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Old 14-09-2014, 07:28 PM
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Peltier experiments.

Y'all know I am the DIY fanatic, why buy it when you can make it.
Picked up a 40mm square 50 watt peltier module, $8:50 ( I'm also cheap ! ).
Idea was to cool the AS120mc down a bit for longer exposures. Managed to sandwich the module between the camera and a big CPU heatsink. I hacked all the bulky heavy metal off just leaving the thermo pipes and the fin array to keep it all lightweight. The Peltier was in direct contact with the copper base plate and a lot of silicon paste. Tested on the bench with 5 volts and it was all working so loaded it onto the Lunt and powered up the laptop so I could connect and read the chip temperature. The camera was in a neoprene sleeve to insulate it.

At 5 volts it took about 30 mins to cool the camera down by about 8* below ambient (17* at the time). The fins were definitely warm but quite within limits. Ran some 30 sec dark exposures ( raining outside ) to look at noise. Seemed to be taking a long time to lower the temp and then I figured out that via conduction it was attempting to lower the temp of the whole focusser assembly through the 2" to 1.25" adapter. So first mod to work on is to isolate them with a plastic sleeve or and plastic adapter maybe.

Upped the voltage to 12v and the camera rapidly shot down to almost zero with quite a bit more heat coming off the fin array so plenty more oomph left in the system yet. I called it quits after about 10 minutes because I was concerned that the heat load from the scope would be too much to protect the peltier.

So next step is to isolate the camera from the scope conductively and although the neoprene sleeve for outer insulation seemed quite efficient I'd improve on that as well.
I got condensation on the camera window, not sure if it was inside or outside ( very damp rainy day ) but I need to address that as well.

I believe that with a little more work I can get delta of at least 25* or better below ambient. Note that todays experiment was without forced cooling by fans or coolant and even at 12 volts I could still place my hands on the fin array and the copper tubes near the base plate were hot but not unbearably so.

Anyway here's a pic of the setup. Note there is very little weight in that array of fins.

Only thing I forgot to do was to upload the darks off the laptop to take a look at the noise ... oh well, tomorrow will do
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Old 15-09-2014, 07:51 AM
Garbz (Chris)
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Very nice. How does this perform from a noise point of view? Can you post before and after stretched images or find a program to do some math and give you some RMS noise figures?

Also any concerns about condensation inside the camera?
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Old 15-09-2014, 10:31 AM
julianh72 (Julian)
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Note that todays experiment was without forced cooling by fans or coolant and even at 12 volts I could still place my hands on the fin array and the copper tubes near the base plate were hot but not unbearably so.
How good is a water-cooled CPU cooler module without fluid coolant? I would have thought that the heat path being restricted to just 4 copper tubes might really cut its passive heat exchange capabilities?

I've ordered a similar 12V / 60W TEC for my ASI120MC (mine was only $1.91 from eBay China - including postage ), and a more conventional flat "passive" heat-sink with protruding "pins" (see attached photo) - I'm hoping that the good head conduction from the hot side of the TEC straight to the heat-sink pins will allow good heat exchange to achieve satisfactory cooling without needing any fan to shed the heat load.

I'm going to wrap my camera in a cut-off stubby cooler (as you have done) to provide insulation, and I was thinking I might need to use a silica sachet to control dewing on the IR-cut filter - maybe even two, one inside and one outside the IR-cut?

I hadn't really thought about the issue of the TEC trying to cool the whole focuser assembly by conduction - I guess I'll just have to wait and see what transpires!

The datasheet for my TEC suggests I should be able to reach a Delta-T of about 40 deg C at 6 volts, or close to 70 deg C at 12 volts. Assuming the heat sink can keep the hot side to around 40 to 50 deg C, I should be able to get down to at least 20 deg C below ambient without too much trouble, meaning 0 deg C (or maybe single-digit negatives?) at the sensor. (I'm in Brisbane - it's a rare night that ambient temperatures are in the single digits!)

I might need a bigger battery if I want to run as 12 volts, though - it will pull about 5 amps at 12 volts, so my 7.2 A.hr battery will be exhausted in less than an hour. I'm hoping performance is satisfactory at 6 volts, which should mean I can run both the TEC and the scope for several hours. If I need to run at 12 volts to get adequate cooling, I guess I'll buy one of those car jump-starter packs - so much for this being a cheap hack!

More to follow when the bits arrive, and I can get it set up.
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Old 15-09-2014, 02:40 PM
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Chris,
Condensation was on the camera IR window, not sure if it was internal or external but I'll check tonight. A dessicant program may be needed to prevent future ocurrences. It's on the 'To Do' list.
I'll try to grab the darks tonight and take a look. This was more of a 'does it work' test rather than a quantitative experiment.

