Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Air cooled TEC with cold finger DSLR cooling

Gina

By Gina
in DIY Astronomer

Recommended Posts

Gina

Gina

Posted
Posted

I've started serious experiments with DSLR (1100D) cooling with air cooling instead of water cooling for the hot side of the Peltier TEC.

Firstly, with 12v 37W 30mm square TEC and 60mm heatsink and fan I can only get down to +6C with an ambient of 23C (indoors). I'm using a 60mm square heatsink and fan from an old PC CPU. Total weight of about 100g. I also have an 80mm set but that weighs 250g.

Link to comment
Share on other sites
  • Replies 548
  • Created
  • Last Reply
Gina

Gina

Posted
  • Author
Posted

With 80mm heatsink and fan I can get down to -4C for long exposures (testing with 30s repeated without pause) and the 12v 37W TEC. So apart from weight, that could be a viable possibility.

I have a 12v 20W TEC as well and I'll try that. Watch this space :D

Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

All the results so far :-

  1. 12v 37W TEC and 80mm heatsink/fan - EXIF T = -4C
  2. 12v 20W TEC and 80mm heatsink/fan - EXIF T = -1C
  3. 12v 37W TEC and 60mm heatsink/fan - EXIF T = +6C
  4. 12v 20W TEC and 60mm heatsink/fan - EXIF T = +6C
  5. 12v TECs 20W and 37W stacked - rubbish! Even with 80mm HS/fan.

Comments :- The 60mm heatsink and fan gets too hot while the 80mm is a much better heatsink with nearly twice as many fins and much taller too, but it's over twice the weight.

Conclusion :- 60mm heatsink and fan is no use - it can't handle the heat.

Link to comment
Share on other sites
pete_l

pete_l

Posted
Posted
Comments :- The 60mm heatsink and fan gets too hot while the 80mm is a much better heatsink with nearly twice as many fins and much taller too, but it's over twice the weight.

Conclusion :- 60mm heatsink and fan is no use - it can't handle the heat.

That's an interesting result, Gina.

Do you have the vital statistics for those fans/heatsinks - such as the base thickness?

It would be handy to know the Watts/°C rating of each of the heatsink + fan combinations.

The ceramic base of a Peltier isn't really that great a conductor of heat. If you try putting a copper plate (maybe 1 or 2mm thick) between the hot side and the heatsink, that may help distribute the heat coming off the Peltier so it's not all concentrated in the 30mm sq. (i.e. ¼ of the heatsink's surface area) that the Peltier is in contact with.

Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

I'm very much interested too.

The weight side won't bother me overmutch, I've got to calibrate balance on my beast anyway, so calibrating for a bit of extra weight is no big deal.

Good :)
Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

That's an interesting result, Gina.

Do you have the vital statistics for those fans/heatsinks - such as the base thickness?

It would be handy to know the Watts/°C rating of each of the heatsink + fan combinations.

I'll take some measurements and photos but I don't have any info on these heatsinks or fans as they came off old PCs.
The ceramic base of a Peltier isn't really that great a conductor of heat. If you try putting a copper plate (maybe 1 or 2mm thick) between the hot side and the heatsink, that may help distribute the heat coming off the Peltier so it's not all concentrated in the 30mm sq. (i.e. ¼ of the heatsink's surface area) that the Peltier is in contact with.
Yes, I can see how that might help as the heatsinks are aluminium which has only half the conductivity of copper. I think I have some 18swg copper sheet (1.2mm) - I'll give it a try. However the problem with the 60mm heatsink is that it gets too hot. The 80mm one stays cool to the touch. I shall be putting some temperature sensors on soon so can get the figures. But that doesn't alter the fact that the 60mm setup won't cope.
Link to comment
Share on other sites
Earl

Earl

Posted
Posted

Daft question, but have you tried using a upright fan like you have in the house blowing on it also, I do this on my Atiks If im struggling to get to -20 and it works fine for about 5 degrees,

Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

Daft question, but have you tried using a upright fan like you have in the house blowing on it also, I do this on my Atiks If im struggling to get to -20 and it works fine for about 5 degrees,

Not SO daft :) But no, I haven't tied that.
Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

Correction on the weight of the 80mm heatsink/fam combo - it's 285g.

