[volt-nuts] HP3450A Reference Peltier Chambers

[Poul-Henning Kamp]

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In message <F57B1617EE984B10AAD5379A2402DFE6 at D77M7BF1>, "Dave M" writes:

>I was intrigued by the use of a Peltier chamber to control 
>the temperature [...]

It's a very obvious idea, but it runs into one of the widely unknown
footnotes about peltiers:  Don't feed them AC.

The thermal/mechanical stress when you change direction of the
current significantly shortens their life.

I should add that I have not found any studies which say to what
degree this depends on the magnitude of the current, so an oven
balancing around a couple of mA may not be a problem, but switching
polarity on several amps will be.

One complication is the difference in directional efficiency:  The
warm side receives about 4 times as much energy as is removed from
the cold side.

Unless you electrically compensate for this, your PID will be
*really* confused.

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