Selco GENESIS 145, Repair Manual

Page: 13 / 45

13
6.1) INPUT FILTER
The 30Vac - 50/60Hz single phase voltage is supplied to the input
filter board 15.14.43.
Between phase and neutral there is a varistor, which is an electronic
component which, when a voltage of around 500V appears on its
terminals, becomes conductive extremely rapidly, absorbing a cur-
rent peak so as to limit this overvoltage and so protect the other parts
of the machine.
This process is not destructive for the component if the energy brou-
ght into play by the voltage peak is modest as in the case of at-
mospheric lightning. If, however, the overvoltage is high and the
persistence time exceeds certain limits, the varistor is not capable of
supporting this energy and burns out.
This happens, for example, as a result of overvoltages on the electric
line or overvoltages caused by generating sets which are unstabilised
and have insufficient output.
The filter circuit is made using passive components such as a toroidal
inductor and some capacitors, some of them earthed. The filter has
the dual role of containing the machine’s radiofrequency emissions
within the limits specified by legislation and of rendering it immune
to interference from the supply sources.
WARNING
When accessing parts inside the machine, remember that ope-
ning the circuit-breaker doesn’t prevent the danger of electric
shocks.
Therefore:
IT IS ADVISABLE TO PULL OUT THE POWER PLUG