[Mgs] voltage stabilzer

[Paul Hunt]

A heating coil bends a bimetallic strip as current passes through the coil. 
When the strip is heated enough it opens a contact, which disconnects the 
heating coil as well as the output voltage.  When the strip cools down the 
contact closes again and the cycle repeats.  The higher the current through 
the heating the coil i.e. from a high system voltage of say 14v compared to 
a low system voltage of 12v, the hotter it will get, which heats up the 
strip faster, which opens the contact sooner to give a shorter on-time.  But 
once open it cools at a relatively constant rate, so the off-time stays 
relatively constant.  It is this changing length of on-time compared to the 
relatively constant off-time that gives the varying duty cycle, which gives 
the relatively constant average voltage of 10v or so.  If you look at the 
output with a voltmeter or test lamp you will see both the on-time and the 
off-time varying even with a constant supply voltage.  This is because it is 
a very crude device mechanically, you have to take the average voltage over 
several cycles to get a more accurate indication, the more the better. 
Because the gauges work on the same principle (a heating coil bending a 
bi-metallic strip in this case connected to a pointer) variations in the 
average voltage over one or two cycles have little visible effect.  But if 
you look very closely at the gauge, say a fuel gauge about half-full, you 
can see it pulsing up and down very slightly.

PaulH.

----- Original Message ----- 
> It is not really a stabilizer. Quite the opposite, in fact. It pulses, 
> varying the duty cycle.  I don't know what its designed to do...