"Neil" wrote in :

Can anyone recommend a thermostat that does not require a power supply
and can switch a 12v heater?



12V heater??

Please tell me you're not trying to heat a boat with a 12V
heater....please?

A bathroom heater is 1500 watts, about. If we do a little math, 1500 watts
divided by 12V = 125 amps! That might work overnight with a set of 6250 AH
submarine batteries...(c; But, alas, they're about 4 ft X 5 ft X 7 ft high
and weigh a couple tons per cell....(sigh)

Sorry, doesn't float. A boat doesn't have anywhere near enough battery
power to heat anything more than a quick cup of coffee or a soldering iron
for a few minutes.

I also have a joke that goes along with that....

"Nothing is funnier than a boater with a new 4000 watt inverter carrying
his electric heater down the dock with a big smile on his face."

I'm not trying to make fun of you, really. There's a hundred boaters at
City Marina who bought one of those damned 12V heaters Waste Marine sells
in every store. I'm convinced they sell them so they can sell more
batteries, but can't prove it. By the way, they don't need a thermostat.
They barely get warm!

Sorry if it bothered you. You're not alone. Go plug the boat back into
the dock. Thanks. If your boat is gasoline powered, please don't use any
thermostat-controlled 115VAC heater, either! Any gas fumes that get sucked
into that heater at the moment when the points in the thermostat open may
blow up your whole end of the marina! Run the heater in the dark and turn
the thermostat until the heater shuts off. Big spark at 15A off
115VAC....BOOOM!

--
Larry