Ok, so heres the plan. We have a wood burner in the dining room of the house, which puts out copious amounts of heat. We have 3 other rooms that could do with being warmed, so im going to rig up a gated, thermostat controlled ventilation system in the roof space. Im going to use a 12v car heater fan to do the work, using the original resistor network from the car if its a bit too loud, ill check the draw whilst starting/running and fuse it accordingly. I'll be using an old computer PSU to power it. Will be using cables, rods + pulleys to actuate the gates, so we can decide from the dining room which rooms get the heat and which dont, and at what ratios. Now, what im after is what will be the cheapest way to make a variable thermostat arrangement so that its NO until it reaches the pre-determined heat level. Ie, when room temperature in the dining room hits 23 degrees C, the fan turns on and takes the excess heat above 23 C to the other rooms... This does not have to be exact, but it does have to be variable so we can set the temp that we want. No computer is involved, so i cant work that way unfortunately. Ideally it'll be 12v controlled because id rather keep it that way for obvious reasons. Prefer to use parts that will be available locally... Anyone have any ideas? TIA
My immediate reaction would be to utilize a thermistor with an op-amp for amplification and then another wired as a comparator to control a relay for the fan. Another way, if you do not want to work with op-amps, is to utilize a mercury filled bulb, the kinds you find in thermostats, and tie that to two pieces of dissimiliar metal so they will curve and close a switch when the specified temperature is met. One will involve just turning a variable resistor and the othe will involve playing with the metal coil.
Simple voltage divider going into a transistor switching a relay? The same simple circuit that appears in every single standard grade physics paper. I'll give you an example if you want. _C
Hi guys, -Xiachunyi Im not familiar with op amps, unfortunately. Im pretty low on the old electronics scale, unfortunately - I know the basics, but not much beyond it. -Double_C That would be really good, if you would thanks My original thoughts were something like this http://www.jaycar.co.nz/productView...d2=&pageNumber=&priceMin=&priceMax=&SUBCATID= but 47$ is a bit more than i want to pay, really, and it would have to work straight off the 240v source. The other thought was to butcher a 15$ fan heater with a relay, or directly at 240v, and use the thermostat out of one of those, but im unsure of how effective it would be, id imagine it would switch at higher temperatures...
Wouldn't it be much easier just to buy a Thermostat from the store. You can find them for around $5 or $25 and up for an electronic model. They both basically just close and open a relay, and they will also provide some ambiant heat compensation. Might be your best starting point. ^Pretty much like you said, but you can find these at just about any home improvement store, I wouldn't bother ordering online if I could help it.
