> Date: Wed, 02 Jun 1993 10:25:16 CDT
> From: "Andrew C. Green" <dlogics!hermes.dlogics.com!acg@uu.psi.com>
> To: british-cars@autox.team.net
> Cc: acg@hermes.dlogics.com
> Subject: Voltmeters vs. Ampmeters (was Re: TR7 charge indicator)
>
>
> This reminds me, btw, of useless a voltmeter seems to be when compared
> with an ampmeter ("ammeter" in the U.S.?). With a charging problem, for
> example, you get to see the problem expressed in terms of amps of discharge,
> as opposed to a suspiciously low voltage reading that may or may not be
> sinking.
I certainly agree with you regarding an ammeter vs a voltmeter. With
about the same measurement accuracy you get far more information. In
fact, you get almost the exact information you're looking for; current
flow and direction. Since a charged battery in reasonable condition can
have a fair amount of variation in the voltmeter across it, you only
have a general feeling from a voltmeter's reading of the condition of
the charging system. However, when I decided to install a cheap ammeter
in my VW, I developed a bit more sympathy for current auto makers
regarding this choice. An ammeter is a low impedance device and is
installed in series with the charging system. This means both the meter
and the wires running to it must be capable of accommodating a lot of
current. In the case of my VW I would have had to re-route the charging
system through the ammeter. I didn't feel comfortable running thick
cables from the rear of the car where the charging system is to the dash
mounted meter and back again. There are ways around this problem but,
in my opinion, not worth the effort or cost in this case. The simple
solution for me was to install a voltmeter which is a high impedance
device, is installed in parallel with the charging system, can be
mounted remotely with ease and doesn't require heavy cables. Not the
optimum solution but orders of magnitude better than the useless idiot
light the car came with.
Roland
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