Voltage Stabilizer Study 05/02 R. Kwas
Source: Volvo Service Manual for 1971 1800E
According to the manual, the output switches from 12V to 0V, with the long-term average value being 10V (incorrectly called "constant" in manual, possibly due to quirks in translation from Swedish). This average voltage value is a function of % Duty Cycle, defined as the ratio of ON voltage and OFF voltage time.
Solving for duty cycle = 100X10/12 = 83.33%
In other words, the output is 12V, 83.33% of the time, and 0V, 16.67% of the time, the actual time is noncritical. As long as this ratio is correct, the long-term effective voltage is 10 +/- .2V. This is why a failed unit can successfully be replaced by an electronic regulator with a fixed output of 10V.
