I normally set up and take everything (scope, mount, cameras) down each night when I am imaging, but I have lately been trying to leave everything set up when I have a stretch of several clear nights in a row. When I do this I power everything down and cover everything with a nylon tarp. The only thing I bring back inside the house is my laptop. Are there any concerns about leaving the unpowered cameras out over night (premature dessicant saturation for example) ? The temperatures here in Southeast Texas will get down around freezing or slightly below. Humidity is very high and the dew gets pretty heavy.
The dessicant is in the chamber, so that is nearly (but not completely) airtight, so that isn't really a consideration. A bigger worry is the electronics boards in the cameras and electromechanical parts (motors / shutter assembly) getting wet if it is high humidity. Some customers leave the cameras powered on, coolers off, so that some residual heat is produced. Other folks wrap them with a dew strap, or put a 40-60W old-school lightbulb under the tarp to generate a bit of heat so all the gear under the tarp stays above the dew point.
For the record, we are in a high humidity area with ambient temperatures ranging from +30C to -30C, and my equipment is in an observatory. I leave the camera powered up at all times, with the cooler turned off, to try and keep moisture off the circuit cards. I haven't had any problems. If you are anywhere near the coast (e.g. within 30 miles) I would be concerned about salt spray, which can damage the circuit cards and connectors. In that case I do not recommend leaving the camera outside.
Thanks for the suggestions Doug & Colin. For now it sounds like my best bet is to bring the cameras and any other sensitive electronics inside.
Dougm if you have a SBIG model STT and higher, like us on the AstroGram STT-8300M, you don't have to cook the desicant anymore. Just exit any other program and load the old SBIG CCDOPS program. Go down to customer options and turn the "window heater on" and leave it, with no fan on and no cooling. It bakes the desicant inside the chanber with no bother!! Hope this helps, Dr. Hasen Williams, Blue Mountains Obsevatory
No, that will not work. It heats the air outside of the window slightly, to prevent dew from forming on the outside of the chamber window. It will not clear water from inside the chamber. The desiccant must be raised to Oven temperatures to get it to release the moisture. If you have frost on your sensor the desiccant MUST be recharged. We actually recommend you do that before you get frosting, to prevent any risk of condensation corroding your sensor’s pins.
I am assuming that the dessicant used in the cameras is some sort of molecular sieve. We use 3A and 13X molecular sieves in the chemical process industry for removing water from some of our process streams. The sieves are regenerable, but as Doug says it takes high temperatures to do this. We generally regenerate our sieve dryers using a two step process with hot nitrogen. The first (low temperature) step evaporates the excess water in the sieves, and the second (high temperature) completely dries the sieves.
Yes it is molecular sieve. The recommended recharge process is to bake it in a conventional oven at 350 degrees F (175 degrees C) for 4 hours. Make sure you remove the O-ring first, and replace it after it is baked. Insert the plug into the camera as soon as it is cool enough to handle. It may take 24 hours to clear out the chamber of residual moisture.
