Air cooled TEC with cold finger DSLR cooling

[Baffa]

I haven't read everything in this thread but I've been thinking a bit, how good would a huge heatsink covering the entire back of the box instead of that big CPU sink? It would be more compact but maybe it's not as good cooling.

Imagine something like this on the entire backside, http://www.thomex.com/ebrochures/lokenath-patterns-castings/heat-sink-rib-type.jpg (I just found this picture on the net, I don't have anything to do with the company or anything else, just an example!)

[Gina]

Thanks for your input robert However, I dont think that would offer the cooling provided by the Zalman with all it's fine fins and large fan.

[Gina]

Been working out which connections need to go through the camera box and sorting out connections generally. Here is the latest circuit diagram showing where connections pass through the box etc.

[Gina]

Photos of today's progress.

The first three photos are of the inside the box showing connections to the DHT22, temperature and humidity sensor (black, red, white) and camera power (black, yellow) with 4 way connector to permit removing the camera. The male connector was glued to the box side and the wires sealed with hot glue.

The last three show the outside with the TEC control components and connectors. The green one is a twin screw connector for the main 12v supply, the white one for the fan and the black one takes the ribbon data cable.

[Gina]

These photos show the wiring and connector for the 1-wire network. Temperature sensors - on cold finger inside the box and on heat sink and fan casing (ambient) on the outside, terminating on the data ribbon connector.

[Gina]

Box completed I think - except for a pressure equalising membrane which I've yet to work out. I've filled most of the air space with bags of silica gel recently refreshed and the resultant reloative humidity was under 19% with dew point of -3.6C before applying any cooling t the camera So far so good

However, when I applied camera power nothing happened So it's back out to take the scope camera off the scope and bring it indoors to fault find. Guess what... for the first time in several weeks the sky is clear! The wide-field rig isn't finished yet Shouldn't take long to finish it though. Just panicking because it's a clear night and I'm not ready

[squeaky]

I hope it all went OK

[Gina]

I finished the WF rig and did some testing with that last night - focussing system worked well Scope camera I hope to fix today.

[Gina]

In the middle of fault finding ATM. Camera is fine run off battery, next to check the home made power replacement for the battery.

[Gina]

Found the problem - my home made battery eliminator. +ve connection fine but -ve isn't getting through to the -ve connection pad. Maybe I'd be better off connecting directly to the power PCB.

[Gina]

Been trying to get a power input working directly onto the power board in the camera but it isn't working Something silly no doubt Just stopped for a cuppa - probably see the trouble as soon as I get back to it.

[Gina]

Fixed it I remembered from when I took a genuine Canon battery eliminator that the middle connection was connected to the -ve so I've done that and the power supply works These two photos show the initial two wires (black -ve and yellow +ve) and the final three wire connection. The grey wire on the middle battery connection is connected to the black -ve. This is with the camera top removed. The connections are covered by part of the top when replaced.

[squeaky]

You seem to have so much FUN with all this

[Gina]

You seem to have so much FUN with all this

Oh yes - I quite like fiddling about with these things and feel a nice satisfaction when it all comes together and gives good results

I now have it all back together and working on the scope Nice dry refreshed silica gel bags filliing the space around the camera with very little space left for damp air. The relative humidity quickly went down to 20% with the dew point dropping rapidly well below freezing. Ambient temperature was 8C. I've left it running on test while I came in for tea.

The new box and redesign has resulted in a much better and tidier unit. Changing the silica gel bags for drying out is just a matter of taking the unit off the scope, unscrewing the focal reducer (if used) and taking the lid off. I'm quite satisfied with this design - I was a bit unhappy with the previous one.

At present I have no plans for any further mods on this and not bothered about not having computer control - the local manual control works very well. The next item associated with the scope is the filter wheel which is well under way and the subject of another thread.

[Gina]

The scope camera box is working very well Dew point is -16C and I'm running with a cold finger temperature of -14C. Decided to have a go at M31 for a change. Running 2m subs at ISO 3200. Guiding with ST80, QHY5 and PHD as usual. Looking at the RAW subs, the centre is not blown out and I'm getting plenty of outer stars and can clearly see the dust bands so I think a stack should yield good results. I might abandon this when the moon comes up and change over to narrow band. ATM I have 3 cameras but only two computers set up. Also only three USB2 feeds from the mount including the QHY5 guide scope. I've tried a USB2 hub but the cameras didn't like it. So I need to run another USB2 cable through the cable duct and then use two instances of APT on my desktop PC. The netbook has run out of USB ports.

[squeaky]

That all sounds very good. I'll me interested to see the M31 result

[RAC]

The scope camera box is working very well Dew point is -16C and I'm running with a cold finger temperature of -14C. Decided to have a go at M31 for a change. Running 2m subs at ISO 3200. Guiding with ST80, QHY5 and PHD as usual. Looking at the RAW subs, the centre is not blown out and I'm getting plenty of outer stars and can clearly see the dust bands so I think a stack should yield good results. I might abandon this when the moon comes up and change over to narrow band. ATM I have 3 cameras but only two computers set up. Also only three USB2 feeds from the mount including the QHY5 guide scope. I've tried a USB2 hub but the cameras didn't like it. So I need to run another USB2 cable through the cable duct and then use two instances of APT on my desktop PC. The netbook has run out of USB ports.

Have you thought about using a heater on the front anti aliasing filter to help fight off ice?

I used some nichrome wire from a bimetallic strip temperature gauge out of an older car. Its 47 ohms and i can run it from 1.25 to 6.5volts.

Heater for Cmos sensor by meg rac, on Flickr

[Gina]

That's an interesting idea I had thought of possibly heating the filter but not in detail. In fact it doesn't seem necessary with my system. Thank you for posting your neat little heater

[Gina]

The present system works very well for a while but after a couple of weeks or so the thermal conductivity from the TEC to the sensor seems to fail - or at least go down considerably, such that I can only get an EXIF T of -2C at maximum cooling and 20C ambient. I think the problem is that the ABS box is not rigid enough and the weight of the cooler causes movement between cooler and camera. And since the TEC is mounted solidly in the case and to the cooler heatsink, there is movement between TEC and sensor causing loss of perfect thermal contact between cold finger and sensor and between cold finger and TEC.

This is a better design than the previous one by far but the cold finger is longer and the thermal contact with the sensor is not as good even after putting it all back together. There's always at least 4C temperature difference between cold finger and EXIF T whereas in the previous version this was virtually zero. I also had a more reliable TEC to cold finger thermal contact. The difference is that the cooler was solidly attached to the camera in the previous version whereas in this current design it relies on the plastic box. This is clearly unsatisfactory.

The upshot of all this is that I am about to embark on version three. So anyone who thought I'd be giving up on DSLRs and jumping with both feet into the astro CCD camera camp can breathe a sigh of relief - I'm not letting the DSLR side down

[Gina]

I think maybe a new thread might be a good idea as there will be several differences - no only in the camera box but also in the control and power distribution box.

[squeaky]

Sounds like a plan to me

[Gina]

Sounds like a plan to me

New thread is here :- http://stargazerslounge.com/topic/171415-1100d-set-point-cooling-with-peltier-tec-and-air-cooling-v3/

[dp297]

Gina, may I ask u a couple of questions about DSLR cooling?

[Gina]

Gina, may I ask u a couple of questions about DSLR cooling?

Of course what would you like to know?