multimeter advice needed

[Raymond C Drouillard]

On Wed, 17 Feb 1999 13:58:39 -0800 Don Holtz <daholtz at axionet.com>
writes:
>Here is an idea:
>
>Try using a current sensing resistor.  They are usuaully 1mhom (1E-3
ohm),
>and a regular voltmeter.  Put the resistor in series with the load, and
>measure the voltage across it.  For a 1m ohm resistor, 100A would read
as
>100A*.001 ohm=.1V  for 1A => 1A*.001ohm = 1mV.   These values are
readable
>by any resonable DMM, and the current sense resistors should be
available
>at any industrial electronic supply shop (ie.  Electrosonic in Canada).
>
>Note:  I^2R=(100A)^2*(.001ohm)10W, so use at least a 10W resistor!

A few years ago, I read a construction article for a high-current
ammeter.  It was a couple of jumper cable type clamps with a short piece
of copper wire of a known resistance between them.  Small sockets were
provided for voltmeter probes (see above).

>
>
>I seem to remember that inductive current meters only work on AC, not 
>DC!

I have never seen a DC current meter that reads magnetically.  It could
be done with a hall effect sensor, though.  It would be an interesting
construction project.  If you calibrate it to read in the 100A range, you
could read in the 10A range by wrapping the wire through the loop ten
times.

>
>Cheers,
>Don Holtz

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