Air cooled TEC with cold finger DSLR cooling

[squeaky]

I did consider that - I wonder if I could make a more efficient heatsink than that aluminium one. Might think about that later.

Given that copper is so much more efficient than aluminium in this respect, even a non-super-duper assembly should net out with an improvement I think.

The bulk of the heatsink and all the airflow will be outside the box - that's why I cut the box down. But your question has reminded me that I should insulate the heatsink underside to stop it heating the internal air.. oh and... that clip wants insulating from the heatsink or it'll warm up the camera frame. And I thought I had a good idea there... oh well... Thank you for your questions - very helpful if not directly in the way you meant

It's often the way innit? A question generates more than one line of thought when you start considering an answer, but yes, that sort of isolation was what I had in mind; just didn't express it very well.

How far away from the scope are you going to pipe the warm outgoing air? You could use it to keep your hands warm

[Gina]

Given that copper is so much more efficient than aluminium in this respect, even a non-super-duper assembly should net out with an improvement I think.

Yes, you might be right there

It's often the way innit? A question generates more than one line of thought when you start considering an answer, but yes, that sort of isolation was what I had in mind; just didn't express it very well.

Yes, very true

How far away from the scope are you going to pipe the warm outgoing air? You could use it to keep your hands warm

I wasn't going to pipe the air at all - but it's an interesting thought

[Gina]

I have a Zalman CPU cooler that's clearly much more efficient then the old 80mm one and it's only 16g heavier though it would put the centre of gravity further from the focuser giving a greater bending moment. I'm having a rethink on the cooler - don't like such a big heatsink area inside the box even if I can insulate it.

[yesyes]

Another thing to consider is the direction of air flow of the fan. A standard CPU cooler usually blows cold air onto the heatsink. That's not such a good idea in our case as it would blow warm air towards the camera and scope. So I have turned around the fan on my heatsink so it blows warm air away from the heatsink and from the camera. On some heatsinks with non-standard fans this might not be possible (like the Zalman shown in your picture).

[squeaky]

I'd been wondering about CPU coolers (and indeed the PC power supply unit) for some proof of concept tests. I've got a few PC bits and pieces around so I'd be able to try things out.

But first I need to sort out my dob mount, then make light shroud and dew shield, then mod the DSLR...

.. Oh... and remove the chuffin' great slug that's currently climbing up the outside of my camera case!

[Gina]

Another thing to consider is the direction of air flow of the fan. A standard CPU cooler usually blows cold air onto the heatsink. That's not such a good idea in our case as it would blow warm air towards the camera and scope. So I have turned around the fan on my heatsink so it blows warm air away from the heatsink and from the camera. On some heatsinks with non-standard fans this might not be possible (like the Zalman shown in your picture).

The advantage of the Zalman is that it blows out sideways away from the camera and scope.

[Gina]

I'd been wondering about CPU coolers (and indeed the PC power supply unit) for some proof of concept tests. I've got a few PC bits and pieces around so I'd be able to try things out.

CPU or North Bridge coolers are a suitable size. And yes, I'm using a PC PSU but as things are going I might just use the mount supply - have to see how things work out.

But first I need to sort out my dob mount, then make light shroud and dew shield, then mod the DSLR...

.. Oh... and remove the chuffin' great slug that's currently climbing up the outside of my camera case!

Ah yes. Good luck with the DSLR mod There's been a lot of slugs around recently! Horrible things!!

[squeaky]

CPU or North Bridge coolers are a suitable size. And yes, I'm using a PC PSU but as things are going I might just use the mount supply - have to see how things work out.

The thing about CPU coolers is that they are ("should be?") designed to work together efficiently and, I would have thought, that processors produce more heat than a camera chip does; so there's every chance of a good result.

Ah yes. Good luck with the DSLR mod There's been a lot of slugs around recently! Horrible things!!

The mod will be a little while yet, methinks. I'll do a photo run when I do it just in case there are any large differences between this and the 1100, for example.

As for the slug... yurk! No I've got loadsa slime to clear away. Or is that TMI?

[Gina]

I'm going to set up the Zalman on top of the TEC and see how good it is. At the same time I'm attaching the DS18B20s in their little clips I made up, so I can read cold finger and heatsink temperatures once I've got 1-wire working on the Arduino (or I could connect it to one of my Linux boxes and use the software I got working before for my weather station - that's "on the back burner" ATM).

[Earl]

Gina I think your using the wrong type of heatsink have a look at HTPC coolers, lighter and far more surface area.

then saw your post with the zalman, so ignore me LOL.. Zalman for the win

[Gina]

Zalman cooler fitted onto camera on top of TEC . The Zalman copper plate fits the TEC nicely with about a milimetre or so overlap all round the edge.

