Author Topic: Converting a 120 vac Box Fan to use 12 vdc Treadmill Motor  (Read 1771 times)

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Offline WooferHound

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Converting a 120 vac Box Fan to use 12 vdc Treadmill Motor
« on: February 08, 2012, 06:27:10 PM »
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.

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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

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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

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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 12vdc.
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Offline Wolvenar

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Re: Converting a 120 vac Box Fan into a 12 vdc Treadmill Motor
« Reply #1 on: February 08, 2012, 07:20:32 PM »
One time I was playing with a treadmill motor, I had a 6'  2 blader  I had made up for a not finished genny laying on the workbench. Gears started grinding,  it just so happened I also had the right hub size to fit the treadmill motor. I set it all up clamped in the vice, balanced the blade as well as I could, ran some long cords just in case, and powered it up.

I was 25' away from this thing and it was pelting me with stuff it was blowing around. I don't think it got much over a 100-200 rpm but it certainly was moving air, and anything else not heavy or locked down.
Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline niall

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Re: Converting a 120 vac Box Fan into a 12 vdc Treadmill Motor
« Reply #2 on: February 08, 2012, 08:41:09 PM »
interesting about 2 bladers .....

i rembember standing in the back garden holding a 5 foot 2 blade on an alt ...it was windy so i thought ..why not ?

it whipped up really fast ...to fast ....i thought i could just tilt it sideways to slow it down

bad mistake ..2 bladers dont like being yawed , it tried to yank the alt out of my hands....i had to just hold on to it for dear life and wait for the wind to die down a bit ...

Offline Norm

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Re: Converting a 120 vac Box Fan into a 12 vdc Treadmill Motor
« Reply #3 on: December 31, 2015, 09:04:00 AM »
interesting about 2 bladers .....

i rembember standing in the back garden holding a 5 foot 2 blade on an alt ...it was windy so i thought ..why not ?

it whipped up really fast ...to fast ....i thought i could just tilt it sideways to slow it down

bad mistake ..2 bladers dont like being yawed , it tried to yank the alt out of my hands....i had to just hold on to it for dear life and wait for the wind to die down a bit ...
had the same experience with a 2x4 45 degree slants on the ends
tacked 4x6 boards on the ends carved into air foils ...8 mph wind blowing
and you were right 2 blade rs don't like being yawed it was like having an elephant by the tail whew....managed but some difficulty never again !