Gina

An another idea would be to have the 60mm square CPU cooler on the big TEC and the two 40mm heatsinks in a row under the plate, giving more air cooling area.

This might work with appropriate air ducting.

Testing with the large ali plate. Running TEC at 12v 3.33A. Hot side around 80°C cold side - not very yet. I have the cold heatsink also on the plate and it's not cooled below the dew point. There is a considerable thermal gradient along the plate. I'm thinking a rearrangement is indicated. Maybe put the cold heatsink on the other side of of the plate to the big TEC. The small TEC hot side doesn't need as low a temperature as the cold heatsink.

I've found a piece of aluminium 125mm x 65mm x 3mm which I can try. Much bigger than required but worth a try as it's a "bird in hand".

The Peltier TECs have arrived and I'm doing some testing. I have a TEC attached to one of the heatsinks with thermal paste with a 50mm axial fan blowing air into it. With 10v and 2.7A supplying the TEC I estimate the heatsink temperature as about 70-80°C and the cold side just above freezing. The efficiency of these £4 TECs is certainly far lower than the £30 odd 30x30mm one I bought from Farnell Element14. Might be worth paying more for something decent. I did wonder about stacking the 12706 TECs but I don't think so. Later... The cold side has drops of condensate at the bottom so this is dehumidifying.

I have CPU coolers that use heat pipes but these are too big for this purpose. I don't know if it's possible to buy heat pipes in other forms than computer/laptop coolers.

Hmm... Sticking out a long way to the left... Actually the smaller TEC doesn't need to be centred on the larger one and could be a bit nearer the centre of the plate. Also, the heatsinks could be closer together. Anyway, that's all mainly cosmetic, I've got to see if it works yet!

No way!!

CAD drawings of the heatsinks etc. and with the air duct added (shown in transparent blue). In the second drawing the air will be blown into the bottom left and emerge on the right where it will be diverted up to the dome. Condensate will be removed through the hole in the bottom of the air duct.

Just stripped down the ASC and there was moisture in the sealed camera casing. No free water but damp and all the silica gel beads were dark green - saturated. My ability to produce a watertight seal is evidently non-existent! This confirms that the air in the ASC needs dehumidifying continually so that a dry environment is maintained. It needs to be dry enough that no damp condenses in the camera when it's cooled down well below freezing.

I've been examining an axial fan which wasn't working and it doesn't look like a bit of damp would cause it any problems. This leads me to simply putting an axial fan in the bottom of the ASC casing. I can duct the air up to the cold heatsink so that it flows through the fins then further duct it into the end of the hot heatsink. The TEC1-12706 Peltier TECs are due to arrive tomorrow so then I may be able to start experimenting. Unfortunately, the ali plate is on order and not due until around Thursday. I may have a hunt through my stuff in the meantime and see if I can find anything.

The aluminium plate will be 100mm x 40mm x 3mm rather than as shown above (thought I had a piece that size but couldn't find it) so the heatsinks could be separated by 20mm and the fan could go in the gap. Trouble is the format of the duct through the heatsinks is about 40mm x 20mm. I guess a 40mm axial fan might be possibly. Another possibility might be to use a radial fan in the observatory and take the air through a pipe up to the ASC. Standard 12v radial fans have an output port of 18mm x 13mm ie. an area of 234 sq mm. That's equivalent to a circular shape of about 17mm diameter. Since I will no longer be using water cooling, the air pipe could replace the two water pipes. Another thing I'm not sure about is whether the 40mm square heatsink with 11 fins will give sufficient heat transfer - it might get very hot. I have a bigger one with much thinner and many more fins but it's 60mm square complete with axial fan so much bigger. I think that's probably overkill.

I'm trying to work out the best place for the fan and what sort to use. Three possibilities of where to put the fan :- Where the air comes in. The air is damp. Between the heatsinks. Air is dry but cold. After the hot heatsink. Air is warm and dry. The sort of fan is axial or radial. Radial fans are more efficient but I'm not sure how to arrange it.

I always do.

