All Sky Camera Revisited

[Gina]

I'm thinking of moving the fan from directly below the heatsink to inside the observatory.  This means there is positive pressure within the air intake and if there are any leaks there won't be damp air drawn in.  Also the air can cover the whole of the heatsink rather than in a ring where the fan blades run.  The base part of the ASC will be reduced in height too.

[Gina]

Have redesigned parts to allow for the relocation of the fan.  Main change was to the base to take the fan out and increase area of airflow into the heatsink plus increased airflow area in rotating joint.  Also there's a new version of the air intake & support bracket.

Edited October 7, 2019 by Gina

[Chriske]

Not an easy to print, that last one.

[Gina]

It will be printed the other way up.  That way will not require support.

[Chriske]

Yep, thought so too.

[Gina]

Having printed a few of the other parts I thought I'd try printing this in PETG.  PLA is not so good with the overhangs.  I've run out of white so printing it in red.  I expect to print the final version in white - I very much doubt that this design will be entirely right.  Without laser 3D measuring equipment, fitting this to the shed observatory roof will be trial and error.  Not too bad to print - estimated 50m of 1.75mm filament and about 2h printing time.

[Gina]

Printing finished and satisfactory.  Took a bit longer that predicted mainly due to having to reduce speed where there were overhangs.  3h altogether.

[Gina]

Tried the air intake bracket against the roof and it needs altering a bit, as expected.

[Gina]

New design - now printing.

[Gina]

Air vents in the outer housing.

[Gina]

Designed a "roof" to go over the outer housing and cover the air vents to keep rain out.  Any resemblance to a "flying saucer" is purely coincidental 🤣

Edited October 8, 2019 by Gina

[Gina]

Made up a second hotend for my Concorde printer to take 2.85mm filament of which I have quite a lot that I got in a sale.  So now I can print final versions of the ASC parts in white PETG.  Currently printing the "roof".

[Gina]

Been reading up more on Peltier TECs.  Seems stacking is very inefficient.  I think stacking only works in astro cameras because they are only cooling the image sensor.  With my ASC I am cooling the whole camera including all the electronics which is generating heat and therefore there will be far more heat to get rid of.  From this I conclude that double stacking is not going to work for this application.  Another thing I've learnt is that the TEC wants to be as big as possible as larger TECs are more efficient, so going from the 30mm x 30mm TEC I used before to a 40mm x 40mm should give better cooling.  For anything bigger the cost becomes astronomical!

The information also confirmed what I already know and that is that efficient cooling of the hot side is of prime importance, which is why I went for water cooling earlier.  The latter is still a possibility if I find forced air cooling insufficient.  Alternatively, I could go foe a bigger heatsink.  Meanwhile I'll stick with the present design and see how it goes.

[Gina]

I though I had ordered a better quality 40mm x 40mm Peltier TEC but it arrived today and it turned out to be 30mm x 30mm and less efficient than the TEC1 12703 I already had.  It was my mistake so can't argue!  The TEC1 12703 was a lot cheaper.  There are no other 40mm x 40mm TECs on either Amazon or ebay so if I want something better it will have to be Farnell Element 14 or RS online - I don't know any other suppliers.

Edited October 10, 2019 by Gina

[knobby]

I know you said no to stacking but as you have 2 now is it not worth having a crack ?

[Gina]

I can certainly try it with the test rig I used before.

[Gina]

In fact the rig was still on the table from when I tried the new TEC this afternoon.  I now have the dual stack with the two TECs connected in parallel to the 13.8v supply.  Temperature fallen from 19°C to 18°C a mere 1°.  Now trying 12v which I think is about the optimum voltage for these TECs.  Temperature has dropped another half degree!

[Gina]

Running on 10v and it seems better.  Now down to 12.5°C a drop of 6.5°C.   I'll leave it running for a while and see what it stabilises at.

[Gina]

It seems to have settled at 10.5°C - 8.5°C drop.  The previous result for the single TEC1 12703 was much better but I'll check that again.

Edited October 10, 2019 by Gina

[Gina]

This is the only one I can find that meets my spec in RS-online.  Not cheap so I shall try the TEC1 12703 first and only buy this one if I find I need it.

[Gina]

Testing TEC1 12703 only in the rig shown above.

Starting temperature with camera powered = 29°C.  Trying the observatory supply voltage of 13.8v first then I'll see if it's better with a lower voltage.  Now waiting while the camera temperature drops and settles.

Edited October 11, 2019 by Gina

[Gina]

19°C and still going down.  10°C drop.

[Gina]

16°C now.  13°C drop.  Will see if it goes down any more but seems to have settled at that.  Not as good as the previous result with this TEC.  Wonder why....

[Gina]

Gone down another half degree.

[Gina]

And another half degree to 15°C a drop of 14°C.  I'm not impressed!  Should be better in situ with cooler air to cool the hot side and a bigger fan.