Electronic tachos

Routing electrons, it's like herding cats, but some bright spark will
come up with a way one day.

Of course you still have to get the holes back to the battery somehow.

 

The one on my Quota uses a variant of a standard frequency-to-voltage
converter chip. The damping could well be electronic as well as
mechanical.

If there's a dry joint then the electronics could be playing up.

 

In the case of a starter motor circuit the current drawn is such that
even small increases in resistance cause a significant voltage drop.

This is a circuit that draws ~140A from a 12V battery. That's a total
circuit resistance of about 0.085R, of which about 11/12 is the motor
itself.

So adding just 0.07R of resistance will *halve* the voltage drop across
the motor. I can provide workings if you like ;-)

I'd like to say that the proof was in the eating but in order to route
the starter cable away from the exhaust it had to be replaced with a
longer one so it could have been a fucked cable. Either way the problem
went away after this.

 

It's rusting in pieces now.

 

WavyDavy has brought this to us :

They are basically just an analogue meter movement. The electronics
will have a capacitor, which should effectively damp the movement.

Perhaps the above capacitor is breaking down or going open circuit?

 

rb brought next idea :

No need, I will accept that figure. However, the resistance of the
copper cable varies a totally insignificant amount with rise in
temperature.

I would suggest that all you did was fix the poor connections on the
end terminations of the cable. The connection between cable and lug can
become high resistance, as can the connection between lug and the bolt.
Once there is some resistance in a heavy current carry cable, it will
rapidly become much worse with oxidation due to heat build up.