ASI294MC DEW or ICE

Lerager

Hi
Just bought a used asi294mc. I let the Asiair plus cool it down to -15C
I get dew on the, i think must be the sensor. It dont get away after 20 min.
Trying to bake the desiccant tablets, without success.
https://astronomy-imaging-camera.com/manuals/How_to_clean_ASI_camera_and_redry_the_desiccants_EN_V1.2.pdf

I tried to cool it down in interval but after 20 min. a flat still look like this

Tech@ZWO

Lerager
It looks like dew, this is because the humidity is high inside the sensor and they are frozen on the sensor glass when the temperature drops quickly, we recommend you slowly cool the camera to solve the problem:

Before letting it cool down to the target cooling temp, please keep it at 5℃ for 2-5 minutes, then cool it down to the target temp and if this continues to appear, it will basically disappear in 5-6 minutes.

Lerager

Thank you
As I wrote...
"I tried to cool it down in interval but after 20 min. a flat still look like this"

Since the baking failed I have ordered some new tablets and some silica gel.

Tech@ZWO

Lerager Sorry, I missed it.
If the problem still exists after you replace the new desiccant tablets, you can contact the dealer for reapir.

Lerager

Thank you
After New desiccant replacement the dew is stay on for at least 30min
I had the camera inside a dry box for the night. No help.
I cant go to the dealer as I wrote i buy it used from a private user.
I have been looking for a O-ring or a least the measurement but with no luck.

Lerager

I now had succes to cool down to -10c
But it was not so easy. It seems i have to take flats in the process to see if dew is rising.
First down to +5 in one go.
Pause 1 min. Then down to 0c
The in steps.
-2 -4 -6 , 2 min. Between
-7 -8 , 3 min. Between
-9 -10 , 4 min Between
It would would have been Nice if asiair could handle this.
A slider for aggressive + -
Or A user Def. Tabel
Or by a script that can be used to other task.

wizzlebippi

What are the ambient conditions (temperature, humidity, wind) you're trying to operate the camera in? Also, what's the load on the cooler when you stabilize at the target temperature?

EDIT: Probably the most important part, is the frost/condensation forming on the window or the sensor?

Lerager

Thank you.
The test was done inside my OBS.
I gess ambient was +16c
Humidity ? No Rain it was daytime.
No wind
Fan load about 60%
I gess it shows on the sensor.
1) wery small Dots
2) It dont help to turn on the camera heater.

wizzlebippi

Let's start with the sensor then. First, check the o-ring. It should be clean and smooth. If you need to clean some dust off of it, re-lubricate it with a small amount of silicon lubricant. Then, clean the sensor and inside of the protective window by blowing the dust and dirt off with a hand bulb, an optics safe cleaner, and a lint free wipe. I use ROR and Kim wipes, and I'm sure many on this forum have their own methods. Don't worry about touching the sensor because it has a protective glass cover. After getting the camera back together, take a flat and look for dust in sharp focus. If you see any, repeat the process.

The most important part of this is to never face the sensor or inside of the protective window upward to help ensure dust doesn't settle on them.

If you've recently dried the desiccant tablets, then I wouldn't worry about them unless you live in a very humid environment.

Lerager

Than you again.
I had the lid taken off the camera many time trying dry out the camera.
Every time clean the sensor with swab kit.
The O ring looks OK.
My problem is not dirt on the sensor but dew when cool down. All the spot you see on the pic. are dew. As soon the temperure goes up it goes away.

wizzlebippi

Lerager Water needs something to condense on, and it prefers dirt to a clean, flat surface. Hence why the inside of the sensor chamber needs to be clean and dry.

There's really only 2 options for what's happening. Either the sensor chamber isn't sufficiently clean and dry to prevent internal condensation, or the camera body isn't staying warm enough (at least 5°C above dew point) to prevent external condensation. Hopefully it's not both.

If you have some headroom on the cooler, you could try wrapping the front of the camera or disabling the fan. I actually equipped my 294 with a 3 position switch, giving me fan control of off, 6v, and 12v to allow the cooler to better heat the camera. In winter conditions, I even use a dew heater strap around the front of the camera to ensure that it stays warm enough for the cooler to maintain a constant temperature.

Also, since you mentioned the presence of a heater on the 294, there isn't one. It's only heated by the hot side of the Peltier that cools the sensor.

Lerager

Oh yes your right. Dew loves dirt...
But about heating, to prevent it, don't help. The sensor needs to be cool....
My asi294mc has a heater. It's a after market product. But heat only prevent dew on the AR front window.
Here is my heater ( not for sensor dew)

wizzlebippi

The sensor needs to be cooled. The camera body needs to be above the dew point. Since all a Thermo-Electric Cooler (TEC) does is create a temperature difference between the hot and cold sides, the camera's sensor can be up to 40°C cooler than the camera case.

I forgot about the stick-on heater. In my opinion, you're better off with a dew heater strap (not the correct length, I don't remember what I ordered). A 4.5W heater is nothing compared to the at least 24W the heatsink and fan can dissipate. Plus, the dew heater strap is somewhat insulating.

Lerager

Yes another heater could be better to avoid dew on the AR window. But not on the sensor. If i go to 100% with my heater i can hardly touch the camera body. It must be over 30c but dew still seeing on the sensor. You cant / May not heat the sensor. The chamber simple must be dry so cooling to -10 dont build up. I can do it by slow down cooling. From +15 to -10 in 25 min.
I just want to do it faster. I just found on Amazon a new O-ring. Not that I believe it helps.
It could be the AR window leak.?
Air coming in from the back side....?
Asiair plus v2 beta cooling to aggressive?
But my or other heater wont help. Only heating up the sensor help.

P.S: Here is an article about the same problem. He also cool down for 30 min.
So i guess I might have to live with it.
"the camera cooler is so fast and efficient that cooling down takes mere minutes and has been creating ice crystals on my camera sensor window of the ASI294MM-Pro camera. I’ve not seen that before with this camera, but warming up the temp of the camera causes it to go away, and manually reducing the temp in 2.5° increments over about 30 minutes keeps the ice from forming."
https://www.macobservatory.com/blog/2021/9/22/zwo-asiair-plus-in-depth-review

Thank you.