480 Volt 3 Phase Converter

[Turbo67]

New member here..

I like making things from stuff that was never intended to be used in the manner in which I use them.
For instance, a few years ago a friend of mine had a issue with a lathe he bought. The lathe was 480 volts with no prevision to rewire the motor to 220 other than having an electrical shop re-wind it. I believe it had a Italian motor and it was going to cost quite a bit to rewind it.

I wondered if I could set up a rotary phase converter to produce 480 Volt 3 phase from 220 Volt single phase.

I found a 3450 RPM 5 hp 240/480 volt 3 phase motor in a salvage yard for $25. The same salvage yard had two large transformers with a 2X step up leg for $25 each also.
I spent a day at another salvage yard and covered the bed of my lwb truck with various 3 phase cutoff boxes, electronics enclosures, on / off switches, contacts, etc. I believe I paid 50 for the entire lot. I also salvaged large capacitors from many different air conditioning equipment and industrial machines while there.

I set up the phase converter to be a push button start using the capacitors and a momentary contact pushbutton. The momentary button supplied the power to an electrical contactor, that when applied, connected one leg of the stepped up 480V to the dead leg of the motor using the capacitors to shift the phase for starting. Same principle as a static "phase converter" box. The pushbutton is held in while the main switch is thrown. It takes about a half second for the motor to reach full rpm, at which time you release the button, dropping the capacitors out and the motor continues to run on the two legs.

The transformers stepped up the 220V Single Phase to 480V Single Phase. I used one transformer per leg, for a total of two transformers. There was probably a more simple way, but this worked well.

Once the 480 Volt motor was running, it produced the third leg of the 3 phase power.

I have attached pictures of the set up and the frame I welded together to house it.

I liked the way this worked so well that I next set up my previous rope start rotary phase converter to a push button capacitive start as my next project.

 

[Alan Douglas]

It looks good. I made something similar but lower power, for a 550V motor in my Hardinge UM mill. I used a single step-up autotransformer to get 480V, and then a 480V 3-phase motor to generate the missing phase. The 550V motor runs fine on 480V, for the small projects I use it for.

 

[Turbo67]

It looks good. I made something similar but lower power, for a 550V motor in my Hardinge UM mill. I used a single step-up autotransformer to get 480V, and then a 480V 3-phase motor to generate the missing phase. The 550V motor runs fine on 480V, for the small projects I use it for.

Thanks!

I had to google the autotransformer you mentioned. I did not know that design existed, I have always thought of transformers as having primary and secondary windings and electrical isolation.

It is amazing to me that electrical stuff will work well out of the normal range of voltage. For instance, I wired a number of 270 volt fluorescent lights in my workshop to 240V. These lights are intended to run off the 270V line of three phase current. They work just as well on 240! They have been up for about 8 years now on the same bulbs.

 

[Alan Douglas]

Yes, if you don't need the isolation, it saves copper. Besides I happened to have it (and a couple more as I recall).

 

[Starlight Tools]

Turbo 67

Nice looking unit and well made.

May I suggest one thing though, the two input lines to the RPC, must be through a Magnetic switch.

Let's say you are working along and a power outage happens. If the power to the RPC is not switched off, when you come back to the unit many hours later and find that the power came back on, the unit just sits and hums until you press the start switch and since nobody was there to do that, the generator motor sits and hums until the magic smoke escapes.

I built a few based on the Fitch Williams plans and one was for a friend, and I instructed him to add teh Mag switch, but being cheap he did not use it. A few years later he had to rewind the 10 HP 3 Phase motor as just that had happened. Now I will not make or use one without it.

Actually I have gone to the dark side and use or sell the PhaseMAXX ssytems to my clients, that way, I know they are getting a safe unit which will not violate their insurance policy.

Here is a link to my set-up.

http://www.hobby-machinist.com/show...seMAXX-7TZ-Soft-Start-RPC?highlight=phasemaxx

Walter

 

[Turbo67]

Turbo 67


May I suggest one thing though, the two input lines to the RPC, must be through a Magnetic switch.


Walter

Thanks for the critique. Very good point on the magnetic switch....are those the items that use the "heaters", the thermals that heat up and open the circuit to the switch?

 

[Starlight Tools]

A magnetic switch is a large relay which consists of a coil that has a voltage fed through it and two push buttons One NC and one NO so when the NO switch is pressed it energizes the coil and pulls the armature in, then a secondary contact mounted to the armature and electrically in parallel with the NO switch contacts and keeps the armature held in. When the armature moves in it has the main contacts which allows the main current to flow. Many Mag switches then have a fuse block attached which are "heaters" that detect an overcurrent situation and will break the power to the coil if an overload is detected.

If a power outage happens, the voltage to the coil is lost and the armature opens shutting off the flow to whatever is being controlled. In order to restart the machine, the "on" push button switch must be pushed in to pull back in the armature.


These switches are common on machines over about 2 HP and are mandatory on machines that are remote form the operator.

Walter