Gina

I'm hoping I have the ASC design sorted out. 3D printed casing with water cooling and a small positive pressure applied to the camera enclosure in case the casing isn't completely watertight. Minimal kit up top with the electronics in the observatory. USB cable and a 4 core round cable plus 2 water cooling pipes and an air pressure pipe will go from the observatory up into the ASC casing. The air pressure pipe will also serve as a condensate pipe if any damp does get into the ASC enclosure. The air pressure will be provided by a small radial fan.

I have an EQ fork mount for widefield imaging on the books together with a micro-observatory. Both with many 3D printed parts. That mount will have remote PA adjustment using stepper motors.

With new conical connector. Somewhat more elegant I fancy! 😀

Water cooling is indeed simpler and I have most of that done. Makes for the most compact ASC body too. This is the design making use of the previous parts ie. the conical connection to the mast but it would be better with a new conical part. Dome not shown in this model.

Ouch!!!

Mine has finally cleared after many days in a dry environment and having been warmed up a few times with a craft type hot air gun used at a distance. I was rather afraid it wouldn't clear but it has.

That is a beauty!

Yes, I think you will. I would definitely advise it.

My lens is still drying out. Still showing internal misting.

Welcome to the drenched ASC club!!

The only simpler arrangement I can think of is to put a fan directly on the heatsink. I'm not really happy with that as it will be in damp air when it rains and if it fails it would need the ASC taking down. Also, it might be difficult to tell if it failed - the TEC would overheat and fail and that is not a cheap item! The less there is up in the ASC itself the better really. A fan inside the observatory could provide air pressure for the sealed compartment via the desiccant pot. Another alternative is back to water cooling which may actually be a bit simpler and even if the circulating pump fails there is still water in the waterblock (until it boils).

As I shall have to run the USB cable through the sealed part of the casing anyway, I think I'll put the electronics inside the observatory. At least then if I get a fault in that I wont need to take the ASC down.

Here's a list of things I would like :- Keep the mast pipe. Sealed enclosure for camera and dome - OK almost sealed with positive internal pressure. Simplest possible effective cooling of Peltier TEC hot side. Reasonable appearance.

I still think this is too complicated. Particularly piping air from the observatory up to the ASC.

The enclosure will be in several parts. Bottom - conical section attaches to mast pipe and contains the electronics. Middle - rectangular hole in bottom to fit round the heatsink. Contains the heatsink and has air ducts at the side venting warmed air downwards. Top - contains the Peltier TEC, camera and lens. Topped with the dome and dew heater. May further split parts depending on how the detailed design goes. Whilst it seemed a good idea to use the waste heat from the Peltier TEC to warm the dome, I haven't been able to think of a way to get this heat to the dome without blowing damp air onto it. Decided on the simpler approach of a separate dew heater.

Screenshot of camera, lens, TEC and 60mm heatsink crudely modelled.

Now I'm wondering if piping air from inside the observatory up to the ASC is actually more complicated than water cooling.

I think I'm changing my mind on blowing warm air from the heatsink up to the dome. Even relatively dry air from the obsy is going to have a certain amount of dampness in it (particularly in wet weather) and it would be better if the air in the dome was as dry as absolutely possible. I could still use air cooling of the heatsink but vent the warmed air straight out and just use a small positive pressure of dry air in the camera and dome area.

I'm thinking that heatsink may be too small and I have a bigger one which may be more suitable. Firming up on the design, relatively dry air from inside the observatory could be blown up the hollow mast and into the ASC casing, firstly cooling the electronics then through the fins of a heatsink on the hot side of the Peltier TEC. From there warmed air could be ducted up to the dome and down the other side and out down an air duct to the bottom of the casing and out to the atmosphere. As before, the camera would be lagged to help with the cooling. A pipe could be used to connect the camera enclosure to the relatively dry observatory and carry any condensate away from the camera.

That's the air intake but I need to sort out how and where it escapes too without allowing wet to get in if we get horizontal rain!

I shall have to set up a test rig to check that this heatsink is suitable.

Definitely!!

I think I would like to use the same mast pipe as it provides a good way of mounting the ASC and simpler than attaching it to the roll off roof. Makes it easier to take off for maintenance too. The pipe was used to carry the power cable and water cooling pipes - now it could carry air from the observatory as well as the power cable. For the air supply I would use a 3D printed adapter to enclose the pipe and provide a side-entry. I have a 40mm x 40mm x 20mm heatsink that would fit on the hot side of the Peltier TEC. The incoming air could blow through this and be ducted up and into the dome.

I think somehow I need to keep the air round the camera separate from the air under the dome. Maybe take incoming air and warm it up with the heatsink that's on the hot side of the TEC preferably taken from inside the observatory where it's likely to be drier (warm room perhaps).

I've taken the ASC apart and a few drops of water came out of the camera. Fortunately, any condensation or ice forms on the case of the camera and not on the PCB or components. The sensor will always be warmer than the case. It's clear that if a perfectly sealed enclosure is not possible, there has to be provision for melting ice to drain out of the camera away from any electronics. Condensation of moisture on the camera case will counteract the cooling slightly and there is always going to be some dampness in the air except in very dry weather. If the camera case if cooled below freezing, ice will continuously form on the inside and any outside surface not lagged. It may be sufficient to cool the case to just above freezing and provide a pipe to carry condensate away. Condensate wants keeping away from the hot side of the TEC or it will evaporate and fog up the inside of the dome and also condense on anything cool.