 | Author | Message | < Micro-D/Pascal/Avr ~ Automatic Fridge Switch for Caravans | | eric | | Posted: Wed Aug 30, 2006 8:11 am Post subject: Automatic Fridge Switch for Caravans | | | | Site Admin Joined: 01 Jan 1970 Posts: 311 | J. Swart
At last there is another project for caravan owners.
They are probably all aware of the problems
of a flat battery when they’ve forgotten to
turn off the fridge after the engine has been
switched off. When this circuit is installed
between the fridge and (caravan) battery, these
troubles will be a thing of the past. This simple,
but smart, switch reacts to the increase in voltage
that occurs when the engine is running.
Whereas the normal battery voltage is 12 V, this
increases to a minimum of 13.8 V when the
alternator charges it. With a suitably configured
comparator this voltage difference can easily be
detected, and as can be seen, the circuit consists
of little more than a 3140 comparator and
a relay driver stage for switching the fridge.
P1 sets the voltage at the non-inverting input of
the comparator such that the relay will only be
powered when the battery voltage is above
13.8 V, so only when the engine is running. The
hysteresis introduced | |
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