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All Sky Camera Revisited


Gina

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I don't know how I got this when I can't repeat it.  A test result that cannot be repeated is not valid!  With the latest test the current drawn is below 3A.  Could the TEC have deteriorated, I wonder.

On 02/10/2019 at 17:18, Gina said:

The TEC1 12703 Peltier TEC has arrived and I am testing it.  I have the current thermal jacket on the camera though this will be changed.  Running off my standard supply of 13.8v.  Camera temperature started at 33°C and has gone down to just 5°C, a drop of 28°C.  I don't think that's too bad for single stage cooling with just air cooling.  TEC is drawing just over 3A.

530723809_CoolingwithTEC11270301.png.3a77b0c605d50109442beffbd798d91a.png

 

 

 

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I've been watching your progress Gina, and currently have my ASC ongoing in the background.

I bought one of these: https://uk.rs-online.com/web/p/peltier-modules/4901367 which is 30mm x 30mm.

At somewhere between 12-13Vdc it will pull over 3A; I managed to fit a sensor into the camera body, and with a large copper heatsink and fan, I can get the camera internal temperature to -5C and sensor temperature to around 0 or -1 in ambient indoor temperature of around 20C.

If you can get a copper heatsink rather than an aluminium one, you may enjoy better results.

Also, I started with a cheap Peltier and saw the same reults as you have, i.e. not a great temperature drop.

Marlow industries make respected peltiers and are used a lot here at work.

My camera is wrapped in closed cell foam, and covered in aluminium tape for IR reflection.

This works quite well, and does help with thermal noise.

It's not finished yet as I'm working on a dome heater based on RH using an arduino / DHT22 type setup as my dome fogs up internally indoors, which I guess is expected.

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Tried 11v supply and a further small improvement.  11°C a drop of 18°C.  Still 10°C wore than before.

That's very interesting Jon.  I have used RS-online TECs before and found them much better than the cheap ones.  Guess I'm wasting my time with the TEC1 12703 and should "bite the bullet" and buy decent quality goods!

Edited by Gina
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Maybe - for all the effort that goes into it, you need reliability and if that means spending £30 rather than £3 then it has to be done.

I also thought about 40mm x 40mm but it was too big for the rear of the camera body if I remember correctly.

Cooling the hot side is most important otherwise the cold side will be limited.

Sound like you need more heatsink and more airflow. Sucking air out of the body without an air inlet probably won't work, air has to flow.

In mine, I have a 2" pipe from outside, with a fishtank style sponge filter, going straight into the side of the heatsink, with the fan at the bottom of the case blowing warm air straght out. This way, ambient air is always flowing over the heatsink fins and straight out to atmosphere, allowing higher efficiency.

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Also, looking at your picture above, is that just a 3d printed part around the camera body?

If so, I think better insulation is needed to minimise warming of the camera body from ambient, when it's being cooled - this could also be hindering you.

Do you have any aluminium tape to wrap around it? Or closed cell foam as well? Don't forget the bottom of the camera body, as this is a source of ambient air getting to the body, further reducing efficiency and performance.

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My camera body is 62mm diameter and 40mm x 40mm TEC diagonal is just under 57mm so fine.

My airflow is from the observatory scope room which is very well ventillated - even more so when the roof is open but drier than totally outside.  The air is blown from there with an 80mm fan (I also have bigger ones) up through the air duct to the heatsink - currently 60mm x 62mm x 40mm but I also have an aluminium heatsink about 100mm x 100mm x 60mm.

I agree that closed cell foam is probably better than closed cell 3D printed thermal insulation, I may go for the foam.  The bottom of the camera that's left after taking out the area of the TEC, will also be insulated.  Since the camera temperature will be below dew-point I am enclosing it in a sealed enclosure containing a silica gel bag to dry the air inside.

I think blowing all the warm air up and out at the top of the ASC may restrict the airflow too much.  Using at least some of the warm air to blow onto the inside of the dome to stop condensation seems a good idea but I think I shall vent most of it straight out.

I am now thinking about a major design change.

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Thought I'd try using the large heatsink and 80mm fan as shown below.  Better cooling even though the air coming out is warmer.  Temperature started off at 28.5°C and went down to 7.5°C a drop of 21°C.  That's a considerable improvement and not even using all the fan area.  With that cooler and a decent TEC I should be in business!

