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Re: 72B lives...with reservations

To: lrcar@red4est.com
Subject: Re: 72B lives...with reservations
From: Bob Howard <mgbob@juno.com>
Date: Mon, 28 Apr 2003 16:50:17 -0400
Larry,
   The state-of-the-art (circa 1960 state-of-the-art) MGB electrical
system actually does incorporate a voltage stabiliser.  It's the little
one-inch by 1/2 inch metal cannister above the driver's left knee on the
firewall.  The original unit was a trusty mechanical gizmo that can work
for years and years, or days. I have purchased one that was electronic,
lasted about a week, and its replacement, that was mechanical, that's
three or four years old now.  Moss part #s 131-540 and 131-550 in the
'minor electrical' section.  
   The stabiliser opens & shuts the contacts so that an average voltage
of 10 comes through; the gauges react slowly so that they give the
correct reading.  The units are clearly marked "top" or "up". I don't see
why it should matter, but that's how they are marked, so you might see if
you have one, and see if it's mounted correctly, and that the fastening
screw is snug and grounding properly. 
   Fuel gauge problems are frequently caused by the sending unit, more
frequently than by problems with the gauge. It is possible to adjust the
gauge somewhat, once any problems are isolated to the gauge itself.  
Bob

> Here's a question for the list:
> 
> It seems to me that the temp, fuel level etc. guages work by 
> measuring the current through a resistor. The higher the resistance
(like the
> rheostat in the fuel level sender, or the PTC resistor in the temp
> sensor) the lower the current and the less the bimetalic strip in 
> the guage will heat up.  The problem with this is that higher output 
> from the alternator/generator will result in more current and look like
> lower resistance. 
> I know that some cars which have "real electrical systems", have 
> what is known as a "voltage stabilizer". I'm also certain that there is

> an IC that costs less than $3 that'll take the varying 12-15V that 
> comes off the alternator and regulate it down to a constant 12V. Has 
> anyone done something like this to "feed" their guages, so that they
work
> consistantly (i.e. the apparant level of your fuel tank doesn't vary
> with the mood of your alternator)? What parts did you use?

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