Peltier experiments.

[ZeroID]

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 ! :D ).
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 :shrug:

[Garbz]

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?

[julianh72]

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 :thumbsup:), 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.

[ZeroID]

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.

[julianh72]

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.

[ZeroID]

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 ?

[Garbz]

Oh it does, just in this case the pump is SCIENCE :D 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

[julianh72]

Peltier Thermo-Electric Effect, Heat Pipes...

I think they're just fancy words for Black Magic!

[Garbz]

Isn't all sufficiently advanced science? :D

[julianh72]

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

[ZeroID]

Aha ! hidden away hey ? FIT or TIF will do. Thanks.

[nebulosity.]

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

[ZeroID]

Two ?? !! Probably couldn't afford the power bill :lol:

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 :thumbsup:

[ZeroID]

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.

[julianh72]

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! :thumbsup: ) 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.

[ZeroID]

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.

[julianh72]

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?_sacat=0&_from=R40&_nkw=peltier+tec&LH_PrefLoc=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?)

[julianh72]

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!

[ZeroID]

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 !! :fishing:

Might just buy a couple of TECs to play with. Two stage as you suggested earlier or side by side. More power needed !! :thumbsup:

[ZeroID]

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 !!

[ZeroID]

OK, I now have a modded KM 7D camera. Opened her up and removed the IR cut window from the sensor, got it back together and it worked first time. Everything is PINK !
I'll reduce all the pix I took and post up a 'How to' in case anyone else wants to try it. Generically speaking if you download the Service Manual for any modern camera so you know where to find all the tiny wee screws it is not all that hard to do. The real trick is the miniature ribbon cable connectors which can be a bit fiddly but they all seem to have some form of release mechanism so be patient and have a poke round.
Story to come later.

[PeterEde]

I have a 40D I'm considering modding
Shouldn't be too hard for an avionics tech

[julianh72]

Even though my CPU cooler came with a fan, I was hoping to get away with running it without a fan to avoid vibrations etc. However, even though I've been running the TEC at only 6 volts, I've noticed that sometimes the camera sensor temperature will stabilize at a Delta-T of about 12 degrees Celsius below ambient, but will sometimes then climb back again almost to ambient after a while, especially in warmer ambient air.

It looks like my CPU cooler without a fan can pump the heat from the TEC running at 6 volts effectively as a passive device (no fan), with ambient temperatures of up to about 24 Celsius or so, maintaining a Delta-T on the camera sensor of around 10 to 12 degrees. However, at a certain critical heat load and / or critical ambient temperature, the fan-less CPU cooler can no longer shift the heat without the cold side of the TEC warming up again.

Since we are quickly approaching summer in Brisbane, and evening temperatures can stay at 24 degrees or more, I need to do something to maintain effective cooling - so I thought I'd put the fan on and see what happens. The fan is rated at 12 volts, but since I'm running my TEC at only 6 volts, I thought I'd run the fan at 6 volts as well.

And the results?

Wow!

The fan runs more slowly than it does at 12 volts (no surprise there!), but importantly, it runs silently, and apparently free of vibrations (which is good!)

Secondly, the top radiator and copper heat pipes go from feeling warm-to-hot without a fan, to feeling quite cool to the touch - barely warmer than ambient -so the fan forcing is REALLY helping!

And with ambient temperature of 28 degrees, the camera temperature sensor dropped quickly from around 15 degrees (which was about the best I could do without a fan) down to just 2 degrees Celsius - and it stays there! That's a Delta-T of 24 degrees Celsius, compared to a (sometimes-unstable) 10 to 12 degrees that I was getting before!

I'll definitely be trying the fan-forced cooler outside next chance I get!

[ZeroID]

I can see a fan in my system happening real soon. The 6 volts to the fan is good idea, I already use 5v and 12v to the fans on the Newt.

