Hi Lee,

Apologies for the of topic nature.  One can always use a PIC or Stamp
to control the PJ cooler system.  Thermal mass being what it is there
is not much of a rush if you do not have to do very accurate temperature
control.  Simple setpoint controller can easyli be implemented.

You  would monitor for over temperature and current to prevent damage
to the PJ cooler modules.

> > combo PJ/heat sink/12V fan for ~$25 (HSC# 16106).  It was originally
> > intended as a cooler for non-metallic Pentium Chips.  A drop of water
> > will boil on one side and freeze on the other.
>
> I think Mike is exagerating. :-)

I think not.

> As I recall, you get about 20-25 deg C temperature difference from
> one side of a Peltier junction device to the other side.  You can
> stack them (multiple stages) for more.  Transferring the heat energy
> is not free -- there's a not inconsequential current consumption.

The temp difference can be over 150 degC.  The problems are when the
hot side gets hotter than the solder that is used in the assembly and
the whole unit destructs.  I would be cautios about using them for
heating as the efficiency is only about 25% you don't gain much over
just using a heating element and you risk toasting the PJ device.

For cooling you have to dissapate 4 times as much heat as what you
are actually pumping.  It also means that the cold side heats up
pretty fast after you turn of the pump as the heat from the hot side
now can 'run back' with the pumping current off.

I have done a design analysis on a PJ water cooler that almost worked
well except that the efficiency is so poor and a large temp gradient
does not help any.  The water cooler actually uses a 60 mm x 60 mm
PJ cooler device and a LARGE 120 mm x 120 mm x 30 mm finned heatsink
with a large fan (I have a box of these for sale, see my SirPlus page)
and there still was not quite enough to get all the waste heat out.
With two fans the water coolers work a treat and make a 60mm dia by 6mm
thick ICE brick that after it reaches a predetermined thickness
is allowed to melt free (current switched off) and floats to the
top of the cooling space, the cooler turns on and starts to make
another ice brick.

So in heating mode

   Ambient    PJ     Box
   20W    +   80W =  100W

and in cooling mode

   Ambient    PJ     Box
   100W   =   80W +  20W

You are correct about the current consumption obviously and the potential
for stacking the devices but you usually only stack them 2 or 3 high so
with just 25 degC you could only get a temp difference of 75DegC and much
more is atainable as long as one keeps in the device limits.
{
 Just had a look at the RS components (UK) catalog at some specs.  They have
 got quite a range now 15 in total with a stacked module, a ring module
 and a fan cooled module.  Smallest is 0.32W of pump largest is 120W which
 is what was used in the water cooler.  Max temp is listed as a conservative
 85 degC but 110 degC for the Fan cooled unit.  Max temp differential is
 65 .. 70 degC for the single stage units and 83 degC for the stacked units.
}
You have to build a pyramid with more cooler required to cool the cold one
with a minimum recommended ratio of 2:1 but better at 4:1 unless you only
use a small fraction of the coldest coolers capacity.  Expensive.

   -50 degC
                     XXXXX
     0 degC       ===========
                  XXXXX XXXXX
    50 degC =======================
            XXXXX XXXXX XXXXX XXXXX
   100 degC =======================
            |||||||||||||||||||||||
   BIG fan

Cheers
--
Kalle Pihlajasaari   kalle@ip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer