Controlling millivolt fireplace with Wi-Fi wall switch

Question

My whole house is setup with Wi-Fi wall switches. They're just like basic 110V wall switches, but they can be controlled via Wi-Fi. I'm in the U.S. I'd now like to enable my fireplace. The fireplace runs today from a standard wall switch, it's not a millivolt switch. The switch turned on releases the gas, lights the pilot, and then turns the gas on full via 3V DC.

So, I'm in a place where I need to control extremely low voltage DC with 110V AC. I thought about an SSR, but AC-DC relays don't seem to exist. I thought maybe an A.C. SSR-25AA that I had laying around would complete the millivolt circuit, but resistance doesn't seem to change with the SSR. Would it on an electromechanicsl relay? I then thought about transforming the AC to DC, but I was hoping for something smaller with fewer components. While testing, I found that when I switched from 1K to 10 ohms, the multimeter's resistance turned on the fire. Switching back up turned it off. Maybe a resistor on my SSR would work?

What is the best way that I could switch low voltage DC with house AC? Can AC being on just complete a simple DC circuit somehow?

Thanks.

Answer 1

I think the approach you're taking is reasonable. I assume the wifi switches need 110VAC in to power themselves?

AC in DC out SSRs are rare but they do exist. I was able to find this one for a reasonable price:

DC60SA3

That should work but if it doesn't, a regular old mechanical relay will definitely work. It has metal contacts inside just like your old light switch.

For example: https://smile.amazon.com/JQX-13F-Power-Relay-PTF08A-Socket/dp/B00NWHJ5N6/

The AC Output SSR you have won't work with DC because AC relays contain a 0 crossing detection circuit to switch right when the AC voltage is 0. Since your stove will never put out 0v, it will never turn on, and if it does somehow it it may never turn off. See this document for more info: http://www.crydom.com/en/tech/newsletters/solid%20statements%20-%20ssrs%20switching%20types.pdf

Answer 2

AC (coil) Relays are a thing. Thats the easiest way to do it. There are AC SSRs too, but no cheaper.

You can also do it with optocouplers. This kind (LTV8141) has 2 leds so it runs off AC. Of course the output will momentarily go off at 100Hz, which probably doesn't matter, but a capacitor might be needed on the output

^{simulate this circuit – Schematic created using CircuitLab}