[ZeroID]

Thanks for that Steve, had a quick read through to see what problems you ran into and any solutions. Looks like we've got a ways to go yet. The small size and construction of the ZWO makes it an easy candidate for a cooling mod. Haven't even considered control so far.

[julianh72]

Thanks for the links Steve - lots of reading there, and I'm a great believer in learning from the successes of others!

As ZeroID says - the ZWO cameras are an ideal candidate for this sort of hack - the aluminium body makes a great thermal interface between the sensor and the cold face of the TEC. Also, since they ship with an IR-cut filter (on the colour cameras, or clear glass on the monos), the sensor is inside an almost sealed enclosure, so I'm hoping there is very little risk of "frying" the electronics with unwanted moisture, but I'll put a silica desiccant pack inside anyway. I've had lots of dew dripping from my camera's body, but none on the sensor or IR-cut filter (so far).

The thing that got me onto this experimentation path is the drastic drop in price over the last year or so to acquire an entry-level astro-camera set-up. My total outlay so far:

. US$299 for the camera (ZWO ASI120MC) shipped to Brisbane, running off freeware software (once I finalize on a preferred software chain, I'll make a small donation to the developers of my preferred apps)
. AU$1.91 for the Peltier TEC (including postage)
. AU$29.00 for the GPU cooler

I already owned the 12 volt SLA battery that I'm using to power it, and everything else (cable connectors and cable ties, etc) came out of my "box of bits".

At those prices, I could easily afford to buy the camera, and even take a bit of a risk in tinkering with it.

[ZeroID]

Hmmm, forgot about the IR cut filter on the front. Must take note next time I'm using it. I'd like to keep the chip sealed and I haven't got a clear window for it. I can probably fit a CLS or 80A to the nosepiece as an option.

[Peter Ward]

You are not trying hard enough :)

Here's my twin-peltier + twin-turbo PGR mod

[julianh72]

I guess that's why you have the Ferrari prancing horse as your avatar!

[Peter Ward]

Err...not quite...picture of real reason attached ;)

[sharpiel]

Is that to reverse global warming?

[Poita]

What sort of temperature drop do you get with that setup? I've modded my PGR with passive cooling but have been considering a peltier/fan setup for solar imaging.

[ZeroID]

OK, clouds killed any viewing tonight but I ran up the Peltier with a fan both on 5v on the end of the Lunt. Got down to a reasonably stable 1.2*, ambient was 15*. I did experience some fluctuations up to 3.5* and down to .2*. Not sure why this happens
Camera was in double neoprene sleeve, you can only just feel the cold through that. Radiator array was hardly even warm.
But I will need to add some silica or similar, definitely some fine dew on the window. But there isn't much room down there for even the small packets I thought would fit. I'll give this some thought.

Was hoping to have a go at Siding Springs comet but there was high thin cloud to start with and then it got worse. :shrug:

Here's a few pix of my setup. Please ignore the crude temporary ( honestly !! ) wiring.

[Peter Ward]

Unaided, my camera will typically warm up to 60 degrees C . With the coolers active the internal temp drops to around 20-24 C.

[julianh72]

I spoke to soon!

Brisbane's summer humidity has really kicked in over the last few nights, and I've had massive amounts of condensation on the IR filter the last few days (but none on the sensor itself, as far as I can see).

Looks like I'll be running un-cooled, until I can get a dew-heater mod added to the front of the camera.

Oh well - I always need something to do on those all-too-frequent cloudy nights!

[ZeroID]

Plenty of 'Cloudy Nights' over here at present. Peltier experiments on hold at present while I get my guiding and control sorted. Added another PC and reduced cabling to pier but haven't had a chance to test the system live yet.
Once that is sorted I'll get back to the Peltier experiments and try and source a cheap Canon DSLR or similar to have another go at IR modding.
If I can find a way to manage dew in the ZWO ASI120 I will remove the IR cut filter on that and see how it works. Might order a clear glass window for it. ..... hmmm, that has just given me another idea.

