On 2/12/2013 12:18 PM, Jon Danniken wrote:
On 02/12/2013 09:18 AM, The Daring Dufas wrote:
On 2/12/2013 11:01 AM, Jon Danniken wrote:

My thoughts on a 2"x2" opening would involve increasing the size to
4"x4" (or even 6"x6") and installing a little computer fan into a frame
to fit. It would be trivial to built a thermostat to turn the fan on
with a thermister and a small signal transistor and a couple of
resistors, or you could go the lazy route and use a prebuilt electronic
thermostat.

You would, of course, need to supply a source of low-voltage to the cold
frame if you decided to go this route, but it would have the benefit of
being automated.

Jon


Why not one of those solar powered vents you can buy fits the top part
of a car window? The things are inexpensive enough to play around with
then take apart, modify and use the parts to build whatever you like. ^_^

http://www.amazon.com/Solar-Powered-...061073-5857430



http://tinyurl.com/bc6k2go

Hey, even better, as you wouldn't need to supply power or do any
designing, and since it is the sun that is causing the overheating,
you'll always have sunlight for the solar cell.

There do appear to be quite a few poorly-made units out there, though;
this model is more expensive, but seems to have better reviews:

http://www.amazon.com/Round-Solar-Bo...sim_sbs_auto_2


Jon


I remember finding one of those solar window vents at a thrift store and
it was a dollar. I'll cruse the thrift stores for items I can take
apart to experiment with and it costs very little to come up with parts
for projects. ^_^

TDD