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5 hp 3 phase motor to a 3/4 hp single phase..?
(Pete Logghe) wrote in message . com...
"Paul" wrote in message ...
Well I gave up on finding a cheap 3 phase motor today and bought a new one.
I paid $172 out the door with a 2 year warranty (5 hp). Its a Chinese model
but hey
they company I bought it from said it was good and all the mining companies
around
here use them all the time. So I guess I will find out! At some point
during today I
ran out of "I am willing to drive around forever to find...cheap." Anyhow
next in
line I've got to connect this to a pony 3/4 horse single phase motor that I
have...
to use as a starter. Any ideas? The 5 hp motor has a 1 1/8" spindle and the
other
has a 5/8" spindle. I think I might try to make a sleeve to attach them end
to end.
Other than that pulleys perhaps? But that might take up a bunch of room.
Anyhow that's where I'm at.
Reno, Paul
For a 5 horse motor, ALL you need to get it started is a small
starting capacitor... About $5.00 worth. New.
Someone else will chime in, but I would go with about 500 mfd. 370 volt.
It's not too critical. The start button adds the starting capacitor.
When you take your finger off the starting button, it is no longer
connected.
The 5 horse motor wil snap up to speed. No sweat. Really.
Forget the pony motor.
Pete
5hp is way too small to bother with a pony, a 20 hp, maybe.
A higher voltage start cap wouldn't hurt. They make a real mess when
they blow up. If you add run caps, go for higher voltage and make
sure they don't use PCBs. I've had one or two run caps blow up as
well (which is an even bigger mess than the start caps - they just
start on fire)
Personally, I prefer to run low voltage, or at least low current
through the push buttons and use contactors to switch the caps in and
out. You can get a pretty good arc disconnecting the start cap.
It is good practice to put in a contactor that drops out and
disconnects all loads if the power drops. Perhaps not absolutely
necessary, but it could save you if Murphy is having a fun day.
Your motor is probably 3750 rpm. They work, but I'm not convinced
newer motors make better phase converters. I even managed to burn up
one 5hp unit and I think the 7.5 hp one I have now is starting to get
toasted. Probably time to drag out the meters and figure out how much
power is being wasted and retune accordingly.
Check out Hanrahan's article for wiring diagrams.
BTW, I got a 780 rpm 20 hp motor for $10 for the new shop. Now that
was a deal :-) For that, I'll probably use a pony and add in an old
computer to monitor and autotune it by switching in run caps as
needed. That's a ways off.
Paul
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