With CP80-EOS I had a pretty good idea of what I wanted to achieve, it has been there in my head for quite a few months. The construction had a few challenges but the results were satisfying. If I was saying “this is it! done! Game over!” I would be lying. Most of us who enjoy building/tweaking “stuff”, always end up thinking about a little thing they could have done better or differently. It is normal and it is just the result of working hard on something: we eventually come up with another or better idea that makes you start working on a Rev. 2!
Well, this is exactly what happened to me with CP50X.
The first thing that got me thinking was the fact I don’t want to deal with low temperatures that could cause condensation on the body. So Basically, every time I used the CP80-EOS I set my temperature controller between 6 and 10 C. But at these temperatures how much of an insulation do I really need for the body?
The next thing on my list was the Thermal Mechanics behind CMOS cooling. Everyone who has played with a box cooler knows that once the cooler is on, it takes some time to see any temperature drop in the Exifs. But really what happens locally is that the CMOS temperature will not drop until the surrounding materials (including the air concealed in the body) temperature goes down. In other words, the first thing that a DSLR cooling box does is cooling the camera body using chilled air as medium. This is the time consuming part. It is heavy, somewhat open, filled by air which acts as a thermal insulator – the perfect recipe for a big time constant.
By combining these two thoughts I came up with a somewhat hybrid idea which is to completely lose the cooling box and install the cooling device on the body itself. By doing so:
- I cut down on the total weight
- I simplify the design
- I reduce the insulation job to the strict minimum
- I cool the body directly and I do not rely on (forced) air convection to cool it down
First, I need a lightweight and rigid frame. I can use the same white acrylic I used before to build a decent frame.
Next, my custom T-ring represents a fantastic way to mechanically attach the frame to the camera body.
Finally, while clearly not optimized as a hot plate heat sink, my internal heat sink has all the features I need: a pod for the Peltier element and two sets of retention mechanism. I just need to make something adapted for hot plate cooling (by this I mean that my internal heat sink was optimized for a low CFM fan such as the one I used in the CP80-EOS – there was no need for a high power fan to recirculate the small amount of air concealed in the box).
Now, onto what I needed to find.
I need to find a way to fasten the Peltier element to the body. I know that I cannot directly attach it to the body as I need a perfectly flat surface for the TEC. A cold plate will be required to interface between TEC and body.
Because direct cooling is much more efficient, if not controlled properly the Peltier element will freeze humidity on the body. The temperature controller used with CP80-EOS is an ON/OFF type which is inadequate to maintain a metal cold plate at a certain temperature. A PWM (Pulse Width Modulation) type will be much more adequate and will allow accurate control. And its probe will have to be installed on the cold plate for accurate control.
Finally, a TIM (Thermal Interface Material) is needed between the body and the metal cold plate. Using a compound is not practical and does not allow for much surface imperfections (camera bodies are anything but flat!). So I decided that I wanted to use a Thermal Pad with enough Z-compression to comply best with the camera body.
Hmmm, how to?
The only place I found direct cooling to be remotely viable was the location around the 1/4″ threaded hole at the bottom of the body. It surely isn’t flat! In fact my T1i’s bottom has these small grooves shaped-in. Fortunately enough, they are not too deep and the TIM should take care of them just fine.
This threaded hole represent the only usable retention point I could use in addition of my custom T-ring. Retaining a Peltier element with a single screw is quite unusual in the cooling industry but right now it surely sound good enough. I planed on stacking hot plate (heat sink), Peltier device, cold plate and TIM and using this one 1/4″ nylon screw to hold it all together. With the help of the frame and of the T-ring this will work.