Okay...I've finally got this thing assembled to a point where I can start doing some stuff with it.....I've insulated it the best I can, I've submerged the cable connections externally in oil so they can't draw air in and I've purged the system with Nitrogen gas to remove the majority of the oxygen.
I'm currently doing a test run with just the air con unit and internal fans going...no pc or load.....I'm really surprised at how long it is taking to pull the temperature down.....I was starting to think there was something wrong with the air con unit or my insulation job was rubbish.
With my previous build which was just filled with air and the inner box was the insulation board then it would pull the temp down to -20c in a matter of dunno perhaps 5 mins and -30c in about 10 mins....somewhere around that area.
I've been running the new chamber for over an hour now and just hitting -11c.... :-/
The temp is still going down slowly but surely......I think it is the heat capacity of the alu chamber.....it weighs over 62kilos so has the same heat capacity as about 3 imperial gallons of water.......that's gota take some cooling.....think I'm just used to instant temp drops with my previous system....still going down....-13c now.
The reason I'm doing this with just the Nitrogen in there is to leak test it. The chamber was sealed at ambient of +20c and I completely evacuated the purge sac.
Leaving it run at low temp in this sealed state will drop the internal pressure by between 2 and 3 psi so if there are any leaks air will be drawn into the chamber.
After several hours I'll turn off the cooling and allow it to return to ambient temps as the temps are returning to ambient I'll open the purge sac line....if air has been drawn into the chamber then as temps return to normal the purge sac will be expanded as compared to its previous evacuated state.
It's not a particularly accurate method but it should be good enough to show me if there are any substantial leaks.
I'll do the same again tomorrow when I have purged the Nitrogen out with butane.......the butane will produce an even lower pressure...perhaps as much as -10 psi .......so that will give an even more rigorous test.....if all is good with that then I'll be able to load the chamber with liquid butane and try booting up
Finally got down to -22c without load after several hours of no load running......doesn't seem right to me...just took too long to get down there and is some 8c higher than the low I could get before.....although I am monitoring the temp on the outside of the alu chamber rather than the air/gas temp inside as I was before....guess I won't really know till I try some loaded trials.
I'll monitor how long it takes to return to ambient.....if the problem is my insulation job isn't good enough then I guess it will return to ambient quite quickly....other than that may be an air con unit problem...or just the additional heat capacity...not sure.Edited by technogiant - 10/17/13 at 1:09pm