/I was just wondering about using themocouples for an
/alternate power supply?
A very perceptive question!!! And . . . believe it
or not, it's not really to far out of reach . .
at least in principal.
/AFAIK they are used on missiles and bomb { as in H,
/as in serious big bangs } fuses.
Actually, the device you're refering to is a "thermal
battery" which is still a chemical battery like the
ones you use in your flashlight. In this case, the electrolyte
doesn't work until it's heated to a molten state at about
700 degrees F or hotter. We did a design review to consider
a thermal battery in our latest upgrade to the AQM-37D,
high altitude, Mach 4 target. These batteries are attractive
for weapons systems because of their ability to deliver
a lot of watts for a short period of time (generally limited
to 10-20 minutes). They store very well (shelf life on the
order of 10-50 years) and come to life in about 100-300
milliseconds after the thermite is touched off inside by
an electrical squib from outside. We decided not to use
it this time due to some changes in our lauch protocols that
would have risked reduced reliability in other areas of
the target's performance. But back to your original premise . . .
Thermocouples are capable of delivering useful amounts of
energy. One of the most common examples are the early
electric gas valves for furnaces that took advantage
of a remote thermostat. A thermocouple on the pilot
light was connected in series with a thermostat
in the house and a coil in the gas valve. The output
voltage of these thermocouples was only 150-200 MILLIVOLTS
so the valve coil was a special design. The CURRENT
available was considerable so there was a useful amount
of energy but a common mistake of installers or
repair-persons unfamiliar with the technology was to
wire with ordinary 22AWG thermostat wire and throw away
too many millivolts in the conductors. I discovered this in
my first exposure to such a system in a house I was
renting about 25 years ago. The house had been remodeled
in the summer; the thermostat moved and rewired. In the fall,
the system wouldn't work and it was very late one Saturday
night when my wife and kids were complaining about how
cold it was. Managed to get it up and running with a quick
rewiring job of 18AWG.
During WWII, a radio receiver was available in Europe
powered by a "thermopile" situated on top of a kerosene
lantern. I'd like to see one in a museum some time,
I've only read about them. Here's the basics:
Each dissimilar metal junction in a hot environment
(say 1200-1500F exhaust gases) works "against" a
companion cold junction (blast tube with ambient
100F max air?). A hot-cold pair of chromel-alumel
couples will get us about 0.03 volts. Now the tricky
part, hook about 100 pairs in series, zig-zagging
in and out of the exhaust pipe without leaking exhaust
gasses and you've got 3 volts. A current of 10 amps
seems possible . . . Hmmmm . . . 30 watts. There
are very efficient step up regulators that can boost
this to 12 volts and leave you 2 to 2.5 amps of snort
to run things with.
There may be other metal combinations that deliver more
voltage . . . the kerosene lamp device ran at much lower
temperature differentials and seems certain not to have
been THAT complex. Further, exhaust gasses weren't under
so much pressure . . .
I think a wind driven device of some kind is more
practical but the thermopile idea is not as far
fetched as some might think. Anyone else have some
thoughts about this?
Regards,
Bob . . .
AeroElectric Connection
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