DIY Solar Tracker System

The "Modular" design will allow you to construct any size solar tracker, single or dual axis, and adapt it to any type of device. Photovoltaic PV solar panels, Solar Concentrators, Solar Heaters Solar Cookers and even mobile and marine trackers are possible with our modular design. The new circuit designed by Mike Mladejovsky, PhD uses an inexpensive comparator integrated circuit and Darlington pair transistor outputs to drive up to a 1 amp DC motor. While this circuit can drive large motors it is also possible to build mini-trackers with input voltages as low as 3.6volts. The sun sensor is simplified using only six LEDs and the drive units are slew type designs driven by planetary geared drill motors which provide lots of torque and are self locking.

As always you can build our trackers from recycled parts and cheap readily available materials but we will also be making pre-made components available as well as inexpensive kits. The circuit kit and fully assembled circuit boards will be available starting early in June 2010.

The new drive units use a motor and gear set from a battery powered screw driver or battery powered drill providing lots of torque. A worm gear is adapted to the chuck or drive shaft and it turns a spur gear much like how a slew gear works. For the first build I am using a Skill Twist battery powered screwdriver and the drive unit designed to handle a 2watt solar PV panel. For the second build I will construct a heavier drive unit using an 18 volt power drill motor

I do not have all the pictures available from the first build so if you have any questions just post them on our comment section or send me an email and I will provide you with more details. The first step is to dismantle your screwdriver, remove the batteries and cut off the handle. Drill a small hole near the end of the motor and feed the motor wires into the housing and solder them to the motor contacts as shown. Drill two pilot holes in the end of the plastic screw driver plastic housing which will be used to attach the screw driver to the gearbox housing in the next step.

The next step is to make the worm gear and attach it to the drive. Cut a piece of threaded rod 10cm in length and file down one end to fit tightly into the skill driver chuck and file the other end to fit tightly into the center of a bearing. I used a recycled roller-skate wheel bearing for this drive. Next cut one bottom (96mm x 96mm) and two side pieces (37mm x 96mm) out of ABS flat stock to make the gear box housing. In one of the side pieces layout and drill a center hole (17mm) and two mounting screw pilot holes to match the screw driver chuck and the two pilot holes drilled in the previous step. Assemble the gearbox housing with the side braces as shown in the picture below, with the worm gear firmly inserted into the screwdriver chuck mount, thread on a nut and press the bearing onto the worm gear then secure the screw driver on to the housing using two screws. The end of the worm gear with the bearing should just touch the side panel inside surface. Drill a hole in a piece of ABS flat stock equal to the outside diameter of the bearing, trim it square to fit the height of the side panel and then cut it in half and cement it to the inside of the side panel to hold the worm gear bearing in place making sure the entire worm gear assembly is aligned with the screwdriver. Place a small amount of epoxy around the end of the screwdriver chuck then thread the bolt to make contact and epoxy the bolt onto the worm gear as shown below.

Cut a piece of threaded rod for the spur gear approximately 10cm long. File down one end (8 to 10mm) to match the inside diameter of the spur gear, press the spur gear onto the shaft and epoxy. Note that this need to be a very tight fit to prevent the spur gear from slipping on the shaft. We must raise the spur gear to match the height of the worm gear so we will make a small platform by laminating several small squares of flat ABS together. Once the height is matched add another square piece with a hole drilled to match the diameter of the bottom of the shaft. This will act as a shaft guide and bearing surface so make sure it is loose enough to rotate freely but tight enough so there is no sideways movement. Cement the platform into place making sure the spur gear meshes with the worm gear while the spur gear shaft is perfectly vertical. Be careful not to make the spur gear / worm gear contact to tight or it will bind.

Next step is to make a bearing surface on the spur gear shaft that will hold the shaft where it penetrates the top of the drive housing. Measure about 6mm above the top surface of the top of the housing by placing a flat piece of ABS across the top of the housing sides and next to the shaft measure up 6mm then lock two nuts together with the bottom of the two at the 6mm mark this will serve as a guide for filing the shaft. Use the edge of a large flat file and file down a 6mm section just below the nuts to end up with the shaft as in the bottom right picture. You can make the diameter equal to a 1/4 drill which you will use later to make the split bearing.

Take a piece of flat ABS stock to make the top of the drive housing and estimate where the hole needs to be drilled for the spur gear shaft allowing for overhang on all four sides of the drive housing which will be trimmed off later. Drill a hole slightly larger than the 3/8 shaft diameter that will fit over the spur gear shaft. Making sure the spur gear shaft is perfectly vertical; tack cement to the top of the drive housing to ensure it is properly in place. Now mark the under side of the housing top on all four sides, remove it and trim it. Make sure to mark which side is up and after trimming it place it back in the same position and securely cement it into place.

The split bearing holds the spur gear shaft in place while allowing it to rotate freely. Note that you can place two of these on top of each other for added strength (you will need to file down more length on the shaft to accommodate the second split bearing). To make the slit bearing first drill a 1/4" hole in a flat piece of ABS plastic then trim around the hole to make a 25mm square. Next simply cut the square in half through the center of the hole. Making sure the shaft is perfectly vertical cement the split bearing into place as shown. Let the cement dry and then check the rotation of the shaft by driving the motor in both directions. The shaft should rotate perfectly on its axis and have no noticeable wobble.

This step you will add reinforced mounting holes to the gear box on the end opposite of the worm gear assembly. Follow the pictures below and cut out small rectangles to make reinforced bolt hole mounts. You have to make sure there will be enough clearance to insert a mounting bolt. For each side first cut a top and bottom piece cement then add a vertical piece let the cement dry a little then add a inside vertical piece and a outside vertical piece. Let the cement dry and then drill holes making sure you drill is as square as possible to the gear housing. If you are off and can't insert a mounting bolt just enlarge one of the holes slightly for more clearance.

