In message <51.3d78e8d8.2db539d2@aol.com>, BillHUCK@aol.com writes
>I have a problem with the concept of automotive ammeters.
>
>Should anything go wrong with the shunt, all power shuts off.
>Is that shunt not just one more link to possible failure? Bill Huck
>
Been watching this thread with some interest. I too have thought about
adding an ammeter, but don't want to cut into the loom or route the
entire current supply through a small meter with shunt.
But ...
It seems that all the current from the battery (apart from that for the
starter motor) passes through one brown wire between the starter
solenoid and the control box. This wire has a finite and fixed
resistance, and will therefore exhibit a voltage drop, proportional to
the current and its length, and inversely proportional to the
cross-sectional area of the copper used.
It seems quite feasible to me to take a thin connection to both ends of
this wire and bring them up to a meter, read the voltage difference, and
translate this into current flowing through the wire. A sensitive
movement might do it, but it might need a couple of transistors to
amplify it to get a reading. I haven't done the calculations, but could
if pushed!
The advantages are: no breaking the loom; no high current feed behind
the dash; no 'something else to break'; no voltage drop created by the
meter; and it could be removed for concours.
Disadvantages are: you need a sensitive meter; you may need to amplify
the voltage drop to get a reading; you will have to calibrate it,
possible with a digital voltmeter and a known load, or measure the gauge
and length of the brown wire and calculate.
I'm sure someone out there has done this. Or tell my why it can't be
done.
Regards
--
Alan F Cross
|