single or three phase?

[totl]

I need some help understanding this. As I stated in a previous thread (ac to dc power) I have a permanent magnet motor which is electronically commutated to develop variable speeds. Input voltage is ac. It is then rectified to dc for control and then through an inverter curcuit with 6 transistors thru 3 leads to the (labeled) single phase ac motor. There is a separate ground which attaches to the body of the motor. When this motor is separated from the electronics and spun backwards it produces ac voltage since it is a permanent magnet motor. I show voltage from any combination of the 3 leads as it operates as an alternator. My question is this: Is this true 3 phase voltage being produced and if so how can I test this? Help is appreciated.

 

[ljcox]

A diagram would help us to understand what you're talking about.

You would need to use an oscilloscope in order to determine whether the output is 3 phase.

If is really 3 phase, the voltages should sinusoidal, of equal magnitude & separate oin phase by 120 degrees.

 

[tcmtech]

It sound like a typical permanent magnet type three phase servo motor to me.

Being it was driven off of an inverter at a variable speed and its got three interconnected wires its not going to be a single phase motor.

 

[Reloadron]

For those curious this is the original thread that started things.

The problem remains the same in that nobody seems to know what exactly you have for a motor.

If you have a 3 phase motor it should resemble the attached based on all your post and 3 wires exiting, additionally I show a 3 phase rectifier block.

Something you can try is measuring the resistance from wire to wire as in what would be L1 to L2, L2 to L3 and L3 to L1. They should be equal. Problem is that most PM motors as you describe in your original thread, that I have seen and worked with were DC motors. So try some resistance checks.

There was also this from your original thread:

ac to dc power

The motor is rated as 1 ph, 60hz, 3/4 hp, 120/240 v @9.6/6.8 amps, 0-1400rpm

Ron

 

[tcmtech]

I see. Its a 120 volt 60 Hz single phase input that feeds a a small inverter unit that drive the motor. Its a mix and match label. Its single phase feed but an actual three phase motor that runs on 120 volt three phase power produced by the little variable frequency drive unit.

I have something similar that came out an odd tread mill. Its a three phase motor, non PM type, but the original mill it came from labels it as a single phase powered motor system.

As far as using it as a PM alternator for a wind generator it should work just fine but your total amps output still cant be ran continuously over the single phase input rating the unit originally had so 10 amps is about all you are going to see from it at best without burning it out. Short overloads will be fine but not extended runs.

 

[totl]

Only 10 amps? Even as 3 phase?

 

[Reloadron]

@ tcmtech, what are you reading or seeing that I am missing? You seem to have this all figured out as I wonder? How did you come up with this?

It sound like a typical permanent magnet type three phase servo motor to me.

Being it was driven off of an inverter at a variable speed and its got three interconnected wires its not going to be a single phase motor.

How the hell did you know it was inverter driven? I know you are the duty guru on this stuff.

Ron

 

[tcmtech]

How the hell did you know it was inverter driven? I know you are the duty guru on this stuff.

I felt a disturbance in the force.

He mentioned the inverter in the first post plus I read the link you posted where he mentions 1000 uF 200 volt capacitors being in the control box and 6 transistors in a power control circuit. From that its easy to deduce that its most likely a small 120 volt powered VFD unit and a special application 120 volt three phase motor. His just happens to be a PM type one.

(At least he is not stumped by how his air conditioner works.)

 

[tcmtech]

Only 10 amps? Even as 3 phase?

The output will still be limited by the size of the windings which in this case where designed to handle a 9.6 amp load split over the three of them.

Sorry but no free lunch on the amp capacity.

 

[Reloadron]

Nice figuring it out. I was like...how the hell did he come up with that?

To The OP

This guy is the duty genius at figuring stuff like this out. He also can build anything from an old welder.

Ron

 

[KeepItSimpleStupid]

We made a heavy duty mixer that way. A VFD and a 3 phase motor. Done: Variable speed, High torque.

 

[BrownOut]

(At least he is not stumped by how his air conditioner works.)

Or stumped by how his PC sound card works.