[KYHAM] Tyler KI4BUM Doghouse 12 volt fan

[David A. Smith]

Hi Tyler,

If your project were for the space program, a simple dished disk made of
bimetal � a simple snap on and off thermostat would probably be used because
it consumes no power and can handle about 5 amps would be used.  Using a
5-amp switch to control 15 amps almost brought Apollo 13 to an end.

There is something special about people that want a hi tech doghouse � lucky
dog!  If you can scrounge a sealed vapor pressure actuated bellows type
thermostat, they would be ideal for your application.  Again, they consume
no power.

An electronic thermostat can be quite simple � a small thermistor and
adjustable pot to turn on and off an NPN transistor which actuates a relay.
Here we have the power consumed by the relay to be concerned with but the
relay supplies the full voltage to the fan.  The relay will draw current �
more as it approaches closure.

A latching relay used in conjunction with a Schmitt trigger � a snap action
two-transistor circuit consumes very little power.  I use several of these
to control my solar array to charge wet cells at plus 12 plus 36 and minus
36 volts.  If you are ever up in the Monroe, Michigan area let me know and I
will show you the arrangement.

I hope that this is helpful.  My e-mail is good in QRZ.

Dave Smith W8YZ