Gina

I'm definitely going for water cooling for the ASC - the passive cooler is inadequate and feeding dry air to a fan is more awkward than water cooling. The waterblock is smaller than any sort of heatsink/fan arrangement. I'm now working on the design of the ASC parts.

Guess what??? I've fixed the seemingly duff pump. Having relaxed watching a bit of TV I decided to take the pump apart and see if I could see anything. I did, a couple of little bits of what looked like plastic in the impeller. Removed them, put the pump back together and resisting the temptation to test dry, I connected it to the reservoir and half filled the reservoir with water. Put the pipe from the pump into the reservoir and applied power - pump worked fine ?. Oh well I shall have a spare tomorrow! Connected the water tubes to the waterblock and mounted it high up. Applied power to the pump and it forced water through all the pipework and waterblock flushing out all the air. I believe this is going to work. From previous experience, water cooling is an extremely efficient method of getting rid of heat.

The term "steep learning curve" comes to mind!

I've tried that but no joy. I even tried with the waterblock below the reservoir. Tried tapping the pump, forcing water through it in the normal direction but nothing worked. I know these pumps can fail if there's no water in them when switched on but I haven't let that happen. I checked the spec of the pump i was using and it can pump water up 2m. The new one I've ordered can lift 3m. Actually, a couple of feet will be sufficient on the observatory. On re-reading your post, the bottom of the reservoir is at the same level as the pump with the reservoir having at least 5" depth of water. It's the waterblock (that cools the hot side of the Peltier TEC below the camera) that has to be higher than the reservoir. The pump never works with negative pressure.

I'm getting a bit fed up with the way things are going wrong these days. Whatever I touch seems to break!

Hmmppfff... the little water pump has gone wrong - about every 5s it draws 200mA for about a second and is not pumping! Had to order another but this time a slightly bigger one (5W rather than 3.6W).

While the new camera casing bottom part is printing I have set up the waterblock on top of my anglepoise lamp connected by silicon rubber tubing to pump and reservoir. There doesn't seem to be any problem with the waterblock a lot higher than the reservoir and pump - ATM a couple of feet but I'm hoping it will be alright with several times that.

Now to design some 3D printed parts for it...

I have round waterblocks with pipe connections on the back which I think will be easier to use in the ASC than the square one with connections on the side. The size is about the same as the camera. This photo shows camera and waterblock upside down. The tubing shown is rather small and I have ordered some larger size silicone rubber tubing (8mm bore 12mm OD x 5m).

When trying to attach the 3D printed base plate to the passive cooler I found a problem with the threaded holes. I thought they were M3 but they aren't. Not M4 either but something in between. Then it occurred to me that they might be Imperial, maybe 4BA with a size of 3.6mm. I used to have 4BA screws but don't know if I can find any now. I do have the original supplied screws so will probably use those and modify some of the design to suit. Or I might leave that for now and try some water cooling experiments.

I just have to modify the design of my present camera housing a bit to accommodate the Fujinon zoom lens and 3D print it. I can then provide a thermally insulated and sealed camera enclosure with the passive cooler. Last night I was using an 80mm fan to blow cooling air through the fins of the passive cooler as well as running the Peltier TEC at it's most efficient. This doesn't bode well for using the passive cooler without fan in the summer so water cooling is looking more relevant and I shall be doing some testing.

To go lower in temperature I shall have to make a proper rig. A casing for the camera to provide thermal insulation and desiccant to remove the moisture plus proper pressure to hold the camera body to TEC and TEC to cooler. There is still significant noise at 0°C so it will want the temperature taking down lower. That could prove difficult in a warm summer should we get one again.

Hmm... Can't get it any cooler on the table. I guess 20°C below ambient isn't too bad as I haven't got any thermal insulation round the camera so it's taking all the water of or the atmosphere.

I don't see why not.

15°C 10°C 2.7°C 0°C.

Currently taking a set of darks. 15, 10, 5, 2.7, 0 degrees C so far.

I'll set up the ASI 120MC-S with Peltier TEC and passive cooler and run the TEC off a bench PSU to control the cooling and take a series of darks at various temperatures. I'll use an exposure of 15s as this seems likely to be what I would use for nighttime images. I'll leave the gain at 50 as that was what I did the sky tests at.

ATM the passive cooler is looking best due to simplicity of use. Of course, this would work better if the air had an unobstructed path with the cooling face vertical but that is impossible unless I had a big block or angle of copper but the extra thermal resistance might negate the improvement due to orientation.

Another way of getting relatively dry air up to the ASC for cooling I though of was an air duct from the scope room with a fan at the scope room end but I think this would be quite difficult to implement.

Central heating systems have problems with airlocks - radiators need venting occasionally as do the highest parts of the pipework.

Air can be dissolved in the water but should be released in the reservoir, again if a sufficient flow to get over the reduced pressure in the waterblock.

The possible problem with water cooling is that the waterblock is going to be the highest part of the system and could suffer from an airlock unless the pump is powerful enough to flush the air out. I think I shall have to do some experiments. I do have the necessary parts. A copper waterblock 40mm x 40mm x 10mm, 12v pump, plastic pipes, etc.

Vibration may be a problem with cheap fans whilst high quality ones with low vibration probably wouldn't stand up to the environment. I'm going off fan cooling. The passive cooler looks like being the easiest though water cooling is interesting and would make for a smaller, more streamlined unit with less windage. This is a very exposed location particularly from the SE.

These photos show last year's ASC before it was destroyed in a fierce storm. This uses a passive cooler about 4" square and 3" high. The cooler survived the storm and is a contender for the next build.

Possibly.