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From: Kristian Jonsson
>The other day I was going to test two electrical rev. counters. One was
from
>an Avanger and the other from a Hunter. On the back they where similar:a
>flat connection and a pin connection. Now if you look at the electrical
>diagram, (take the Alpine, it is similat in that area), It looks like the
>rev counter is supposed to be in series after the ign.lock and before the
>coil (and the whole item to earth) But it is not working that way. I made a
>paralell connection, + from the ign.lock (or battery) to the flat one and
>connecting the round (signal?) pin to the - side (distr. side). . Now it
>worked.
>This is NOT according to the electrical diagram. Something is wrong.
>Tell me electrical Wizard !
>What is the principle of this rev. counters??
Smiths tachs use a built in current transformer to trigger the internal
electrics. This is why the rev counter is shown in series with the coil
+ feed , bewteen the ignition sw and the coil. The wire induces a current
into the transformer when the points close, then and internal amplifier
kicks a small voltage on the transformer output, into a larger voltage,
which in turn drives another pulse timing circuit.
If you have put the tach in parallell across the ignition to coil feed wire,
and it works, then you probably have an electronic ignition on your
car instead of points huh?
When the tack doesnt work right with electronic ignition, most people
double wind the wire around the cuurent transformer, to keep the
transformer from saturating due to the much higher dwell.
If my guess is right, the reason your setup works, is becuase
putting the tach across the tach feed wire, has reduced the current
going through the tachs transformer by about a factor of 2, which
will have the same effect as doubling the tansformers turns.
Hope this helps.
Jarrid Gross
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