GBM,

I'm curious why the manufacturer recommended against adding an ammeter
to the circuit. Generally these devices have very little measurable
effect on the current flow or voltage, so I'm puzzled about the
recommendation.

As to measuring current, there are several solutions but the problem is
that most of the "cheap, common" hand held devices will measure amperage
instantaneously, where as I believe what you are looking for is a graph
of the consumption over a very long period of time. In other words, I
think you really want the total amount of energy consumed by the system
over a given period of time, which in your case appears to be at least
one or more complete refrigeration compressor cycles.

To my very limited knowledge I'm aware of nothing "off the shelf" that
will do this, but just a very quick search on Goggle produced this link:

http://www.ferret.com.au/articles/16/0c006616.asp

which offers a TOPTRONIC T202 multimeter with a built in inductive
ammeter which can be then coupled with the CABAC TBM515 data logging
device. NOTE: I've no interest in either of these companies, nor have I
ever used either product. The above information is only an example of
how to capture the current draw over time. Any other product that can
measure current and log the data would work.

The advantage to this approach is that virtually no expertise is
required to capture the information you require, nor would you need to
modify the existing circuity in any way (the ammeter clips around the
wire and measures the current flow inductively), but you will need to
purchase two devices that you might otherwise not need. In my opinion,
I'd think both of these types of instruments would be useful for
debugging additional electrical issues in the future, but I tend towards
overkill in these matters.

Alternatively, one could build their own embedded system using a few ICs
(I would suggest checking out the PIC16 micro-processor line from
www.microchip.com) but this approach presumes some familiarity with
electronics.

Hope this helps,

Robb



GBM wrote:
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