Need to design a small disconnect circuit

[[email protected]]

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 ?

 

[Bill Jeffrey]

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 ?

Sounds like you need a small moisture sensor driving a FET. Moisture
sensors usually are looking for (ahem) moisture, but there is no reason
one shouldn't work for detecting frost or ice. The sensor is easy to
make - two electrical contacts in close proximity but not quite
touching. Put a small DC voltage across the contacts, and look for the
small current that results when they are bridged by moisture. I'm sure
Google will turn up hundreds of sensor designs.

Bill

 

[[email protected]]

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 ?

http://www.workaci.com/pdf/freeze.pdf

Kinda like a howitzer for a mosquito.

But you are looking for Thermistor Probes if all you want is a sensor
and they are readily available. Just do a search on that and see what
you get.

Peter Wieck
Wyncote, PA

 

[[email protected]]

thanks everyone for ideas. I will look up information. pls if you have
any more ideas do let me know.

 

[Ross Herbert]

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.

 

[Bennett Price]

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.)