[Tigers] Amp Meter (Ammeter)

[Tod Brown]

I think what you were looking at when you disassembled the ammeter was 
the "shunt" wire (which does look quite a bit like a paper clip).  The 
electromagnet (or coil) is attached to the needle and causes itself and 
the needle to move when a current moves through it.  Since the meter 
carries all of the current coming from the generator or alternator 
(upwards of 30 amps, possibly), not all of the current could pass 
through the coil without damaging it.  (The coil should be small and 
light weight so that it can respond rapidly).  The shunt is just what 
the name says.  It is a pathway for most of the current to travel 
without passing through the coil and is connected in parallel to the 
coil.  It is a careful matching of the resistance of the coil and the 
shunt which determines the maximum current the ammeter can handle.  An 
ammeter works on the same principle as an electric motor - pass a 
current through a wire embedded in a magnetic field and the wire will 
experience a force which can be used to produce a rotation.

Cheers,

Tod
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