Anyone know anything about wiring up a thermistor (sp?)

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.
Reply to
Roy
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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?
Bill
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Reply to
William B Noble (don't reply t
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
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.
thermistors are needed.
Reply to
Bushy Pete
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.
Reply to
Don Foreman
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.
Reply to
Ecnerwal
What's the current rating on the fan? Is it an electronic BLDC type?
Best regards, Spehro Pefhany
Reply to
Spehro Pefhany
Lots of info on thermistors at
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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.
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?Ref=18501&Row=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!
Reply to
Don Foreman

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