How do I work out the power output of an electric motor?

Question

I have been buying 3 hp 2 pole single phase motors on ebay and I dont reckon they have the torque of an old 2hp 2 pole non chinese motor i have. Does a 3hp 2pole motor have the same torque as a 3hp 4 pole motor? I bought an intem 3hp 2pole for my lathe and run it through pulleys back to 1440 rpm and this motor seems to be the full 3 hp, I think it is far better made than the picton motors. When i burnt a motor out the other day i took it to work and the sparkie said he would be very surprised if it was really 3 hp. Will measuring the current tell me? I reckon if I work them to hard the current will go through the roof anyway. These motors dont have thermal overloads fitted.

Answer 1

There is a way to calculate the torque on a motor, but most of the information is difficult to check for. I wouldn't buy anything chinese, they try and produce as much as possible without research.

If your rotor is a low quality and the wiring and laminations aren't good it won't have much power. That is why name is important.

A four pole motor is slower but have more torque than a 2 pole motor. If you take that the magnetic field must push the rotor further with the same power available then it must have less torque.

Answer 2

you don't tell us the voltage so I cant make any calculations for you

however I work as an electrician  and have found that the world does not have a consistent voltage or frequency

if you buy motors on the Internet then you WILL have to know your local Voltage and Frequency to be able to make an informed decision

3hp at 110V at 60Hz will not be the same motor as one at

3hp at 240V at 50Hz and neither will work properly at the others supply