3 Phase converter + 480/ 208V transformer ?

Mar 10, 2007 10 Replies

I currently run a 5HP RPC to produce 3 Phase 240V. I am considering a transformer to step up to 480V 3ph for a 480V lathe. A friend suggested that I should be careful not to buy a transformer with too high a kVA rating because it may overload my phase converter while powering up. So I am looking for advise on what I should consider as an upper kVA size transformer so as not to overload my 5HP RPC. The lathe has a 3HP motor. Thanks so much! Stan



I'm not going to try to come up with sizing but have you checked the price of transformers relative to a 240V 3P motor?

Wes

its likely WAY cheaper to RE-motor the lathe than to get the transformer

or they MIGHT make Boost VFD's too 240 3p in 440 3p out

But transformers are very expensive compared to motors

I was looking at used transformers in the $200 range and I had assumed that finding the correct mounting for another motor would be a headache. Considering the weight and hassle of a transformer, perhaps I should explore replacing the motor. Thanks, Stan

Stan

Pist a good picture of the motor's dataplate. Most modern motors are of standard frame size.

i

First, did you check to see if the existing motor on the lathe can be switched to 220?

Most machinery can be switched by changing the wiring configeration in the motor electrical cover. European motors have six wires coming out of the windings and US motors usually have nine. Usually you have to change the tap on the control transformer or worst case, change the coil on the starter contactor.

Remember that every time you got through a transformer you lose 5 or more percent of your power in loses.

John

Perhaps if you remove the cover plate on the motor you may find that the motor will operate on either 208 or 440 by simply restrapping. Most 3 ph motors have this feature. Steve

I've never tried it, but maybe some one out there may know the answer. A standard 220/440 volt 3 phase motor has 6 windings, and you wire them in 3 parallel windings for 220v and 3 series windings for 440v; right! Now on your phase converter motor, you connect the incoming

220v to the center tap of the 440v series winding and connect the output to the 440v tap. The motor windings should act like an autotransformer and step up the output voltage.

DBW

Not all 460v motors are dual voltage. Just yesterday I scrapped one that was 460v only (Reliance Duty Master).

i

Most two speed (or more) motors are single voltage only.

Gunner

Political Correctness

A doctrine fostered by a delusional, illogical liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.

That's an interesting comment, I did not think about it, but it makes sense. Thank you.

i

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