Here is an idea that will cost about $150 and do a lot more than measure the
amps.

A Hobo 12-012 data logger with internal temp and RH sensors and 2 external
sensors.
http://www.onsetcomp.com/Products/Pr...a_loggers.html
Plug a temperature sensor in one of the external inputs and an Ampsense Hall
effect current sensor on the other. http://www.ampsense.com/

With the free basic Hobo software you can capture the data and load it into
a spreadsheet. That will give you the external temp and RH, internal box
temp and amp draw on a common timeline.

Besides adding insulation you can do a few other things. The Danfoss DC
compressors are most efficient when they run a slow as possible to maintain
box temperature. They actually use less amp hours when they run 90% of the
time. You can experiment with the thermostat circuit resistor to adjust
the speed.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"GBM" wrote in message
...
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