In a message dated 98-06-12 03:42:42 EDT, james.carpenter@ukaea.org.uk writes:
> There is another type of ammeter, it uses a shunt resistor, and a high
> impedence voltmeter calibrated in amps. Work out the voltage drop in
> the shunt, you have the figure in amps. You could even wire one up to
> mesure the current draw from the starter. This shunt can be wired
> anywhere you want to messure the current, then you have two low current
> wires going to your voltmeter.
James,
You are right, but getting a matching meter for a Spitfire will be a problem.
The typical "Smiths" voltmeter used in the British cars of this era, which
would match up nicely, are very low impedance devices. I wouldn't want an
industrial type meter in my car, which is about the only choice you would
have.
Also, even though you are using a shunt, there can still be considerable
wiring changes required to properly measure the current. If the shunt is not
located properly, and the wiring changes correctly made, the ammeter/voltmeter
will read a charge current when some loads are switched on. In other words,
the wiring changes would almost be the same for the shunt as for the ammeter,
except you wouldn't be running the high current wires into the cockpit.
If you can fine a high impedance meter that you like, your suggestion would be
very good. Perhaps a digital? It wouldn't match up very well, but it might not
look too bad.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
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