Hi Guys,

Is it feasible to run a Quincy QT-5,5 HP Air compressor off of a phase
converter? Would I be better off changing the motor to a single phase
unit? Any help would be appreciated.

Joe...

wrote:
Hi Guys,

Is it feasible to run a Quincy QT-5,5 HP Air compressor off of a phase
converter? Would I be better off changing the motor to a single phase
unit? Any help would be appreciated.

Joe...


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

wrote:
Hi Guys,

Is it feasible to run a Quincy QT-5,5 HP Air compressor off of a phase
converter? Would I be better off changing the motor to a single phase
unit? Any help would be appreciated.

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

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


"Jon Elson" wrote in message
rvers.com...
wrote:
Hi Guys,

Is it feasible to run a Quincy QT-5,5 HP Air compressor off of a phase
converter? Would I be better off changing the motor to a single phase
unit? Any help would be appreciated.

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

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.



wrote:
Hi Guys,

Is it feasible to run a Quincy QT-5,5 HP Air compressor off of a phase
converter? Would I be better off changing the motor to a single phase
unit? Any help would be appreciated.

Joe...

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

i

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