Cold Batteries [RE-wrenches]

[R. Sparks Scott]

>two shunts in series with meter split across both would have to be strapped
together with very heavy copper, maybe soldered.

	Windy;

	Right again, but I have a hard time figuring out why anyone would even
want to do that, except as a very short term, temporary solution to a
one-time measurement problem. Even then, a DVM is a better choice used on
one shunt for an odd level measurement than to fool around with series
shunts. Maybe if you had two meter movements of differing sensitivities
that you wanted to use in two remote locations? Connecting a movement to
each shunt would negate any resistance in the high current connections,
because the resistance would be out-of-circuit for the meter's purposes.
	Shunt sensitivity can be adjusted upward very easily, although it's a
permanent change. One has only to use a file or grinder on the edges of the
shunt 'shims' (the thin conductors soldered between the brass contact
blocks). This has to be done while using a sensitive DVM setting, observing
the mv output of the shunt while drawing a known, steady value of current.
This will increase the resistance of the shunt upwards, allowing, for
instance, the 600A/50mv shunt I had in the junk box to be converted into a
500A/50mv shunt for use on an E-meter.
	Series connecting shunts is also not necessary to connect multiple meters
of the same sensitivity. My system has two 50mv meters connected across one
shunt, with no discernable change in accuracy. The meter movement's
internal resistance is insignificantly high in comparison with the very low
resistance of the shunt, so no functional change in the shunt's resistance
is induced by the second (or third, fourth, etc) meter. If you were tempted
to go hog wild connecting multiple meter, I'd suggest using a separate
shunt screw terminal for each meter movement. Mine just happens to have
8/32 tapped holes on the top and each side.
	I have prepared a web page document on this subject for another member of
the list. If anyone else is interested in viewing it, go to
<http://www.mrsharkey.com/wrenches/shunts.htm>. I haven't proofed it
throughly, so let me know if you find any inaccuracies.

	-S

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