890773777_CoolingwithTEC11270302.png.0e203af29c9f6d78b7cd2bb0dffbcb35.png

Edited by Gina
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I could blow the air through like that or in the bottom and out the sides - more conventional and easier to arrange to attach to the ROR.  I'm thinking maybe let the air flow out one side totally unobstructed but the other side part of the airflow ducted up to the dome.  The result will be bigger printed parts but this is well within the 1ft (300mm) cube printing volume of my main 3D printer.

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I did start a thread, but only got as far as camera and lens combination...

You have the fan at the side of the heatsink, meaning you need plenty of ambient air coming in from the other, with none of the warm air stayin in the enclosure.

My fan is underneath (think upside down PC CPU cooler) and vents straight out of the bottom of the case. I also put an aluminium shield around the heatsink, open at the air inlet pipe, to help all the air going in passing the heatsink and back out.

I will update my thread as and when I'm happy with performance, but haven't documented / photographed each step.

 

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The idea is to put this on the underneath of the Peltier TEC out in the open with free air movement over it.

I'm thinking I might go back to standard dew heater rather than blown warm air.  Seemed a good idea but now I'm not so sure.

Edited by Gina
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Side view of ASC.  It would be attacked to the side of the ROR with a bracket with the NOFAN well out in clear air.

614837766_Screenshotfrom2019-10-1122-36-01.png.0e9d054941aac90bbd6175e82b736304.png

Edited by Gina
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On a previous version of my ASC I used the large passive cooler as exactly that - passive - just relying on convection of air over the fins.  With the cooler horizontal this was not as efficient as it would be if the air was free to move straight up between the fins.  But it was almost good enough.  The results were given in the post dated 6th July.  Seems to me that the NOFAN should work well in any orientation and with copper heat-pipes and large surface area it should be more efficient.  I guess I could try the arrangement I used before though I would improve the mounting but the NOFAN would be much easier to mount.  Must give it some thought.

On 06/07/2018 at 14:32, Gina said:

Before continuing with the construction details I'll take a pause to give some results.

So far I have found the camera cooling to be quite adequate and I doubt the ambient conditions would get much worse.  Last night the breeze had died and there was little if any air movement across the cooler meaning that all the cooling was by convection.  Cooling was significantly less than when there was an easterly breeze but still adequate to kill noise and hot pixels.  I would imagine the visual results will be a lot better when the weather is cooler and we get real astronomical darkness on a clear night.  As for daytime use - no problem even in full sunlight, though the sun does spread somewhat.

A couple of images.  Firstly taken last night just before midnight UTC (1am BST) - 60s exposure and camera gain of 150.  With 4m delay between captures the camera temperature dropped to -9°C and rose to -5.5°C by the end of the exposure.  HIGH level cooling with 13.8v on the Peltier TEC.  This is a screenshot of the KStars FITS Viewer with cropping and contrast enhancement in GIMP.  

1119897574_Screenshotfrom2018-07-0600-07-32.thumb.png.0504a6e636019b1ff808f62a6baf031a.pngµ

The second image is a daytime shot taken in the morning a few days ago with virtually no cloud - contrails instead.  32µs exposure and gain of 0.  LOW level cooling with 5v on the Peltier TEC.  This is a full scale image as written to disk, converted from FITS format to PNG in PixInsight with no other processing.  This also shows the coverage of the fish-eye lens image on the camera sensor.

Light_001a.thumb.png.2e52c7f6f31d960236e34775ad578486.png

Edited by Gina
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Regarding cooling the Peltier TEC hot side, I currently see three options.

  1. Large aluminium cooler with forced airflow
  2. Large aluminium cooler passive
  3. Nofan

It would save work without forced airflow.  Nofan seems best but costs money.  Still considering but favouring 2. or 3.

Whichever cooler I use, I need to make space for dew heater resistors (unless I vent warm air from the cooler up to the dome, which I've pretty much rejected).  It would also be nice if I could include remote focussing.  Here is the current assembly without cooler.

76321597_Screenshotfrom2019-10-1218-17-56.png.a2f582ecdd23c8d1bdc0f825b80656bb.png

I think dew heater can go around the bottom inside of the dome.  That may still leave room for a focus lever.  I'll add to the drawing...

Edited by Gina
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Decided on the cooler, finally.  Read some reviews of the Nofan and it seems it's almost as good as water cooling and better than normal air cooling.  Decided it was well worth a try.  Bound to be better than the aluminium Artic Alpine 11 Passive that I already have without fan.  The cost is not that much compared with the overall cost of the project (and astro related items).  As they say "Don't spoil the ship for a ha'p'orth of tar".

Edited by Gina
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