[ZeroID]

Getting back on track finally, except for clouds of course !!

Got the Toucam working through the 80mm f5 for guiding using Metaguide and GPUSB on the laptop.
Added my beam splitter from an earlier project into the optical chain which gives me a 12mm reticule EP at the same time. :thumbsup:

Then got FireCapture working to the ASI120 from the desktop for imaging via the LUNT which meant I could put it back together with the TEC and fan\radiator. So I cannibalised the 5v\12v switching box from the Newt, mounted that to the pier and wired it separately to the TEC element and the fan so I can also switch those individually. It's all plug'n'play now. :P

Then to tidy up and minimise any interference possibilities I rerouted all power cabling to the east side of the pier and imaging cables (2) to the west. The only signalling cable to the west side is the ST4 guiding. The AC line goes to the scope heater, and the rest are DC anyway.

I can switch cameras between scopes easily target dependent and I can mount the SONY DSLR to any as well.

Just wish I could manage the weather as easily ..:shrug: :D

[ZeroID]

Weather is still #@%*##!!! so I'm still fiddling. Managed some sky time on Monday night for a bit of testing through cloud gaps.
Discovered I'd put the TEC element in backwards (DOH!!) so it was warming the camera. Scratch that test for the evening.

Ran some longer exposures in avi on 47Tuc, 8 secs per frame. Gave me some video to stack which was interesting despite the poor seeing. But camera definitely needs the Peltier going as noise really gets obvious otherwise. TEC is now fixed.

The Beam splitter idea introduces too much aberation and reduces light to the guider so that is now gone. 45* Diag in place instead to get focal length correct and the Toucam is so light I don't see any flexure issues. All cables are supported at the mount head and top mounting plate so very little strain on the optical train.

Weather is looking hopeful for later this week although the moon is not !

[ZeroID]

Weather is brilliant today so tried some solar imaging. haven't processed it yet but also tested the Peltier and AS!120 combo.
Ambient was 16.2* about 10 am, at 5v to TEC and fan I got to 8.8* within 10 mins and it held there. So switched to 12v and within 15 mins I was at 2* and still sinking. About 20 mins later I had -4* and ice film forming on the sensor (I'd taken the IR filter out ). By this time ambient was at 20* so 24* delta no problem. Ice\Dew is now the problem !!
How the heck do you manage that ?
How do the professional Astro cameras manage it ?
I've fitted the IR window back on to seal the sensor off but I may have to give the camera a gentle warm up to dry it right out and reseal it. Then the problem becomes how to keep dew\ice off the window ?
I'm contemplating using a wee tube to blow a fraction of the warmed air from the fan on the heat sink onto the window. Possibly a light draft might just keep it clear.

Hopefully the weather will hold this evening and I'll have a go with guiding and the DSLR with a CLS filter in front.

Better go and process some solar for now, if it's any good I'll post something up of the big sunspot currently visible.

[Peter Ward]

Just like a cold can of XXXX on a warm summer's day, too high a delta-T will always cause condensation (and eventually icing).

Pro cameras, such as SBIG, have sealed chambers with desiccating plugs, plus the chamber window is heated.

Further, the CCD chamber temperature is stabilised to 1/100th of a degree to allow accurate dark frame calibration.

Sure, lowering the camera temperature helps....but there are limits on unsealed systems.

[Bassnut]

Youve just hit the brick wall I did :P. Ittl be interesting to see how you get round that little problem :thumbsup:.

[ZeroID]

You're no bl00dy help at all ... :lol: ..

Working on it.
Several ideas of creating a dry gas purged chamber in front with a clear optical window and using a smidgin of the warmed air off the radiator to blow across the external surface of the window to keep it from icing up.
Some silica in there might also help. The new setup has more room internally so I can hopefully fit a small bag or two inside.

