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  #1  
Old 28-12-2018, 11:29 AM
glend (Glen)
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Hot Night Imaging Techniques

Hot night's are terrible for imaging even with cooled cameras, as TECs struggle to achieve their Delta Ts due to lack of cooler air to remove heat from the heat sink. In the past i have tried to boost the rather pathetic capacity of my ASI1600 fan, by aiming a CPU fan into the intake of the camera fan. This airflow boosting does often seem to help cool the camera case, which can build up retained heat, and allows the TEC heatsink fan to pull down a little better.
I know, from my cold finger DSLR build days, that the size of the heat sink, and it's composition (such as a copper heat pipe type heat sink) achieves better extraction than stock aluminium types.
Two stage TECs might be an option (if your camera is out of warranty) but without an airflow boost, or superior extraction composites, does it achieve much?

So my question to the thermodynamic experts (maybe Rowland) is, assuming a hot night, does the increased volume of air passing over a given sized heatsink, or the case it is attached to, really improve performance or is it a plaicbo effect?

Last edited by glend; 28-12-2018 at 12:03 PM.
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  #2  
Old 28-12-2018, 12:01 PM
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Marke (Mark)
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What temp are you running it at Glen my 1600 has no problem at -15 even on hot nights in winter I go to -20
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  #3  
Old 28-12-2018, 12:11 PM
glend (Glen)
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Quote:
Originally Posted by Marke View Post
What temp are you running it at Glen my 1600 has no problem at -15 even on hot nights in winter I go to -20
Typically I run at -20 or -25C. On a hot night where the ambient is 25C or more, the camera cannot pull down to -20C, but yes if your willing to drop back to -10 or -15c then it is doable but you get case heating as well, indicating the the fan is undersized for heat extraction and thus the fan is bogged in trying to shed heat of both the TEC and that transferred to the case.
I would add that all my master dark and bias library files are made at -20 and -25.
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Old 28-12-2018, 12:18 PM
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Marke (Mark)
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honestly I cant see any diff in my images from -15 to -20
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Old 28-12-2018, 03:13 PM
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ChrisV (Chris)
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I've completely forgotten what I learnt in year 2 thermodynamics (many years ago). But isn't it just related to the temp difference between the source of the heat and the surrounding air. So whack a temp probe on the camera and see what it is - if you can get one on the peltier element. If it's much more than ambient then the fan should help. If not placebo is usually a third of any drug effect in a clinical trial

My ignorant 2c worth ...
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  #6  
Old 29-12-2018, 03:44 AM
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Quote:
Originally Posted by glend View Post
So my question to the thermodynamic experts (maybe Rowland) is, assuming a hot night, does the increased volume of air passing over a given sized heatsink, or the case it is attached to, really improve performance or is it a plaicbo effect?
Yes of course. Anything that increases the mass flow rate of the air over the heat-exchanger inside the camera will increase rate at which heat is rejected from the sensor (and hence transferred to the air). With all else equal or unchanged there are some effects to consider in determining the overall outcome in this case, for example:

1. Lower air density at higher ambient temperature reduces the mass flow rate of air (between say 30C and 5C ambient this is in the order of 10%)

2. The addition of the fan raises the air velocity and hence raises the mass flow rate of air and could easily counter the effect on the reduction in mass flow rate of air caused by the air density reduction, given a reasonable increase in flow velocity with the fan. Whether the fan is pushing air or pulling it OR both, make sure there are no flow leaks and that the fan is well sealed at the inlet/outlet to maximise the effect.

3. Without modifying the camera internally, an additional air precooler (possibly a Peltier type) for the air could certainly work if it could sufficiently lower the air inlet temperature to the camera. If you're out in the field near your car, you could "plumb" some flexible duct from a car air conditioning vent to your camera heat exhanger air input. That would be a very easy mod - just some duct and duct tape.

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Last edited by JA; 29-12-2018 at 04:39 AM.
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  #7  
Old 29-12-2018, 05:42 AM
glend (Glen)
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JA I like your pre-cooler suggestion, and I think I still have a 60W TEC here somewhere, from my DSLR cold-finger days. Heaps of 12V power in the observatory to run the pre-cooler. I would need to find some small ducting. It occurs to me that the PC liquid cooling system that I sold early this year would have been great for a pre-cooler build, given that it had it's own mini radiator. Cumbersome for sure, but if wall mounted and ducted toward the camera it could work to.
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