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Trying to find kit to power motor will wall A/C Answered

I am sure this has been asked about a thousand times in a hundred places but I can't seem to get the search terms right to find these other questions.

I want to get a 3-5 HP induction motor for a table mounted tool. Is there such a thing as a pre-made kit to allow me to power it with wall current? Any idea where I could buy such a thing? I am based in the USA and want to use a 120 outlet. I want to do it as safely as possible, so finding something not homemade by my own amateur self would make me happy. Obviously no kit would fit all possible motors, but I know enough to make sure I match the requirements of any kit.

I appreciate any help and advice!



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Jack A Lopez
Jack A Lopez

1 year ago

Well, I think it is worthwhile to contemplate how much electrical power is needed for a 3 to 5 horsepower (HP), single phase, induction motor.

The reason why is because I think 3 HP is kind of near the upper limit of what a typical 120 VAC mains circuit can supply. By typical, I mean the rating for the wires supplying current to the outlet, and the breaker in series with those wires, is usually only rated for a maximum of 15 or 20 amperes (A).

You should check inside your breaker box, to see what number is printed on the breaker for this circuit you intend to use for powering this big effing motor.

As I was saying before, the naive calculation for converting horsepower (HP) to watts (W) is to just multiply by 746 watts per horsepower.

So 3.0 HP, is 3.0*746 = 2238 W

And the naive calculation for electrical power, in terms of voltage and current is: P=V*I or I= P/V, or

I = (2238 W)/(120 V) = 18.65 A

The actual amount of current the motor draws, depends on what it is doing, or more descriptively, on how hard it is working. For example on startup, there is usually a big current surge, as the motor takes energy from the mains, and puts it into rotational kinetic energy of its rotor, and other spinning things attached to that rotor.

Sometimes that current surge dims the lights briefly.

Anyway, I guess where I am going with this story, is you might need to install a new circuit, just for this motor. That is a breaker, plus thick wire, plus a switch to turn the thing on and off.

I do not think these things exist as "a kit." Rather, the individual components, like circuit breakers, thick wire, switches, outlets... these are sort of the ingredients an electrician uses, when he or she wants to build a circuit, to deliver power to some specified electrical load.

By the way, regarding the question of how thick the wire should be, I think the word is "ampacity"


You know, there are tables and stuff, to tell you the maximum current a pair of wires can withstand, without getting uncomfortably hot.

For purposes of testing your motor, and the circuit for powering it, including measuring the current if you have tools for that... it might be convenient if you set it up near the breaker box, since that way, only a short length of wires would suffice to reach the motor.


1 year ago

With that amount of power on 120 Volt you will be over the limit for residential use.
Even if you would have 3 phases at your disposal it would be a big undertaking unless the power is already close to where you need it.

I assume you need high torque for your application?
If so you could consider going the DC route.
You can quite often find old treadmills on the hard rubbish.
Usually they fail with the belt r a worn out motor.
For the later it is a simple job of replacing the carbon brushes and to lube up the bearings.
The simple models come with a controller that can be modified to work without the actual treadmill.
I know what you think now: It won't have the power I need....
Hear me out though...
Induction motors come with 2 prefered speeds, 1440 or 2800 RPM.
These DC motors however can go much faster than that, so a pulley or gearbox can be used to match the required shaft speeds.
So you get the torque you need from a fast running motor with a reduction.
And the same reduction applies to your power so you might be able to run it all with enough torque on a standard 10A outlet ;)