-----Original Message-----
From: Morgan Olsson <mrt@INAME.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Friday, January 22, 1999 3:54 PM
Subject: Re: Thermoelectric Cooler (peltier) help required.


At 14:20 1999-01-22 -0000, you wrote:
>I am using a PIC as a controller for TEC (peltier) devices. I monitor
>various temperatures and adjust a constant DC current to achieve the
>required results. Eight (identical) peltier devices are assembled to a
'cold
>plate' thermally in parallel. Electrically they are in series and they draw
>approx 2A from the 12V supply.
>When the design was presented for 'peer review', someone stated that the
TEC
>devices should be electrically connected in a series/parallel arrangement
to
>improve efficiency.
>He couldn't state the reasons for this. I can't think why a simple series
>connection should be less efficient. He didn't mean driver efficiency, just
>thermal efficiency of the peltier devices. Does anyone out there  know if I
>ought to follow this up or just ignore it?

Thermoelectric (Peltier) devices are often stacked in series (Mechanically)
in order to extend the temperature delta. They are also arranged
(mechanically) in parallel in order to extend the useful cooling surface.
Is it possible that your peer reviewer meant that a series parallel
arrangement of the peltier devices could extend the useful temperature delta
and usable surface area? Perhaps the remark was not intended to apply to the
electrical circuit configuration.  I have created such cooling units myself
by using series and parallel peltier devices in this way.  It may be worth
your time to check it out.  I think it would benefit you more to respond to
a peer review comment rather than ignore it.

Best regards,

Richard



Right, that is bullshit.  It is about optimizing the drive voltage and poer
supply.

On the contrary: power supplies are more efficient at higher output voltahe
due to less percentage loss in the rectifier (and also in cables,
connectors etc), so connect them in series!

To get the best efficiency, you shall keep from PWM or on/off, instead
control a SPS to deliver just the reqiuered voltage, to minimize R*I losses
in the peltier.

OK, if you have a lot of elements another good method is to shift between
say 3 parallel x 2 series, and vice versa to have two modes with "lossless
conversion" (just a relay)

Good luck
/Morgan
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