I have taken a standard 120vac box fan and converted it to run on 12vdc using a treadmill motor. I had been thinking about this since I got some more solar panels for Christmas 2010 and I have seen the dump load controller dumping continuously every afternoon after about 12:30 noon. I hated to see this power being wasted so I needed something that would pull a higher current that would benefit me in the afternoons. My solar power system works without an inverter and I use the 12 volt power straight off of the battery.
In all simplicity all I did was unscrew the factory motor and replace it with a Treadmill Motor, I changed the power switch too. This took me a fairly long 6 hours to do because I didn't buy any parts and used stuff that was collected in my shop, and I am really picky about stuff that I build and it always takes me longer than it should when I build stuff for myself
An L bracket was added to the back to keep the fan from falling over from the weight of the motor. I used some corner brackets and bent them to fit the existing brackets on the treadmill motor. Drilled and bolted everything together, and discovered that the motor was spinning the wrong direction for the blades. So the motor was wired in reverse polarity to get the proper rotation direction, I hope this is OK for a treadmill motor?
The motor that I used is rated
2.5 Horse Power
120 volts DC
18 amps
7100 RPM
CW rotation
Class 8
I used 5 minute epoxy glue to attach the blades to the motor. I had to cut out some plastic in the center of the blades to get a good flush fit. The hub of the blades was exactly the same size as the flywheel on the motor so I glued the outside edge of the blade hub to the flywheel.
I took it inside and hooked it up to my solar power. While it was running the voltage was measuring 12.3 volts and it was pulling 1.5 amps which comes out to 18.5 watts. It runs about as fast as a factory fan set to Low speed and I did not need a speed control. Nice pleasant whoosh sound that is not offensive at all. The motor stays cool to the touch even after hours of operation.
After testing I replaced the factory plastic blade guards which required a little cutting to accommodate the treadmill motor sticking out the back. It weighs about 5 times more than the factory fan and pulls about 1/5 of the power. I just run it during the day when the system is dumping power. I ran it late one night and when I turned it off I was reading a 10v battery voltage which went up to 11.7 volts when I turned the fan off. I'm real happy with the results of this project and I am enjoying it right now as I am writing this..
I got the idea from other members that had done the same thing and were claiming amazing efficiency running from 12dc.
An Efficient 12V Ceiling Fan - by SamoaPower
http://www.fieldlines.com/board/index.php/topic,128905.0.htmlSolar 20'' Box Fan - By Ghurd
http://www.fieldlines.com/board/index.php/topic,143414.0.html