Compressor advice needed

Hi Guys,
I just picked up a real nice upright compressor at a steal of a price.The bad news is the motor is 208v/416v 3ph.I'm not an electrical whiz like some on this board are and was looking for advice on the most practical and inexpensive way of getting it up a running on 240v 1ph.Is there a practical way of running a dedicated static phase converter with some kind of transformer to it or in the end is the most practical and inexpensive way of getting the job done is to swap out the motor for a single phase unit?Any advice would be greatly appreciated.

Thanks,
Dave

Motors are not usually rated for a single voltage, unless it is a "definite purpose" motor, which this may indeed be.

208 is sure to be found in a great many sites, but not 416. 480 Delta is a lot more common than is 416 Wye, which would imply 240 volts line-to-ground, which is itself quite uncommon.

I would check with the manufacturer and see if this motor is specifically restricted to 208 and 416, or if a range of voltages, such as 208-220/440, 208-230/460 or 208-240/480 is acceptable.

A motor's FLA will decrease as the applied voltage increases, unlike purely resistive loads, where the FLA will increase as the applied voltage increases.

I'm pretty sure you could run it on 240 volt three phase without hurting anything. You don't need any transformer if it's wired for the lower voltage.

Air compressors start and stop a lot, so a rotary converter might not actually be the best idea. A good static converter with start capacitor sized to start it within about 0.5 seconds might work well. It would not be very expensive, and if you built it right you'd get about 75 - 80 percent of the nameplate horsepower.

Stevco makes a really nice potential relay rated at 50 amps for about $20, available at Grainger. If you used that to cut out the start cap when the motor came up to speed, you might even be able to get by without using a contactor. Most electrolytic caps (the kind most used for start caps) will overheat if you start a motor more than about every 2 minutes, so you have to take that into account, and possibly use the aluminum can type run caps for starting.

Air compressors frequently have VERY funky horsepower ratings, which I've never been able to figure out. Hopefully the motor on yours uses the 'normal' horsepower rating and also gives a service factor. The nameplate horsepower times the service factor will give you what I call the actual horsepower. I figure 75 microfarads per actual horsepower to get the proper size for the start cap.

For a 10 hp motor with SF 1.15, this would work out to 862 mfd, so a start cap rated for 250 volts and 800 - 1000 mfd would start that motor up in half a second. Then the potential relay (which is normally closed) would cut the start cap out during running.

You could add some run caps for better performance. Let me know if you need to figure the size of these.