Re: [ATM] Electronics help needed - temperature control

[Mike Lockwood <melockwo@uiuc.edu>]

Gil,

Gil McFarlane wrote:
> $2500?  My plan is much, much more modest. I want to bring the
> mirror and mirror mount to what I expect to be ambient temp. for
> that night's observing - like an air conditioned dome. I then open
> it up, let fly. I don't expect to chase the temperature after
> opening - I just want to have the mirror at a stable low temp at
> the beginning of observing. Will that matter much? Don't know. Will
> it be fun to try? Yup.

Yes, for about 1/2 hour or so (or possibly longer), or until the 
ambient air drops a bit below mirror temperature.  I have done this a 
few evenings this week in my driveway - scope inside at 70F, outdoor 
highs of 75-80F, wait until sunset, take scope outside, enjoy Saturn 
at 500x!  Did this with my 10" F/5.5 Newt and my 12.5" F/12.5 Cass.

That gets me my planetary observing "fix" for the evening, which is 
way better than watching TV.

> I'm thinking of using the lower section of my large old Coleman
> cooler to hold my icy water and a U shaped pipe (save room for
> soda), then have a closed air circuit blowing this cool air around
> my mirror and its mount. Desiccant needed to dry the air out.

The only danger here is cooling the mirror too much and then having it 
dew up.

For most mirrors an electronic control will simply keep the fan on all 
night as the cooling of the air out races the cooling of the mirror. 
So, unless you have a nice thin mirror, I find a high-low-off 
switch-wired setup to be cheaper, lighter, and easier to make.

Maybe I'll put a wiring schematic on my web site....

Mike Lockwood
http://bi-staff.beckman.uiuc.edu/~melockwo/index.html

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