Date: Tue, 13 Jun 2000 08:47:04 -0400
Reply-To: Ezra Hall <ehall@TOGETHER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Ezra Hall <ehall@TOGETHER.NET>
Subject: Re: Thermostat for Dometic Fridge (fan), found at Newark
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-----Original Message-----
From: David Beierl [SMTP:dbeierl@ibm.net]
Dunno -- you're looking for a contact thermoswitch. Standard industrial
part in many flavors, but not sure how to get one at retail.
snip
Of course, I should have looked first! Checking my catalogs,no luck in
Grainger or MSC, but Newark electronics has TO220 packaged, close at temp,
thermal switches, $7. I will order a 40Deg C (104 Deg F) thermo switch, the
lowest temp offered.
If the fridge works on gas, then the thermocouple is working. See below...
> If my memory serves correct, there is a solid
snip
Good guess...the "solid wire" is a coaxial thermocouple. One end sticks
into the flame and the other end screws into the gas valve. When the t/c
is in a flame, it generates a few millivolts which (astonishingly) is
enough to hold the gas valve open after you open it by pushing the
button. The connection to the LED panel is a single wire from the gas
valve, goes (IIRC) to an inline plug a foot or so away from the LED panel
connector.
David
I must have disconnected the wire at the gas valve, now I know where to
look, thanks!
Ah, so the Seebeck junction is in the gas valve? That makes sense since the
body of the gas valve is a large heat sink to keep that side of the
junction cold. Does the gas valve actually use a solenoid to hold it open?
I would think a bi-metalic structure would be more efficient, but that is
neat if it actually uses a solenoid. Hard to believe 10 or 20 millivolts at
low current is enough to energize a solenoid, but I have seen stranger
things. When I was a kid I recall reading a description of an oil lamp with
a bunch of serially connected thermocouples used to power a radio during
wartime, I think it was a Russian invention. Of course, now we have those
Semiconductor Peltier junctions, I imagine one of these could power a
solenoid well.
If it is truly a coaxial thermocouple (never heard of such a thing) that
would imply an insulated core and the junction at the tip of the wire? Or
is the name misleading?
Thanks for your tips.
Ezra
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