Homemade Thermopile

[David Williams]

-> Do the cross-sectional area, distance between or shapes of the
-> junctions effect the output?
-> Are there an optimal number of junctions to be placed in series?

A problem if you use metal wires is conduction of heat along the wires,
so it gets from the hot to the cold junctions without doing anything
useful. If you use very long and/or thin wires to minimize conduction,
you run into a problem with resistive losses.

The shapes of the junctions shouldn't have any effect, provided they
are good electrical connections.

The more junctions, the better.

dow

 

[Eeyore]

Honeywell make a thermopile that sits in the flame of the pilot light
on a gas water heater and produces a volt or so to hold the gas relay
open. Flame goes out, gas shuts off. These things are sold as
replacement parts for gas water heaters... about $30... about the size
of a cigarette butt on a long wire.

And the conversion efficiency is ?

Graham

 

[clare at snyder.on.ca]

Honeywell make a thermopile that sits in the flame of the pilot light
on a gas water heater and produces a volt or so to hold the gas relay
open. Flame goes out, gas shuts off. These things are sold as
replacement parts for gas water heaters... about $30... about the size
of a cigarette butt on a long wire.

It is MILIVOLTS of output. At Microamps

 

[Johnny B Good]

It is MILIVOLTS of output. At Microamps

You're probably in the right ball park regarding the millivolts
(probably around a hundred or so) but wrong with regard to the
micro-amps. It's probably an amp or two feeding a hold-in solenoid using
no more than half a dozen turns of very thick wire. You don't need many
ampere turns to generate the necessary magnetic flux to do this job.

Remember, the solenoid doesn't need to generate a pull in force (that's
your job when you hold the button in , it just needs to hold the
armature in which only needs a small magnetic force compared to that
normally associated with pulling the armature in over its operating
range.

 

[clare at snyder.on.ca]

You're probably in the right ball park regarding the millivolts
(probably around a hundred or so) but wrong with regard to the
micro-amps. It's probably an amp or two feeding a hold-in solenoid using
no more than half a dozen turns of very thick wire. You don't need many
ampere turns to generate the necessary magnetic flux to do this job.

Honeywell spec is 30MV for all their "thermocouples"
There are also "thermopiles" which are 750MV.Also called PowerPiles.
Powerpiles have 2 wires from them that connect either to terminal
screws or blade type connectors.
Thermocouples (30mv) have a screw-in monolithic connector.

Thermopiles are roughly 8mm in diameter, while thermocouples are
closer to 4mm.

Both my old furnace and my water heater use 30MV.

A 750MV system generally has a maximum holdin curent of 285ma and a
minimum holdin of about 125ma(drop-out). Coil resistance is 2.25 ohms
plus/minus 0.5 volts.
Minumum operating voltage is 125mv.

On a 30mv system, coil resistance is an incredible 0.015milliohms
according to Ascot on a 820 Nova gas valve.
I have never seen a current spec for a 30MV system.

 

[clare at snyder.on.ca]

mV as in Millivolts- yes.

30MV would be 30,000,000 volts! ITYMM "mV" as in 0.03v so I'll assume
you meant mV each time you've used MV. That aside, I thank you for the
information (I was merely taking an 'educated guess' at the voltage


Yes, at such low voltage and an amp or two, you need a very low contact
resistance.




I presume you meant " plus/minus 0.5 OHMS" You got me again.
.


That looks like a confusion of units. It seems more likely that they
expressed the resistance in ohms and appended the milli since 0.015 ohms
is 15milliohms. IOW, a not so incredible 15milliohms (although that is a
low enough resistance to be _almost_ incredible

They claimed the resistance was virtually impossible to measure.