Karl,
Since you are drawing 2 amps that sounds like it's truely operating at
1/2 hp.

I have heard of "constant torque" VFD's.
Never seen "constant horsepower" in the literature.

So, since hp = rpm x torque,
if you cut the rpm in half, you are going to get only 1/4 hp.

I think the best bet is to get the pulleys for the 3.5 reduction, and
use a 1 hp motor and VFD.
Or, if $ is most important, rig up a jack shaft, for a secondary
reduction.

If you go to the 1 hp & VFD, it's best to get an "inverter duty"
motor. My motor man tells me the insulation on older/standard motors
will break down over time. I have one "inverter duty" motor on a VFD
with no probs, one unknown on a VFD that has been fine for years
(intermittent duty), and had one old motor that wound not work on a
VFD.

Dave J.


On Sep 15, 7:00*am, "Karl Townsend"
wrote:
My apple water bin dump uses a .5 horse 3 phase 220 VAC motor attached by
pulleys and belt to an outboard motor prop in a tube to pump water. Maybe 1"
head at 100+ GPM. I just measured the current draw on this motor at 1.5 amp,
2.0 amp, and 2.2 amp with a clamp A-meter.

Its a 1725 RPM motor with 2.2 reduction to the prop, so the prop turns about
800. Its a NOISY operation. The prop cavitates *and pulls air even with all
the deflectors I can install to stop the vortex. (I've only lived with it
since 1988)

I bought a prop that will throw a guestimated 3 times the water per
revolution. There's no way to know until its installed. I have the physical
room to change the pulleys and get a 3.5 reduction or about 500 RPM. That's
most likely too fast and too much water.

OK, now to the question. Will installing a VFD and running the motor at 50%
speed have a good chance at working? Or, do I need a larger motor and VFD?
I want to move the same amount of water.

Karl