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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


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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


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Default pump design help

Sounds like you need to run a much lower pitch prop. If it is
cavitating, you are just wasting energy. Are you running it in a tunnel?
Pitch? Diameter?

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


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On Mon, 15 Sep 2008 11:16:18 -0500, RoyJ wrote:

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


Sounds like you need to run a much lower pitch prop. If it is
cavitating, you are just wasting energy. Are you running it in a tunnel?
Pitch? Diameter?

Sounds reasonable to me. Lower pitch is like more reduction on the
pulley. If the noise comes from the cavitation then the lower pitch will
solve it. If the noise comes from vibration or gear noise just from
turning 800RPM then lower speed won't help at all, of course.

How noisy is it with no prop?




--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
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Sounds like you need to run a much lower pitch prop. If it is cavitating,
you are just wasting energy. Are you running it in a tunnel? Pitch?
Diameter?


I need to run lower RPM to get rid of the cavitation. I'll need a higher
pitch to still move enough water. My question is do I need a larger motor
and VFD.

Karl




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Karl Townsend wrote:
Sounds like you need to run a much lower pitch prop. If it is cavitating,
you are just wasting energy. Are you running it in a tunnel? Pitch?
Diameter?


I need to run lower RPM to get rid of the cavitation. I'll need a higher
pitch to still move enough water. My question is do I need a larger motor
and VFD.

Cavitation comes about because the pressure on the lifting surface of
the prop blades falls below the vapor pressure of water*, and the water
"boils".

For a given pressure differential across the prop, a higher pitch prop
is going to have to generate more lift, because it'll be working at a
less advantageous angle.

All else being equal, if playing with pitch and speed without adjusting
diameter will get you there, a lower pitch, higher speed prop should be
the way to go. Theory says you should be able to do this with a larger
diameter prop, to get your volume at a lower pressure differential
followed by a nozzle to get the pressure up -- but this is where the
fluid dynamics part of my brain starts flashing a red light next to a
sign that says "ask a real hydrodynamicist". So I may try it myself at
home, but if I were going to take your money to try it I'd be playing
with scale models at a wet bench -- and I'd start by advising you that
you'd spend your money more effectively with a real hydrodynamicist.

I'd suggest that you consult a boat racing site or expert, because they
deal with cavitation all the time. But expert racers can have notions
that are quite divergent from reality; myths and legends that were the
best that science could come up with in 1908 somehow get carried forward
to 2008 as if hundreds of physicists and mechanical engineers hadn't
spent their entire careers improving the state of the art.

So, consult a boat racing site or expert, but bring your salt shaker.

* Ya, ya -- I'm simplifying. So sue me.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
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On Sep 15, 7:00*am, "Karl Townsend"
wrote:


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


My thoughts are reduce pitch to reduce cavitation. Increase diameter
to increase flow. Since you are running in a tube, increasing
diameter might be difficult. So another off the wall idea would be to
run two props on the same shaft. Maybe with the first prop slightly
lower pitch than the second prop. This is likely to be a poor idea as
I am more of a EE than ME. I am sure someone will pipe up with why
this is a good or bad idea.

Dan

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Karl Townsend wrote:

Sounds like you need to run a much lower pitch prop. If it is cavitating,
you are just wasting energy. Are you running it in a tunnel? Pitch?
Diameter?


I need to run lower RPM to get rid of the cavitation. I'll need a higher
pitch to still move enough water. My question is do I need a larger motor
and VFD.

Karl


I might start with the VFD. If it's cavitating I'd expect it's being
driven too fast, and slowing it down to stop the cavitation may still
give you the same flow since the cavitation isn't helping the flow.
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On Mon, 15 Sep 2008 09:00:13 -0500, "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.


Call amusement ride builders like Arrow Dynamics, S&S or Vekoma, or
your local amusement parks that have these ride systems - does the
Mall Of America have a log flume or 'Tunnel Of Love' style dark rides?

The standard propulsion method for the boats in a flume ride is a
small propeller in a cast aluminum or bronze vortex cone, direct
coupled to a submersible well pump motor. Four stand-offs between the
vortex base and the mounting bolts on the shaft end of the pump,
debris screen optional. Creates a nice current, and motor cooling is
never an issue.

And they do make inverter duty submersible well motors.

-- Bruce --



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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.


Na, I'm not totally re doing something that has run 20 years. But I'd like
to try a different prop - it might be better. If not, I'll go back. My only
question is if this motor will have enough power at 1/2 speed. Do you know
how to figure that?



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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.


Na, I'm not totally re doing something that has run 20 years. But I'd like
to try a different prop - it might be better. If not, I'll go back. My only
question is if this motor will have enough power at 1/2 speed. Do you know
how to figure that?


It likely will be fine. You could also change the pulleys to get the
ratio you need. Indeed, you could find the correct speed using a VFD and
then replace the VFD with the correct pulleys to get the prop speed you
need at the full motor speed and put the VFD on the shelf for the next
project.
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On Mon, 15 Sep 2008 12:49:06 -0500, "Pete C."
wrote:


Karl Townsend wrote:

Sounds like you need to run a much lower pitch prop. If it is cavitating,
you are just wasting energy. Are you running it in a tunnel? Pitch?
Diameter?


I need to run lower RPM to get rid of the cavitation. I'll need a higher
pitch to still move enough water. My question is do I need a larger motor
and VFD.

Karl


I might start with the VFD. If it's cavitating I'd expect it's being
driven too fast, and slowing it down to stop the cavitation may still
give you the same flow since the cavitation isn't helping the flow.


Indeed.

