Projects


Walking Beam Stirling Engine Kit
Small Back Up System
Thermoelectric Lamp







































Solar Tracker

The tracker uses two calculator solar panels to detect where the sun is. The motor is controlled by a DPDT relay which is activated by the circuitry. The tracker has some switches in the base which allow it to return to centre at night.

Update 15/02/10:
I found the tracker to be very picky, I'm looking for ways to improve it. I don't recommend that you build this tracker as it's a little too picky to get it to work properly I've left the instructions here for reference though.

How is it supposed to work ?

The motor is wired to go west by default, if the sun is to the east it powers the east pointing solar panel which reverses the motor direct. It goes whichever direction until the centre solar panel is pointing at the sun, which powers a transistor and stops the motor. If there is no strong light, the tracker returns to centre, it has some switches in the base that tells it where the panel is pointing, and this moves it in the appropriate direction until the centre switch is tripped.
 

 



Here is the tracker being tested in the sun. It works!
 
For the base you need to cut two lengths of 2x2 about 70cm long  actual size may very depending on your solar panel. And two horizontal pieces about 6" wider than your solar panel.  You an screw these together in a H frame arrangement. You can see I had to cut a slot out for the motor, you may have to do the same, you might have to vary this arrangement depending on your motor.

To attach our moving solar panel to the windscreen wiper motor we'll use a flat metal bar.
Measure the width of your solar panel and cut the metal bar to about the same size using a hacksaw.

Next mark the centre of the bar and drill a small 2mm pilot hole, next you can gradually widen the holes up to the size of the motor shaft. It's a good idea to test the final drill bit size to make sure that it will be a tight fit on the motor - use a piece of scrap metal to test.

After you have drilled the centre hole, drill four other holes 2 either side at 2" intervals - use the 4mm bit for this. This is so you can attach the wooden solar panel frame to the metal bar.

The photo on the right shows the test hole I drilled.

Nex I built a U frame and screwed that onto the metal bar.

This is then bolted onto the wiper motor.

In order for the tracker board to know where the solar panel is pointing there are two switches, one micro roller and one reed switch. The roller switch runs along a raised MDF platform. In the photo I am marking a template for this.

This is the roller switch the runs along the MDF platform. The MDF track is fitted so that the switch only actuates when the panel is pointing slightly west. The MDF track is cut to a circular  template shown above, make sure you round of the leading edges so the switch cannot get caught anywhere (I broke a few this way....)
 The switch is screwed to a block of wood which sticks out from the U frame. I just screwed this bloxk through  it's side. Make sure you rill holes for the screw so they don't split the wood.

The reed switch is an old cycle computer switch, it's actuated by a small magnet when the panel is pointing dead centre.

 Now cuta piece of timber approx 30mm by 50mm by 18 mm thick. It needs to have an angle of about 45* on one end.


Now cut out the cardboard shroud for the centre solar panel.


I covered it in electrical tape to try and absorb any stray light. I'd recommend using black cardboard instead as the electrical tape is actually quite reflective


THis is the tracker sensor. There are two calculator solar panels that detect where the sun is. By default the tracker goes one way, but when the angled solar panel sees light this tells the tracker to reverse the motor. This is needed because the solar panel always starts in the centre  (for overcast days too) so the tracker can move east.

 


Nex build the frame for the solar panel. This is just a simple box frame with two holes drilled at the ands so you can bolt this to the U frame. You also need to add a shelf for the electronics to fit on.

I taped three relays together using electrical tape. This makes the motor controller much easier to handle. There are three diodes two to stop back emf from the relay coils and one to stop back emf from the motor.



From your finished relay block their should be the following wires.

Positive (+12V)
Negative
Motor STOP
Motor Reverse

Motor Connection 1 (no polarity)
Motor Connection 2 (no polarity)


Here's the motor control relays, these can turn the motor on and off an reverse it's direction.


This is the motor control board, you can see the potentiometer that I used to adjust LDR sensitivity.


Old Circuit



Improved circuit (untested as of 02/01/10).I didn't realize at the time but the old Circuit draws the relay coil current all night which can add up to quite a bit of power. Strip board has not been updated to reflect the new circuit though.
 
Now you can fix all the electronics in place, I used some screw blocks to connect all the wires together. You can see in the photo that I am testing it to check it works. Once all the electronics is fixed you can wire in the motor to see if it works in real sunlight. You'll probably have to readjust the LDR potentiometer if you had it set for artificial light.


Testng:

Hopefully, it will all work first time and not need any adjustment. But if it doesn't here are some pointers,

  • The tracker only goes one way when in sunlight:
                The east solar sensor is too sensitive, adjust the resistance until it goes the right way. If                     the east sensor if very sensitive light can reflect off the inside of the plastic tub and trip                     the east sensor making it think the sun is not where it is.

                OR there is a fault with the wiring board, check the above before looking here.
  • The tracker does nothing in the sun
                Possibly the LDR potentiometer is set wrong, adjust until it moves under bright light.
  • The tracker moves away from the sun and not towards it.
                The motor is wired the wrong way round, switch the wires.
                The sensors might be wired the wrong way around.
  • When the tracker returns to centre it just oscillates back and forth.
                The centre and reverse switches are too far apart, the centre switch should trip just as the                 roller switch comes to the end of it's track.

  • When the tracker returns to centre it goes the wrong way sometimes and tangles the wires
                Reverse the position on the reverse switch, i.e use N.C instead of N.O


Hopefully you should have it all working now, you just need to add the finishing touches. I recommend you treat all the timber with something water proof. I added a cover over the electronics to keep it dry, it's a good idea to add a plastic disc around the base to keep the water off the switches and tracks.
You will need to either weight the tracker down heavily or fix it to something to prevent it being blown over. I used a couple of deceased car batteries for this. I also added a wire holder to prevent the wires getting tangled up, I just used a scrap of 2x2 and drilled a hole in it for the wires to run through. Then I screwed this to the base.


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