jell@km21.zfe.siemens.de (Thomas Jell) writes:
>> ... although the Lucas method apparently used a
>bimetallic electromechanical device of some sort, which chops the voltage
>up into pulses which average out to a lower voltage.
>
>exactly how they do it, fine English workmanship. If you have a broken one,
>take the time to look into !
I have one of these "regulators" in my XKE--I mean _had_. When I got
my car back on the road last year, the thermal regulator had long been
deceased, so I decided to replace it with a 7910 (-10 volt solid state
voltage regulator) instead of the kludged bimetalic element that was
original--after all, in '64 cars were built without transistors, and
this seemed like a good mod. WRONG. The regulator controls the
duty cycle of the voltage to the panal instruments, which themselves
operate with a bimetallic strip and not a moving coil. Having a cheesy
bimetallic regulator is actually superior, because it introduces the
correct temperature coefficient. Now my gauges have a noticable drift
as the cockpit warms; I will break down and purchase one of them
old fangled thermal regulators and trash the 7910 when I have a bit
of loose change!
>>BTW, I have heard 10v, 6v and 4.5v as the voltage these things are
>supposed to regulate to. Anybody know?
My manual says 10 volts, but the author was misinformed about the
function of the regulator. The mean voltage will change as a strong
function of temperature. Think about it. How much can the voltage
really vary coming out of the battery (okay, assuming a running
engine and working generator)? Maybe 13 volts at the low end (idle
with no current from generator, which is in cutout) to 15.5 V cruise.
20% or so worst case and a lot less in just cruise--and why would
the designers care about this error? Maybe someone out there
believes they do, but my overwelming impression of the design teams
of the '60s and '70s is that they are definitely not of the anal-
retentive type! So why did they see a need for the regulator? My
hypothesis is that there was simply an intolorable amount of thermal
drift. Maybe the folks who are amusing us with their radiator flow
debate want to join in here... ...although I hope Ray Gibbons
has put that issue to rest.
-greg
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