[Gina]

Test results for Zalman cooler with 12v 37W Peltier TEC running at 80% approx - manual control with 12v 8A LED strip PWM controller shows -9C EXIF T.

Open camera, frost on exposed part of cold finger, ambient temperature 24C and RH 62% according to my weather station. Repeated exposures of 30s at ISO 100 with no pause. Camera capped but stray light showing in image is displaying no sign of dew or frost. Zalman cooler block feels cool to the touch rather than cold but at least it isn't warm so not too many degrees above ambient. I haven't got sensors fitted yet.

[squeaky]

Blimey that looks like a big beast!

Good result then?

[Gina]

Blimey that looks like a big beast!

Good size, yes - not that heavy though

Good result then?

I think so

[squeaky]

Great :0

Right... I'm off cloud dodging.

[Gina]

I'm not going to bother with cloud dodging until the moon's out of the way

[squeaky]

I don't have any choice really. I want to make sure that my friction and tracking are right before we get a good night so that I don't have to waste it doing tests.

Originally I could do 30 sec subs on my dob and only have to bin one out of five (sometimes two but not often), so I want to get back there at the very least. Until the mount tightened up I'd been thinking that I might get up to 40 or even 60 sec subs. No answer back yet on how to do optimal settings so I'm sorting out other bits and bobs on the mount. I've got some decent adjustable feet now, so I can swap out my proof of concept ones, and I want to redo the DC power socket because every touch breaks the contact; and I want to look at using a PC's PSU to drive it because I've got too many darn cables around to trip over in the dark. Oh, and finish making my shroud, and yet to even start a dew shield, plus looking at maybe a mini heater on my secondary which is always first to get covered with dew. Really mini. I have one of those plug in air fresheners which I think have a tiny heater in them, so I'll have a look..

But apart from that I'll just be twiddling my thumbs and watching the Olympics.

[Gina]

Now have DS18B20 temperature sensors on cold finger, heatsink and away from the camera picking up the ambient temperature. Connected to Arduino and displaying the three temperatures on the screen (Serial Monitor as it's called). Not yet on the LCD display - I'll do that later.

No cooling and no exposures all are showing the same temperature of 22.75C.

No cooling but with continuous exposures EXIF T = 24C, cold finger = 23.19C, heatsink = 22.69C, ambient = 22.00C

[Gina]

EXIF T is -8C

Cold Finger temperature is: C: -8.50 F: 16.70

Heatsink temperature is: C: 26.75 F: 80.15

Ambient temperature is: C: 24.00 F: 75.20

[Gina]

EXIF shows temperature -8 C

ColdFinger temperature = -8.25 C = 17.15 F

Heatsink temperature is : 26.75 C = 80.15 F

Ambient temperature is : 23.50 C = 74.30 F

So the Zalman cooler is holding temperature to just 3C above ambient. Not bad

[Gina]

So far so good Air cooling is satisfactory and provides sufficient cooling with the 12v 37W TEC to give a decent -8C sensor temperature with an ambient temperature of 23 or 24C. I have an Arduino reading the temperatures using 1-wire digital thermometers. The cold finger temperature and EXIF T are very nearly equal so controlling the cold finger temperature should give good temperature control of the image sensor.

Next I need to get the Arduino reading the humidity from the DHT11 from which the dew point temperature can be calculated. Also, it will be interesting to see how low the RH gets in the box when sealed and containing several bags of silica gel.

I also need to make the box seal around the Zalman cooling block. For this I'm planning to use an offcut of the rubber roofing sheet I used on my observatory.

[squeaky]

Those results look pretty darn good to me.

I can't wait to see your shopping list and "how to" photos

[Gina]

Those results look pretty darn good to me.

Yes, I think so

I can't wait to see your shopping list and "how to" photos

I'll be posting photos as I go along and I'll post a shopping list shortly. I have a pretty good idea of what I'll be using now.

[squeaky]

You do realise that you've got wa-a-ay too much muscle there?

Imeantersay... you're currently using "cooling air" at 23C in an ambient of 23C... so in winter, when it's a mere 5C, for example, you'll be able to make your own liquid Nitrogen!

[Auntystatic]

The DHT11 has a minimum range of 0degC@30% humidity, in case you didn't know, that's why I went for its replacement the DHT22 much greater ranges, more expensive tho

Are these readings with just the one tec or are you still doubled up? and can you let us know the tec number as these advertisers vary their wattage calculations so much you never know which one your actually getting