I got Vance's water pump dyno set up in the hangar today.
I very carefully adjusted the position of the motor in the frame
to be certain the axis of the motor coincided with the pivot
axis of the frame. I then static balanced the whole rig by adding weight
to the top of the motor to compensate for the motor mounting flange
on the bottom of the motor and the weight of the frame.
I used a digital fish scale that can read down to one oz.
With the motor off it reads zero. With no water in the system
and the motor running it reads three ounces (.19 pound) due to
friction in the pump bearings and seals and V belt inefficiency.
That is a torque of 39 inch ounces (.2 foot pound) at a motor
RPM of about 3600 RPM. That is .14 HP if my arithmetic is correct.
BTW at 746 watts per HP that is 104 watts. At 12 volts that would
be a current draw of about 8.7 amps assuming the DC electric motor
was 100% efficient. At 80% typical motor efficiency that would be
about 11 amps.
I then put some water in the system and the 30 amp 220 volt circuit
breaker promptly blew and the motor smoked. It worked fine in Vance's
shop. Just my luck the CC motor decided to take a crap just as I was
getting ready to take some good data. Vance is coming over to have a look.
If necessary I will buy a new motor.
Paul Lamar
Paul - definatly do not buy a new motor - we can come up with an alternate
rig using
a DC type motor which wll give us speed flexibility as well as a power
requirement.
That motor resided for a long time next to my mill which averages about a
bushel of aluminum chips every other month - so I suspect it injested
some and perhaps arced over. Vance
I am going to take the motor off there and take it apart today and see if
I can figure out what went wrong.
Paul Lamar
When I took Vance's motor apart it was history. The rear bearing had seized and
burned out one of the coils. On Vances recommendation I stopped in at Harbor
Freight and bought a CC 5 HP 220 volt motor. $80 on sale. Spent the day adapting it to
the existing dyno mount and static balancing it. Now works great. Pump runs
at 4500 RPM at 40 gal per minute and generates about 5 psi across the pump. I am not
happy with the valve that vance used as there is always a press. drop across it even
when it is wide open. With the original ball valve there was no drop
when it was wide open and one could see almost 70 GPM at 4500 pump
RPM.
At 40 GPM and 4500 pump RPM the digital fish scale was reading about 1 pound
one ounce or 1.06 pounds. Lever arm is 13 inches or 1.08 feet. Torque was
therefore 1.15 foot pound. At 3650 motor RPM that is about .8 HP.
Again BTW that would be 597 watts or about 50 amps if it were a 100%
efficient electric motor. Typical 80% electric motor efficiency
would be about 62 amps.
4500 pump RPM is of course only about 3400 engine RPM so we are
still not at take off or climb RPM. Worst case for cooling would be
at a PSRU ratio of 2.17 would be WOT around 6000 engine RPM and
about 8000 pump RPM.
Next step is fit the 8 inch pulley on the 5 HP electric motor
and run the pump at 7200 RPM to check the flow and HP.
My guess is it will be at least double.
One or two more days and the pump is coming off the test rig
and going on the dyno engine.
Paul Lamar
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