I've looked on eBay and there's a 60mm heatsink and fan which is far more efficient looking than my 60mm and which weighs 227g (8oz). That is lighter than the 80mm and with the smaller size, more suitable for the box I'm using. Here's the eBay link :-

http://www.ebay.co.u...=item20c81369e2

Here's more info from the manufacturer :-

http://ca.startech.c...et-A~FANDURONTB

Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

I've decided to carve things about to fit the 80mm cooler as this fits the bill. -4C EXIF T will be sufficient I think. I really want to get rid of the water cooling - it's a real pain. I don't know why the 12v 20W plus 12v 37W TECs stacked didn't work. Maybe the top TEC needs to be a higher power. I do have 12v 50W TECs so could try that but I think I'll settle for the single 37W and -4C.

Link to comment
Share on other sites
pete_l

pete_l

Posted
Posted
I don't know why the 12v 20W plus 12v 37W TECs stacked didn't work. Maybe the top TEC needs to be a higher power.
Yes. For the lower TEC, it consumes all the power you send it and converts that into heat. In addition it passes through all the "cold" it suck out it's cooled side and passes that through as heat, too.

The second TEC then creates all the heat from it's own power supply and then passes through all the heat from the first TEC (i.e. the first TEC's consumption AND from it's cooled side).

So if your first TEC consumes, say, 20 Watts and cools by another 5 Watts (rather optimistic ;)) and the second TEC consumes 100Watts, it will have to cool by the 20 + 5 Watts that's passed to it from the first TEC. Meaning it passes 25 + 100 Watts through to it's heatsink.

All to get rid of 5 Watts of original heat

Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

A 5v 20W with a 12V 37W on top seems to work and I can get -15C with water cooling. But a 20W and 37W doesn't work with air cooling even with the 80mm cooler. Yes I did get both TECs the right way round! ;)

Anyway, as I said I'm going for the 12v 37W TEC on it's own with the 80mm cooler. I have cut the box down by 20mm so that the heatsink is level with the box top. I'm going to cater for the extra weight by upgrading my focuser. I really have to admit defeat on the Skywatcher Crayford - I've tried but it just won't do!

Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

Here are some photos of the butchered camera and heatsink. I removed the viewfinder and penta-mirror and cut back the plastic of the top to clear the heatsink. The camera is still working perfectly :D One heatsink clip (home made) can be seen in the last two photos.

post-13131-0-94409800-1343857360_thumb.jpost-13131-0-13460600-1343857381_thumb.jpost-13131-0-16739800-1343857393_thumb.jpost-13131-0-61595800-1343857397_thumb.jpost-13131-0-77518100-1343857400_thumb.j

Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

I weighted the above assembly together with the lid and it came to 770g - not too bad. There's still the Arduino, display and a few other odds and ends to be fitted which will add a bit to the weight but not by a lot.

Link to comment
Share on other sites
pete_l

pete_l

Posted
Posted

Those are good pictures, Gina.

Are you planning to fill those air-gaps at the top and on the left? Putting insulating foam in there, instead of leaving them empty will help reduce cooldown times, as the TEC won't have to cool down all the excess air. It'll also help reduce air currents, too.

Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

Those are good pictures, Gina.

Are you planning to fill those air-gaps at the top and on the left? Putting insulating foam in there, instead of leaving them empty will help reduce cooldown times, as the TEC won't have to cool down all the excess air. It'll also help reduce air currents, too.

Thank you :) Some of the space will be taken by the electronics and silica gel bags but filling the rest with some blocks of polystyrene foam would be a good idea.
Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

To do today :- Second heatsink clip, cut lid to go round heatsink and add a "bump" to cater for the lump on the camera top on the RHS (with two buttons). On the last camera, cutting this part off the camera top reduced the camera to a door stop! I don't know why but I'm not risking it again. Then add the power MOSFET with ferrite ring and some of the other electronics. I have now received the switch mode power modules from Hong Kong but not decided whether to use one of those for camera power of stick with the LM317T. In either case I shall use a separate over-voltage crowbar using thyristor and zener diode plus fuse.

Link to comment
Share on other sites
squeaky

squeaky

Posted
Posted

Silly question #49...

Since you have some copper sheet around the place (left over from your original cold finger?) would there be any value in cobbling together your own heat sink in copper?

Silly question #50...

Are you going to duct the cooling air in and out so that the warm air doesn't heat up the rest of the camera and the incoming cold doesn't deposit moisture in there?

Link to comment
Share on other sites
Gina

Gina

Posted
  • Author
Posted

Silly question #49...

Since you have some copper sheet around the place (left over from your original cold finger?) would there be any value in cobbling together your own heat sink in copper?

I did consider that - I wonder if I could make a more efficient heatsink than that aluminium one. Might think about that later.
Silly question #50...

Are you going to duct the cooling air in and out so that the warm air doesn't heat up the rest of the camera and the incoming cold doesn't deposit moisture in there?

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 :)
Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.