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Re: adding an ammeter to a RBB (& water)

To: Barney Gaylord <barneymg@ntsource.com>, <Duinhoven_Hans@emc.com>,
Subject: Re: adding an ammeter to a RBB (& water)
From: Larry Macy <macy@bblmail.psycha.upenn.edu>
Date: Fri, 20 Oct 2000 17:18:57 -0400
Gotta agree Barnry. That is pretty much why I have ammeter that is not
hooked up. I got it in a little panel with an oil pressure gauge and a temp
gauge. The panel has 3 holes and that is what was in the 3rd hole when I got
it. My 78 Midget has an idiot lite for the oil and amps, but a gauge for the
temp, but I never liked it (H,N,C type), I wanted to know the tewp. The
whole shebang fits under the dash and I like its unobtrusiveness, but I
never hooked up the ammeter. Didn't see the need nor think it was worth the
risk. 

Larry

At this exact moment in time 10/20/00 4:11 PM, "Barney Gaylord"
<barneymg@ntsource.com> made the profound statement:

> Okay guys, break it up.  It's obviously time for a disinterrested third
> party to referee this event.
> 
> When your electrical system is working properly, either an amp meter or a
> volt meter will fluctuate in basically the same direction at the same time
> and tell you pretty much the same thing, that all is well, and therefore
> the primary effect of these instruments will be to take your eyes off the
> road occasionally.  In this case the voltmeter wins, because it's easier to
> wire and carries less current through the wiring harness, but in reality
> they're both pretty useless, which is why most cars have neither of these
> instruments installed from the factory.  You know the factory would never
> want to imply that anything could ever go wrong with the electrical system.
> 
> The real value of these instruments comes when something does go wrong with
> your electrical system.  Here you may have overcharging, undercharging, or
> no charging at all.
> 
> When overcharging, the amp meter will be reading a few extra amps.  But you
> may get the same reading if the battery is simply discharged and the dynamo
> is working properly, so that indication is not particularly definitive.
> However, a volt meter pegged at 20 volts is a pretty good indication that
> your generator is about to suffer internal meltdown.
> 
> For mild undercharging, the amp meter could show zero, or possibly a few
> amps in the red, and the ignition warning light may still not be glowing.
> But you could see this same condition if you just turn on the headlights
> and all of the accessories at the same time, particularly if you have a
> generator with more limited current capacity than an alternator, so that
> indication is not particularly definitive either.  An amp meter sitting
> constantly at 0 tells you practically nothing, but a volt meter sitting
> constantly at 12 volts tells you that the battery will surely be discharged
> eventually.
> 
> For the no charge condition the ignition warning light comes on, so you
> already know it's discharging, so what more can these instruments offer?
> An amp meter reading -10 tells you it's discharging, but you already knew
> that, and that reading won't change until you switch off some accessories
> or kill the ignition switch.  The volt meter on the other hand offers up
> some useful information at this time.  With the charging system disabled
> and the car running on battery only, your most important concern may be the
> state of charge of the battery, especially if you are at the time on an
> expressway to nowhere and have no service port handy.  11.5-12.5 volts
> means a fully charged battery and some time allowed to get where you're
> going without having to panic.  10.5-11.0 volts means about half
> discharged, and you had better have plans on where you will be in the next
> hour or so.  Anything under 9.0 volts means about the same thing as a fuel
> gauge pointing at empty, you had better be home, or at a service shop, or
> be prepared to walk.
> 
> The point of all this is that the amp meter is indicating the rate at which
> current is flowing in or out of the battery, but those same readings can be
> seen under very different circumstances, some good and some bad.  As a
> result you may become unnecessarily concerned, or otherwise ignore a real
> warning signal, because the thing is not telling you WHY.  The volt meter
> tells you much the same thing that the amp meter does while the system is
> working properly, but when it's in trouble the volt meter is telling you
> the state of charge of the battery, which could be a lifesaver.  But then
> that is why I carry a small DVM in the tool box.
> 
> My money says $20 for a DVM, a dime for the volt meter, a nickle for the
> amp meter, and two cents for my own advice.
> 
> $.02,
> 
> Barney Gaylord
> 1958 MGA with an attitude
>   http://www.ntsource.com/~barneymg

Larry Macy
78 Midget

Keep your top down and your chin up

Larry B. Macy, Ph.D.
macy@bblmail.psycha.upenn.edu
System Administrator/Manager
Neuropsychiatry Section
Department of Psychiatry
University of Pennsylvania
3400 Spruce St. - 1015 Gates
Philadelphia, PA 19104

 Ask a question and you're a fool for three minutes; do not ask a
question and you're a fool for the rest of your life.



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