In article ,
Grunff wrote:

I think based on all the good advice so far, I'm going to go for
a two pronged approach. I'll set up a calorimiter, and use the
resistor method discussed elsewhere in the thread, and I'll also
get a data logger (as fast as I can afford) and do the
measurement that way as well. Should be interesting to compare
the results.

Might be useful to look at the LEM Hall Effect Current
Sensors. This would do isolated current sensing with
minimum voltage drop. eg, Radiospares 257-414 is 10V
dc out for 200 Ampere-Turns full scale input. Simply
pass 20-turns (of insulated flexible wire) through the
central hole and it is 10V out for 20A in. The voltage
drop caused by the sensor is just the resistance of 20
turns of wire.

There are other HE sensors from LEM which give a precise
current ratio. For example one of these could be used
to provide a an exact 20A:20mA ratio, with the 0-20mA
going sideways into a calorimeter, or to a (digital)
integrator, or to a data logger.

--
Tony Williams.