Here's a CAD drawing of aluminium plate, camera, 2 Pelter TECs and 2 heatsinks. Air would be blown from left to right, being cooled below dew-point in the LH heatsink, condensing out the moisture and then being warmed by the RH heatsink before being directed up into the main ASC body and dome. Heat is removed from the camera body by a 30x30mm TEC and transferred to the ali plate. Below this is a 40x40mm TEC which grabs heat from the plate (and hence top TEC) and left heatsink and transfers it to the right heatsink. Hence, this multifunction unit removes heat from the camera, moisture from the air and heats the dome to prevent dew on the outside. Next to add the air ducting and fan.

After two circuits of the garden (about a third of an acre) looking in every nook and cranny I eventually found it in an old stockbox - a steel box about 5ft x 3t that went on the linkage on the back of the tractor, used for moving livestock between fields along the road. I needed my long grabber to retrieve it as the box has a top and it's all rusted up. The package was well out of reach by hand. Yes, I too have sometimes had packages left in the dustbin!!

Not the postman but Amazon Prime. Now I have a perfectly good post box and several good sheds to put packages in if I'm out but where did Amazon delivery put it???!!! Somewhere in my quite large garden. How I have to find it!! I've already looked twice so now I'll have to don wellies and search the more overgrown areas. Fortunately they took a photo but ATM I can't place it!

Been thinking about whether I can combine the dehumidifier with the camera cooling to improve power efficiency. Looking at temperatures :- Camera may be -20°C Cold dehumidifier plate/heatsink - a degree or two above freezing Hot side of dehumidifier maybe 20-30°C (or more) Both temperature differences are easily obtained with Peltier TECs. TECs could be stacked with an aluminium plate between with the dehumidifier air cooler mounted on the aluminium plate.

One possibility to reduce condensation in the lens would be to provide thermal insulation of the lens from the cold camera body by using a 3D printed plastic for the CS to T2 adapter instead of the supplied aluminium one. That would then just leave the optical window in the camera itself. Any dampness in the camera would probably condense on the cooled camera body in preference to the electronics or window but I'm rather concerned where it might end up. I'm concerned about cold, damp nights with lots of moisture in the air so I'm still thinking that keeping moisture out of the ASC would be best. I'm unlikely to want to image when it's actually raining.

The lens is directly on top of the cooled camera body and is likely to be several degrees below freezing. I have had moisture inside the lens when I've used it outdoors without the dome and outer ASC casing. OTOH warm air circulating around the lens might warm it up enough to prevent condensation. I'll try it. Then there's the question of how to heat the air. I might try combining cooling the camera with heating the air. Although far less efficient than water cooling, it might be sufficient, particularly if I used two stage Peltier TEC cooling. Using water cooling is not necessarily carved in stone.

Ordered a pair of TEC1-12706 Peltier TECs plus a pair of 40mm square heatsinks from Amazon (Prime) arriving tomorrow or Saturday. OK cheaper on ebay but wouldn't get them until Wednesday or Thursday next week. I have a variety of fans I can choose from. The heatsinks would go on either side of the Peltier TEC.

Both the cooler and heater heat exchangers can be simple CPU heat sinks. 3D printed ducting could carry the air round the system. The air coming out will be warmer than the air going in due to the inefficiency of the Peltier TEC but warmed air is what we want for feeding up into the dome to stop dew both outside and in (though the dehumidified air should not contain much moisture). Seems to me this doesn't need a particularly efficient Peltier TEC and the ultra cheap Chinese ones should do. It only needs to cool the air below dew-point. I wonder if I can make this small enough to put inside the ASC casing. A small tube would be all that is required to take the condensate away.

The simplest dehumidifier would be to blow the air through packets of silica gel which would need replacing every so often with fresh or dried packets. However, experience has shown that the silica gel gets "full" pretty quickly even with the air indoors. The other way is to cool the air below dew-point so that the water condenses out. I could do this with a Peltier TEC. Of course the dried air would then need heating otherwise the dome will be cold and dew will condense on the outside. I guess the cooled and dried air could be passed through a heat exchanger on the hot side of the Peltier TEC and warmed up for feeding up into the dome. This would become a combined dehumidifier and dew heater. Hmmm... I wonder...

Yes, that is just what I was thinking as an alternative. I shall have to think how I can manage it. Ideally, dry(ish) air from inside the observatory. OTOH is the air in the observatory dry? Alternatively, I'm wondering if I could make a tiny dehumidifier.

4 hours into the print and it's gone wrong!