Working 1100D cold finger sensor cooling with TECs and water cooling

[yesyes]

Is that -9°C below ambient or as absolute temp?

-9°C absolute. Here is my current test setup.

The heatsink is a PC CPU heatsink with 3 heatpipes. It barely gets warm when its fan is running (blowing away from the heatsink, not towards the cold finger). Then there is the 60W TEC (visible) and below it is the 30W TEC surrounded by insulation foam stuck to the cold finger. Below the cold finger is another layer of insulation foam and then there is a 5mm thick acrylic piece holding everything together.

The -9°C were measured at the sensor you can see in the image. It is surrounded by a piece of 0.3mm copper sheet filled with thermal paste and screwed directly to the copper of the cold finger (again thermal paste in between the 2 copper sheets). Thermal paste is also applied between cold finger and lower TEC, between the 2 TECs and between upper TEC and heatsink.

I was wondering if this thermal paste is actually as effective when it is below 0°C or if it only works properly when warm. But is seems to work fine for others.

[Gina]

That's why I'm asking. I'm applying quite a bit of pressure on mine. I was just wondering whether it might be too much pressure... I'm still struggling getting it anywhere near cold enough. Now using a 30W and a 60W on top, both 30x30mm and both 12V. The lowest I had it was -9°C directly next to the cold side of the bottom TEC. The far side of the cold finger has never gone below zero. I've put it aside for now and continued with a different project. Maybe a fresh start in a while will give me a different perspective on it...

I think those TECs are probably too powerful though admittedly not much more than mine and I got -15C with an ambient of 15C or so. Without continuous imaging I got -22C.

I suggest you wait until I've done my tests with lower power TECs Chris - or try some lower power ones yourself. If lower power is the answer the cooling required for the hoit side will be lower and air cooling may be quite adequate.

[yesyes]

I think those TECs are probably too powerful though admittedly not much more than mine and I got -15C with an ambient of 15C or so. Without continuous imaging I got -22C.

I suggest you wait until I've done my tests with lower power TECs Chris - or try some lower power ones yourself. If lower power is the answer the cooling required for the hoit side will be lower and air cooling may be quite adequate.

Yes, that's why I've put this on hold for now and continued with something else. Waiting for you to run tests with the various TECs.

[astrovirus]

What hits me as a striking observation is that with your double stacked TECs, you don't get much deeper cooling then I get with my single TEC. Now there might be differences in other factors influencing this, like thickness of the copersheet used for the cold finger (1,5 mm in my case), but it appears to my that stacking 2 TECs doesn't bring much extra besides complicating the design, or am I wrong?

[Gina]

Two interesting TECs from Hong Kong

1. 5v 2A 20x20mm 3.6W Refrigerating Power
   
2. 5v 4A 20x20mm 6.7W Refrigerating Power
   

[Gina]

What hits me as a striking observation is that with your double stacked TECs, you don't get much deeper cooling then I get with my single TEC. Now there might be differences in other factors influencing this, like thickness of the copersheet used for the cold finger (1,5 mm in my case), but it appears to my that stacking 2 TECs doesn't bring much extra besides complicating the design, or am I wrong?

Well, I tried several single TECs and couldn't get below freezing when the camera was taking continuous images. But I can try a single TEC when I get the lower power ones. The lowest I've got ATM is 20W and that was what I started with in the testing.

[Gina]

I've now sorted out fastening the cold finger onto the camera. One bracket uses the slots on the sides of the viewfinder where the eyeshield normally goes the other goes over the boss of the tripod bush. These were cut out and bent up out of 20swg copper sheet. The shape and bends are shown in the two diagrams and the final fixing in the two photos. By suitable bending of the brackets, a moderate force was applied to the water block and thence to all the thermal interfaces including the cold finger onto the sensor. As for sliding sideways, a plastic frame will position the smaller TEC but I've yet to sort something out for the bigger one, though I doubt it would move far.

[Gina]

The replacement TEC (plus spares) arrived this morning so I'm all set to finish off and then test again. No chance of any AP for some time but I can at least test the cooling and condensation.

The Astronomik 12nm Ha clip filter also came this morning from Modern Astronomy - that was quick - next day service Have ordered several things from Bernard at MA though and always had good service Thanks Bernard Wonder when I'll be able to test that

[Gina]

Just tested the camera out (with the view through the window) with the netbook and it's still working fine. Next I'll put it back in the box and connect up all the electronics. Then I'll be waiting for the torrential rain to stop or at least ease off, so I can take it out to the obsy, put it on the scope and connect up the water cooling.

[Gina]

A dry and ATM clear night Have camera with repaired cooling all set up on the scope and been testing it. Silica gel sachets have only been in a couple of hours and I got a bit of condensation and icing at full cooling at -25C. Half cooling produced a temperature of -9C. Then I turned the cooling up to full and the temperature dropped to -25C with a short exposure every minute. No condensation showed at -20C but began to show at -24C and turned to ice at -25C. The temperature remained at -25C for several minutes and I concluded that was about as far down as it was going. Ambient temperature was 12C. Leaving the camera in live view with the cooling turned to zero resulted in the EXIF T rising to 23C.

Conclusion :- repaired and tidied up cooling is working a bit better than before RESULT

[Stu]

Hurrah! Excellent news

Will you get any imaging done tonight?

