I wired 2 DC powered run-hour meters into the circuitry which opens the
solenoid valves for my refrigerator and freezer. Only 1 valve is open at
once. If you don't have this, look for something similar in your system
(thermostat, on/off switch, etc.) About once a week I enter the run-hours
into a spread sheet and look for anomalies. It's highly consistent, so if
something is out of wack, I know it right away.

As mentioned, the amperage is not constant, but if you watch your gauges
you'll see that the amperage quickly becomes constant (in my case once the
expansion valves have closed down.) Doing a you can come up with an average
amperage per minute.

My system consists of a Glacier Bay 1/2 HP 12V DC motor driving a Bitzer IIY
compressor with an 18F plate in the frig and a 0F plate in the freezer. I
have Carel electronic thermostats which allow me to accurately set the on/off
points which measure plate temp. This is important. The unit cycles on
demand. When it starts it draws about 40A and then drops to about 30A after
about 5 minutes. My system draws 85AH per day in the Caribbean where the
temp ranges from 80 to 90F and the water temp is 80F. I'm quite happy.

-- Geoff

"GBM" wrote in news:4Zw7g.72646$fd.56060
@read2.cgocable.net:

What is the best way of measuring the power drawn by a boat's refrigeration
unit?

Is there a way to do this without any expensive instruments?

I was thinking of installing an ammeter in the line to the compressor to
determine the current draw, but manufacturer does not recommend this. Even
with that, I would need an hour meter or some such device to know how often
and for how long the compressor runs.

I would like to test existing installation, then add some "temporary"
insulation to the inside of the box and then test again to see what
improvement I might get if I added permanent insulation.

GBM