# How to start 3phase motor with single phase supply

hello..
i am doing a project of drilling machine in which i have use 3 phase motor but i dont have 3 phase supply in available at my working lab.. is there any chance to start 3 phase motor efficient with single phase supply for testing purposes.

Thank you
Jack Arsal

Usually it's done with a capacitor, but you'll need some knowledge to calculate the correct values. Also it's easy to burn one coil with this method.

You can start and run a 3ph induction motor by using as capacitor across one of the phases, but it will never run at rated power, and the phases will be out of balance, but sometimes, it's good enough. It will also depend on if the motor is star or delta connected. A better solution, if you have the space, is to use a larger 3ph motor, driven by a single phase motor, to act as a sort of generator. But if you simply want to use the drilling machine, then buy a single to 3 phase inverter, they are not too expensive, compared to changing the 3 ph to 1 ph motor, The single phase motor will be physically larger than the 3 ph, and may not easily fit the machine. The nature of your project, and cash available can effect your choice. If 'the project' involves drilling holes, compared to measuring currents, say.

Just to test the motor, you can use your single phase power.

The problem is STARTING the motor to turn. If you can spin the motor fairly fast, with no load, then apply the single phase power to one winding, the motor will continue to turn.

Paul

Paul_KD7HB:
Just to test the motor, you can use your single phase power.

The problem is STARTING the motor to turn. If you can spin the motor fairly fast, with no load, then apply the single phase power to one winding, the motor will continue to turn.

Paul

sir my main task is to test drilling power of machine for this purpose ,load is must

Jack_Arsal:
sir my main task is to test drilling power of machine for this purpose ,load is must

Then you will need as previously suggested, a single to 3 phase inverter, sized to suit the motor.

Imagine it would be more expensive than an appropriately sized single phase motor though.

Jack, why? If it is important, and you need to measure numerous parameters of the 3ph drill, (type testing?) then you will need a decent 3 ph supply. The cheaper inverters are not quite the same as 3ph mains. If you change the motor to single phase, then it is no longer the same machine. If you want to measure torque/speed, knowing the motor type/specification, and gear/belt ratios you can calculate (with a margin of error) a number of things that you may think you need to measure.
If it is a case that the 3ph drill is wanted to be actually used in a single phase environment, and you want to see if it works, and would be useful, then as mentioned a 1 to 3 ph inverter would be useful. You can transfer it to other 3ph machines as they are acquired. Get one rated more than you need, e.g. 1kw motor, get 1.5kw inverter, because 3ph machines are cheaper, and you will want more power, you always do.

wrt wrapping a cord round the shaft to spin it with one phase connected, -don't snag the cord, and if you can't get at the motor star(neutral) point, it may not work -i.e phase to phase is 1,732 times the neutral to phase volts

If you are unsure of what you are doing, call in professional help, don't believe what anybody says here, because we have no idea of your situation.