Cool it

The CCD is cooled with a peltier element (TEC1-03510). It’s sandwiched between the two pieces of anodized aluminium secured to chassis:


Not very visible, perhaps this is a better view:


From the top: CCD, cold tip, peltier element, block of aluminium and finally the large heatsink.

The peltier is surprisingly hungry and will draw 10A at 4,16V. I thought I could get away with using two small 6V toroidal transformers with an LT1084 regulator¹, but the temperature drop was quite modest unless I let the peltier draw the maximum the transformers would supply, so I decided to get a bigger PSU:


The ATX-PSU for powering the peltier element. The jumper wire is between PWR_on and GND.

I chose an EVGA 550 B3 ATX psu, because is 100% modular. The power rating was not a part of the considerations, but having so much juice at my disposal I became curious if I could use cascaded TECs (I have some large TEC1-12706 lying around for a fog-chamber I never came around to building).

As usual I hadn’t thought it through, so I wasted time inserting the extra peltier element between the aluminium block and the chassis, only to see an even more modest temperature difference. I like modesty, but for dog’s sake, this was too much.

If I had done my homework, or just used my brain, I would have realized that the new heatsink must be something like an order of a magnitude larger than one already in place. The small heatsink cools the CCD well, but peltier elements are not very effecient and waste >90% of the energy used for transporting heat from the cold side to the hot. A second TEC must handle all this waste heat on top of the desired temperature drop (and the 2nd TEC is of course also <10% efficient).

Maybe there’s a trick to it, like running the 1st TEC at low power and the second at it nominal rating. However, this would require better insulation and/or more patience than I have.

So I’m back, to just one heatsink, but I will install fans on the heatsink, as the moderate airflow from the ATX-psu on the heatsink gave an additional drop of 1°C, for a temperature on the cold tip of -6°C when running the TEC at 4,0V.²

[1] The LT1084 is ‘only’ rated for 5A, so it may have to be replaced by an LT1083.

[2] See the post The weather for today for a view of the thermometer.


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