Julian,
The fin array has 6 thermotubes and they certainly seemed to be doing the job OK. At least I will be able to warm my hands on a cold night. They work on an internal evaporative\condensation cyle with a wicked coolant inside. I may point a fan at them if required from the floor to assist but I'd rather not introduce any vibration at the scope.

I have a different adapter to try with a much smaller volume of metal in the build but I may chuck it up on the lathe and turn out the internals by a few mm and add a plastic sleeve to reduce the conduction effect. The screw can work through the plastic ok.

6 volts will not make a big difference to temp reduction I suspect. 5 v only got me 8* although if I fix the conduction issue it might do better. 12 v was pulling about 4.5 amps so you are going to need some more power capacity. I'm lucky, I have 240 vac to the OB so it is just a power supply connection.

Winter I can get single digit ambient nights but most of the year is double digit.
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Old 15-09-2014, 05:29 PM
julianh72 (Julian)
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6 volts will not make a big difference to temp reduction I suspect. 5 v only got me 8* although if I fix the conduction issue it might do better. 12 v was pulling about 4.5 amps so you are going to need some more power capacity. I'm lucky, I have 240 vac to the OB so it is just a power supply connection.
Thanks for the explanation on the heat-sink set-up - I assumed that your heat sink needed a circulating (pumped) fluid flow in order to be able to shift the heat load from the hot face to the fins.

I suspect the operating voltage WILL make a big difference on the lowest temperature I can reach at the sensor, but I'm hoping that 6 volts will get it "low enough", especially with a bit of insulation etc.

At 6 volts, my TEC can supposedly pump "up to" about 30 watts of thermal load at ambient temperature, before ultimately reaching a Delta-T of "up to" 40 deg C.

At 12 volts, it should be able to shift about 55 watts of thermal load at ambient temperature, before reaching an ultimate Delta-T of "up to" 70 deg C.

The time to reach thermal equilibrium will depend on how many amps you push through the TEC (more volts = more amps), and how good the thermal insulation is. In a perfect world, you only want to cool the sensor, but with this set-up, you have to cool the whole camera body, and deal with the "parasitic" heat load as well.

What temperature I actually see at the sensor will depend not only on how many volts / amps I am running, but it will also depend on my thermal efficiency (e.g. conductivity between interfaces, and "parasitic" thermal load, such as trying to cool the whole focuser assembly), and especially, the ability of the heat sink to keep the hot side of the TEC down to no more than about 50 deg C, say.
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Old 15-09-2014, 06:55 PM
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As I said, I don't think 6 volts will get you far enough. Isolating the camera will help and reduce the parasitic (nice description) thermal load but delta 40 at 6 volts, I doubt it. At best maybe 20.
I'll be happy to get 25 -30 drop. A quick look at the darks from yesterday show a marked drop in hot pixels but I can't view the longer exposures as it errors Windows Media.

So on that subject. The AS120mc takes avi video. There must be an option to capture in another raw or similar format but I can't find anything in FireCapture. Is there something else I should be using for long exposure DSO imaging ?
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Old 15-09-2014, 08:53 PM
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I assumed that your heat sink needed a circulating (pumped) fluid flow in order to be able to shift the heat load from the hot face to the fins.
Oh it does, just in this case the pump is SCIENCE Fascinating stuff heat-pipes, it really is a mash together of many physics principles. An airconditioning unit without any moving parts. http://en.wikipedia.org/wiki/Heat_pipe
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Old 15-09-2014, 09:33 PM
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Oh it does, just in this case the pump is SCIENCE Fascinating stuff heat-pipes, it really is a mash together of many physics principles. An airconditioning unit without any moving parts. http://en.wikipedia.org/wiki/Heat_pipe
Peltier Thermo-Electric Effect, Heat Pipes...

I think they're just fancy words for Black Magic!
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Old 16-09-2014, 07:15 AM
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Isn't all sufficiently advanced science?
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Old 16-09-2014, 09:09 AM
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The AS120mc takes avi video. There must be an option to capture in another raw or similar format but I can't find anything in FireCapture. Is there something else I should be using for long exposure DSO imaging ?
I'm still just coming to grips with my camera, so I haven't played with all the options and settings yet, but in the "Capture" panel of FireCapture, there is an option for "Type", which has the following capture options:
AVI, SER, BMP, FIT, TIF
I think you need to enable "16-bit" first in the "Camera" panel to get TIF as an option.

Check out the FireCapture "Help" pages here: http://firecapture.wonderplanets.de/help/index.html
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Old 16-09-2014, 09:24 AM
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Aha ! hidden away hey ? FIT or TIF will do. Thanks.
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Old 16-09-2014, 09:33 AM
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Cool stuff, I'll be interested to see what you can come up with.

Have you thought about stacking two TEC's together? I found it worked well when trying to get lower temps with passive cooling.