Ive had the same issues with 3ph fans..run them too fast and they
simply stop pushing air, so had to throttle them back to a lower speed
and voila! they started pushing air again.


"Obama, raises taxes and kills babies. Sarah Palin - raises babies
and kills taxes." Pyotr Flipivich
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"Karl Townsend" wrote in message
anews.com...
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.


Na, I'm not totally re doing something that has run 20 years. But I'd
like to try a different prop - it might be better. If not, I'll go
back. My only question is if this motor will have enough power at 1/2
speed. Do you know how to figure that?


First, the mass of water moved and the head determine the hp, ignoring
frictional losses, so gearing down and changing the prop pitch to move
the same amount of water should require the same hp so I'd start with
the motor you have now if you gear down with pulleys. If a vfd gives
constant torque but now the motor is running slower, then it will
develop less hp so you need a bigger motor. hp=torque*rpm/5252 in sae
units, so right now at .5 hp at the motor you are getting 1.52 ft-lbs at
1725 rpm. If you wanted .5 hp at 863 rpm that means you need 3.04
ft-lbs of torque, and if you want to get that by running a 1725 rpm
motor at half speed with a vfd that would be a motor that makes 3.04
ft-lbs at 1725 rpm or a 1 hp motor. Clear as murky mud? :-)

--
Regards,
Carl Ijames carl.ijames at verizon.net


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Carl Ijames wrote:
"Karl Townsend" wrote in message
anews.com...
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.

Na, I'm not totally re doing something that has run 20 years. But I'd
like to try a different prop - it might be better. If not, I'll go
back. My only question is if this motor will have enough power at 1/2
speed. Do you know how to figure that?


First, the mass of water moved and the head determine the hp, ignoring
frictional losses, so gearing down and changing the prop pitch to move
the same amount of water should require the same hp so I'd start with
the motor you have now if you gear down with pulleys. If a vfd gives
constant torque but now the motor is running slower, then it will
develop less hp so you need a bigger motor. hp=torque*rpm/5252 in sae
units, so right now at .5 hp at the motor you are getting 1.52 ft-lbs at
1725 rpm. If you wanted .5 hp at 863 rpm that means you need 3.04
ft-lbs of torque, and if you want to get that by running a 1725 rpm
motor at half speed with a vfd that would be a motor that makes 3.04
ft-lbs at 1725 rpm or a 1 hp motor. Clear as murky mud? :-)


You mean mass flow rate and head determine the HP, ignoring all
efficiency contributors.

By my calculations you should need 1 lbf-ft/sec to move 100gpm at 1"
head, or about 1/550th of a horsepower.

At 100% efficiency he should be able to gear down a gerbil to do this;
0.5HP should be overkill by a factor of about 270:1.

(1" head)(.43 psi/" of head)(144 sqin/sqft) = 5.2 lb/sqft of pressure.

(100gpm)(0.125 cuft/gal)(1min/60 sec) = 0.208 cuft/sec

(5.2 lb/sqft)(0.208 cuft/sec) = 1.09 lb-ft/sec.

So how much noise _does_ 0.499HP worth of cavitation make?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html


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Karl Townsend wrote:
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)

If you need 1/2 Hp delivered to the prop, then you need a 1 Hp rated
motor at 30 Hz to deliver 1/2 Hp. Below rated speed, all induction
motors are constant torque. Above rated speed you get constant HP
output. So, running a 1/2 HP motor at 30 Hz, it will pull rated current
at only 1/4 Hp, and long operation at 1/2 Hp load will smoke it.

Jon
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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 really doubt you can make an outboard motor prop cavitate with a 1/2
Hp drive. It takes real HP input to the prop to do that. My guess is
it is just sucking air due to turbulence, I don't know what sort of
deflectors you are using, maybe some screens one inside the other would
stop the rotation. Making the intake the largest diameter you can would
help the air to not be trapped in the water.

Jon
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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.


Na, I'm not totally re doing something that has run 20 years. But I'd like
to try a different prop - it might be better. If not, I'll go back. My only
question is if this motor will have enough power at 1/2 speed. Do you know
how to figure that?



I can guarantee you will not get 1/2 Hp out of a 1/2 Hp-rated motor at
30 Hz. You will get 1/4 Hp at rated load. It scales linearly with
frequency (speed) below the rating point. If you try to load the motor
to the rated mechanical output, it will draw twice the rated input
current (roughly) and smoke.

Jon
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On Tue, 16 Sep 2008 11:41:30 -0500, Jon Elson wrote:

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.


Na, I'm not totally re doing something that has run 20 years. But I'd
like to try a different prop - it might be better. If not, I'll go
back. My only question is if this motor will have enough power at 1/2
speed. Do you know how to figure that?



I can guarantee you will not get 1/2 Hp out of a 1/2 Hp-rated motor at
30 Hz. You will get 1/4 Hp at rated load. It scales linearly with
frequency (speed) below the rating point. If you try to load the motor
to the rated mechanical output, it will draw twice the rated input
current (roughly) and smoke.

Jon


In this case available torque is more or less proportional to current.
Hence the need to halve the HP when you halve the speed.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
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On Mon, 15 Sep 2008 09:00:13 -0500, "Karl Townsend"
wrote:



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


Before you change the prop, try wiring in the VFD and seeing if you can get a
decent flow at a lower speed with the existing setup. If it's either
cavitating or (worse) pulling in air, it may well pump better at lower speed
anyway.

Is the lead in to the prop properly streamlined and gently divergent? Pressure
drop before the prop is your enemy. Higher net-positive-suction-head is your
friend to avoid cavitation.

Mark Rand
RTFM
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