Induction motor on Trace DR series = Results of test [RE-wrenches]

[Mr. Sharkey]

Since I did receive a couple of messages saying that there was some
interest in the results of my testing, here's what I found when actually
powering the pump motor with the inverter:

Test #1, Grid power:

After installing a suction hose and attaching the delivery nozzle, the pump
was plugged into the grid outlet and started. A mixture of Biodiesel (about
two gallons) and Stoddard Fluid (mineral spirits and red dye used at the
factory for calibration) flowed though the pump and back into the 5 gallon
bucket which the supply hose was drawing from.

AC amps = 10.3 as measured with cheap AC amp clamp.

Test #2, Trace SW series:

As a benchmark, we ran the pump motor on my Trace SW2512 (serial #00013).
Batteries consisted of four series strings of 450 Ah lead-calcium telephone
batteries connected in parallel for a total of 1,800 Ah. PV charging
sources were disconnected for this test.

DC volts = 12.45 (E-meter)
DC amps = 60 (E-meter)
DC watts = 747 (calculated)
AC amps = 10.3 (amp clamp)
AC amps = 6 (SW metering)

We pumped about 20 gallons like this. Nothing different noted about
operation from that when using grid power.

Test #3, Trace DR series.

Time to get serious. Set up the Trace DR1512, using a Hinemann 175 amp
circuit breaker, 50mv/500A shunt, 2/0 fine-strand cables.  Batteries
consisted of a 13 year-old set of T105's which have only been lightly
cycled during their life. Started and stopped the pump motor multiple times
to check ability of DR to start pump motor. No problems noted. Motor does
make a noticeably louder hum.

DC volts = 11.35 (Fluke 77 DMM)
DC amps = 73 (Fluke 77 DMM via shunt)
DC watts = 828 (calculated)
AC amps = 10.3 (amp clamp)

After letting the pump run for about 20 minutes and pumping 250 gallons of
fuel, the motor was uncomfortably hot to the touch. Battery voltage was
down to 11.24 volts, but not dropping quickly. We shut down the pump to
test restarting. Battery voltage at rest after pumping, 12.1 volts. At this
point, the AC motor did not reliably start. Startup torque seemed
inadequate, and in many cases, the motor would only start if the delivery
nozzle was opened to allow fuel to exit the system. I tried using a 90 watt
incandescent lamp to keep the inverter out of search mode, which did help a
bit, but startup was still hit-or-miss. At motor starting, battery terminal
voltage dipped to 10 volts. During the times when the AC motor would not
start, the lamp was dim, and battery voltage was down around 8+ volts. No
overload indicators were noted on the DR.  (using factory default
middle-of-the-dial disconnect/overload setting).

Conclusions:

The amp clamp I was using is obviously being confused by the motor's power
factor. I can't quite find any other explanation as to why the DC side
shows only 700-800 watts, and the power as calculated on the AC side comes
out closer to 1236 using the value from the clamp.

The DR inverter seemed to run fine with the induction motor as a load. It
did hum a bit, but it didn't get hot, the fan was running at low speed, and
the air exiting the enclosure was cool.

The AC motor in the pump assembly did get awfully hot, but then I did
notice that the name plate shows the duty cycle as 50%. I wanted to let the
motor cool to ambient and repeat the test using grid power to see if the
motor got equally hot, but the pump's owner had time restraints, and didn't
want to wait that long. He did call the distributor and found out that a
continuous duty motor may be available. In any case, the existing motor
will not be suitable, as this pump setup will be required to deliver
quantities in excess of 1,000 gallons at a time, and the duty cycle on the
motor will prevent this from being accomplished in a timely manner no
matter what type of power is being used to run the pump.

The failure of the pump motor to start after it had been run for two-thirds
of it's duty cycle, I attribute mostly to the age and condition of the
batteries we used. After pulling out 30 Ah or so, the terminal voltage was
inadequate under load to supply the inverter with enough power to fully
start the motor. I expect that a fresh set of well broken-in and regularly
exercised T105's would have no problem supplying the snort needed to keep
the motor starting after such a small discharge. There are also
work-arounds if low SOC becomes a problem, including opening the delivery
nozzle and/or starting the truck's engine if needed. The heat in the motor
also could have had an effect on the ability of the motor to start at lower
SOC.

So, next up is testing on a continuous duty motor. In the meantime, I'm
going to recommend that they go ahead and purchase the DR inverter, unless
someone here can interpret these results differently that I did.

-S

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"History has never been kind to people who fail to control their leaders"
-Mark Stanley

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