# Building Solar Panel for battery run fan



## moreanimals (Jul 10, 2014)

I have a small fan(O2 Cool) I bought that runs off 2 D size batteries I want to use to help cool my rabbits outside. 

I figured I have 2 choice on running the fan 1) rechargeable batteries (solar panel to charge D size batteries) or 2) build solar panel to run fan directly.

Option1: I have found lots of info on creating chargers for A and AA batteries but nothing on the larger D size. I understand when creating a charger you have to have more voltage than the battery to charge it. so a 1.5v 2500mAh D size battery; would take 4 cells wired in a series to get 2 volts, however I am having trouble determining how many amps each solar cell should be(size to cut the cells). I have 3x6 solar cells left from another project so my understanding that is 3.6 to 3.0 amps. The other area I am having trouble figuring out is if I am charging more than 1 D battery - I would normally charge 2 or 4 at a time - do I have to increase the voltage/amp to charge multiple D size cells. Obviously I don't want to overcharge them and limit the life of my rechargeables. Even if I don't use this option for my current fan project I would still like to build a D battery charger for other items I have (flashlights, etc)

Option2: Since my fan is DC I would think I should be able to build a panel just to run my fan when the sun is shining and bypass the batteries all together. However if I go this route would I determine what I need by actual power usage? 2 x 1.5v=3v 2500mAps x 2 = 5000mAps and build a panel with those specs? what size cells(full, half of 3x6) would I need wired in a series?

I would love to understand the differences of the 2 scenarios above regarding building my own panels.

Any input is greatly appreciated -


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## Peasant (May 18, 2013)

I have a 10" O2 Cool fan. Nice little unit, very efficient. I technically run it on solar, but the power produced by my panels runs through a charge controller, battery, and inverter before it gets to the fan.

For what you want to do, I'd consider a couple different methods.

First might be using D battery adapters that use AA batteries. Sanyo makes them. Fan won't run long this way, and you'll constantly have to be switching out batteries. I personally would skip the replaceable battery approach, whether D or AA.

If I wanted to run my fan directly on 12V I'd modify the AC adapter that comes with the fan. I think you have a 5" fan (not sure about voltage of that), but the AC adapter for the 10" fan converts 120V into 12V. Output is 0.5 amps @ 12V. Cutting off the transformer and putting some terminals or quick disconnects on the wire should allow you to charge it off any 12V battery. That's what this guy did. Appears to work. If you really wanted to hack it, you could pop it open and rewire it so you didn't need a specialized plug.

I personally wouldn't run it directly off a panel, you're likely to fry the fan with too much voltage and/or amperage. A charge controller can be used to control output of panels. A battery in between is even better to buffer panel output.

When plugged into AC, my fan draws 8.3W on high, 5.4W on low. That's 0.69 amps @ 12V on high, 0.45 amps @ 12V on low. Say an average of 0.57 amps.

A panel in the 10-12W range will produce this. These can also produce ~18V, not sure what this voltage would do to the fan. I'd at least use a small adjustable charge controller to make sure it's getting the right voltage.

If you used an external battery and ran the fan for, say, 12 hours a day, you could get by with something like a 14 ah alarm battery, though you'd be running it down pretty far every day. A 35 ah battery like this would give you 2-3 days autonomy, though you'd need a larger panel to charge it (100W range).


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## moreanimals (Jul 10, 2014)

Thanks for the info - I agree running from batteries would get old soon! - the 02Cool I got is a 5 inch and only runs off batteries - 2 D cell so no AC on this fan. You mentioned on yours you knew how much amp and watt on each speed, how did you determine that? from the manufacture specs or from some type of gauge meter? I was trying to avoid getting any extra equipment to run the small fan but I guess getting the amps right is harder to accomplish than I thought


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## Peasant (May 18, 2013)

I used a Kill-A-Watt to measure Watts, then did the math to figure amps out at 12V. Some of this power draw is the conversion from 120v to 12V, but not much.

As far as I can tell, the 5" fan is not 12V, it's much lower (closer to 3V I think since it only uses 2 D cells). That might be a bit more of a challenge to run directly off a 12V panel or battery. You'd need to step the voltage down.


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## wy_white_wolf (Oct 14, 2004)

Why reinvent the wheel? Get 1 or 2 of these and modify them to fit your needs.

WWW


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## Cyngbaeld (May 20, 2004)

http://www.amazon.com/s?ie=UTF8&page=1&rh=i%3Aaps%2Ck%3A12V%20Radiator%20Cooling%20Fan

Maybe one of these would work better? Already set up for 12vdc. I'd get a 12vdc deep cycle battery and a cheap charge controller.

Make sure you size the solar panel so that you do not discharge your battery too deeply. 

http://www.amazon.com/s?ie=UTF8&page=1&rh=i:aps,k:12v timer I'd also put a timer on the fan.


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## wy_white_wolf (Oct 14, 2004)

http://www.amazon.com/White-Solar-P...UTF8&qid=1405362938&sr=8-6&keywords=solar+fan

WWW


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## MoonRiver (Sep 2, 2007)

wy_white_wolf said:


> http://www.amazon.com/White-Solar-P...UTF8&qid=1405362938&sr=8-6&keywords=solar+fan
> 
> WWW


Really bad reviews on that guy.


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## Jim-mi (May 15, 2002)

That tiny 5 inch amazon fan is so small and weak you would have to hold it a foot away from your face to even feel it . . and that close-- the noise . . .
And the pv panel . .1/3 of a watt . . . .super weak

those things are only intended to blow some air over electronic circuit boards . . .


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## moreanimals (Jul 10, 2014)

Thanks for the idea of looking for a pre-built - but obviously not all products are quality out there. The cost of a pre-built solar fan was a lot more expensive than I expected - so I think I would come out better charging D cells with a solar panel. The manufacture(O2 cool) said it should run 40 hours on battery life - hard to believe. 
With this option I can put charger in full sun but it doesn't matter where my fan is (sun or shade) - I would just need 2 sets of batteries (1 in fan and 1 charging). However how to I make sure I don't overcharge my batteries? any ideas?

This youtube video shows a guy that charges D cell with a 6v 1.5watt solar panel [ame]http://www.youtube.com/watch?v=PfsB7HjrQhs[/ame]


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