Air cooled TEC with cold finger DSLR cooling

[Gina]

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!

Oh yes I agree I could get away with less but the trouble is finding a suitable cooler. That Zalman was the lightest heat pipe type I could find at the time. I may have another search of the web but I don't really want to go on spending money in the hope of finding the absolute optimum setup.

[Gina]

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

I don't expect the temperature of the air in the box to go below freezing though I guess it could in the depth of winter. I think the DHT11 goes down to 20% humidity and until I test it I have no idea of how low I can get the humidity. I am quite prepared to change to the DHT22 if if looks necessary. The decoding needs to be different as the DHT22 has a different data format but I think that has been done and I can look into that later.

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

This is with a single TEC - 12v 37W 30x30mm :- http://www.ebay.co.u...984.m1439.l2649

These are from a UK supplier and dearer than ones from Hong Kong - the spec is slightly higher.

[Gina]

Been working on the heatsink seal. Here are some photos :-

1. Thin copper plate with part bent up round temperature sensor, slipped under cold finger. Insulation tape over the bare sensor wires.
   
2. TEC fitted onto cold finger.
   
3. Rubber sheet cut to clear TEC with holes for heatsink fixing bolt and bracket.
   
4. Rubber sheet fitted round TEC and over fixing bolt.
   
5. Cooler fastened to camers - Top view. Heatsink temperature sensor in copper clip under fixing thumb nut.
   
6. Bottom of camera showing cooler secured with aluminium plate, rubber heat insulator and bracket hooked over tripod bush.
   

[Gina]

I did a web search for heat pipe coolers and the one I've got is the cheapest and lightest I can find so that's that

[Auntystatic]

Thanks for the link Gina, I was holding off cool modding my 1100d as it was the only astro cam I had, but I did the baader mod on my older 5D so I'm waiting to try that out when we manage to get a clear night. if it works out as good as I'm hoping then its on with the 1100d mod, I think to insulate the boards against dew I will use the electrical varnish instead of all the white heatsink paste, because that stuff will get everywhere if I use it.

I have also seen a mod for the qhy5 where a finger was used off the back of the chip and made contact with the rear case, this cooled the sensor down quite nicely and gave good results.

The dht11 data sheet gives these values, as the temperature drops the humidity detection gets worse, I just didn't want you going slowly insane wondering why you would get so odd readings as the temp inside your case dropped

Measurement Range

0℃ 30%RH

25℃ 20%RH

50℃ 20%RH

[Gina]

Thanks for the link Gina, I was holding off cool modding my 1100d as it was the only astro cam I had, but I did the baader mod on my older 5D so I'm waiting to try that out when we manage to get a clear night. if it works out as good as I'm hoping then its on with the 1100d mod, I think to insulate the boards against dew I will use the electrical varnish instead of all the white heatsink paste, because that stuff will get everywhere if I use it.

Yes, good plan It gets everywhere when I use it too. I haven't put it on the back of the imaging board on this camera - I'm fed up with finding it everywhere!

I have also seen a mod for the qhy5 where a finger was used off the back of the chip and made contact with the rear case, this cooled the sensor down quite nicely and gave good results.

That's great - thanks for the link - very interesting

The dht11 data sheet gives these values, as the temperature drops the humidity detection gets worse, I just didn't want you going slowly insane wondering why you would get so odd readings as the temp inside your case dropped

Measurement Range

0℃ 30%RH

25℃ 20%RH

50℃ 20%RH

Ah I see - thank you Perhaps I should order a DHT22 just in case. Actually I cold do with a better humidity sensor for my weather station. Think I'll order a couple from Hong Kong.

[Gina]

I've ordered a couple of DHT22s from a UK supplier - the Honk Kong suppliers are quoting an unknown delivery time. blamed on the Olympics! I want one for my weather station anyway and I might as well use the same type for the camera.

[yesyes]

I'm changing everything to DHT22 too. The DHT11 give nothing more than a rough estimate. Accuracy of +-2°C is just not good enough.

[Gina]

Ah yes, the DHT11 doesn't seem up to much - just as well I only bought one Delivery for the DHT22 is stated as 2-3 days so maybe I'll wait until I get those reather than debug the DHT11 code. I'll be interested in how you get on with the DHY22, Chris

[yesyes]

Oh, I've used them already and they work great. The Arduino code is in my EOS cooling controller sketch.

[Gina]

Oh, I've used them already and they work great. The Arduino code is in my EOS cooling controller sketch.

Oh good - thank you Chris - I'll check that out

[Gina]

Assembly to date with box, camera, cooler, lid and seal, weighs 815g. To be added :- Arduino, DHT22, LCD display, pot and knob for LCD contrast, other electronics. I've ordered a SteelTrack focuser and adapter for the SW FR/FF from FLO. Hoping to be ready for use later this week.

[squeaky]

How much weight did you save by cutting down/off all the various bits of the camera?

