| Electronics > Projects, Designs, and Technical Stuff |
| Line voltage thermostat (e.g. HTM611A) |
| (1/1) |
| leblanc:
My house has baseboard heaters (electric heating). The thermostats switch the 240VAC directly. They're single-pole thermostat so one of the two lines is always energized. I'll called the switched one "L1" and the other one "L2". One of my thermostats is a programmable thermostat (TRIAC controlled). I figured it must be powered by putting a transformer across L1 and L2 (e.g. something like 240VAC to 12VAC, followed by a rectifier and then a DC/DC. However, when I looked at the user manual for it, I found that this thing only has an two wires, one for input (i.e. line voltage from the breaker panel) and one for the load. The other side of the load just goes back to the breaker panel to connect to L2 (well it goes back to the same electrical box as the thermostat first, but it doesn't connect to the thermostat). How would you speculates this thermostat gets powered internally? Hint: there is a 500W minimum load (and 3kW max). I see a few possibilities: * The device only gets powered when the load is ON and we have some kind of Rogowski coil from which we take power. When the load is OFF, we run off a battery or supercap. * The device only gets powered when the load is OFF and we just take our supply in parallel with the TRIAC (the load would be small enough that the load-side of the TRIAC is close to L2). When the load is ON, we run off a battery or supercap. * The device uses a combination of the two and does not rely on a battery or supercapCan you sketch your guess of what the schematic would look like? I don't think it's #1 because you wouldn't want your heaters to turn on periodically in the summer. Although #3 would work the best, the added cost is probably not worth it. So I think it's #2. |
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