[jfroux_1]

Please help me with my rotary converter motor 7.5 hp! I’m following the procedure in this document http://www.practicalmachinist.com/FitchWConverter.pdf but I can’t balance the voltage. My L1 and L2 are stable 117 and 120 (measured with the ground). I don’t know why, but I need to put at lease 100 uf of capacitor for the Cp (between A and C / A=T1, C=T3) to get a decent voltage measurement between the leg and the reading is crazy Vab = 230 Vac = 285 Vbc = 462. When I put more capacitors Cp at 168 uf I get Vab = 229 Bac168 Vbc = 385. I just don’t know what to do to tune my legs and balance the voltage of my rotary conventer motor 7.5 hp. Thanks in advance for your support.

[generaldisarray]

I think you have your leads wrong on your motor. Caps wont fix that.

[Jim Dawson]

What generaldisarray said, swap the motor leads, at the A and C connection points and see what that does. And check it under load, I used 3 stove top elements as a resistive load for initial setup. Then did the final tuning when running the lathe. I had to play around with my connections a bit to get it to balance. Unloaded T1-T3 (A-C) is about 256, but loaded it's 240,240,239 (when I checked it today). I also used the FitchW pdf as the basis for my design.

EDIT: Are you sure you have the motor properly wired for 230V? T1 1-7, T2 2-8, T3 3-9, and 4,5,6 connected together.

[generaldisarray]

EDIT: Are you sure you have the motor properly wired for 230V? T1 1-7, T2 2-8, T3 3-9, and 4,5,6 connected together.

Thats what I meant, It sounds like the leads are mixed-up on the idler.
A converter with zero caps is not that far out of balance.

[jfroux_1]

Thanks for your comments. I just swap yellow and red, still the same results. As you can see on the pictures, there is only 3 wires coming out of my motor. I don't know which one is T1 or T2 or T3 and I though it was not very important... I guess I was wrong

Here are my connection to the capacitor
And here is the L1 and L2

[Jim Dawson]

The answer is in the first picture, the data tag on the motor. It's a 575V motor, you need a 230 or 230/460 motor. That motor will not work.

[jfroux_1]

I'm new to this... Thanks. Now I have to find a 10 HP 230/460 motor to run this 7.5 HP 575

[Jim Dawson]

Would you explain what you are trying to do here, I'm now a bit confused. Do you need 575V, 3phase for the end use?

[generaldisarray]

Would you explain what you are trying to do here, I'm now a bit confused. Do you need 575V, 3phase for the end use?

that makes two of us.

[jfroux_1]

I didn't know we can't use a 575v to build a rotary converter motor. Now I that I know that, I'll find a 10 hp 230/460 V and I'll use this 7.5 hp for my air compressor. Does it have to be 230/460? If it is just 460V on the nameplate is it ok?

[Jim Dawson]

I didn't know we can't use a 575v to build a rotary converter motor. Now I that I know that, I'll find a 10 hp 230/460 V and I'll use this 7.5 hp for my air compressor. Does it have to be 230/460? If it is just 460V on the nameplate is it ok?

Not 460 only, but could be 230 only. If your input is 230 then you need 230 volt motor. When I say 230 volt that includes 220 to 240 volt.

Do you have 575 volts available to run the air compressor with that 7.5 motor?

[jfroux_1]

Not 460 only, but could be 230 only. If your input is 230 then you need 230 volt motor. When I say 230 volt that includes 220 to 240 volt.

Do you have 575 volts available to run the air compressor with that 7.5 motor?

No I don't. I thought the 10hp 230/460 volts would be able to feed the 7.5 hp 575 volts

[handlewanker]

Hi.....No matter what you do it will not be a practical way to get 3 phase from single phase with a DIY rotary phase converter.

You "can" balance the legs with no load on but as soon as the load is applied the voltages will go out of balance.........I spent 2 grand on a commercial rotary phase converter to run a Bridgeport mill because of that problem.

If you run a 3 phase motor under load with unbalanced voltages long enough you risk burning out a winding.

It is impossible to manually adjust the capacitor values for voltage balancing on the legs with a fluctuating load.....that's why commercial units have electronic circuitry to do the balancing on the go as the load varies.
Ian.

[Jim Dawson]

Hi.....No matter what you do it will not be a practical way to get 3 phase from single phase with a DIY rotary phase converter.

Ian.

Ian, I'm going to disagree with you on this one. My DIY 15 hp RPC holds about 2 volts phase to phase under varying load. Unloaded my A-C leg is about 10 volts high (250V). As long as you are able to hold ~+/- 10% the motor will be fine at full load. With the normal fractional load, the voltage can vary even more without damaging the motor.

[Jim Dawson]

Sorry, without a transformer in the mix there is no way to get 575V out of 230V in. A rotary phase converter is Vout = roughly Vin. It converts single phase to 3 phase, but does not change the voltage too much. With proper balancing, Vout can = Vin +/- 2% or so phase to phase.

[jfroux_1]

Thanks for you input. I knew nothing about rotary convert few weeks ago. I thought it would be nice to run my air compressor and have 3 phases 575 volts in my garage. My main goal for now is to run my compressor (35 CFM). If I trade this 7.5 HP 575 volts for a 10 HP 230/460 will I be able to use this new 10 HP 3 phase motor with my 1 phase 220 volts in my garage to run my air compressor (for now I'll forget the idea of runing a rotary converter).

[jfroux_1]

Thanks for help. I just found a 230/460 10 HP motor. It has 12 wires coming out of the motor with numbers on it. How should I connect those wire? The wire draw I have there is only T1, T2 and T3.

[jfroux_1]

Sorry, I just looked all your posts and I saw that Jim gave me the right wires connection a while ago. I'll try...

[Jim Dawson]

Thanks for help. I just found a 230/460 10 HP motor. It has 12 wires coming out of the motor with numbers on it. How should I connect those wire? The wire draw I have there is only T1, T2 and T3.

12 wire motors are normally 2 speed motors. You have to get the wiring correct. Wire per the data plate on the motor.

Sorry, I just looked all your posts and I saw that Jim gave me the right wires connection a while ago. I'll try...

That was for a 9 wire, dual voltage motor. Do not use that connection for a 12 wire motor.


EDIT: There is still the issue of limited power available in your garage. At 30 amps available, you really don't have enough power to run more than 5 HP (about 23 amps on 230 single phase)

[Jim Dawson]

To run at full capacity a 35 CFM compressor needs about 10 HP, and to run on single phase 230 V that's about 50 amps, do you have that much power available in your garage? A 3 phase motor will only develop about 2/3 of it's rated power running on single phase, and you still need a way to start it. You could use your rotary phase converter parts to build a Static Phase Converter to start the 10 HP motor. But at best it's going to develop about 6.5 HP running on single phase, and unless the unloader valve works well the motor may not start the compressor at all. Have you considered a Briggs & Stratton to run your compressor?