Do ALL of the bits HAVE to be on the camera box? Can some of the control and electronics be put in a hand controller box, so to speak, which could be put somewhere on your mount that wouldn't affect balance?

[Gina]

How much weight did you save by cutting down/off all the various bits of the camera?

Not sure - have to check, but probably between 50 and 100g.

Do ALL of the bits HAVE to be on the camera box? Can some of the control and electronics be put in a hand controller box, so to speak, which could be put somewhere on your mount that wouldn't affect balance?

Depends how many wires you're prepared to have going from the control box to the camera box. It's a good point. I was originally going to do it that way but seem to have changed over to putting it all in the camera box to save wires. Let's compare the two methods :-

Electronics in camera box :-

1. USB cable (hub in camera box for camera and Arduino).
   
2. 12v power for TEC with voltage regulator for camera. Direct 12v to Arduino.
   
3. Power Ground.
   

Electronic in seprate box :-

1. USB to camera
   
2. 12v power for TEC with voltage regulators for camera & DHT22.
   
3. Power Ground
   
4. Signal Ground
   
5. PWM to TEC control.
   
6. PWM from fan control.
   
7. 1-wire sensors.
   
8. DHT22 humidity/temperature.
   

[Gina]

I terms of cables, this can be USB and power in both cases with a data cable added for the separate box. The data cable could be multicore cable such as used for alarm systems (which is 6 core) or a ribbon cable.

Apart from saving a bit of weight in the camera box the separate box has the advantage that the display can be in a position where it's always easily visible. On the camera box there would be times when it's in a very awkard position. There is also the backlight LED on the display which would need shielding from the camera. Adding a data cable is a very minor issue compared with plastic water pipes!

I'm fast coming to the conclusion that a separate box on the pier would be the best option.

[squeaky]

The pro's do seem to outweigh the con's here, don't they?

Multi-core cables would be the way to go perhaps - this because it's much easier to get seals by using proper cable glands. Plastic ones are very light, so in the camera box you should still net out with a comfortable weight win.

[Gina]

The pro's do seem to outweigh the con's here, don't they?

Yes, I believe they do.

Multi-core cables would be the way to go perhaps - this because it's much easier to get seals by using proper cable glands. Plastic ones are very light, so in the camera box you should still net out with a comfortable weight win.

I want connectors on the camera box so that I can remove it completely while the cablles are secured to the scope to stop them tangling up and getting hooked up on things. I'm thinking of using ribbon cable for the data cable - I have plenty and I have the IDC connectors. There is less chance of cross-talk with ribbon cable with alternate wires earthed. Alternatively, CAT5 cable with it's twisted pairs is good for data transmission. 4 pairs is just right. I have ooodles of that too and connectors plus crimping tool. Ribbon cable is the most flexible for bending at the mount axes.

[squeaky]

Hokay

Something like this: cable tidy might help out too with staying tangle free.

[Gina]

Hokay

Something like this: cable tidy might help out too with staying tangle free.

Yeah - have got one of those

[squeaky]

I've got yards of the stuff kicking around. There's also corrugated tubing which is thinner, so while there are no spaces as with the spiral - it might be a shade lighter size for size. Unfortunately I don't have any of this lying around the place so I can't do a comparison for you.

(Power connection on the Synscan now hard wired since the socket was very temperamental. WATER removed from my AZ encoder and motor assembly! About half a gallon of condensation cleaned out of my finder. Both mirrors cleaned. All meant that I didn't get any testing done last night, which was a bit of a bummer 'cos that was my best sky this week. More cloud dodging planned for tonight.)

[Gina]

When I bought that cable tidy spiral stuff I didn't realise it was so big - I didn't use it. I'm using cable ties and stick-on clips.

[squeaky]

There are a whole range of sizes - if you have an electrical wholesaler anywhere near you you'll be spoilt for choice

[Gina]

There are a whole range of sizes - if you have an electrical wholesaler anywhere near you you'll be spoilt for choice

Yes, I thought so

Been attaching connectors to the camera box and wiring them up. Decided to use a terminal block for the 12v power. The data is a 5x2 IDC ribbon connector in a PCB header, wired directly to the pins. I've decided to supply the camera power with the data - the current is low enough - and that will allow me to turn the camera off without removing all power. APT sometimes wants the camera turned off and on again.

Data connections are :-

1. Gnd
   
2. DHT22 data
   
3. Gnd
   
4. 1-wire data
   
5. Gnd
   
6. Camera power
   
7. Gnd
   
8. Fan PWM
   
9. Gnd
   
10. TEC PWM
    

I shall derive the 5v for the DHT22 from the 12v supply. Maximum current is stated as 2.5mA so that's easy.

[squeaky]

I shall derive the 5v for the DHT22 from the 12v supply. Maximum current is stated as 2.5mA so that's easy.

5kΩ resistor and a 5v zenner?

[Gina]

5kΩ resistor and a 5v zenner?

2.7k and 5v zener will give 2.8mA