[Roadsters] Tech talk: Bimetallic Strip Gauge Regulator

[John F Sandhoff]

With the discussion concerning replacements for the dash gauge
voltage regulator, I thought I'd toss this back out. Old-timers to the
list will recognize it... :-)

[my apologies if this has already been stated and I missed the message]

The instrument regulator consists of a special two-part piece of
metal (the bimetallic strip) and a small heating coil. This simple
design produces a square wave voltage output that averages out to
about seven volts (if my old notes are correct). But this simplicity
is actually more complex than it would seem.

The bimetallic mechanism also acts as a temperature compensator.
The gauges work by bimetallic strips as well; internal coils heat a metal
strip and move the pointer. In colder weather it takes more power to get
the same movement. Thus, in colder weather the mechanical regulator,
itself being heat-sensitive, automatically provides more power (longer
'on' time) when cold and less when hot, helping gauge accuracy. Keep
in mind that over the seasons the temperature inside the car can vary by
a hundred degrees.

It can also compensate for voltage fluctuations, but the charging system
should be doing the heavy lifting on that end.

-- John
     John F Sandhoff   sandhoff at csus.edu   Sacramento, CA

p.s. Hooking the two wires up backwards will result in the gauges
beginning to move up, then dropping back and staying at zero. The
regulator will probably get toasty as well. It also needs to be grounded
to work, otherwise the gauges will read way too high.