Jo
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Old 16-09-2014, 02:02 PM
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Two ?? !! Probably couldn't afford the power bill

One step at a time. If I can get the temp I want for minimal effort then I'll be happy. Working on the KISS principle
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Old 17-09-2014, 09:19 AM
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A few pix of my Peltier setup and update on changes.
Switched to a low mass adapter, less metal and contact. I may need to add an extender to the nosepiece that will also reduce the parasitic heat loss. I may also add some neoprene around the lower focusser area so to reduce any losses there as well. A plastic internal sleeve would be the next step if required.

Double layer neoprene insulation which also covers more of the front of the camera. There is now about 10mm of it and being in contact with the body should stop moisture condensation on the outside.

Took the opportunity to thoroughly clean all the dust from the ZWO internals and I've got some Silica capsules to add to manage the dew problem.

The two knurled knobs hold the array and TEC against the camera with a strap of hi temp plastic so hot & cold areas are isolated from each other. I will put a sleeve over the knobs (they do get cold) although they only have a small threaded connection but every little bit helps.
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Old 01-10-2014, 10:56 AM
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I was hoping to use my TEC with a conventional "passive" aluminium heat-sink with protruding "pins". I was hoping that with good heat conduction from the hot side of the TEC straight to the heat-sink, this would allow sufficient heat exchange to achieve satisfactory cooling without needing a fan to shed the heat load. However, early trials with a heat-sink and the TEC running at only 6 volts showed this wasn't going to work - the heat-sink got VERY hot to touch (maybe 70 to 80 degrees Celsius, at a guess?), and the camera sensor on the cold side of the TEC only registered a temperature drop of a couple of degrees C below ambient. Clearly, I need something with a LOT more heat-moving capability to get the heat away from the hot side of the TEC.

So I found myself a cheap CPU cooler with “Heat Pipes”. (Thanks for the idea, ZeroID! ) This unit comes with a fan, but I thought I’d have a go at installing it as a passive device first, and fit the fan only if I need to.

So I disassembled the fan from the CPU Cooler, and mounted it and the TEC onto the back of the camera body, using silicone thermal pads to get a decent conductivity path between the elements. (I’ll probably use more efficient thermal grease for the final assembly, but the silicone pads are nice and clean for trial assembly / disassembly / modification.) Then I wrapped the camera body in a cut-off stubby cooler to provide insulation to minimise the amount of stray heat leaking into the camera body.

I hooked the camera up to my laptop, and used FireCapture to read the image signal and sensor temperature. I set the exposure to 30 seconds, with Gain pushed right up to 90%, to generate as much image “noise” as possible. (I probably wouldn't use these settings for actual image capture, but I wanted to see how much image noise this sensor-cooling set-up can suppress.)

FireCapture reported the sensor temperature was about 28 Celsius (this is indoors in Brisbane on a spring evening, remember!)

I then hooked the TEC up to a 6 volt SLA battery running through a multimeter to measure the amps. The meter showed the TEC was pulling about 1.5 amps initially, but straight away, the sensor temperature started to drop, and as it fell, the amperage also dropped off a little bit as well.

The bank of cooling fins on the top of the device were getting warm to touch, but not hot - I would guess around 30 to 35 degrees Celsius or so. The finned block of aluminium at the base of the heat pipes, which is in contact with the hot side of the TEC was even warmer, but not burning hot to touch - I would guess about 50 degrees or so. The camera body that I could feel at the bottom end of the insulation "skin" was getting very cold to the touch (but not freezing cold). After about 5 minutes, the sensor had stabilised at about 14 degrees Celsius, and the meter was showing about 1.3 amps.

Not bad - I had achieved a Delta-T of around 12 to 14 degrees Celsius on my first attempt!

But does it work?

Yes!

I have attached a sample "dark frame" showing the image noise with the sensor at ambient of about 26 degrees Celsius, with a 30-second exposure with 90% Gain, and a second shot showing the image noise when the sensor had dropped to around 14 degrees Celsius (using the same 30-second exposure / 90% Gain). The noise level is certainly much better - toggle back and forth between the two images to see the difference more clearly.

Both images are straight off the camera as captured in FireCapture, with no “Dark Frame” suppression, and no post-processing of any kind.
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Click for full-size image (Testing Peltier TEC on ZWO ASI120MC.jpg)
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Old 01-10-2014, 12:39 PM
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Excellent !!! Confirms my results and for the price (cheap as chips) is a worthwhile modification. I got down near zero but my ambient was quite a bit lower.
Haven't had a chance to go further as had to refix the Ob roof again after some 100 kph winds 'dislodged' it ( into the neighbours garden) again. And Weather hasn't been helpful either.
I am also now looking at attacking my poor old KM 7D DSLR ( no longer used ) with an IR cut mod and a cold finger. It suffers from some corner amp glow so I haven't used it much but as it has almost no value sales wise being only a 6 meg sensor I can afford to experiment on it. Downloaded the Service Manual so I can figure a way in. I'll document the process in case it helps anyone else. From the photos in the Manual I may be able to mount a big cold plate across the back on the alum frame. Looks like I might need another TEC soon.
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Old 01-10-2014, 01:05 PM
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Looks like I might need another TEC soon.
They're ridiculously cheap if you don't need one "right now" - just shop from Chinese suppliers on eBay. To get the best prices, make sure you set your "Item Location" to "Worldwide", not just "Default" or "Australia only":
http://www.ebay.com.au/sch/i.html?_s...fLoc=2&_sop=15

