Introduction: Peltier Cooling for ZWO Astro Camera
After stumbling on these two YouTube vids showing how to add cooling to an uncooled ZWO Optics Astro Cam
I thought I'd give it a go myself.
My completed mod is shown in the image above.
Step 1: Tools & Materials
- A drill with 4mm & stepped drill bits.
- Files (round & flat)
- Dremel or similar with circular blade attachment.
- Soldering iron with solder, flux etc plus heat shrink tubing.
- Craft knife.
- Hollow punch set.
- Screwdrivers (posidrive & flat)
- 1/4"-20 Tap & Die (optional)
To start with you need a ZWO Optics camera, an uncooled version, pretty sure they all come with the standard M4 & 1/4" tripod mounts on the back but you'll need to check this.
I used my 224MC for this mod.
- 12vdc Fan for Intel sockets 1150, 1155, 1156 or 775. I chose: ARCTIC Alpine 11 Pro Rev.2 because of the anti-vibration & price.
- TEC1 - 12703 12v 3a Peltier Thermoelectric cooler 40mm x 40mm. These are available in many places.
Main control & power input box: PROJECT BOX ENCLOSURE 79 X 61 X 40MM
- Satellite power distribution box: Junction Box 60x36x25mm
- 2mm EPDM rubber sheet at least 100mm x 100mm square.
- 1/4" diameter solid copper rod at least 100mm in length (optional).
- 6mm neoprene sheet at least 200mm x 200mm square including neoprene adhesive.
- 7 core cable 5a rating as this
- Cable strain relief boots.
- Various length M4 nylon bolts with matching washers, nuts plus some butterfly nuts to match.
- Thermal transfer compound suitable for aluminium use.
- Laser cut aluminium parts as per attached drawings, all from 2mm aluminium. 2 x GASKET TEMPLATE will need to be cut.
- 1 x 40mm x 40mm x 6mm block of aluminium
You can see that there are 2 CAMERA BACK drawing files, one is with the center 1/4" tripod mount cutout & one without, which route you take is up to you.
Step 2: The Metalwork
After receiving the laser cut aluminium parts, they will all need to be de-burred to remove the rough edges.
You could alternatively have the parts water jet cut as I believe this gives a better finish and de-burring would not be needed.
Step 3: Making the Gasket
- Laying one of the GASKET TEMPLATE pieces on to the EPDM rubber sheet, carefully mark out the positions of the four M4 securing holes as well as the larger temp sensor mounting hole.
- Remove the template piece from the EPDM sheet & using suitable hollow punches cut out these marked holes.
- Line up both GASKET TEMPLATE pieces with these holes either side of the EPDM sheet & secure with some of the M4 nylon bolts, sandwiching the EPDM firmly between.
- Using a sharp craft knife, carefully cut away all access EPDM from the GASKET TEMPLATE pieces including the central square cutout.
- Remove the nylon clamping bolts to reveal an EPDM gasket.
Step 4: Camera Back
Through trial and error I found that I could aid cooling further by utilizing the 1/4" tripod mounting hole in the center of the camera.
Doing this gets the cooling finger around 5mm closer to the imaging sensor and directly behind it.
This step is optional, this is why I have included two CAMERA BACK drawings, one with the central hole & one without.
- File a slight taper on the end of the copper rod to ease the cutting of the thread.
- Using a 1/4"-20 UNC Die, cut a thread on the copper rod as per a normal thread cutting procedure. Cut a little more thread than is needed, (around 5mm actually required), as it makes it easier to handle.
- Using a 1/4"-20 UNC Tap, cut a thread in the central hole of the CAMERA BACK piece, this wont take much, possibly only two turns at most.
- Test fit the threaded copper rod in the tapped hole, it should screw in easily and be perpendicular to the CAMERA BACK face.
- Carefully test fit the threaded rod in the tripod mounting hole of the actual camera, again this should screw in easily without damaging or putting strain on the camera casing.
- Now secure the CAMERA BACK piece to the camera using just two M4 nylon bolts inserted in the outer tripod fixings of the camera.
- Screw the threaded copper rod through the CAMERA BACK piece and in to the actual camera's central tripod mounting hole. Do this carefully, do not over-tighten and stop as soon as you feel it tighten.
- Carefully mark and cut off the protruding excess copper rod with a hacksaw. If you scuff up the surface of the CAMERA BACK piece as I did, don't worry too much as steel wool & metal polish remove a lot of the scratches and the thermal compound takes up the slack.
- More than likely the threaded copper grub screw you have now made will be slightly proud of the CAMERA BACK piece and difficult to tighten, again, using a hacksaw cut a slot in the top to allow the use of a flat screwdriver, not too deep mind, just enough.
- Use a file to get this newly made copper grub screw to sit flush with the external face of the CAMERA BACK.
- Like I said earlier, use steel wool and metal polish to remove the worst of any scratches made to the CAMERA BACK piece during this process.
