Quote:
Originally Posted by Startrek
Thanks for replying Glen
Much appreciated
I got up this morning at 5am and did some more testing
The 2600MC cooled down to -10C @ 90% power consumption which was better than yesterday
Took 40 x 60 sec Darks and temperature dropped down to - 9.2C @ 98% power consumption and hung around - 9.0C to -9.2C for the whole duration
I am taking Darks inside the house which is warmer than outside by a few degrees ( ambient around 22deg ) however the humidity is ridiculous at 90 to 95%. Sydney has had 80% to 100% humidity for the past week.
A couple of observations and take always from testing -
According to ZWO the 2600MC has a designed working humidity range of 0% to 80% and a Delta T of 35.0C below ambient, so I am pushing the camera and cooler to its absolute limits and marginally beyond
As soon as the capture plan is completed the camera’s temperature drops back down to a nominal -10C within a minute.
Ive always taken a photo or two of the laptop screen at the start of each capture ( too lazy to look at logs ) and checked a few photos back in January/ February this year when temperature and humidity would be higher than the rest of the year. Camera was running at -8.8C to -9.1C with power consumption of 75 to 80% ( time was around 11pm )
This morning when I finished the capture and set the warming function , the camera warmed from -10C to +0.1C in less than a minute. ( normally it takes 3 to 5 minutes )
So I can only conclude that the 3.5 year old cameras cooling system is less efficient than when it was brand new ( my newish 2600MM proves that as the coolers are identical )
Humidity (more so than temperature) must play a huge roll in cooler performance as Sydney’s humidity is ridiculously high night and day this past week and will remain so until the weekend
Once the humidity drops to average or normal ( say 60% to 70% ) I’ll take some more Darks and see how the cameras cooler performs, hopefully a big improvement , fingers crossed.
Martin
|
Hi Martin,
yes l think that is the crux of it. Even in ZWO's own literature for the 2600mc and 2600mc they state:
" *The Delta T 35℃ is tested at 30℃ ambient temperature. It might get down when the cooling system is working for a long time. Also, as the ambient temperature falls, the Delta T would also decrease."
So from each of those statements I would conclude:
1. Its limits are a Delta T of 35 ºC at an ambient temperature of 30ºC, so -5
ºC camera temperature.
2. After some/long time cooling (?) the camera temperature may go down further.
3. Delta T of 35 ºC is the maximum temperature drop possible. At say 20 ºC ambient who knows what's possible, but given their comment, a -15 ºC camera temperature is unlikely. As to whether even -10 ºC is possible, it may be a little too close to the limit which is what you may be finding. Perhaps even manufacturing variation between the Peltier coolers or fans in the devices is enough to account for the differences between the 2600mc and 2600mm. It is hard to be certain.
One thing though operating at higher relative humidity, means the ambient air used for the cooling has a greater water content. This means that importantly that the air, in the context of heat transfer, will have a higher film heat transfer coefficient, since typical film heat transfer coefficients for liquids are 1 to 2 orders of magnitude times higher than those for gases. Now the humid air may only contain a few grams of water per kilogram of dry air, so it won't be as extreme as a 1 to 2 orders of magnitude, but it's enough to make it different.
A higher film heat transfer coefficient means the cooler has more difficulty in lowering the Aluminium fin temperature (for a given heat flux) whilst transferring heat across the air film boundary layer at the Aluminium / air interface where most of the heat is being exchanged. This results in a slightly higher aluminum fin temperature than with dry air and thus a slightly reduced ability in transferring heat from the sensor.
Best
JA
PS: I was going to suggest exactly as Glen did that the use of an auxiliary fan might get you to where you want to be. That also gives me another thought along the lines of your thoughts of your (possibly) aging 2600mc camera and that is, perhaps the fan maximum airflow varies or is different either due to aging or other factors. You could possibly test the differences (or not) between your two cameras with an airflow meter.