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step motor total amps

Hi everyone

Im in the beginning stages of building my first CNC router. Ive been setting up and programming CNC machines for the past 15 years however I dont know much about  building them so please go easy on me. 🙂

I will be plugging into a 20amp 220 volt circuit and wanted to know if the total amount of amp from all electronics needs to equal 20amps or less?

For example if I have a spindle/router that runs at 11amps does that mean my stepper motors would have to be 3 amps each or less? (one X axis , one Y axis and one Z axis motor)

Would it be a problem if I have  3 stepper motors at 6 amps each (18 amps total) and a spindle/router at 11 amps ?. Total combined 29 amps.

From what I understand that would mean all stepper motors and spindle would need to be running at full capacity in order to exceed 20 amps which is very unlikely.

Any input or advice would be appreciated.





Hi Matt and welcome to the forum

A 20 amp fuse is more than enough to run your machine.
Your spindle will not draw 11 amps while running as that is an absolute maximum rating.
My 2.2kw Spindle draws 1 amp at no load and doesn't pull a lot more when machining.

Your stepper motors may be rated at 6 amps  but that is not a 220 volt rating. And this is where power transformation comes into effect.
Power (w)= Volts x Amps.

So for example a 60 volt 6 amp stepper motor will draw 360 watts of power. So at the mains side of your power supply with 220 volts then the current draw at the power outlet =  360w / 220v = 1.6 amps
We will be generous and round that up to 2 amps per motor to allow for massive losses, so 3 motors will draw 6 amps total at the power outlet.
Stepper motors do not pull their maximum rated current but only 2/3 of their ratings so that is 4 amps total for all 3 stepper motors worse case scenario at the 220 power outlet.

You will not even come close to tripping your circuit breaker.

Cheers Peter

Thanks Peter!

Very helpful information.

This forum is amazing.