Larry wrote:
"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!

Er.............I think he means a 12-volt Eberspacher or similar, using
diesel to heat the boat? If I'm wrong, your maths is correct, but but I
would find it difficult to believe that anyone could be so mad!