E.g. my TEC1-12706 cost just AU$1.91 (including postage), and was delivered in Brisbane within about 10 days of placing an order.

If you want something with some SERIOUS cooling power, you could go for a TEC1-12730 for just over $30, which can pull 30 amps at 15 volts (if your power supply can manage it!), with a Qmax of 250 watts! (It's probably over-kill for the ZWO ASI cameras, but something with a lot of grunt might be an option for a DSLR body, either by fixing to the back of the camera if you don't want to totally disassemble it, or put the whole camera body in a cold box?)
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Old 01-10-2014, 10:08 PM
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I've just done a follow-up run, connecting my TEC to 12 volts to see what happens - still running as a passive device, with no fan, and testing conducted indoors with ambient temperature of about 24 Celsius.

As expected, the ammeter shows a lot more current (about 3 amps at 12 volts, compared to 1.5 amps or so at 6 volts). Also as expected, the camera sensor reports that the temperature dropped faster than when I was powering the TEC at 6 volts, and it got about 2 degrees Celsius lower than I could get at 6 volts. This time, the big top radiator got quite hot to touch (maybe 70 degrees Celsius or so), there being a lot more heat to shift than at 6 volts.

But then, the camera sensor temperature started to climb almost as quickly as it was initially dropping, so I unhooked the battery, let everything stabilize again, and tried again - with the same result: initial rapid cooling, a short period of "thermal equilibrium" a couple of degrees cooler than I get at 6 volts, followed by temperature rise at the sensor.

Here's what I suspect is happening:

As long as the top radiator stays cool enough to re-condense the fluid in the Heat Tubes, it can pump heat away from the hot side of the TEC, and everything works nicely. However, if the top radiator gets too hot to allow the fluid to condense effectively, the Heat Tubes lose their ability to pump the heat efficiently, and the whole CPU Cooler assembly gets quite hot, and the TEC starts to heat up, including the cold side.

If I then shift back to a 6 volt supply to the TEC, it stabilizes for a few minutes while the top radiator cools down again, and then the sensor temperature drops again.

It looks like my rig can pump the heat from the TEC running at 6 volts effectively as a passive device (no fan) with ambient temperatures of up to 24 Celsius or so (maybe even a bit more?). However, the heat load from the TEC running at 12 volts exceeds the radiator's capabilities in still air (no fan) at around 24 degree Celsius; I suspect it would work fine with the supplied fan fitted, and it MIGHT even work as a passive (fan-less) device for ambient temperatures of somewhat less than 24 Celsius. (Your critical temperature could be different, depending on the passive capacity of your cooler, the heat load of your TEC, the thermal efficiency of your insulation and interfaces, and so on.)

Since I'm getting a reasonable Delta-T at the camera sensor with the TEC running at 6 volts without a fan (with a corresponding reduction in image noise), I'll probably run my cooler at 6 volts with no fan, at least for my first few imaging sessions, before I experiment with other voltages, with and without a fan.

Anyway, enough with the desk-top tests already - it's time to take this baby outside and get some REAL pictures!
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Old 02-10-2014, 07:55 AM
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Thats about what I experienced in first tests at 12 volts. Others have gone to lquid cooling to control this. Although I think forced air will help I think you'd need a bigger radiator surface to make a big difference.
I have several power supply options so trials at 9v or so might be an idea. And I have yet to give it another go with the camera body more isolated from the focusser assembly ( the parasitic load ) to see how low I can get.
I have several more of those arrays, I may chop one to see if I can feed water through the pipes with a wee aquarium pump I've got hanging around. I could always pipe it from the outside fish pond as a heat dump, the fish would love it !!

Might just buy a couple of TECs to play with. Two stage as you suggested earlier or side by side. More power needed !!
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Old 03-10-2014, 08:55 AM
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Just an update re the moisture problem mentioned earlier. Some of the gear we get at work comes packed with small sachets of Silca gel, about the size of the salt and pepper sachets in cafes.
I reckon I can get 1 or 2 of those inside the ZWO body and I have enough to have spares. Just give them a zap in the oven for a few hours to dry them out, store in a sealed jar.
See how that works... go away clouds !!
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