Step 5: Main Structure
- Lay the CAMERA BACK on the camera's rear face and insert the copper grub screw through and in to the central tripod mounting hole of the camera, if using this method.
- Lay the EPDM gasket on, carefully aligning the holes with the CAMERA BACK piece.
- Place the MAIN aluminium piece over this aligning the four M4 securing holes with the EPDM gasket & CAMERA BACK making sure that the camera's USB port is at 6 O'Clock and the rectangular section of the MAIN aluminium piece is 90 degrees to this. Mine is to the right hand side.
- Secure together using M4 nylon bolts cut to the correct length for a nice snug fit.
- Place a nice blob of thermal compound over the copper grub screw, if used.
- Smear a thin even layer of compound on the 6mm x 40mm x 40mm block of aluminium and squeeze in to the square cut out of the gasket compound side down.
- According to the dimensions for the cooling fan I used there should have been only 4mm between the mounting surface and the underside of it's heatsink, so given that there is now 2mm of the aluminium block protruding above the surface of the MAIN aluminium piece and that the TEC1 is 4mm thick, I thought this would be enough but I found that it still was not a secure enough fit and I overcame this by shaving down the feet on the fan's mounting cradle, see images, you'll need to check this on whichever fan you use.
- Fit the fan's mounting cradle to the MAIN piece, securing with nylon bolts, washers and using butterfly nuts on all bolts except the one located inline with the camera's USB port. This just eases removal at any time and the one inline with the USB port does not have room for a butterfly nut.
- Figure out which side is the cold side of the TEC1 by very quickly connecting it to a AA battery, placing the TEC1 between your lips which are far more sensitive will help but be quick, it is easy to destroy the TEC1 by running it without a cooling heatsink.
- Smear a thin even layer of compound on both sides of the TEC1 and place on to the protruding aluminium block cold side down facing the camera.
- Now place the fan and heatsink on the top of this and secure the assembly to it's mounting cradle.
Step 6: Wiring & Control
- Using a Dremel with the circular blade attachment cut out a section in the lid of the Main Control & Power Input enclosure and mount the Thermostat Temp Control unit.
- Use a step drill to cutout holes in the enclosure for the DC jack input socket, the 7 core cable outlet (allowing for strain relief) and if fitted, the fuse holder.
- If using a fuse, solder the +ve in from the center pin of the DC jack socket to the fuse holder.
- On the fuse outlet side solder 2 wires, 1 will be a direct +ve feed to the fan & the other is the +ve feed to connection 1, the +ve in of the Thermostat Temp Control Unit, see next step.
- The Thermostat Temp Control unit should come with markings showing where to make +ve & -ve connections but in case it doesn't, refer to image 2 where block connectors four connections from 1 on the left to 4 on the right are as follows:
- +ve in, main supply to control unit
- -ve in and also common -ve feed via 7 core cable to the Satellite Power Distribution (S.P.D) box
- +ve in link cable from pin 1 for relay
- +ve out, feed via 7 core cable to Peltier +ve (yellow wire in my image)
A common -ve to the fan -ve & TEC1 -ve
A +ve to the fan
A +ve to the TEC1
Two connections to the temp sensor
Step 7: Insulating
This might sound strange to add an insulating layer to the camera as we are trying to cool it but before doing this I did read many articles of similar projects where cooling was hindered by the dew formation on the camera and that by suppressing this dew formation further cooling could be achieved without needing more energy to do it.
Very simply make a snug fitting insulating jacket for your camera from 6mm neoprene and slide on.
Step 8: Testing
Prior to use you will need to know how the Thermostat Temp Control unit is setup & functions and unfortunately the unit itself does not come with any instructions whatsoever but thanks to Buddy Moore for creating a set of instructions that I will include here. (see PDF Download below)
The video I have posted here shows a timelapse of the cooler working without the camera powered on, so no image sensor heat at all.
It shows the starting ambient temp via the temp sensor against the external casing of the camera as 23.8°C.
The timelapse covers almost exactly 45min of realtime before the temp bottomed out at 0.7°C and dropped no more.
At this point I then attached the camera's USB cable and connected it to my laptop running SharpCap Pro 3 where the internal temp of the camera is shown as -0.5°C
After 1min and still connected to SharpCap the external temp read 1.5°C while the internal was showing as 3.8°C
Step 9: In Action
Just a few images showing the setup in situ on my Celestron CPC9.25 scope.
Excuse the noise on the video, it's my dSLR's noisy lens autofocus.
Step 10: Results
Here are some resulting dark frames taken as 10 x 10min subs through SharpCap Pro 3.
Image 1 is without any cooling and max temp was 29.7°C
Image 2 is a 4x zoom in of image 1.
Image 3 is with cooling and max temp was 7.3°C
Image 4 is a 4x zoom in of image 3.
You can see that the noise is vastly reduced.