Converting a 240v ac fan to 12v dc.

I have a collection of dead workshop floor fans, and a couple of the 24v motors you see in broken kids electric scooters. In this project I combine the two to make a workshop fan that runs of 12V dc.

I've converted a floor fan, but you should be able to convert most fans to 12 or 24 volts, its all in the mounting of the DC motor.

I picked up the fans from a previous employer. All had a burned out earth wire, and were written off. When the earth wire burns out it melts the insulation off the other live wires, so its not worth repairting.

How did the earth wire get burned out?

Boiler makers used the fans to keep cool while they were working on the big dragline buckets. The buckets are big enough to fit a car in, so the boiler makers take their tools and fans in with them. Sometimes the welding earth electrodes are connected to the bucket at a different potential to the mains power earth. These fans have rubber feet, or are hung from overhead, which keeps the different earth potentials apart. But if a fan is bumped over, it's metal case makes contact with the bucket, and ZAP! Exit one fan. Its a hard life for them.
These scooter motors are getting easy to find. The cheaper of the electric scooters models are easily broken and discarded. I picked up one from a work mate who's kid tried to drive his scooter up a road kerb at full speed, ruined the front tyre and suspension. The motors can be bought new for about $35. Try... http://www.monsterscooterparts.com/24v30mowisp.html http://www.oatleyelectronics.com.au The smaller 200 watt scooter motor would also work fine for this project, though I haven't tested it.
I removed a fan from one of the floor fans, and was happy to discover it matched the shaft diameter of the 300watt motor perfectly. One less job for the lathe. The motor and fan were mounted on the corner of my bench with a couple of clamps and a 12v battery connected up. Whoosh! Heaps of air flow, I think maybe more than it moved when it had the 240v motor. It was drawing 4.2 amps at 12 volts, which is only 50 watts. That's good, it means the motor isn't working too hard, and wont overheat or wear out too quickly.

With the 12v dc motor proven to work, I removed the old 240vac motor and control box from the floor fan.

Then I worked out the best position for the new motor and made a bracket to suit.

I've used a floor fan, but any 240v fan could be converted to 12v with the right motor and mounting.

A closer look. I used nylock nuts on the 1/4th inch bolts, there is a bit of vibration in these floor fans and I didn't want it all falling apart.

Lastly I fitted the fan and front shield.