I want to make a electronic controller to turn a fan(3" muffin type)
when water temp reaches a certain temperature. I know they make water
proof or submersible thermistors, and there can't be too much to the
circuit as one company makes such a fan but its sensed with air temp
and I want water temp.......Fans are all 12 volt DC.. I owuld like to
turn on fan when water temp reaches 81 deg or so and off when it gets
back to about 79 or so degrees.

Any links on circuits etc appreicated or on how to figure out what
thermistors are needed.
--
\\\|///
( @ @ )
-----------oOOo(_)oOOo---------------


oooO
---------( )----Oooo----------------
\ ( ( )
\_) ) /
(_/
The original frugal ponder ! Koi-ahoi mates....

do a search for "comparator" or "quad comparator", or even "op amp"
and you'll get a plethora of circuits -you need a voltage reference (a
pot will do, you need a resistor and the thermistor in series (the
junction of the two being the other feed to the comparator) and you
need a stable power supply (get a 7805) - pretty simple, no?


On Fri, 10 Mar 2006 03:58:22 GMT, (Roy) wrote:

I want to make a electronic controller to turn a fan(3" muffin type)
when water temp reaches a certain temperature. I know they make water
proof or submersible thermistors, and there can't be too much to the
circuit as one company makes such a fan but its sensed with air temp
and I want water temp.......Fans are all 12 volt DC.. I owuld like to
turn on fan when water temp reaches 81 deg or so and off when it gets
back to about 79 or so degrees.

Any links on circuits etc appreicated or on how to figure out what
thermistors are needed.
Bill

www.wbnoble.com

to contact me, do not reply to this message,
instead correct this address and use it

will iam_ b_ No ble at msn daught com
*** Free account sponsored by SecureIX.com ***
*** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com ***

There are a wide range of cars that have thermo switches mounted in the
radiator to do just this, what's wrong with copying the circuit from the car
you pull the switch out of? They will already be suitable for 12 volts and
are fairly weatherproof.

You can also use the standard thermostat from a hot water system on 12 volts
and they would carry enough current to stitch your fan. Might not have the
vibration resistance if you wanted to use it on a car. They would also have
to be mounted dry outside but in contact with the meal surface of the water
holding "tank"?

Cooking thermometers can be mounted to some items and there are ones that
hook up to certain model ovens to turn off the element and maybe ring a bell
when the roast is cooked.

They will have a mounting that can be copied or transferred to almost any
tank you might want to use, or inline with a plumbing fitting.

Fishtank heaters have a thermostat and can be rewired to suit. There are
other options,

Hope this helps,
Peter



I want to make a electronic controller to turn a fan(3" muffin type)
when water temp reaches a certain temperature. I know they make water
proof or submersible thermistors, and there can't be too much to the
circuit as one company makes such a fan but its sensed with air temp
and I want water temp.......Fans are all 12 volt DC.. I owuld like to
turn on fan when water temp reaches 81 deg or so and off when it gets
back to about 79 or so degrees.

Any links on circuits etc appreicated or on how to figure out what
thermistors are needed.
--

On Fri, 10 Mar 2006 03:58:22 GMT, (Roy) wrote:

I want to make a electronic controller to turn a fan(3" muffin type)
when water temp reaches a certain temperature. I know they make water
proof or submersible thermistors, and there can't be too much to the
circuit as one company makes such a fan but its sensed with air temp
and I want water temp.......Fans are all 12 volt DC.. I owuld like to
turn on fan when water temp reaches 81 deg or so and off when it gets
back to about 79 or so degrees.

Any links on circuits etc appreicated or on how to figure out what
thermistors are needed.

You might look at aquarium heater controls.

Try posting on sci.electronics.design if you can build simple elex
from a schematic. You are right, there isn't much to a circuit that
wil do what you want to do.

I'd normally be glad to help more, but I'm about at capacity with
pro-bono projects at the moment.

In article ,
(Roy) wrote:

I want to make a electronic controller to turn a fan(3" muffin type)
when water temp reaches a certain temperature. I know they make water
proof or submersible thermistors, and there can't be too much to the
circuit as one company makes such a fan but its sensed with air temp
and I want water temp.......Fans are all 12 volt DC.. I owuld like to
turn on fan when water temp reaches 81 deg or so and off when it gets
back to about 79 or so degrees.

Any links on circuits etc appreicated or on how to figure out what
thermistors are needed.

For simple, you'd want a thermostat. Boring old bimetallics do a lovely
job at this sort of thing, and switch the power directly. Thermistors
and other (some both better and cheaper than thermistors) temperature
sensors involve a good deal more circuitry - not particularly difficult,
but a lot more complex than a thermostat.

--
Cats, coffee, chocolate...vices to live by

On Fri, 10 Mar 2006 03:58:22 GMT, the renowned
(Roy) wrote:

I want to make a electronic controller to turn a fan(3" muffin type)
when water temp reaches a certain temperature. I know they make water
proof or submersible thermistors, and there can't be too much to the
circuit as one company makes such a fan but its sensed with air temp
and I want water temp.......Fans are all 12 volt DC.. I owuld like to
turn on fan when water temp reaches 81 deg or so and off when it gets
back to about 79 or so degrees.

Any links on circuits etc appreicated or on how to figure out what
thermistors are needed.

What's the current rating on the fan? Is it an electronic BLDC type?


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

On Fri, 10 Mar 2006 03:58:22 GMT, (Roy) wrote:

I want to make a electronic controller to turn a fan(3" muffin type)
when water temp reaches a certain temperature. I know they make water
proof or submersible thermistors, and there can't be too much to the
circuit as one company makes such a fan but its sensed with air temp
and I want water temp.......Fans are all 12 volt DC.. I owuld like to
turn on fan when water temp reaches 81 deg or so and off when it gets
back to about 79 or so degrees.

Any links on circuits etc appreicated or on how to figure out what
thermistors are needed.

Lots of info on thermistors at
http://www.thermometrics.com/htmldocs/proserv.htm

Digi-Key carries thermistors made by these folks.

Circuit: 10K or more thermistor, a pot, coupla resistors, an
LM319 comparator with a bit of hysteresis (positive feedback) and a
relay or MOSFET load switch.

http://www.digikey.com/scripts/DkSea...388888&Site=US

Mouser carries thermistors too, and Mouser doesn't have a $25 minimum
order. A 10K Vishay thermistor from there is 594-2322-640-43103 for
92 cents. LM319 is 65 cents. Shipping is probably 5 bux!