On 1 Jan,
Martin Bonner wrote:

On Tuesday, January 1, 2013 8:19:55 PM UTC, wrote:
As part of another project, would like to take some High Current DC
measurements.



I have a couple of multimeters ... but obviously not going to be any good
for around 80-100A

Ouch! That's a serious current.

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm
shunt, anybody made one of these ?

Ahem. Let's review those school physics lessons shall we?

Volts = Ohms x Amps

So 80A through 1 ohm will generate 80V. Further, the definition of volts
is:
Watts = Volts x Amp

So your shunt resistor is going to be dissipating
80 x 80 = 6400 W = 6.4 kW.

That's a serious amount of energy!

(Of course, what I expect will happen is that your shunt resistor will have
much higher resistance than the rest of the circuit, and bring the current
way down - or possibly kill it altogether.)

I suggest you need something more like 1 milli-ohm, which will produce a
voltage of 80 mV (perfectly within the range of digital volt meter), and
an energy output of 6.4W

http://uk.farnell.com/jsp/search/pro...=1292504&N=401 (for
example) ?

I'd just use a hall effect clamp on ammeter. CPC do a good one for up to
400A.

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