1100D cold finger sensor cooling with TEC and water cooling

[Gina]

Well I braved the elements and went out to the obsy, set up camera etc and did a test run with the one 136W 12v Peltier TEC. Running at the current limit of my bench PSU of 6A, it drew 8v at first. The EXIF T went from 17C down to -1C fairly quickly (a minute or two) and as the cold side temperature decreased the terminal voltage rose to 10.5v. There was just one odd reading of -2C but that was it! Input power of 65W. There was no discernible rise in hot side temperature - showing that the water cooling is very efficient.

It may be possible to squeeze a few more degrees of cooling by increasing the input power but I can't see it being enough to make any significant difference. I may get the PC PSU connected up tomorrow and get 12v on it.

Calculations :- At start-up, I=6 and V=8 so R=1.33 ohms Peltier voltage went up to 2.5v with a temperature difference of something like 15C. If there were no temperature change the current at 12v would be 9.5/1.33 (9.5x3/4) just over 7A. Now if the cooling produced another 3 degrees the peltier voltage would be 2.5x18/15=3v so the effective voltage would be 9v and the current 6.75A. This seems possible but I doubt we'd get much better. Anyway, I'll probably try it on 12v and see.

So with an input voltage of around 10v, 50W 12v Peltier gave -9C and 136W 12v Peltier gave -1C. It might be a few degrees milder tonight but not that much. Of course it could be that the more powerful Peltier is a poorer quality sample.

These results are not going in the right direction!!

[Gina]

Just completed a test run with the single 12v 136W Peltier TEC on 12v PC PSU. It started at 7A and went down to 6A. EXIF T went down to -1C for a while and then rose to 0C. The water cooling system was starting to struggle and water temperature rose to tepid feeling rather than cold - so several degrees rise above ambient (13C). I can improve the water cooling by using the radiator and 120mm fan but I doubt it would give more than 5C lower, so -5C EXIF T perhaps.

I think the next test run will be 12v 50W Peltier next to the cold finger and 12v 136W on top both running off 12v 15A supply.

[nightvision]

....

I think the next test run will be 12v 50W Peltier next to the cold finger and 12v 136W on top both running off 12v 15A supply.

That's the way the manufacturers recommend. I think a plate of copper/ally between the Peltiers would help (as they talk about the Peltiers nearest the heat source being physically smaller) and if the plate was made wider than the heat source device it would allow for the next stage devices to placed side by side between the plate and the heat-sink. This diagram seems to point in that direction: (I think the heat direction is top to bottom)

[Gina]

50W plus 136W TECs running off 12v dropped the EXIF T from 23C to -4C drawing 10A at first down to 9A when EXIF T at -4C. Input power was 120W down to 108W, this was getting too much for the present water cooling system and the water temperature rose to an estimated 30C - it felt distinctly warm though not hot. So if water cooling were to be improved by using the radiator and larger fan this setup might work. These two TECs are the same size.

I am now running a repeat test with the 50W TEC only. Current started at 4A with EXIF T at 25C. I'm indoors for tea ATM but will pop out shortly to see the final EXIF T result. Previously this resulted in a final EXIF T of -9C but the ambient temperature is several degrees higher today.

I'm thinking I might run a test with a 5v 20W TEC to see how well this works. This TEC is 25mm square compared with 40mm square of the 12v ones.

[Gina]

That's the way the manufacturers recommend. I think a plate of copper/ally between the Peltiers would help (as they talk about the Peltiers nearest the heat source being physically smaller) and if the plate was made wider than the heat source device it would allow for the next stage devices to placed side by side between the plate and the heat-sink. This diagram seems to point in that direction: (I think the heat direction is top to bottom)

I've been testing with two devices of the same physical size but I have a 5v 20W TEC that's 25mm square and one distinct possibility will be to use that on the hot side with a 12v 50W 40mm square TEC on top and in this case I'll probably add a 40mm square copper plate between TECs.

[Gina]

Well, the repeat test with the 50W TEC only got down to EXIF T of -1C but the water hadn't really had a chance to cool down fully and was still tepid.

Next tests :-

1. Single 5v 20W 25mm square Peltier TEC.
   
2. Above TEC on cold side and 12v 50W TEC on hot side without copper plate between.
   
3. As 2. but with copper plate between TECs.
   

[nightvision]

Gina I was wondering how much the ambient temp was effecting your results, you were I think getting lower with the single low power device but was it much cooler weather?.

BTW: Some interesting liquids for improved cooling: http://www.electronics-cooling.com/2006/05/an-overview-of-liquid-coolants-for-electronics-cooling/

Potassium Formate/Acetate Solution, seems to be the best coolant

and coolant supplies: http://coollaboratory.com/shop/

[Gina]

Gina I was wondering how much the ambient temp was effecting your results, you were I think getting lower with the single low power device but was it much cooler weather?.

Quite a lot in fact. I would think the temperature reduction would be more or less constant so if the ambient temperature went up by a degree I would expect the same rise at the sensor.

