Hi Randall and all,
I was not very precise when I made my post - Sorry. In my zeal and zest I
did not think it through enough to call it what it is.
Should have said since the the gas gauge is based on a Wheatstone bridge
(with the sender resistance being the variable leg) it should be relatively
easy to convert to a voltmeter.
One thought was that a transistor biased by the system voltage could be used
to simulate the resistance of the fuel guage sender, this would also need
to have an external voltage reference of some sort to keep the voltage level
from affecting the guage reading. I could bias the transistor to use the
full swing of the guage. I'll bet there's many ways to do this.
I agree that the ammeter shows you more. The Ammeter may show zero or full
swing (depending on if your car is on fire or not) - in both cases the
voltmeter would just show zero (even after you saw the smoke), I just
dislike seeing the constant negative reading on the Ammeter - maybe I should
reverse so it shows postive (would make me feel better) or I could put
black tape over the guage (I've heard that suggestion here more that once).
Did not think about it being inverse reading - Guess I could label the guage
inverse as well. Aw heck, while I'm at it I could add a negative power
supply... :)
It's also very fair to ask why I'd want to go through all the trouble to do
this. I guess, at the end of the day, we all like these cars - that in
some way like doing things the hard way or we'd all be driving newer cars
with computers and valves you don't have to adjust. After finish sanding all
the spokes on all my wheels, this seems like a cakewalk.
Take care and thanks for all your feedback and interest!!
Chris
Snip.
> Then I realized the gas guage is already a voltmeter.
Actually, it isn't. It really works on not just current but current
differential. The current through the sender is compared to the current
through an internal coil to arrive at the reading. This is why the reading
doesn't change (much) if the input is 10 volts or 15 volts. It also works
backwards to the way a voltmeter should work, ie full scale is no current.
> Anyone ever tried this? Sound reasonable?
Seems like an incredible amount of work to arrive at something that works
less well than the original, to me. But rather than trying to modify the
gauge, I think I'd be looking at some sort of electronic circuit to sink the
current that the gauge responds to, in accordance with the voltage
presented.
Or just put a voltmeter movement into an ammeter case ...
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