 volts in.

Current is taken not pushed.


Thanx very much rickharris, you really helped me :)

But I'm sorry, I have another question, the following diagram is a servo tester that could run an ESC with a brushless motor, do you confirm it or there is something wrong ?

( I wont use the 4.5 ~ 6.0 V VIN. , I'll relay on the power comming from the ESC )


That looks OK, a basic servo tester. It needs 5/6 volts to drive it though.

should do. The output from the receiver is a variable square wave. Where the width of the square wave sets the output of the ESC. Wider = faster.

The 555 produces such a square wave.

OK, thank you very much rickharris for your help and advices :)