Ignition questions & the Nat semi Injector driver

[Charles]

I originally wrote: 
>> This is only accurate at relatively low current flows where
>> the wire stays cool, though, because copper has a pretty high
>> temperature coefficient!

You wrote:
>There is a good reason for nichrome, but that's not it.
>Nichrome is good because it can glow red hot in a normal atmosphere 
>without oxydizing and burning up.
>
>Bill
>
    That may be true, but I still disagree with you about using copper. 
Try it and see! If you make your shunt for 50 mv, 20 amps is one watt; 
this may be OK if your shunt is physically large enough. On the other 
hand, if you prefer 200 or 250 mv drop... 4-5 watts... a small mass of 
copper wire _will_ get warm enough to significantly affect the 
accuracy. You can see the meter changing as the shunt heats, whereas 
the reference ammeter in series is not changing.
-Charles