10-22-2013, 07:54 PM
In its simplest form you could use a rope. The small motor is just a starter so I don't have to pull a rope. The big motor is a 3-phase from a mill, which now has a single phase motor. The now-spare three phase motor is being used as a converter to power other 3-phase machines.
Pull the rope to get it spinning, then apply single phase to two of the three motor leads. It should run smoothly and quietly, although some don't start at all. I have a 3450 rpm 3-phase that just locks up, but there is another use for it that I'll try to explain in a bit.
With the motor running, it will produce 3-phase power across its leads like magic. Turn it off and run those three phase wires to your 3-phase machine. Pull the rope and apply power, then turn on your 3-phase machine. Ta-da!
Notice that if you wind the rope on in the other direction and start things rolling, you'll see that your machine is running backwards. That's the problem when you use a rope, so use a little motor instead, and things will always starts in the same direction. Turn the little motor off before applying power to the big motor, it will just freewheel along for the ride.
Now about that other motor. Because the big motor is drawing all power through just two windings, it needs to be de-rated -- a 3-horse motor will only provide about 2 horses. You can hang another motor across it and they work in tandem, producing double of the smallest. That's my understanding anyway, the motors I have aren't getting hot so this hasn't been necessary yet.
Pull the rope to get it spinning, then apply single phase to two of the three motor leads. It should run smoothly and quietly, although some don't start at all. I have a 3450 rpm 3-phase that just locks up, but there is another use for it that I'll try to explain in a bit.
With the motor running, it will produce 3-phase power across its leads like magic. Turn it off and run those three phase wires to your 3-phase machine. Pull the rope and apply power, then turn on your 3-phase machine. Ta-da!
Notice that if you wind the rope on in the other direction and start things rolling, you'll see that your machine is running backwards. That's the problem when you use a rope, so use a little motor instead, and things will always starts in the same direction. Turn the little motor off before applying power to the big motor, it will just freewheel along for the ride.
Now about that other motor. Because the big motor is drawing all power through just two windings, it needs to be de-rated -- a 3-horse motor will only provide about 2 horses. You can hang another motor across it and they work in tandem, producing double of the smallest. That's my understanding anyway, the motors I have aren't getting hot so this hasn't been necessary yet.