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I reinstalled the 6" pulley and set up the flow system to pump through my
evaporator cores plumbed in parallel. Pictures are attached.
I borrowed a optical digital tach to measure the actual pump rpm, however
this created an unusual "opportunity". It works by counting pulses, and the
flourescent lights give a reading of 3600 rpm due to the 60 cycle current.
Therefore to measure the rpm, I had to run it in total darkness with a
flashlight illuminating the pulley. I used two strips of foil on the pulley
to reflect light pulses back to the tach. The pump rpm with a 6" pulley on
the 3450 rpm motor was 5160 RPM.
I then plumbed my evaporator cores in parallel as shown in "Parallel cores"
photo. These were hooked to the pump outlet, and full flow tests were
performed.
Motor RPM = 3450 (name-plate reading)
Pump RPM = 5160 (measured by Tach)
Pressure generated at no flow = ~20 psi
Pressure generated at full flow, no evaporator cores in line = 2.5 psi
Pressure with cores in place = 8 psi
Time to fill 5.8 gallons = 14-15 seconds (flowing through rads) = 23-25
gallons per minute.
Current on ammeter = 13 amps = 1560 watts
The current was measured with a clamp-on ammeter supplied by Charlie England.
Interestingly, the current on the motor with no load (i.e. only spinning
itself) was ~10 amps, which I don't understand. I have since been told that
measuring current and voltage can give misleading results on an induction
motor, due to power factor issues, and that an actual watt-meter needs to be
used. Charlie -- thanks for the loan of the ammeter, I will be returning it
tomorrow or Tuesday.
I also tried an 8" pulley, however those tests could not be completed because
the motor drew so much current that the circuit breaker would blow. (About 25
amps after a 50 amp in-rush). An 8" pulley would give somewhere over 7000 rpm
on the pump, but it would not stay powered long enough to make accurate
measurements.
Bill Schertz
KIS Cruiser #4045
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