Thermocouple on old water heater

[Joseph]

I was trying to find out how the safety thermocouples on those old water heaters work. All I can find online is what I already knew--that it shuts off the gas if the pilot light isn't lit. But exactly how?

[Robert Reed]

On our (old) gas furnace it worked like this. A constant small pilot flame is directed at the thermocouple and it outputs enough voltage when hot to energize a solenoid valve in the main gas line. As long as the pilot flame is there, furnace operation is maintained. If for any reason the pilot flame extinguishes, the thermocouple out put goes to zero and the solenoid then closes the valve to the main gas supply.

[Joseph]

Ahh, thanks, Robert, it definitely directly powered a solenoid gas valve on your old furnace.

Edit: I guess that means the output of the thermocouple would need to be a watt or more.

[CeaSaR]

My house heater works the same way. Pilot burning on thermocouple = gas on. I don't know if it is amplified
prior to the solenoid. No schematic. I do know that I have low voltage electric running into it, though.

CeaSaR

[Joseph]

Yeah CeaSaR, my water heater is a few decades old, (Oh my, it could start leaking!) and it has no external electricity supplied to it. (I hope that it is completely off helps it's lifespan.)

The low voltage wires running to your furnace might very well be the thermostat wires.

[CeaSaR]

Yes, they are the thermostat wires. I don't have any schematic or mechanical drawing of the solenoid, so
I don't know exactly how it works. My heater is old too, at least 3-1/2 decades.

I was told a number of years ago that you should leave the pilot light on, even over the summer, to keep
the boiler/heat exchanger area from rusting. The gentle persistent heat helps drive away moisture year round.

CeaSaR

[dacflyer]

the unit is actually called a thermopile...its voltage is very low. in the millivolts, maybe up to 1/2 a volt. the coil in the gas valve is very senitive, the thermopile might have more current than voltage to be able to hold a valve open. not 100% sure, but i do remember that when i used to work in restaurant repair, i'd sometimes come across a gas stove or deep oil fryer and the pilot would not stay lit. a trick that someone showed me was to hold a blow torch to the thermopile and let it get cherry red. that would somehow rejuvinate the thermopile for a few more months until or so. at least long enough til i got the part i needed. usually the same day or next.
i never cut one open to see what makes them tic, but i am sure its probably plutonium...lol
anyone wanna split an ATOM ?

[Robert Reed]

I repaired one of these 30 years ago and its been too long to remember how I did it. But I did have the unit apart and the solenoid coil is but a few turns of very heavy wire. This is definitely a coil that leans to relatively high current rather than voltage. I was amazed that a solenoid could actually be energized by one these pilot devices. Judging by the physical properties of the coil, I would guess it might be receiving a half amp of current.

[Joseph]

I was wondering if it involved a solenoid with fewer turns of thicker wire. Thanks everyone.

[Joseph]

So, the main reason for my seeking information on thermocouples involves the hope for being able to generate some electrical power in the range of 100 watts for a tri-hybrid bicycle--pedal, electric, fuel. Here is a link for a site having some more information. http://www.tegpower.com/index.html

[CeaSaR]

Lest ye forget, for a Peltier device to work as efficiently as possible, the temperature differential between sides
must be rather great. So if you want this device to generate enough voltage AND amperage to power a vehicle
(even something as light as a bicycle), you MUST have a way to create or sustain that differential. All the examples
shown in your link are fine and dandy because they have a hot side (exhaust / radiant heat surface) that is already
powered by some sort of fuel, and a (relatively) cool side (ambient air, possibly with moving air over cooling fins).
The only way I can see to have a constant heat source on a bicycle is to strap the device to the body so it is in
contact with wearer's skin. Just about everything else would be hit or miss, depending on situation or demand.

Give us a sneak peak at what you come up with so we can get in on the ground floor for your new multi-billion
dollar break-through!

CeaSaR

[Joseph]

Indeed CeaSaR! I would gladly share anything really nifty that I can devise.

I am also considering a closed loop steam or a Stirling-type power source. They would be more modernized versions that substitute electronically controlled coils in place of crankshafts. A coil would output power on the power stroke of the engine.

Or maybe some other power source. I was surprised to see dacflyer's post since I was wondering about an alpha or beta emitter as a source of heat for a thermopile. That isn't really an option, though.

Read a apparently true story in a book about Chernobyl. Some hikers were out in a remote area in the Ural mountains and came upon a warm area with melted snow around a big canister. They decided to use it instead of a campfire. Unfortunately, it was a radioactive beta source dumped there some time before.

[mthornton]

re Peltier devices

Living in Canada, we use our wood stove extensively for heat (firewood is free, plentiful & carbon-neutral), and it's often very cold outside (cold air also free). So investigation of these devices may proove fruitful.

Asimov wrote about a society which provided all it's electric energy requirements through massive thermopiles embedded deep below the planet's surface. Hmmmm....

M

[Bob Scott]

Lest ye forget, for a Peltier device to work as efficiently as possible, the temperature differential between sides
must be rather great. So if you want this device to generate enough voltage AND amperage to power a vehicle
(even something as light as a bicycle), you MUST have a way to create or sustain that differential. All the examples
shown in your link are fine and dandy because they have a hot side (exhaust / radiant heat surface) that is already
powered by some sort of fuel, and a (relatively) cool side (ambient air, possibly with moving air over cooling fins).
The only way I can see to have a constant heat source on a bicycle is to strap the device to the body so it is in
contact with wearer's skin. CeaSaR

HA! A human powered bicycle!

[CeaSaR]

HA! A human powered bicycle!

Novel, ain't it?

CeaSaR