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Re: Voltmeter wiring

To: triumphs@Autox.Team.Net
Subject: Re: Voltmeter wiring
From: schuyler grace <>
Date: Mon, 24 Nov 1997 13:38:19 -0800
References: <> <> <>
Tom O'Malley wrote:

> Hi Trevor!
> Trevor writes:
> >  Yes, they are temperature compensated. The accuracy of the
> temperature
> >compensation is usually on the data sheet, and most all are plenty
> good
> >for a fuel gauge situation.

> Solid state voltage regulators are indeed very well temperature
> compensated for their intended purpose.  That purpose is to maintain
> as tight a voltage regulation as possible under a wide variety of
> operation conditions including temperature swings.
> But we don't want that in our LBC heater gauge circuits.  We want the
> stabiliser's average voltage to vary inversely with ambient
> temperature so it offsets the errors inherent in heater type gauges.

To Tom, Trevor, Dan, et al...

What we keep trying to get back to in this thread is a closed loop
system like the original voltage stabilizer circuit in our LBCs.
Admittedly, the loop is only loosely closed by the air gap behind the
car's dash, but it is closed, and the circuit seems to work pretty well,
given the environment in which it functions.

If you really want to solve the problem of inaccurate gauges (without
changing the gauges), you have to do a better job of feeding back the
environment inside the gauge in question to the voltage regulator.  When
I was in college, we were working on an amplifier design, which used
diodes mounted in the power output transistor heat sinks to provide
negative feedback regarding the temperature of the heat sinks to adjust
the bias current applied to the output stage transistors, thus
preventing thermal runaway.  I figure that, by salvaging some old Lucas
wiring and alternator diodes, this circuit could be replicated as a
period-correct modification.  Just use some NOS bubble gum to stick the
diodes to the insides of the gauges in question, string your salvaged
wire and connectors behind the dash to an internally modified voltage
stabilizer, and you're in business!  Oh, yea...a period fire
extinguisher and a set of working gauges tucked in some inconspicuous
location might not be a bad idea, either!

Ken, I'd be happy to write this up (with wiring diagrams, of course) for
the VTR Maintenance pages if Dan hasn't already clamed the project for
himself.   =8^p

Schuyler E. Grace
'73 Spitfire 1500 - FM1183U (with stock voltage stabilizer circuit)
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