Quincy QT-5 Air Compressor

I've heard you can't, but more recently I've heard you can. Here is my personal experience (i.e. not what I've read but what I've learned on my own and know to be true): if you go for the rewiring you may find it was wired for 440V 3 phase so the mag switch may not be large enough to control a single-phase 5hp motor, and new mag switches big enough are really expensive. Also, 5hp single-phase motors are expensive too. That Quincy should unload after a cycle for easy starting (mine does) -- you can check that with Quincy by calling them, that's one reason to deal with a quality US company is you can just call 'em up. If it does unload, then I'd think a phase converter is no problem. Double-check the voltage, though. Lots and lots of big compressors came wired for 440V and yes, the motors can be rewired for 220 but the controls are then not beefy enough and you find yourself needing $250 worth of parts. - GWE

Grant, do you think that the OP could substitute that 5.5 HP motor with a 3 HP motor and a smaller pulley?

i

A 5 Hp compressor-duty motor (single phase) will cost a bundle, unless you get real lucky. A compressor is a pretty severe load for a phase converter, but this Quincy should have an unloader which will help immensely. The remaining problem is the current draw on single-phase

240 V is going to be pretty high, couldn't be less than 18 A running. Due to the high lagging current (low power factor) of rotary phase converters, the line current is likely to be much higher unless you use the power factor correcting caps, too.

Unless you do something to reduce the load (such as reducing the max pressure switch setting or changing the motor pulley) you can't run it from a "static" phase converter. These really run the motor on single phase after starting, and you are lucky to get 2/3 of rated HP from the motor.

Jon

My 3 HP motor is rated or 16A. 16*5/3 = 26 amps.

I would think that the sensible thing to do would be to get a 3 HP motor and a smaller pulley.

i

aaah, I think there is a bit of excess "doom and gloom" here - I have a quincy compressor with a 5 hp single phase motor running on a 20 amp breaker set, no problem - I'd speculate that the three phase motor won't draw a whole lot more power

For reference, you can get a 5hp 240 single phase motor for about $400 - $450 from Grainger, a 3 hp would run $50 less. That puts a limit on how much to spend on this whole deal.

A rotary phase converter should work fine for this but you would want at least a 7-1/2 hp 3 phase motor, if not a 10hp for this hard starting load. I jsut got done building a rotary unit, the motor was fairly cheap but the necessary run capacitors started adding up fairly quickly.

I'd stay away from a static converter. Your compressor will put a heavy starting load on it.

snipped-for-privacy@comcast.net wrote:

Sure. You just get 3/5 as much air, that's all. In fact, I still have the 3HP 3-phase motor and the smaller pulley that came to me on *my* Quincy. Running the air pump slower also means quieter and longer lived, so it isn't all bad. - GWE