Yes, completely true, Meindert. But if the objective is simply to log
on/off cycles, then the voltage divider would be sufficient. It would
even give a crude measure of compressor current (via voltage drop).

Chuck


Meindert Sprang wrote:
"Wayne.B" wrote in message
...

As others have mentioned a current shunt is one way to do this.

However, since you're data logger can also be voltage driven, I think
it would be cheaper and easier to build a voltage divider with a
couple of resistors in series across the compressor circuit.


Indeed: As others have mentioned a current shunt is one way to do this.
You cannot measure the current by measuring the voltage *across* the
compressor. Unles you mean that you want to deduce the current by
subtracting the voltage across the compressor from the voltage across the
battery (that's tw measurements) and divide that though resistance of the
wires. Could be done but you have a resolution problem.

Meindert

I really need to mesure actual amps because the compressor has a "smart"
variable speed control. I found a 25A 50 mv shunt for $10 so I think I will
go that way.

These little 4 chanel Hobo U12 data loggers are neat. What I plan to do is
record ambient, freezer and fridge temps along with amps used for a week on
a friends boats headed for the Bahamas next month. The interior size and
mechanicals of his refrigeration system are the same as mine but
traditionally foam insulated so that will give me a good baseline. This is
a particularly good opportunity because he is a detail fanatic and plans to
record everything he adds to the box.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
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