10hp single ph motor

Hey guys,

A friend of mine is having compressor issues. He has another com0ressor that has a 3 phase 10 hp motor. He had asked me about putting a 10 hp single phase motor on it. I told him not to jump on buying the 1ph motor yet as I thought I had read somewhere on here that a 10 hp 1ph motor is just not efficiant or good. I did a search and cannot seem to find the thread where I may have read that. For what reasons would a 10 hp 1ph motor not work so well?

My friend also talked about a phase convertor. Going by memory from what I've read on this site and not from personal experiance. I told him not to use a static phase convertor in an application like a compressor since it constantly runs at full load.

So, I guess the fork in the road is to either to run a rotary phase convertor or purchase the 10hp 1ph Baldor motor. If he were to run an RPC, would it need to be sized for 15 or more hp? Let me know what you guys think the best direction is to go with this situation.

thanks in advance,
Mark
Berkshire Transmissions
North Adams, Massachusetts

Curious myself

Similiar situation here. I was gonna do a converter / transformer setup. (Since it's what I have on hand. ) But I really didn't wanna get into another "project" right now.

I also have a 25HP motor standing by for a possible pony-idler type setup.

Guess your situation depends on your demand. If you need it NOW, or if you have a little time to build something.

Will be watching......

~Chainz~

I'm not an electrician, but I have run a professional wood shop, and amateur machine shop on a combination of 3ph & 1 ph machines for over 30 yrs. My choice is to have single phase on the compressors, because they often need to be run when it is inconvenient to fire up one of the RPC's. I have both 7.5 (36.6A) Kellogg-American and 5 HP (25A)IR T30 2 stage compressors. When needed for sand blasting, both are run but the KA cuts in & out at lower pressures. For normal shop air, the KA runs alone, but fills both tanks.

One thing that stuck in my mind from a similar Q to yours a number of years ago, is that one of the EE's on the site (or maybe it was over on OWWM) stated that a good single phase cap start motor could often have better starting torque than a 3phase motor. Not enough to make the difference reason for the choice of one over the other if you have 3ph mains. But enough so that you don't need to feel you are giving anything up if you want to stick with single phase on a compressor because you only have single phase mains.

My only advice would be to have good starters on the motor and be sure the heaters are correct according to mfg reccomendations, not just estimated by amp draw. For all practical purposes a 3ph motor does not have anything to go wrong with it except the bearings. A single phase has whatever starting method is used (caps or centrifugal switch or both), and they do fail.

smt