Re: Need to design a small disconnect circuit


Ross Herbert wrote:
On Thu, 13 Sep 2007 14:12:35 -0700, electsrc@xxxxxxxxx wrote:

I need a small circuit that can disconnect AC power (means will have
a
relay) when it detects freezing on coil. I have a non working
appliance that I want to power up but also include a antifreeze
circuit design so that when it senses ice or freezing on the coils
it
powers off/disconnects the relay/power. can anyone help ? is there
any
such circuits
available that can do this job ?


There are a number of electronic thermostat kits available but if you
would like to roll your own then the schematic on this page (lower
portion)
http://www.pk3.org/Astro/index.htm?astrophoto_vesta_sc2_mod.htm might
do the trick. While the author is driving a Peltier device this can be
substituted with a suitable relay. Also, instead of the smd mosfet you
can use a suitable TO220 device. With the existing values the circuit
switches between -19C and +2C so you can play around with the resistor
values in the sensor bridge to alter the range to suit your
requirements.
Take a look at this simple solution:

http://www.grainger.com/Grainger/items/2E552
or http://www.grainger.com/Grainger/items/2E158

But distinguish between freezing cold and icing up. 32F precedes icing.
I'm not sure how you'd go about detecting ice - maybe some photoelectric device (a hunk of ice blocking a path or causing a change in reflectivity.)
.

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