After building my little CP50X-EOS, I was still not completely happy with the results. For sure I had reduced the weight quite substantially, but still the overall noise reduction wasn’t as good as I had hoped for.
But, looking at the performance (temperature and power consumption) data I somewhat realized there was some pure loss out of my original CP80-EOS box cooler and decided it was time for some upgrades!
I quickly identified the source of these losses: the peltier module itself and its cooling.
The module I used originally was a 80 W and 60 C of maximum delta. Because the heat output is very small, it makes more sense to look at low power TEC module but with a large delta. The TEC I used on my CP50X-EOS hybrid design is a 50 W and 70 C of maximum delta and this is what I decided to use on my upgraded CP80X-EOS cooler.
The goal with this TEC was to minimize the amount of heat going through the hot side heat sink which as a result will maintain a lower hot side temperature (thus decreasing the cold side), but also the bigger maximum delta should also decrease the cold plate temperature by a realistic couple degrees.
The last modification I’ve made was the temperature controller. I use the same leg bracket to hook it up to my Losmandy G11 and made the same CP50X-EOS electrical harness to connect the cooling system to it. It looks clean and it is very practical on the field.
I then tested the upgraded CP80X-EOS to my standard test bench (i.e. the same testing procedure I’ve used to test the other systems…), and the thorough results of these tests will published in another page (to come in the next few days!). Some quick numbers though: roughly 50% reduction in power consumption and cooler by 2 degrees. However, the new heat sink added about 5 ounces which made the whole solution just about 3 lbs.
Two days after the test, I went to the OCA observing site at Anza where I did my very first imaging session. There was a lot of firsts that night for me: first time polar aligning, first time using the Losmandy G11 with the under development firmware, first time building a model, first time setting up an autoguider, first time autoguiding, first time using a bahtinov mask, first time achieving focus, first time taking multiple light frames… I had waited a lot of time for that, believe me. And building these cooling systems helped me wait through it! Well they kept me busy while I was acquiring all this gear… Results seem technically good for a first (from what I was then told!), but the only thing I forgot was to align my guide scope and my imaging scope. The red dot finder I used to create my model was installed on my guide scope because of the lack room on my AT65EDQ. That night I chose 2 targets: NCG7000 and M31. I went on NGC7000 first and started imaging, I couldn’t see anything in my subs and figured I probably didn’t collect enough data in a single 300 s frame to see anything, so I kept on going for another hour… I did the very same thing for M31… In the end, I had very good data with 90% excellent frames, no star trails, good color… I just didn’t have any subject in my frame! Well, I had just a small bit of NGC7000 and M31 was just next door. It was a fantastic experience and I can’t wait to go back there and this time I won’t forget aligning my scopes!
Anyhow, just to say that during this first imaging night my upgraded CP80X-EOS cooling system did very well. It maintained the sensor at 20 C (I had set up the inner air temperature to 6 C), my final images were basically noise free . The PWM temperature controller did a nice job maintaining the air to 6 C regardless of the ambient temperature drop throughout the night. In terms of power consumption, I did not know the Anza site had on-site electrical outlets so I decided to make sure my Mobile Power Unit had enough capacity for the night. And it did very well.
Although I was very satisfied with this realization I was somewhat bugged by the added weight the cooler applies to telescopes. It makes balancing in DEC even trickier (not to say impossible…) and I will definitely start thinking at any possible weight optimization.