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I have a 10'x10' shed that gets hot as hades inside, and want some ventilation involving pushing air through a hole I would punch in a wall near the roof peak and screen over so my friends the wasps don't move in. With a gas-powered mower and weed whacker, gas cans, and spare propane tanks for the bbq and camping lantern, it gets thick with fumes, and I'm uncomfortable with how hot it gets in there.

I have myself a salvaged solar panel in a weather-proof frame, which in its former life charged a battery that then ran a string of little LEDs at night. It being March, I don't know what to expect from summer sun in terms of juice production, but I did test with a single 60w incandescent bulb in a reading lamp pointed directly down at the panel. The multimeter registers 6.5v/1.3a at a distance of about 6", and with the bulb just about directly over the panel, just barely 9v/2a. This is direct from the panel; the battery and charging bits have been removed. They had stopped charging and/or holding a charge, which is how I inherited this.

I have a fan in this vein that came from an old external hard drive enclosure which puts out enough air, I think, to do the job: en.wikipedia.org/wiki/Centrifugal_fan

It's marked 12v/0.38a. It would be inside the shed blowing through the opening I make. Solar shed vents sold for this purpose are $40+ and reviews say they all just plain suck and are worthless.

What I'd like advice on is how to take this panel's output, which I can't imagine ever getting above the 9v/2a number, and probably hoping for the 6.5v/1.3a is optimistic, stepped up to 12v at sufficient amps to turn this fan. I found the items below which to my novice eye seem like they might be steps in the right direction:

http://tinyurl.com/457sr8t

http://tinyurl.com/4vkqapo

Am I out of my mind? Could a device like one of the above take the panel's output and put out enough to get me 12v/0.38a if I get enough direct light? Is there some other, better way to go about this based on the panel I have?

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  • \$\begingroup\$ Did a little more research. Would a large capacitor inline between the panel and the fan do the job? I imagine it would charge up and then blow the fan for however long it can, provided the capacitor is above the voltage the fan requires (12v)? \$\endgroup\$ – user3368 Mar 13 '11 at 3:33
  • \$\begingroup\$ Outside the scope of EEStX so not offered as an answer, but... My first thought is add a 2d, light colored roof on standoffs, with ridge- and soffit-vents, to dump most of the heat before it ever enters the building. Some insulation under the inside roof would stop even more. After that, passive venting may be sufficient, but certainly the power venting requirement would be significantly less. Or simpler, just insulate and vent (above the insulation) the existing roof. (Granted, the passive solution may not be as much fun!) \$\endgroup\$ – JRobert Apr 20 '12 at 16:31
  • \$\begingroup\$ Also, if you're truly concerned about volatile fumes and fire, you might not want an electric solution at all or should at least consider a fire-safe fan and pressure venting. \$\endgroup\$ – JRobert Apr 20 '12 at 16:46
  • \$\begingroup\$ A 60 W reading lamp comes nowhere near sunshine levels. If it is not brightly illuminating the panel output should be minimal. What area is the panel? Photo available? It is very very very unlikely that your readings are corrects, sadly. What range is your meter on? It is more likely that yopu are getting 2 mA. Really. Alas. A 9V x 2A panel = 18 Watts (in brigh sunshine) !!!!!!! would be a minimum of about a square foot in area with best available commercial PV cells! \$\endgroup\$ – Russell McMahon Oct 12 '14 at 6:55
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That was a long question :-) You are not out of your mind and think in the right direction.

In fact you can get twice much amps you need for your fan. So yes, get one of these modules, and add some extra capacitors on the output (some 10'000 uF) to help it deal with FAN's pulsed current consumption & startup current.

You can even get way bigger fan, cap will help to start it and it will work even if you have just 30-40% of the power it needs. You just need separate switch for DCDC board and FAN - so that you turn DCDC first, and after 1 second - FAN (so that cap is charged).

And finally, direct sun gives much much more juice than 60 Watt lamp. So you really need more powerful fan & more powerful DCDC.

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Thank you for taking the time to reply. That's a big help. Two questions:

  1. Could you please clarify what you mean by "You just need separate switch for DCDC board and FAN - so that you turn DCDC first, and after 1 second - FAN (so that cap is charged)."? I understand the general idea of charging the capacitor to give the fan the boost it needs to start, and I think you are saying panel -> dc/dc converter -> capacitor -> fan is the wiring sequence, but I don't understand the "separate switch" part and the "after 1 second" part.
  2. I was able to start and run a smaller 12v/0.17a fan directly via the panel's 9v/2a output (see below). Do you think is there a way with caps that I could start and run the 12v/0.38a fan the same way if the caps gave the fan the initial push? This might mean not having to buy anything (I have a variety of caps on hand). I did try to wire it the panel and the bigger fan together, but it wouldn't start, and even with a push (I spun the fan, both directions) I would not run. I'm confused about how 9v/2a could start and run a smaller 12v fan, but could not run the bigger 12v fan even if I started it manually.

Thanks!

More to add just to contribute the to world of Google search results for someone else at my level that this might help:

  • BarsMonster is absolutely correct about the sun versus my lamp... I took the panel outside in moderate sun in March in North America and it generated the same 9v/2a I'd seen with the 60w lamp right on top of the panel. I take this to be the max the panel can produce. This is not what I expected as an electronics novice. I thought sunlight would be faint compared to the 60w bulb practically sitting on the panel. Go sun!
  • I was able to connect the panel directly to a much smaller fan (cpu fan from the old days) that wants 12v/0.17a, and 9v/2a would start and run that fan w/o a converter or capacitors etc. So I guess the boost from the capacitor BarsMonster described could get the larger 12v/0.38a fan going, then what the panel puts out could keep it moving, albeit more slowly than full speed.
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(This was a month ago - did you get it working?)

My reckoning is that the capacitor won't help, but the DC/DC converters are exactly the sort of thing you need. They look like they're rated for sufficient power as well. The only concern might be what happens when the output drops below that which can run the fan but not yet zero; if the fan is stalled, does it dissipate current as heat in the fan or DC/DC converter? Depending on the converter, intelligent ones will go into "brownout" mode and switch safely off in this situation.

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