Paul,
Thanks for this info; you make it clear. We kneed to archive this.
CR
On 4/18/2015 10:30 AM, PaulHunt73 via Mgs wrote:
> The MGA and MGB Jaeger gauges use a completely different method of
> voltage regulation to the MGB Smiths gauges, and the system voltage
> can vary significantly on both types - albeit a little less with
> alternators. Effectively the earlier system uses a Wheatstone Bridge,
> which is where with three known resistances you can arrange for a
> voltmeter to display the resistance of a fourth unknown resistance,
> and this is independent of supply voltage. The three known
> resistances are in the fuel gauge (two being magnetic coils), and the
> unknown is the tank sender of course.
>
> MGB Smiths gauges use a thermal voltage stabiliser which outputs an
> average of 10v over time regardless of system voltage, and thermal
> gauges, both using heating coils wrapped round bi-metal strips.
> Despite being called a 'stabiliser' the factory stabiliser is actually
> switching system voltage on and off about once per second, once the
> ignition has been on for a few seconds. At high system voltages you
> get a relatively short 'on' time compared to the 'off' time, and at
> low system voltage you get a longer 'on' time, always averaging about
> 10v. The tank sender simply varies the current through the gauge
> heating coils. Because the gauges are thermal they are very slow
> acting which means unless you look very carefully you can't see the
> pointer moving as the voltage goes on and off.
>
> PaulH.
>
>
> ----- Original Message -----
>> From looking at the wiring diagram of the MGA I see that it doesn't
>> have a voltage stabilizer to feed the gas gauge & sender; it depends
>> on the output voltage (V) of a terminal on the control box.
>
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