> >A Peltier device doesn't inherently care about ripple, but
>>it does get less efficient as the AC component increases.

> OK, thanks Olin. I do remember there was some discussion about it a 
> while
> back, but seeing this is going on a spacecraft it looks like I best 
> take
> "reasonable care" with the output.

Functionally it won't care about ripple in terms of short term 
performance -

*** BUT  ***

lifetime is reduced or even much reduced by ripple due, AFAIK,  to 
micro thermal cycling effects. Presumably there will be an upper 
ripple frequency above which this becomes unimportant. Murphy's job is 
to keep your ripple frequency well below this safe limit.

________

Maxim app note mentions only efficiency loss with ripple

" ... . Because current ripple above 3% degrades the TEC's cooling 
efficiency, a high switching frequency is recommended for easy 
filtering of the AC components. "

        http://www.maxim-ic.com/appnotes.cfm/appnote_number/1757/

______________

Here's a spacecraft Peltier application with some discussion on 
Peltiers and ripple.

... sensor value. Inductors were added on both sides of the TEC's, 
reducing the ripple to less than 10%. This guarantees adequate 
lifetime of the Peltier heat pumps. The proportional current 
controller, when compared to a simpler on-off (bag-bang) control, is 
necessary to maintain adequate lifetime of the Peltier heat pumps due 
to the long required operating life (years). High ripple or frequent 
on-off switching under full load would reduce the lifetime 
dramatically.

From:    Thermal design of a Spaceflight Plant Chamber Payload. 2003. 
NASA / Uni of Colorado at Boulder.

        http://www.colorado.edu/ASEN/asen5519/2003-01-2583-Temperature-doc.pdf

Note that they used inductors to reduce Peltier ripple. A modest LC 
may be more compact for you than C alone.

Also, probably of relevance to you
"For missions with limited power availability, the controller can be 
current-limited (range, heat only, cool only, payload power 
budgeting). Under normal operation, the supply voltage limits the 
maximum possible current through the TEC resistance. At full PWM duty 
cycle (100%), the TECs operate at 50% of maximum allowable current for 
highest efficiency, limited by the available supply voltage."







        Russell





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