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Protection
for your Electrical Appliances
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Here
is a very low-cost circuit to save your electrically
operated appliances, such as tv, tape recorder, refrigerator,
and other instruments during sudden tripping and resumption
of mains supply. Appliances like refrigerators and air-conditioners
are more prone to damage due to such conditions.
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| The
simple circuit given here switches off the mains supply
to the load as soon as the power trips. The supply can
be resumed only by manual intervention. Thus, the supply
may be switched on only after it has stabilised. |
| The
circuit comprises a step-down transformer followed by
a full-wave rectifier and smoothing capacitor C1 which
acts as a supply source for relay rl1. Initially, when
the circuit is switched on, the power supply path to the
step-down transformer X1 as well as the load is incomplete,
as the relay is in de-energised state. To energise the
relay, press switch S1 for a short duration. This completes
the path for the supply to transformer X1 as also the
load via closed contacts of switch S1. Meanwhile, the
supply to relay becomes available and it gets energised
to provide a parallel path for the supply to the transformer
as well as the load. |
| If
there is any interruption in the power supply, the supply
to the transformer is not available and the relay de-energises.
Thus, once the supply is interrupted even for a brief
period, the relay is de-energised and you have to press
switch S1 momentarily (when the supply resumes) to make
it available to the load. |
| Very-short-duration
(say, 1 to 5 milliseconds) interruptions or fluctuations
will not affect the circuit because of presence of large-value
capacitor which has to discharge via the relay coil. Thus
the circuit provides suitable safety against erratic power
supply conditions. |
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Click on the Image for its larger version
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