BTW: Some interesting liquids for improved cooling: http://www.electronics-cooling.com/2006/05/an-overview-of-liquid-coolants-for-electronics-cooling/

Potassium Formate/Acetate Solution, seems to be the best coolant

and coolant supplies: http://coollaboratory.com/shop/

That's interesting - thank you

[Gina]

I'm running the single 12v 50W Peltier test again but this time with radiator and 120mm fan to cool the water. Ambient is lower than this afternoon too.

EXIF T = -4C ATM

[Gina]

Changed from a series of 10s exposures with 5s pause to 1/100s exposures to image on a far hedge in daylight and EXIF T has gone down to -6C.

Less use of image sensor means less heat generated and hence cooler can produce a lower temperature.

[Gina]

On changing to long exposures eg. 100s the EXIF T rises to -2C whereas on short exposures of 10s or less it's -6C

[Gina]

My 5v 20W Peltier has gone walkabout or got a great big gremlin sitting on it! So I thought I'd run the two 12v Peltiers again but with the radiator water cooling. It's certainly better than before. Gets the EXIF T down to -4C on long exposures and -6C on short ones - occasionally -7C. That's just marginally better than the 50W on its own. Current started at 10A and settled down at 9.5A so that's about 115W which the water cooling is coping with. The water block on the hot side felt decidedly warm - not surprising with over 100W passing through it.

[Gina]

Been running a test for condensation using a terrestrial view of the trees etc. on a distant hill. Using an exposure of 1/500 at ISO 100 with a repeat rate of about 10s the heat output from the imaging sensor and processor is reduced to a minimum. This allowed the EXIF T to go down to -8C. I'm getting some condensation around the edge of the image. Later I'll take the camera off, take out the clip filter and see where the condensation actually is. I think there are some improvements I can make inside the camera case to help with this.

Using live view to enable me to adjust the focus the imaging circuitry was running at full stretch and the EXIF T rose to -1C.

I think the cold finger is lacking heat conductivity. The centre of the Peltier coolers are a good three inches (75-80mm) from the centre of the sensor, it is essentially an inch wide except where it broadens out to cover the 40mm square Peltier. It is also only 22swg ie. 0.7mm thick. I have a digital temperature sensor on the cold finger right next to the sensor and intend to add another on the cold finger on the opposite side from the Peltier to give the Peltier cold side temperature. Empirically, I can tell there's a considerable temperature difference between the sensor and the back of the Peltier as the latter gets covered in ice before the EXIF T reaches 0C.

I will lag the cold finger outside the camera once I've decided on which Peltier(s) to use - the inside is already lagged up to the sensor.

[Gina]

Here's a couple of photos showing the camera with Peltier cooler on the end. The build-up of ice on the exposed parts can be clearly seen. As time went on this ice grew and grew, giving up it's latent heat to the cold finger and reducing the cooling.

[Gina]

I'm proposing a rethink on the Peltier cooling of my 1100D as I'm not happy with the present system. I'm considering putting one Peltier TEC inside the camera, reducing the distance from TEC to sensor and reducing the exposed cold area. This should improve the efficiency and may reduce condensation. This will want a lot of looking at but the idea I have is shown in the attached diagram.

[yesyes]

So this is basically a hot finger system then?

[Gina]

So this is basically a hot finger system then?

If I use two Peltiers it will probably be a cool finger or a tepid finger - or even a warm finger if I find one TEC enough.

[yesyes]

you could even use thicker copper sheet between the 2 peltiers for better heat transfer. Or even a proper heatpipe.

I think one of the limiting factors is that the copper sheet is quite thin (I use 1.2mm).

[Gina]

you could even use thicker copper sheet between the 2 peltiers for better heat transfer. Or even a proper heatpipe.

I think one of the limiting factors is that the copper sheet is quite thin (I use 1.2mm).

Yes, I intend to use a thicker sheet - I have some 18swg = 1.2mm that I got when I first looked into doing this. That was when I found that there was no way that thickness would go in so I ordered a sheet of 20swg and 22swg. The latter would go in.

[RAC]

From the testing i have done i would say you wont ever get enough cooling to the back of the peltier in the camera. It will cook.

[nightvision]

From the testing i have done i would say you wont ever get enough cooling to the back of the peltier in the camera. It will cook.

I thought something like that however maybe it could be used on low voltage with the next one on full power and only turned up a little once the finger was cold.

[Gina]

Thank you chaps I was planning to use a 5v 20W one inside the camera and a 12v 50W outside. A bit of heat inside the camera would help with misting up perhaps.

[Gina]

Still can't find my 5v 25mm square Peltier TEC Wish I could get myself more organised

[RogerTheDodger]

I have that trouble, everything I put away "safely" takes me hours to find... everything else takes even longer

[Auntystatic]

That's because the safe place keeps moving around behind your back, I have loadsa stuff in my safe place can't wait to find it again.