[volt-nuts] HP3450A Reference Peltier Chambers

[Dave M]

Yes, I'm aware of the problems with AC drive to a Peltier.  However, the 
3450A drives the chamber to 43 degC with DC, so that isn't a problem.  In 
fact, it's a pretty simple drive circuit, runing stable state at 1.5 - 2 
volts.

My interest is in how best to fix the components to the Peltier.  Seeing a 
picture of the innards of the 3450A chamber would help.
I have a few 12V Peltier junctions of various powers ratings, and have no 
other thoughts as to what to use them for.  Making a small chamber to 
ascertain the zero tempco point of my reference zeners seems to be an easy 
project.  This isn't for a constantly-on instrument; it's for short-term 
data gathering.

Thanks,
Dave M


Poul-Henning Kamp wrote:
> --------
> 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.