# How to calculate how much voltage/current my brushless motor needs?

#### zemanekj

Joined Jan 31, 2019
58
I have been putting together a homemade brushless motor for a while now, and have posted several questions on this site which were kindly answered. Thank you for answering my prior questions.

Now, my question is this - I am putting together a brushless motor and am almost finished. Therefore, I am trying to figure out how much voltage/current the motor needs to work. I'm not sure what equation to use to figure that out. I've collected variables which are most likely important:

3 phase motor
4 teeth per phase (12 teeth total)
12 loops of wire per tooth
Strength of an individual magnet is 1.4 Teslas (14 N50 magnets in total)
Length of the stator (and magnets) = 10.4mm
The radius of the stator = 10.8mm

What other variables should I be looking for? I'm not looking for anybody to solve this problem, just point me in the right direction - like what equation(s) I should use. I'm putting this motor together without a manual so I have no specs. to go off of. Obviously, this will affect what kind of power supply I buy, as well as what ESC I buy too. Any help is appreciated.

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#### MrChips

Joined Oct 2, 2009
21,664
Here are some motor currents to consider:

1) Startup current
2) Run current with no load
3) Run current with full load
4) Stall current

If you have a variable DC power supply you can test your motor voltage and current requirements. If the PSU does not show load current, put an ammeter in series with the PSU.

#### zemanekj

Joined Jan 31, 2019
58
Here are some motor currents to consider:

1) Startup current
2) Run current with no load
3) Run current with full load
4) Stall current

If you have a variable DC power supply you can test your motor voltage and current requirements. If the PSU does not show load current, put an ammeter in series with the PSU.
Thank you for the response. Unforchunetly, I do not have a DC power supply yet so I can't do that. I am just in need of the equation so I can figure out what kind of power supply I need in the first place.

#### MrChips

Joined Oct 2, 2009
21,664
Here are some calculations.