Motor conversion

[mastertech]

I have a single phase, 60hz, 480V power supply, and I want to run a 3phase, 60hz 480V motor from that power source. Is there a way I can do that, using a condenser or something, and what are the risks of doing that? Thank you.

 

[teco]

mastertechlease advise motor power(hp/kw)speed andtype of load.
kind regds

 

[TheDOG]

The easiest solution is to use a VSD.
You will have to oversize the drive by 1.732 (sqrt 3) times ie. 10Hp motor will require a 20Hp drive. This is because the current rating of the input bridge rectifier.

 

[busbar]

Discussed in usenet groups rec.woodworking and rec.crafts.metalworking
480V 1ø is a bit unusual from my experence, but there are likely regional variations.

 

[bhrollin]

Yes, I have built many balanced voltage rotary phase converters that produce good enough three phase power to run motors at full nameplate horsepower if they have a service factor of 1.15 or better. Just put 12mF per horsepower of run capacitors rated for your voltage between each of the single phase lines and the third winding on the motor you will use for your converter. Connect a single phase line to each of the other motor windings. Now, once the motor is running you can tap off each winding and you will have pretty good three phase. I've looked at the phases on a scope and the pahase angles are very good. That is the 'manufactured phase' is 90 degrees between the two incoming lines. The waveform of the manufactured phase is not a perfect sine wave though.

The trick to getting this motor running is to use a relay to kick in more capacitors between one of the single phase lines and the third winding (manufactured phase) of the motor. Use about 75-100mF per horsepower of start capacitors or run capacitors. These are in the circuit when the motor is started. They throw it out of balance enough to start. Once it is up to speed, the relay is opened and the capacitance is again perfectly balanced.

bhrollin@syr.edu

 

[electricuwe]

To TheDog:

Before operating a drive with three-pase input in that way the manufacturers manual should be checked:

The DC-Link Capacitor might not be suitable for that kind of operation.In a 20hp-drive used for supplying 10 hp from single phase line the current in the DC-link capacitors is larger than at operation with rated load from three-pase line.

Furthermore the control unit might not allow operation from single phase line.

 

[TheDOG]

Electricuwe:

That is true! The manufacturers manual should always be checked.
I believe most manufacturers allow for this type of operation, and usually have a safety factor built in ie. Twice the rated Hp, instead of 1.732. There is also an increase in ripple voltage, which will affect the capacitors. This can be overcome by adding a DC link reactor and/or another capacitor bank of the same value (if reccommended).
Most drives do not have "true" input voltage sensing circuits. Wire the active to L1 and L2 and the neutral to L3.