Author Topic: R & R - building new Stevenson Shield - Questions  (Read 640 times)

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Offline azkiwi

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R & R - building new Stevenson Shield - Questions
« on: July 15, 2018, 11:18:32 AM »
Not quite sure which sub-group to post this in - so please move as necessary.

I'm refurb'ing / rebuilding my 7-8 year old Stevenson shield (desert heat and dust storms are killers) and I'm thinking of adding a solar powered fan to it.  I have some small solar panels 2.2v, 45ma, which I can wire in series / parallel to get close to a 5v, 80ma level, which, according to a spec sheet I reviewed will comfortable drive a 3 inch / 80mm computer case fan.

Question is, what's best?  Fan at the bottom of the 'box', blowing air in, or at the top - blowing it out.  Either one will be moving air around, but which one is the most efficient for air flow?

Prototype testing  with a 2 in gap all around the bottom, and a 1.5 in gap all around the top, the test tracks .8F to 1.3F higher than the mean of 3 stations (old ones, good for something) currently in the old shield.  When I put a 2nd top - raised 2in - and overhanging by 2in each side, I drop it to .4F to .9F in direct sun exposure.  Playing now with ventilation etc. If I can drop it to a constant .4 / .5 F, I'll be satisfied.

Beauty of all this is it's not an "oh hell, gotta build a new box quick-like" and I can play around a bit.

Anyway, I'd  grateful for any feedback or advice.


Ken

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Offline DaleReid

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Re: R & R - building new Stevenson Shield - Questions
« Reply #1 on: July 15, 2018, 03:05:45 PM »
Most of the professional grade (reserach, big bucks, government, etc.) that use fans suck air OVER the instruments, not blow it.  I guess there is a concern that if you are going to the trouble to move air, you don't want the heat of the fan motor contributing to any error.
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Offline azkiwi

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Re: R & R - building new Stevenson Shield - Questions
« Reply #2 on: July 15, 2018, 07:08:01 PM »
Thanks Dale.

It's tracking - the prototype box - about 1.6F high, with both shields in direct afternoon sun. Prototype has only a light coat of white primer, so that's an issue right now. Over the next couple of days I plan to increase ventilation holes / slates and see where that leads me.  Plan on getting the 80mm x 80mm 5v fan tomorrow on Amazon's special day.


Ken

Offline Old Tele man

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Re: R & R - building new Stevenson Shield - Questions
« Reply #3 on: July 15, 2018, 08:25:56 PM »
FYI, the original 'cotton field' Stevenson Shields were all "white washed" white and not painted white...something about the lime being more "reflective" than paints which can sometimes actually be absorptive to infrared energy.
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