[Mgs] Cooling issue, revisited

[Rick Lindsay]

Hey Paul, et al.,
   There is a potential point of confusion when using
digital meters.  The meter display does not
continuously represent the measured parameter like an
analog meter (damping ignored) but rather, it updates
itself at a quarter-second to one second rate.  This
typically isn't much of a problem because most things
we measure are static or better put, steady-state.  
   The (somewhat) rapidly pulsing stabilizer output is
NOT steady-state and not in sync with the meter's
sample-and-hold circuit.  Therefore, it is easier to
evaluate the output of an old style analog meter or
even a test light when evaluating a pulsing source.
   My son is a nuclear physicist in his fourth year of
college.  When he was home at the start of the summer
(read: that time gap between end-of-term and
start-of-summer-job where huge quantities of mom and
dad's food is consumed) I had the stabilizer out of my
MGB.  (The fuel and temp gauges did not work so I knew
where to look for the problem.  It turned out that the
stabilizer's mounting screw was loose and and enough
rust had grown between the two to insulate the ground
(earth) connection.)  I put the stabilizer on my bench
power supply and an analog meter across the output.  I
first applied about 9 volts to the stabilizer and it
didn't cycle.  Allen recorded 9 volts in produces 9
volts out.  We then brought the input voltage up to 12
volts and the stabilizer cycled with a duty-cycle of
about 75% on - 25% off.  Allen soon realized that all
that calculus he studied was just put to use.  Even
though the output voltage, when on, is 12 volts, it is
also 0 volts when off.  The output must be integrated
over time.  When that is done, the AVERAGE output is
still 9 volts!  He was fascinated that a mechanical
device was putting the math to use so practically! 
Ahhhh, youth.

Regards,

rick
--- Paul Hunt <paul.hunt1 at blueyonder.co.uk> wrote:

> Or a test-lamp, all you are looking for is the
> output of the stabiliser 
> (light-green/green) is switching on and off.  But
> then if the digital meter 
> *does* switch between 0v and 12v, then the
> stabiliser probably *is* OK.
> 
> If it reads a steady 12v check the physical mount to
> the firewall, it needs 
> a good ground to work.  If that's OK then the
> stabiliser is probably dead.
> 
> It normally takes 2 or 3 secs to start switching
> when first turning on the 
> ignition, then switches about once per second after
> that.
> 
> PaulH.
> 
> ----- Original Message ----- 
> > It is hard to test using a digital multimeter,
> because of the way it
> > works - the digital meter gives you an
> instantaneous reading, so will
> > jump around between 0V and 12-14V (unless it's an
> advanced one with an
> > averaging device).  An old analogue multimeter
> will show more
> > effectively.
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