I've also reduced the parasitic thermal loss with some insulation and reduced surface contact area at the junction of focusser and camera. The window will be ahead of that so it can be managed thermally seperate.
Fingers crossed .. ;)

What do the commercial cooled cameras do to manage it ?

[ZeroID]

Ooops, didn't see this first.
Thanks Peter. I think I can duplicate the sealed chamber and plug idea. I have enough hardware, now all I need is a 1.25" clear glass filter for the front window.
Heating... maybe airflow or maybe a resistive collar.

Here's a pic of the proposed setup. It's an unusual 2" adapter I acquired somewhere with a tapered collar, thus reduced contact surface. Insulators will go on the flat surface and I could wrap a resistive heater around the barrel and filter assembly (Couple of 1.25" EP extenders with a temporary yellow filter on front) that protudes forward of it into the focusser tube.
Or the warm air idea of course.
I may drill and tap another hole into the side of the adapter opposite the lock screw for a silica plug to screw into.

(Can you tell I'm having a quiet day at work ... ;) )

[ZeroID]

OK, scrap the above configuration. Not enough internal space to get silica inside and there are some mechanical problems internally. I have a new idea that looks quite easy to implement and is mostly reversible should it not be as successful as I'm hoping. Details on that later.

But, heating the window is the next problem to be solved. In a simlar setup to the above, ie the window being forward of the adapter how much heat is required to maintain a temp sufficient to keep it from frosting up ? Pretty sure I can build a resistive ring that will give values in the half to quarter watt region but is this sufficient ?

I'm pushing the window out ahead of the camera to reduce thermal transfer back to the sensor etc. I could push the window back inside the adapter and use an airflow but that might introduce more moisture.

[ZeroID]

OK, here it is. A lucky combination of available parts.

First pic shows it in pieces. A 2" collar I had off an old focuser, the 1.25" ASI nosepiece with an extension on it and a 1.25" to 2" adapter. The collar perfectly fits the outer shoulder on the ASI 120. I will drill 4 x 5-6 mm holes in the nosepiece to open it to the silica.
Second pic, partially assembled with 3 silica gel packs inserted. The holes will expose the chamber to their effect.
Third Pic, the adapter seals off the silica collar and slides into the OTA focuser.

Now all I have to do is design a heater unit to wrap around the front filter glass and replace the yellow filter currently standing in with a clear glass unit. I'll also modify my neoprene outer cover to include the silica collar. Contact through that region is actually quite small, corner to edge so parasitic thermal loss should be manageable.

Looks quite cool too, just like a real one. :thumbsup:

[ZeroID]

And complete with TEC, radiator and fan system mounted, neoprene sleeved and yes, the holes are drilled in the nosepiece ... and I've blackened the edges. I've even sandwiched the neoprene between the adapter and the collar as extra insulation to minimise heat loss to the OTA. Only conduction path is up the thin walled nosepiece.

Window Heater is the last item to work on. I'm using a 2" extender on the scope to enable focus and it has a slotted top collar so I may be able to use that to get wiring inside to the heater.

The question now is how many clouds do you think this will bring on ? :question:

[ZeroID]

And success ! :thumbsup:
Small piece of rubber tubing slotted into the radiator fins and directed at the front window through the slot in the 2" extender body.
Ambient temp at start was 22.2*. I got down to -1.8 at 47 mins and 12 volts. ( after 20 mins at 5 volts to see how it went ). Held temperature for an hour and 40 and no icing up or dew internally or on the front window and a clean good image of the houses on the ridge 5 km away.

Interestingly when I finally powered off the temp was back up to 11* within 4 minutes which just shows just how much heat transfer is going on. I'll improve on some of the insulation layers as well to minimise that.

I just need the clear filter window, some fresh dry silica bags and we're ready to have a go at some DSO imaging. If I can't get a clear glass window I'll grab a UV\IR filter instead. If I can get a 24* delta on a 10* night I'll be more than pleased but I reckon there is a bit more in it yet.

Here's a picture of it up on the scope.