Getting 480 Volts in a Single phase envirionment

[Rich Carlstedt]

Just to pass on the info.
last night I finished wiring a "home made "
3 phase conversion at a friends shop and wanted to pass the method and the results to others.
He has a 15 inch Nardina lathe with a 480 volt Delta wound motor.
this means it cannot be reconfigured for 240 as there are only three wires coming out of the sealed/baked windings. to make matters worse, it is also a 2 speed motor (ie 850/1700).(more wires)
His shop has 60 amp 240 single phase power.
The motor is rated as 6 KVA and when talking to the factory, it seems to be a 7 1/2 HP motor ( NO HP listed on name plate, as it is "custom").
We installed a 30 amp double braker in the power panel (ie 12 KVA ~)
This fed a surplus 11 KVA step down transformer (480 to 240) BUT we had to reverse the feed so it was a step up transformer (derate slightly) to go from 240 to 480 volts.
Then we went into a disconnect box (480 V 15 Amps single phase).
This fed two things, the "control transformer" in the machine (makes 120 and 24 volts) for relays and brake, AND a Hitachi S100 480 Volt 7.5 KVA inverter.
these inverters go for about 500 to 600 bucks .
The inverter is really for 3 phase input/output, but by feeding it single phase input, you need to downrate it. it will handle 16 amps output max ( not tested)..
The lathe runs beautifully. it pulls 3 amps in high speed no load , so the inverter has plenty of room.
When I was able to pull 9 amps, all three legs were perfectly balanced.
the ability to run in either speed was impressive . i expected some balking by the inverter, but as long as motor power is off (ie. 0 Freq!) the two speed switch can be thrown and the control comes online smoothly when called for
My friend is tickled pink as they say..

I what to thank members of this board for the words of knowledge and suggestions made !
Rich

[dannystooblue]

I have a question, I have almost the same thing going on as you have described here. I have a 3hp 440v 3-phase motor on a clausing lathe. there are 6 wires coming out of the motor. the name plate does not say that it is 220/440, it is clearly marked only 440. All i have is single phase electric running a 5hp 220v rotary phase converter right now. is it possible to rewire this motor for the 220? it says also on the tag that it has double windings.

Danny

[Rich Carlstedt]

Danny
normally a 3 phase 220/440 motor has 9 leads.

A Three phase delta motor can have 3 or 6 depending on the manufacturer, but these motors are single voltage to the best of my knowledge.

A 440 Two Speed motor will also have 6 wires, and I have to assume that is what you have with your lathe.

There is a way to wire a RPC to convert to 440, but I have never done that ..Yet.. so I can't comment.
I believe you will have to follow what I did above, or get a new motor.
Rich

[dannystooblue]

Rich, what would be the advantages of using an inverter instead of a RPC? How much would the transformer run, ballpark?

Danny

[Rich Carlstedt]

A transformer , say 5 K (watts) probably will run a hundred bucks surplus.
But I have no way of really knowing that..The big one I used on my buddies setup was free.
If you can find a Industrial building being torn down, you can get them for nothing. Junk yards also are a source EXCEPT...if it is burned out !
I make all my own Static and RPC's. have built over 50 of them
The advantage of a VFD is quieter operation than a RPC, and lower power consumption.
If power costs are not an issue, or noise, then a RPC is fine.
RPC's are cheaper if you build one, but not if you go out and buy one, than a VFD is less costly
Rich