Gina

I think proper O rings or 3D printed TPU sealing rings would be a much better bet than silicone sealant. I need to change hat from botcher to engineer!!

It was failed sealing that caused the problem with desiccant to dry ordinary air. Maybe I should re-examine my sealing method - I relied on silicone bathroom sealant. For the few days during which the casing stayed sealed and the air dry, the ASC worked perfectly with the water cooling. Except it needed a bit more than the 2W dew heater I was using - that is not a problem.

Print failed. I'll see what tomorrow brings...

3D printing the casing. About 3 hours left. Rather than directing all the warm air up and out of the dome, I shall have holes in the base plate and let some escape out the bottom. The idea is to maintain a reasonable airflow over the heatsink fins for best cooling.

-8.5°C and it's been there for a while now. Just added a barrier to restrict the airflow from one side of the cooler to see how much it affects the cooling. Went down a bit more but now on the rise and back to -8.5°C. A bit later -- Seems steady at -7.6°C.

Shut down and powered off and removed the TEC1-12706 leaving just the smaller Peltier TEC running at 12v. Camera temperature has got down to -7.8°C and still slowly going down. Conclusion - the TEC1-12706 is not suitable for this application (though it worked for the dehumidifier). Nowhere near the -20°C I got with water cooling but not bad. Restricting the airflow a bit by directing some up into the dome may reduce the cooling a bit but we'll see.

Running a test with stacked TECs but it's not good! First of all the temperature gradually dropped to around 2°C then rose again to 5°C. With the single 30x30mm TEC it got down to -2°C. Running at 11v and just over 5A. This is very disappointing. Mind you, it is using a lot of power (over 55W) whereas with water cooling the TEC runs on 20W and then there would be some power wanted for a dew heater but I doubt it would want 35W!

This shows the idea.

Now I need to work out how to vent the warm air to the atmosphere whilst stopping rain coming in when the fan isn't running. I'm thinking a cone to direct the air into the dome via the camera and out round the edge of the dome and an outer cone (maybe the cone shaped top of the casing with a smaller cone inside. With just the 30x30mm TEC and air cooling albeit blown by a fan, I think the cooling may not be enough. I could use a double stacked Peltier TEC cooler using the TEC1-12706. This would take more power than water cooling but provides warm air for dew prevention. If I use water cooling I would need to add a heater which seems daft. Plus the air cooled system might not be much less efficient once dew heating is taken into account.

Base added.

I may have a new name for my ASC - "An OriGinal All Sky Camera" ?

Preliminary design of the casing with room allowed for the focus motor. I'll probably add the motor mounting to the camera casing. .

Dome designed and added. Then there's the focus motor mounting and the main casing.

Camera with cooler. Green cone is focus gear (teeth not shown), red is camera casing, sealed and provides thermal insulation

The 60mm fan sends a lot of air through the cooling fins and I'm not sure whether I want all that air directed up to the dome, one side could go straight out to the environment with just a hood to keep rain out.

The first test got down to -2°C now on the second with more fins but lower ones and it seems to be about done at 0.7°C. Looks like the new cooler wins contrary to expectations. Maybe the bigger air space helps cooling. I'll go with the new taller cooler then and design the ASC casing and air ducts to suit.

Now testing with the new cooler replacing the waterblock in the ASC. The camera temperature is slowly coming down. The fan is pretty noisy run from the full 12v. I could do with rigging up some digital thermometer chips for reading temperatures with this sort of testing. With the aluminium adapter ring for the lens and no warm air blowing over the lens it has steamed up. Camera image sensor has not yet got down to freezing - still a degree or so above.

The length of the fins is the same for both so the number x height will give the comparison. LH 16x32 = 512 and RH 27x20 = 540 so the RH one seems slightly better. I could test both.

The CPU cooler I ordered arrived today but the fins are further apart and fewer than I thought but deeper. Whether this is as good, better or not as good as the one I already had I don't really know. I guess totalling up the surface areas of the fins should tell me. Base is the same size. Here's a photo of them both - new one on left.

I think I shall go for the simplest approach to this and try a sealed chamber for the camera again. I can use a 3D printed plastic adapter ring for the lens to thermally insulate it from the cold camera body and hopefully this may let the lens warm up above dew point. I've concluded that a standard axial fan should not fail from damp air as the motor part will be warmed by the current flowing through the motor coils and the air RH will probably be above dew point anyway. A standard CPU cooler on the hot side of the Peltier TEC may produce enough cooling whilst the warmed air can be fed up into the dome. Clearly this will be less efficient than water cooling but may be sufficient. It's worth a try. If the 60x65mm CPU cooler is not enough I have a heat pipe type with larger fan and cooling fins.

Yes...

Rain overnight forecast for here

This is proving problematic and I'm wondering whether to separate the dehumidifier from the camera cooling. The only part that actually needs dry air is the camera, the lens and dome can have warm air blown over them to prevent condensation. Maybe I should go back to the idea of sealing the camera and including desiccant like the cooled astro cameras do.

I have the larger heatsink on top of the big TEC on the plate and the two small heatsinks underneath. Then, just for testing, I have a 50mm axial fan blowing through both heatsinks. There is not enough cooling of the hot side of the TEC to get the cold side down below the dew point so it needs more air blown through it.

Taken the camera out of the bottom of the casing and sat it horizontally on the table and the temperature has decreased a couple more degrees so maybe the casing wasn't helping airflow into the camera. The inlet was a lot bigger than the fan and shouldn't have affected the air flow. However, I can easily give the camera an open mounting bracket. I've also tried focussing and think I may have it a bit better.