Automatic Solar Powered Extractor Fan for a Hot Garage

Having put together a nice little garage for my Marlin kit car, I discovered that it was like an oven on a sunny day so I decided it needed an extractor fan to keep everything cool.

As there is no electricity in the garage the obvious way to go was 12v solar power!

I had a look to see what I had knocking around and found a sheet of 3mm MDF for the back plate, a small extractor fan/light unit ,recovered from a caravan, an old room thermostat for a central heating system and, on Amazon, I found a 10w solar panel and charge unit for £30. I had a spare battery for the Marlin which will be kept up to charge as a bonus :)

I worked out that the best place to mount the fan was at the top of the roll up door.

Step 1: First Steps and Redesign

I decided to mount the unit on the bolts that hold the frame of the garage together, the top of the MDF panel was cut to the angle of the roof slope with 2 holes for those bolts to pass through.

I looked at where everything would need to go ..... and realised that I would do better not to have the charger/controller in the garage...I also had to think about how it would switch off and on, I had worked out that I would need a relay to reverse the operation of the room thermostat which only had a normally closed contact when the temperature is lower than set point, I realised though that this would mean that the relay would be energised when ever the fan was not running that would be unreliable in the long term so I took the room stat apart to see if I could modify it and yes I could, it had the normally open contact, though without a screw terminal so I just soldered my wire inside the unit.

Step 2: Mounting the Solar Panel

Right next to the garage is a small shed and it seemed that the corner of the roof would be the perfect place for the solar panel, to that end I made a plastic bracket to screw it onto the barge board, led the wires through the wall and mounted the charger/controller on the wall just below the panel. The battery went on the floor under the table below and the charging circuit was up and running!

Step 3: Constructing the Main Unit

Once the fan and light assembly had been stripped and cleaned I bent the ends of the panel down to stiffen it up and sprayed it black.

A hole was tripanned in the MDF panel to fit the fan shroud and wooden blocks were glued and screwed onto the MDF panel to attach the newly reassembled light panel.

The thermostat was mounted just above.

Step 4: External Fan Shroud

The fan housing was of a size that I struggled to find anything to match so I cut a couple of rings of drain pipe and cut a slit down 1 of them and a section out of the other to make a piece of pipe that would slip onto the fan shroud.

I cut a square of flat plastic, trepanned out the centre hole and glued it all together with a filler glue to get a nice strong fillet at the joint.

Step 5: Outside Grill

To stop any thing getting into the fan I made up a grill of expanded aluminium by forming it around a piece of drainpipe using a wooden mallet. The grill was stuck in place with araldite.

Step 6: Final Build Up of Fan Unit

Once some wooden blocks were glued and screwed on to the back of the MDF panel to attach the outside shroud the back panel was painted black all the parts were bought together and final fitted.

Step 7: Hidden Wiring

The final cable, between the fan unit and the charger/controller in the shed, was passed through the tensioning strap tunnels along the top and sides of the garage and through to the shed at floor level this cable is all but invisible, pictures show it whilst being installed.

Step 8: Final Installation and Testing

The panel was screwed in place inside the garage and last wires attached. I cut out a round hole in the tarp for the outer shroud to pass through and it was screwed through to the wooden blocks, clamping it all in place.

I wondered why the fan was not running and realised that the temperature in the garage was higher than the top set point of the thermostat, this was easily resolved by removing the setting knob which allowed me to wind the stat further out until the fan burst into life.

I have now set it to get the garage to a sensible temperature with the fan switching on and off as required.

A nice little bonus is that I also have a light in the garage for those long winter nights when the fan will not be required.