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# Thread: Retro a 3 phase to single phase

1. Looking at your photos, it looks like you have 220 coming in on the two legs?

Is it 110 per leg? I had it in my head that you supplied 110 on two legs and that would/could create the 106-130 in the third phase.
In his example he was using 110 on each leg, just trying to figure out your diagram. My electrical training was a long time ago.

2. ## Rotary phase converter (single phase 240 to three phase 480)

Making three phase is possible and fairly easy. Don't let the disconnects, contactors, and so forth phase you because you don't need to be this elaborate. We simply had access to the parts for free. Small 3 phase setups often don't even need a single phase startup motor you can simple get them spinning by giving them a kick or with a start capacitor.

Our Setup:
30HP 3 phase motor
1HP 1 phase motor
A few pulleys, a belt, and some wires etc.

How it Works:
The 1HP single phase motor spins up the 30 horse power three phase motor (otherwise the inrush current will trip your breakers) then a series of contactors open and close to disengage the small motor and apply power to the large motor. Once power is applied to the large motor it generates the third phase on the third leg. We balanced the phases by trial and error with capacitors until all legs were within +-2 volts.

This video was taken before we wired in a 100 amp feeder directly from the house panel. We can run our Hypertherm 1650 at a constant 85 amps.

Feel free to PM me if you have any questions.

3. Originally Posted by cjsamples
Looking at your photos, it looks like you have 220 coming in on the two legs?
If the 3ph motor is 220, then you use the 1ph 240 supply to feed the RPC, this produces a third conductor phase that if accurately balanced by tuning provides 240v between any two phases.
Al.

4. ok, so you are talking about the 2 legs of 110 from a 220 breaker? It is on two different phases so that part would be good to go. then use some capacitors to bring up the third leg to +/- 2 volts.

I had everything in my head correct until the mention of caps. Who, what, where? Let me go back and see if I can decode the diagram. The letters are a little smashed on my screen.

Lukewarm: That is how the guy had his set up. little motor to spin the big one, flip the switch and presto, 3 phase. Any idea what size 3 phase I would need ot run the little 1/4 hp cross feed motor?

5. As mentioned earlier, if you are replacing the spindle with a DC motor, it would be cheaper and easier and quieter to put a small 1/4 hp VFD to run the axis motor.
Al.

6. Something like this?
1HP 115 Volt -- USE AS A PHASE CONVERTER PLUS GET VARIABLE SPEED, Model JNEV-101-H1, Single Phase Input ONLY, Three Phase Output, variable frequency drive, variable frequency drives, ac drive, vfd, afd, frequency drive, drive, inverter, adjustable sp

At 1 hp that should run everything. I didn't catch that it could be purchased for what I am going to pay for the DC motor. \$131.
Duh!! See I learned more than one thing tonight. I should just go ahead and purchase that thing right now.

7. Generally the 120v in 220 out are low HP, the 240 in 240 out are usually a better choice, unless it is just for the 1/4hp.
Al.

8. ## trying to buy local

Ok, so I spoke with a guy locally here to purchase a VFD. Told him what I was powering and he mentioned that the VFD would be fine for motors running constantly. The cross feed table is a switch on/off deal. Motor only runs when it is switched.
So now I purchase 2 VFD or 1 VFD and make the spindle motor swap.....sheeesh!!
1/2 hp VFD is around \$65 and then the 1HP for the spindle would be \$118.

Having the VFD for the cross feed makes sense as all of the limit switches will operate normal.

Now just have to decide how to proceed. Thanks for all the input.
Chris

9. Originally Posted by cjsamples

Having the VFD for the cross feed makes sense as all of the limit switches will operate normal.

Chris
You will however have to switch the limits over to the VFD control inputs, you should not switch the power to the VFD for on/off over travel control etc.
Al.

10. So use the control terminals on the VFD to interrupt power to the motor? Or use the existing relays and switches that shut the motor off?

11. Yes the fwd/rev/off switches should be tied in with any limit switches etc to the low voltage VFD control, any contactor on the input should be controlled by a E-Stop operation only.
Al.

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