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SandwichBear
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# Posted: 26 Jun 2014 02:27pm
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I bought a small fan for possible use to assist in venting of hot air behind my propane fridge. The fridge will be in a sealed and insulated cabinet, vented to the outside near the bottom and the top.
My question:
The fan is made to run on 2 "D" batteries. Can I wire this to my 12v fuse box / battery bank by simply using a resistor in-line with the wires? I see inexpensive resistors that do 12v to 5v, but not 3v. (I need 3v, since the batteries are 1.5v in series... right?)
Ideas / thoughts / corrections / insight?
Thank you,
Chris Harne
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rayyy
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# Posted: 26 Jun 2014 04:51pm - Edited by: rayyy
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I just bought this little 12 volt blower fan off of Ebay.It is working great.At night when I shut down the generator I can run this off my battery bank for air circulation.http://www.ebay.com/itm/Car-Cooling-Air-Fan-Auto-Vehicle-Truck-DC-12V-24V -Adjustable-Silent-Cooler-Speed-/300953177257?pt=Motors_Car_Truck_Parts_Accessories&h ash=item4612350ca9&vxp=mtr
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razmichael
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# Posted: 27 Jun 2014 12:06am
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Very good chance the fan would run fine at 5 volts. Simple resistors will not ensure a steady voltage if and when the input changes (it is much higher when being charged. In addition you may have a lot of heat so a heat sink is needed. You really need a linear regulator or Buck circuit - Google 12v to 3v and you will come across a number of schematics.
Example of schematics
I have one schematic I used but it is on my home computer and at the moment I am in the Rocky Mountains travelling. I built a bunch of these a number of years ago so I could use the inexpensive puck type LED lights in my old Pop Up Camper.
You can also buy completed 12 to 3 converters easily. What I would really suggest is you just pick up 12v computer cooling fans. They are very cheap and will do the job fine without dealing with any conversion. In the RV world there are numerous examples of Propane Fridge Modifications that add fans that pass air through the absorption fins to increase the efficiency of the fridge.
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groingo
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# Posted: 27 Jun 2014 09:46am
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Thats what I did, grabbed it out of a defunct power supply and now it vents my battery box, runs as long as batteries have juice (constantly)and only pulls 0.250 Amps so draw is insignificant and it runs super quiet.
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SE Ohio
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# Posted: 27 Jun 2014 09:04pm - Edited by: SE Ohio
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Sandwichbear,
For about $30 you can buy a 12 volt fan. Mine is an O2 cool or the like. Or you could fashion a 12 volt to 3 volt circuit based on a LM317, with resistors, perfect board, project box, etc. you may end up spending about the same? Radio Shack will have everything you need for the LM317 based circuit.
Another alternative would be to find someone's discarded Harbor Freight solar panel controller in working condition. Connect to 12 volts and it has outputs for 3, 5, 6, 9 and 12 volts. Many folks end up upgrading from the HF controller so these might be plentiful. However, you might again be out $30 or so with shipping if you cannot find locally.
My cabin is wired for 120 but supplied with 12 volts. I cut off the O2 Cool 12 volt "cigarette lighter" adapter and hard wired a polarized (one prong bigger than the other) plug so I get correct +/- (fan could run backwards if plugged in wrong). Fan makes all the difference on muggy nights!
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basewindow
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# Posted: 28 Jun 2014 05:12am
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Got an old computer lying around? Most of the fans in these are 12v and are perfect for this.
Or look on E-bay and you can pick them up new pretty cheap.
My Off-grid place has exactly this set up for the propane fridge and it works really well.
Google search the topic and there is plently on info on how to do this.
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TheWildMan
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# Posted: 30 Jun 2014 09:04am
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Its been around 70% humidity and 90 degrees around here, I got a 12 volt fan a few years ago for $10 at an auto parts store and wired it into the system near my cot. runs off solar charged batteries and uses about 10 watts an hour. does a good job keeping me cool at night and during the day if I sit on the cot
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Dekagoldwingers
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# Posted: 3 Jul 2014 11:50am
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My friend has a couple of computer fans that he has wired directly to medium sized solar panels that he has mounted in his greenhouse. The fans provide air circulation when the sun gets warm. He used solar panels that he found with cracks in them and are no longer weathertight but stay dry inside the greenhouse. Works very well.
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sparky1
Member
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# Posted: 6 Jul 2014 10:03am
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Most Desk top computers have at least 2 12 volt fans some have 3. .I have about 30 old 12 volt fans from junked computers. Radio shack sell them also.
need (2) wire fans ,3 wire might be 5 volt.like Lap tops.
sparky1
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