Jump to content

Banner.jpg.b83b14cd4142fe10848741bb2a14c66b.jpg

Canon 1100D Cold Finger Peltier Cooling - WIP

russellhq

By russellhq
in DIY Astronomer

Recommended Posts

  • 3 weeks later...
  • Replies 145
  • Created
  • Last Reply
Dave_D

Dave_D

Posted
Posted

arduino sketch almost complete and then onto the build (which i'm a bit nervous about because i only have my working 1100d). had a really annoying time trying to get the encoder not to bounce around like skippy so i worked out a 3 button system, 1 button to cycle through the 4 screens and 2 buttons for raising and lowering the setpoint. works quite well actually.

2 questions though...

1. which sensor are you guys using to measure the peltier temperature?

2, Gina, did you make any enquiries about that dehumidifier?

anyways, here's a little vid.

http://vidmg.photobucket.com/albums/v369/vanityassassin/VID_20140714_213706_zpsgteuoamx.mp4

Link to comment
Share on other sites
Gina

Gina

Posted
Posted

Cold finger temperature measurement is using a DS18B20 1-wire digital thermometer.  These are accourate to half a degree C and work down to -40C.  I use a DHT22 to measure temperature and humidity of the dry chamber.

No, I haven't yet persued the dehumidifier element.

Link to comment
Share on other sites
  • 2 weeks later...
Dave_D

Dave_D

Posted
Posted

So, i got my sketch almost completed and ironed out a temperature oscillation problem as the peltier temp approaches the setpoint temp. seems to me that due to the nature of thermodynamics, there is always going to be a small rate of change of temperature, but, once the coldfinger is down close to the setpoint, the temperature stabilizes after about 5 minutes with a fluctuation of plus/minus 0.2 degrees.

Does this seem reasonable or should i poke the sketch around a bit more?

Had it down to -2 so far...

Link to comment
Share on other sites
Dave_D

Dave_D

Posted
Posted

the DHT temperature sensor example sketches have a dewpoint calculator

// calculate the dew point
double DewPoint(double celsius, double humidity)
{
  double a = 17.271;
  double b = 237.7;
  double temp = (a * celsius) / (b + celsius) + log(humidity/100);
  double Td = (b * temp) / (a - temp);
  return Td;
}
Link to comment
Share on other sites
Thalestris24

Thalestris24

Posted
Posted

I did some experiments of this too a couple of years ago - there's a thread about it here somewhere.  You certainly can make a difference but you need to cool the enclosure below freezing to get the sensor temperature down anywhere near zero C.  The trouble is the thermal resistance between the sensor and other heat emitting parts in the camera to the outside.

What I did find, is that cooling the metal frame via the tripod bush was quite effective.  The frame goes right inside the camera and near the image sensor.  It is electrically connected to the shield over the imaging processor board too though how good the thermal conductivity will be I'm not sure.

I used a cast aluminium box to contain the camera with the latter fastened to the box with the tripod bush.  The Peltier TEC was placed on the outside of the ali box with thermal paste between it and the box.  A large CPU cooler took away the heat produced by the hot side (thermal paste essential here too).  You'll need thermal insulation around the box or you'll be using all your cooling to produce ice on the outside of the box.

If you can manage to seal the box to keep damp out then several bags of silica gel will keep the camera dry and stop condensation.  This sealing is easier said than done I have to admit. 

It's worth replacing the camera battery with an external power connection.  You can get a battery eliminator if you don't want to open up the camera.  The memory card isn't necessary as you can disable saving to card from the Menu and only use the USB connection.  This way, if you set the mode to "M" and power to "ON", access to the camera isn't necessary.  It can be switched on/off by switching the external power.

Hi

I'd like to have a go at this though I would be concerned about condensation... Still, I intuitively feel this could be overcome - somehow!

Louise

Link to comment
Share on other sites
Gina

Gina

Posted
Posted

You need a well sealed box including an optical window to let the light in but not moisture.  Then silica gel bags can take the remaining moisture out of the air inside the box.  Professional camera often are flushed out with dry inert gas before sealing,

Link to comment
Share on other sites
Thalestris24

Thalestris24

Posted
Posted

Hi Gina

Yeah, not easy! Especially when I want to use it with a Canon lens... I believe the sensor is itself sealed (it's my mono 1100d) but the rest of the electronics would need protecting from condensation. Perhaps a spray on conformal coating? Anyone tried that?

I'll have to mull over the options...

Louise

Link to comment
Share on other sites
Thalestris24

Thalestris24

Posted
Posted

Ok - I'll bear that in mind - if I ever get around to attempting anything! I don't think I'll try a cold finger - too risky! At the same time, a cooled enclosure probably won't cool the sensor efficiently but might be good enough for longish exposures with darks. I'll have to read through all the wisdom here and elsewhere :)

Thanks

Louise

Link to comment
Share on other sites
Gina

Gina

Posted
Posted

Good luck Louise :)  There's lots of info about.  I don't blame you for not risking a cold finger mod - needs a lot of dismantling with the risk of damage.  Not a big problem with a cheap second hand camera but quite a different matter for an expensive debayered DSLR.  I have had considerable experience with designing and building miniature electronics projects - I did it for a living, I was a profeessional R&D electronics engineer.

Link to comment
Share on other sites
Thalestris24

Thalestris24

Posted
Posted

Good luck Louise :)  There's lots of info about.  I don't blame you for not risking a cold finger mod - needs a lot of dismantling with the risk of damage.  Not a big problem with a cheap second hand camera but quite a different matter for an expensive debayered DSLR.  I have had considerable experience with designing and building miniature electronics projects - I did it for a living, I was a profeessional R&D electronics engineer.

Hiya

I think it might be a future / side project. No rush and I don't even have the camera at the moment though I have an unmodded one. Alas my mono had a fault so had to send it back :( I asked JTW how much it would cost to upgrade to their ultimate cooled version - reply was "Euros 999 plus 3 months waiting list". Much as I'd like one, that's too much and too long! I think my aim won't be so much to cool it to sub-zero, rather to try and prevent the sensor getting too hot. I have a plan to use the mono 1100d with a 300mm lens (F5.6) and narrowband filters. That means numerous long exposures... Previously, when I used my standard 1100d it would get quite hot (according to APT) if I tried to do, say, 600s exposures. Not helped by being indoors at 'room temperature' so not even getting the proper cooling effects of wintry nights! So anything I can do that could potentially limit the in-use temperature rise would be good. Gary Honis' version looks doable. Maybe could even be improved upon. Anyway, some mulling and deep thought required.

Cheers

Louise

Link to comment
Share on other sites
Gina

Gina

Posted
Posted

When I was looking into this a year or two ago I found at least two dew point algorithms but I'm afraid I don't remember where ATM - try Google.

Link to comment
Share on other sites
Davey-T

Davey-T

Posted
Posted

Ok - I'll bear that in mind - if I ever get around to attempting anything! I don't think I'll try a cold finger - too risky! At the same time, a cooled enclosure probably won't cool the sensor efficiently but might be good enough for longish exposures with darks. I'll have to read through all the wisdom here and elsewhere :)

Thanks

Louise

Hi Louise,

I bought a S/H  Geoptek cool box which I've rebuilt (looked like it was thrown together)  and modded to take my 60da, haven't taken any pic's yet but it holds a steady -5 in the daytime, useful for taking darks after the event, the only draw back is that it draws 10amps so not much good for field work :) the manual claims 2.5 amps ?

Only got it set up for TV Powermate at the moment but looking to mod for lens attachment, will post pics if/when skys clear

Dave

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.