Searching \ for 'Thermoelectric Cooler (peltier) help required.' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=thermoelectric+cooler
Search entire site for: 'Thermoelectric Cooler (peltier) help required.'.

Truncated match.
PICList Thread
'Thermoelectric Cooler (peltier) help required.'
1999\01\22@094707 by Gerry Cox

flavicon
face
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? Experiments could take a lot of
time which I do not have. I can't find anything in manufacturers data other
than keeping ripple low.
Any help appreciated.

Regards,
Gerry Cox.

1999\01\22@104311 by Arthur Bailey

flavicon
face
>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
{Quote hidden}

Peltier elements are approximately a solid state equivalent of a
thermodynamic heat pump. Heat pumps pump the most heat power when the
temperature difference between the two sides is small. So, in general your
peltier elements will operate more efficiently if they are thermally in
series. On the other hand,  I have read somewhere (perhaps the Melcor  Corp
product info) that real peltier elements are most linear when operated
between about 40-80% of the maximum usable temperature difference.

Cheers,
Art Bailey

1999\01\22@105925 by keithh

flavicon
face
I'd guess that heat flow through peltier devices is analogous to
current flow through a group of batteries.

If you are trying to create a small temperature difference
over a large area, parallel devices give the most area.

If you want the biggest temperature difference, then
series is better but gives the smallest area.

Individually, bigger temp differences mean a bigger thermal gradient
to work against, thus more current and thus I2R losses.

The best method probably depends on your app.
Are you cooling a tiny CCD or somthing larger?

Just my guess...

1999\01\22@155546 by Morgan Olsson

picon face
>Peltier elements are approximately a solid state equivalent of a
>thermodynamic heat pump. Heat pumps pump the most heat power when the
>temperature difference between the two sides is small. So, in general your
>peltier elements will operate more efficiently if they are thermally in
>series.

Correct, if temperature difference is big AND the colder side peltier is
much smaller than the hot side.

This is because the hot side pump has to pump also the R*I loss (in form of
heat) generated by the cold side peltier, and that is usually much more
than the total cool effect.

Regards
/Morgan

>On the other hand,  I have read somewhere (perhaps the Melcor  Corp
>product info) that real peltier elements are most linear when operated
>between about 40-80% of the maximum usable temperature difference.
>
>Cheers,
>Art Bailey
>
>
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   Morgan Olsson                       ph  +46(0)414 70741
   MORGANS REGLERTEKNIK                fax +46(0)414 70331
   H€LLEKS               (in A-Z letters: "HALLEKAS")
   SE-277 35 KIVIK, SWEDEN                   spam_OUTmrtTakeThisOuTspaminame.com
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

1999\01\22@155549 by Morgan Olsson

picon face
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?

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
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   Morgan Olsson                       ph  +46(0)414 70741
   MORGANS REGLERTEKNIK                fax +46(0)414 70331
   H€LLEKS               (in A-Z letters: "HALLEKAS")
   SE-277 35 KIVIK, SWEDEN                   .....mrtKILLspamspam@spam@iname.com
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

1999\01\23@161122 by Dwayne Reid

flavicon
face
Gerry Cox 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.

Sounds fine to me.  I did some research into the application of peltier
devices used as generators several years back and don't remember any such
problems that your co-worker mentioned.  The only thing that I found
non-intuitive was that TE coolers do NOT like PWM power - I always found
better efficiency if the PWM was smoothed to DC first.

Look at it this way.  Standard coolers manufactured by Melcor consist of
(IIRC) 128 elements connected in series electrically but connected in
parallel thermally.

Come to think of it - the only problem I can see is if the modules are
somewhat different and do not drop the same voltage.  This will cause the
higher resistance modules to dissipate more power than the lower.  You
should be able to easily measure to see if this occurs and if it is a problem.

dwayne


Dwayne Reid   <dwaynerspamKILLspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(403) 489-3199 voice     (403) 487-6397 fax

1999\01\24@061745 by paulb

flavicon
face
Dwayne Reid wrote:

> The only thing that I found non-intuitive was that TE coolers do NOT
> like PWM power - I always found better efficiency if the PWM was
> smoothed to DC first.