Enjoy

Stu

[Gina]

Two problems tonight (having sorted out a computer problem) - full moon and a scattering of clouds, so I very much doubt it but I'm out in the obsy now and playing about. I think the silica gel needs longer to absorb the moisture as I'm getting condensation and freezing. But at least with the cool night i can easily get down to -26C even when running long exposures. The cooling is now working much better - I'm wondering if that TEC that failed was on it's way out before.

[Gina]

With long exposures running (40s with 3s pause) I was able to maintain -15C with 50% PWM and with the capability of -26C at 12C ambient I think the cooling is completely satisfactory and it should be possible to maintain a set point of -15C even in a heat wave. With "normal" UK weather I think a set point temperature of -20C should be no problem.

I'm looking forward to getting the lower power TECs and trying those in the other camera - there doesn't seem much point in messing about with this one any more. Using the maxim "If it ain't broke, don't fix it"

I've yet to secure the water cooling tubes on the mount and when I've done that I'll take some photos and post them.

[Gina]

Here is the final (I hope!) circuit diagram of the PWM Peltier TEC control and camera power supply.

[RAC]

Gina have you done any dark file noise tests at different temps? I found no gain going less than about -3degC. I did shots at -18 with no gains. I leave mine at -8 so there isn't any freezing over problems. I also need to run a heater on my focuser to stop the front of my MPCC fogging over.

[Gina]

Gina have you done any dark file noise tests at different temps? I found no gain going less than about -3degC. I did shots at -18 with no gains. I leave mine at -8 so there isn't any freezing over problems. I also need to run a heater on my focuser to stop the front of my MPCC fogging over.

Not since redoing the cooling system. I might do some tonight unless the clouds go away.

[Gina]

Gina have you done any dark file noise tests at different temps? I found no gain going less than about -3degC. I did shots at -18 with no gains. I leave mine at -8 so there isn't any freezing over problems. I also need to run a heater on my focuser to stop the front of my MPCC fogging over.

Which camera was that with? Do you nean you didn't get any further reduction in noise below -3C?

I didn't do any very long exposure noise tests last night but I'm hoping to do some soon.

[George]

Great project Gina, not used my 1000D since I got the QHY8 but I'm tempted to dig the DSLR out and have a play

[RAC]

Which camera was that with? Do you nean you didn't get any further reduction in noise below -3C?

I didn't do any very long exposure noise tests last night but I'm hoping to do some soon.

Both my 1000d's show very little to no improvemnet going any lower than about -3C.

[Gina]

The 1100D is lower noise than the 1000D anyway and it may not be necessary to go very low. I can go to about an hour's exposure at ISO 1600 at around freezing point as I recall before noise becomes a problem but I'll try to find my older data where I did long exposure noise tests. It may well be that such extreme cooling as -15 to -20C is not becessary. I shall be conducting real life tests whenever the weather improves and I can do some imaging. I now have a 12nm Ha clip filter which I want to try out on the fainter DSOs so I'll be looking at long exposures at maybe ISO 3200.

I shall also be doing experiments with my other 1100D (wide-field/finder) with other Peltier TECs of lower power rating when they arrive from Hong Kong as I think I may well be able to use lower power models and reduce both power requirements and cooling required of the hot side. I'm hoping air cooling will be possible without too much weight. The present water cooling for the scope camera is alright and keeps the camera weight right down with a very light water block but it is a bit inconvenient. I'm also thinking about helping to provide a more convenient and cheaper system that others can adopt.

Here is my best effort yet with data limitations due to the weather, using cooling to -15C. The Veil Nebula with the star field of the Milky Way :-

[Gina]

OK... I've found the test data from some time back when I was experimenting with Peltier TEC and water cooling. This was with a cold finger but with the Peltier TEC on the outside of the camera. This is a quote from my earlier thread on water cooling with Peltier TEC and cold finger. I see that I was using ISO 3200 and didn't quite get down to freezing using one TEC of 12v 50W on the external part of the cold finger. This would tend to indicate that I should be able to get away with a single TEC (maybe with lower power rating) inside the camera with the much more efficient cold finger. Anyway, as I said, I shall be experimenting with the other 1100D when the other TECs arrive.

Right... Got up to having finished the test run right up to and including a one hour dark sub at ISO 3200 with cooling, resulting in an EXIF T of 1C. I think the results are pretty darned impressive!!

Here's a couple of JPEGs scaled to 1024 pixels wide for here, uploaded to Photobucket and imaged here.

1. 3600 secs = 60 mins = one whole hour at EXIF T = 1C with Peltier TEC & water cooling
   
2. 3600 secs = 60 mins = one whole hour at EXIF T = 28C without cooling
   

[RAC]

When i did some tests i uesd 5min as i wanted to know what the difference was for the sub length i was going to use to image with.

These were stretched to the same amount and they are of the exact same part of the frame. I just used Canon DPP, its a 200% crop with the brightness adjustment over at 2.

5min @ 20C

5min dark +20deg by meg rac, on Flickr

5min @ -5C

5min dark -5deg by meg rac, on Flickr

[Gina]

If you're satisfied with 5 minute subs, fair enough

[RAC]

If you're satisfied with 5 minute subs, fair enough

Haha yeah. I do 10min ones sometimes but there's a bit much flex in my setup for any longer. Im wanting to change over to a refractor at some stage when i find a good one for the right price, i'm sick of reflectors.

[Gina]

I can wholeheartedly recommend the Skywatcher Evostar 80 ED DS Pro