Im looking to control my furnace with a mosfet transistor (IRL530N), witch works well with my arduino for DC loads. Would it work as a furnace switch (24vac 100mA) ?
Thank you !
Yes. or You could use Relay. It just on and off then you can go with relay.
NO! A mosfet will not switch ac. A relay would be fine
Allan
ps 100mA and 24v is only 2.4 watts -a very small furnace - are these numbers correct?
allanhurst:
ps 100mA and 24v is only 2.4 watts -a very small furnace - are these numbers correct?
I suspect that the 24V 100mA is just a relay that switches the furnace.
stuart0:
I suspect that the 24V 100mA is just a relay that switches the furnace.
Sounds like control voltage to me as well. I don't understand why people are trying to control the 24Vac line for the furnace when it would be easier to hack the thermostat and control the temp sensor instead.
You go away for a few days, you control the furnace with a hobby device, the device fails, the furnace runs on and on, you destroy the gyprock in the house, you have no nsurance.
.
Totally agree with larry.
If you want to control the furnace use a power tail or similar to control the supply.
Leave the internal workings of the furnace alone !
What is a furnace BTW , in the UK gas boilers are common, a furnace to me could imply several things and i am not conversant with the terminoligy in the US and Canada.
Thanks for your replies.
Yes, the 24vac 100mA is the control current only that feeds into the thermostat. Closing the circuit will turn on the furnace. My thermostat is still the mechanic mercury bubble one and this is what Im planning on doing to hack it, bypassing the bubble with a microcontroller. Same what a Nest would do.
The furnace is a propane gas powered appliance that sits in the basement and that blows air trough burners and circulates it through the house.
i have created the thermostat and multiple thermometers spread around the house, talking through wifi to a MQTT server. The central unit makes sense of the messages to determine when to turn on the heat...
Im just missing the last bit witch is the practical switching of the furnace itself...
If anyone else have any insight into using 3.3vdv to close a 24vac 100mA circuit, I would appreciate.
D.
I am using an arduino to control my furnace. The house was built with a gas furnace, and I added a solar drainback system about 30 years ago. This means 2 thermostats. I got tired of fooling with 2 thermostats when I wanted to turn the heat up or down. I now use an arduino to run the furnace. Its been in operation for about a year now - works great.
I built an AC "circuit on" detector by using an LED and an opposing diode (because it is an AC circuit), and mechanically coupled the LED with a LDR (light dependent resistor, or photo detector), inside of some shrink wrap tubing. You can also buy these devices, but I didn't want to pay the shipping for a cheap device.
I rewired the thermostat circuit so that the thermostat and the arduino in series with the furnace. I also added the "circuit on detector" so that it is on when the thermostat closes. The arduino detects that the thermostat is calling for heat, and the arduino decides what to do about it. It first turns on the solar. If that doesn't work (because the solar tank is too cold), then it turns on the gas (which always runs, just like the original circuit)
I use a Sharp S108T02 solid state relay to contol the AC. They cost about $5.00. I have used these relays on several projects - including one where the arduino turns on a "security light", which is 110 VAC.
You cannot use a MOSFET - that only will work for a DC circuit. Most furnaces are controlled with low voltage AC.
The obvious answer is to use a mechanical relay. What's stopping you from doing it that way?
Of course cdj15's solid state relay looks nice too.
Thanks again for your answers. I realized that the internal diode on the mosfet will not let the AC current work.
Ill probably go with cdj15's suggestion... S108T02 looks great and very flexible for different uses.
My main reason to use the mosfets is just availability, since i bought a big lot of them to drive LEDs, and china takes ages to deliver.... Ill get an order for the ssrs.
D.
Don't overlook PhotoMOS SSRs ... they can switch DC or AC.
Here, I've created a search filter for them at Digi-Key for 150mA-500mA and 100V or higher.