 This relates back to the thread on LED brightness.  The difference is
that the series chain of Peltier modules achieves a higher voltage drop
and runs at significant power making it really worthwhile to use SMPS
techniques.

 The equivalent curcuit for a Peltier device is a "back EMF"
proportional in significant degree to the temperature differential, in
series with an internal resistance.  Power dissipated in the EMF
equivalent does useful work (cooling) whilst power disssipated in the
internal resistance is deleterious to performance (it actually heats the
"cold" side!).

 The significant point is that the "back EMF" is very much a constant.
PWM without an inductor and commutation diode, preferably a capacitor
also, simply biases the internal resistance much harder for a fraction
of the time.  Unfortunately, the power dissipated by this resistance
varies as the square of the current, whilst power achieving useful work
in the "back EMF" (situation is identical in a motor, BTW) varies
directly with the current.

 IOW, delivering twice the current for half the time generates twice
as much waste heat.  In a motor, this is a minor nuisance but can
perhaps be designed around.  In a Peltier cooler however, it is
absolutely antithetical to the primary goal.

 The other aspect of PWM, indeed as I am given to understand, frequent
and repeated cycling of the power, is that the thermal response of these
devices is instant and their thermal mass quite small.  You will thus
produce a thermal alternation and through expansion, a mechanical
oscillation which is stressing the structure of the device.

 Not a Good Thing, so I am told.  It is recommended to drive them with
a power supply which ramps up the drive current relatively slowly and
keeps it constant.  Raw DC from a battery charger is not advisable.  A
well-designed SMPS, more to the point.
--
 Cheers,
       Paul B.

1999\01\24@104228 by wwl

picon face
On Sat, 23 Jan 1999 14:10:01 -0700, you wrote:

>Gerry Cox 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.
>
>Sounds fine to me.  I did some research into the application of peltier
>devices used as generators several years back and don't remember any such
>problems that your co-worker mentioned.  The only thing that I found
>non-intuitive was that TE coolers do NOT like PWM power - I always found
>better efficiency if the PWM was smoothed to DC first.
Could this be due to them acting as a generator when off ? Would
shorting the pins during the 'off' cycle help?

1999\01\24@131807 by Rich Graziano
flavicon
face
-----Original Message-----
From: Morgan Olsson <.....mrtKILLspamspam.....INAME.COM>
To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU <PICLISTspamspam_OUTMITVMA.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
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   Morgan Olsson                       ph  +46(0)414 70741
   MORGANS REGLERTEKNIK                fax +46(0)414 70331
   H€LLEKS               (in A-Z letters: "HALLEKAS")
   SE-277 35 KIVIK, SWEDEN                   @spam@mrtKILLspamspaminame.com
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

1999\01\25@053921 by paulb

flavicon
face
Boy, this discussion is really heating up!  (Groan!)

 I trust my previous summation, to which I have privately received a
favourable confirmation by someone with practical experience, fully
clears up the matter of PWM including the corollary that grounding the
device during an "off" period would not only prevent the cooler from
working, but result in its rapid demise.

 The matter of stacking coolers is fascinating.  They must be stacked
in a "pyramid" with heat-distributing plena between ("heat pipes" come
to mind for this application), where successive lower layers have a
multiple of units inversely proportional to the efficiency of the units.

 If for example, the efficiency of the device is 25%, then you will
require four devices in the second layer; 16 in the third etc.  At this
rate, overall efficiency drops precipitously (exponentially to the
number of layers) and it is easy to see why cascaded Peltiers are rarely
used and *not* for primary cryo-cooling!

 Even in a cascade however, the optimal performance and temperature
differential presumably relate directly to current, and for the same
device, each of the units in the same layer as well as each layer would
best be electrically wired, all in series.

 In most applications, Peltiers are used purely for the convenience of
servo-control of temperature.  For this purpose, it is often convenient
to use another system (conventional evaporative/ condensation
refrigeration cycle using mechanical compressor) as the primary source
of "cool" and the Peltier as the vernier.

 Whether or not there is room for improvement of efficiency as was
hoped some 20 or 30 years ago to the extent that they could rival the
refrigerant compressor, at present they appear to be neither efficient
nor cheap.
--
 Cheers,
       Paul B.

More... (looser matching)
- Last day of these posts
- In 1999 , 2000 only
- Today
- New search...