If you decide to build something like a bandsaw and the only thing available to you is a 3 phase motor, there are at least 3 ways that you should be able to do this without a problem. When I built my bandsaw, I had a good 3 phase motor that I had picked up at an auction just laying around the shop, so instead of having to go out and shop for a single phase motor, I decided to just use the 3 phase motor, but change it to single phase power because I did not have 3 phase power available to me in my shop.
I will explain 3 easy ways to change the power to 3 phase. The first method is that you can use a start capacitor rated for at least 240-300 volts from a motor of about the same size as the motor you want to run, and you will also need a momentary contact switch. The 3 phase motor you want to run must be rated at 208-220 volts. Hook 2 of the 3 motor leads to a double pole single throw switch (DPST) and the other lead to a start capacitor, and the other capacitor lead is connected to a momentary contact switch that is in turn connected to one of 220 volt leads, it does not matter which one. To start and run the motor, turn the switch to the "on" position and just momentarily push contact switch. Don't hold the switch down for more than one second as it will damage the capacitor and could even cause it to burn up or blow out. To reverse the rotation, switch any two leads on the 3 phase motor. A 3 phase motor running in this manner will produce about 2/3 of its rated horsepower.
This first method is the one I used to make a homemade bandsaw and although it seems complicated, it is the easiest way to operate a 3 phase motor after you assemble it. I was able to later convert the motor on the saw to a single phase motor once I got one.
Another method is to spin the 3 phase motor by using a small single-phase motor. Connect 240 volt single phase to a 240 volt switch (DPST switch). The motor will then start and run. Then unplug the starting motor. You may have to reverse the leads to gain proper rotation. But again the motor will produce about 2/3 of its rated horsepower.
The last method is to make a phase converter by using a small single phase motor connected to a 3 phase motor. Then connect 220 volt to the 3 phase motor and use those 2 leads and the remaining lead as 3 phase power connected to a 3-pole switch. This will give you 3 phase power to start and run a 3 phase motor. After the motor is started you can turn the single phase motor off. If you want to run the motor the opposite way then change any two leads and this will reverse the motor. A 3 hp motor will produce enough power to run a 5 hp motor at full capacity.
Methods one and three are shown in the above diagram. Unfortunately the picture is not the clearest, but it might help in understanding the methods. Method two is self explanatory so I did not provide a diagram for that. This was a great way to save me some money when I built the saw that I made with my 3 phase motor.
Article Views: 7308 Report this Article