QHY9 CCD freezing issues - where's the magic bullet ?

[skybadger]

I have a qhy9 CCD camera. it comes with a little dessicant container that screws to a port on the outside. The first time out it froze on the coverslip of the ccd. 

And the second , and the third. So I bought some dessicant fabric from Browns and cut it to shape inside the CCD chamber, removing the tiny old dessicant strips. 

I also added the extra front window to the body which was meant to improve things. 

What I found out was that the without the 'extra' front window sealing the body, the front of the camera was open to the air and the dessicant wasn't actually doing anything useful since it wasn't connected to the ccd chamber. 

So I also revamped the dessicant - now I had a great big container of self-indicating dessicant attached, and a line to purge with argon and the front window attached to seal the body. I'd have thought that was enough. It looks enough compared to the few grammes of dessicant in the previous tube. Its a car petrol inline filter btw attached to gas line hose using quick lok gas fittings and valves.  

At this point I find the argon hissing out through the connector holes and through the body screw holes when I purge. 

So I sealed the screw holes with teflon washers

I also sealed the connectors (usb 2 and 8-pin din power) on the inside with styrene resin , rolled about a touch to make sure it covered all the interior of the connectors. 

Then I re-purge with argon and find the front window isn't really sealed, you can feel the flow past the edge of the window when you get close. 

But it operates down to -20 reliably. and has done for about 3 months. 

Until tonight. when Voyager decides to take it down to -36, as it can do if the camera is disconnected and re-connected. Lord knows why. At that point I suspect the reduction in internal pressure due to the water freezing out pulls in more air from the outside. which should be being dried by the dessicant, but its still got a whale of ice on the front coverslip up past -5 and climbing. 

Its also got a heater on the coverskip . Well, that seems ineffective. the big silver thing is my homemade rotator slip ring. The green thing on the coverslip immediately surrounding the ccd detector areas is the resistor-heated anti-dew heater. 

Has anyone got a magic bullet for this or are they all this bad at dewing up and freezing ? 

Lovely clear night of imaging aborted while I warm it up, remove the camera from the scope, remove the dessicant pad, put it in the oven in a tin with other dessicant to reactivate, re-assemble, gas purge and then reconnect and re-align . 

FFS.!! Seething I am. 

 

 

Edited October 5, 2021 by skybadger
sp.