The LED arrangement in the LM339 circuit below uses two rows of three LEDs with each LED connected in parallel, the two rows are connected in parallel but reversed polarity. The sensor array is made with three west LEDs and three east LEDs. A 1meg resistor and a 10n ceramic capacitor (103z) are also in parallel with the sensor. The sensor LEDs provide input voltage for two comparators on the LM339 chip with the variable resistor R2 providing a "dead zone" or sensitivity adjustment. Each comparator output is fed into a transistor Darlington pair which in turn drives the DC motor. The rail voltages are provided by two batteries connected in series with the center tap providing the ground reference. We have tested this circuit with 2 single cell lithium-ion batteries providing +/- 4.2 volts and two 12 volt lead batteries, the LM339 is rated for input voltages from +/- 2 volts to +/- 18 volts.  This circuit is the result of the design efforts of Mike Mladejovsky, PhD EE who helped us solve issues with the solar tracker #3 circuits via the Electronics Tech Online Forum which we highly recommend to anyone needing help understanding electronic circuits.  Many of the components in the following parts list can be substituted with equivalent components such as using an AN6912 comparator instead of a LM339. We use 5mm clear green super bright LEDs with a 40deg viewing angle but any clear lens LED should work for the sensor. 1/4 or 1/2 watt resistors are adequate, fuses should be placed on each rail and a DPDT switch can be used also.

• U1/U2 - LM339 quad comparator
• Q1 - TIP42C Power Transistor
• Q2 - TIP41C Power Transistor
• Q3 - 2N3906 Transistor
• Q4 - 2N3904 Transistor
• R1 - 1meg ohm
• R2 - 1k ohm trim pot
• R3 - 10k ohm
• R4 - 10k ohm
• R5 - 10k ohm
• R6 - 4.7k ohm
• R7 - 2.7k ohm
• C1 - 10n ceramic capacitor
• M - DC motor up to 1amp
• LEDs - 5mm 563nm Hi Green Water Clear

Below is the printed circuit board artwork for the LM339 circuit. The board is 4.0cm x 4.0cm as measured by the hash marks. The traces are 1mm which should allow you to etch the board using the lazer printer method. On the artwork "B" indicates the battery connections, "M" is the DC motor connections and the LED connections are at the top left. The red dots indicate connections to the positive +12volt rail, the green dots are the -12volt rail connections and the yellow dots are the virtual ground.Resize this image to approximately 8cm width and maintain the aspect ratio and you should get the proper size printout depending on your printer. Check the width of the bar at the bottom and right after printing it should be exactly 37mm.

Below is an updated version of the PCB, we have reversed the orientation of the power transistor Q1, changed the pad layout for the potentiometer and enlarged the pads for the all the external connections, the power transistors and the potentiometer.

Sun Sensor Unit

The Sun Switch sensor uses green GaP LED's to sense the position of the sun. When a GaP LED is pointed directly at the sun it will produce around 1.7 volts across the leads. By simply placing two or three of the LEDs in series you can provide enough potential to drive TTL logic inputs on a bridge driver.

The bridge driver circuit itself is simple and very easy to build. You can use any bridge driver chip that has TTL (digital input control) and is suitable for the size of DC motor to be driven. Parts to build a Sun Switch, motors, bridge drivers and LEDs, can be found in scrap electronics or computer hardware. This page describes a motor drive built with a L6202 chip and a sensor built with 5mm GaP LEDs.

Cut a 2" length of 1.5" ABS pipe which will be used as the sensor housing. Use the tool shown below to mark 3 lines spaced at 10mm around the circumference of the pipe. The tool allows you to easily mark lines perfectly perpendicular to the pipes axis by adjusting the pipe in the tool then rotating it with a drill while marking it. Also mark a cut line as shown which will be used to trim the pipe housing before attaching it to the drive unit. The tool is required because it is rather difficult to cut pipe at a perfect 90deg angle with a hand saw.

Layout the position of all the LED holes on the sensor housing as per the diagram below, there will be eight rows with three LEDs in each. Four rows of LEDs are connected in parallel and connect to either the east motor drive circuit or the west motor drive circuit. Center punch and drill the 24 LED holes in the sensor housing making sure that each hole is drilled perpendicular to the sensor housing axis and that each set of three holes are aligned parallel to the sensor housing axis. Each row is spaced 43 deg. apart and each LED is spaced .375" apart in each row. The east and west LEDs are separated by 23 deg. Use a proper size drill bit which will allow each lead to be firmly pressed into place. You can simply drill some test holes in a scrap piece of ABS to find the proper drill bit diameter.

Build two LED sets consisting of 4 rows of 3 LEDs. You can build a simple tool by cutting in half a short piece of 1.5" pipe and using it as a jig to solder the LEDs. Lay out and drill an identical set of LED holes on the tool before you cut it. Place the LEDs making sure of correct polarity then solder the leads using light strand wire.

Insert both sets of LEDs in the housing then insulate the leads with tubing or tape. Make sure you know the positive and negative leads of both sets of LEDs. Cut and cement a shadow plate between the east and west LED sets. Chamfer the edge of the plate and mount it parallel to the last row of the west LEDs.

Trim off the bottom .5" of the sensor housing. The cut should be as close to 90 degrees to the pipe axis as possible as the sensor must align properly with the bearing in the drive housing.

The Sun Switch sensor is basically an array of LEDs arranged on a curved surface. The sensor array is divided into an east and west array and separated by a vane which cast a shadow. When LEDs are exposed to direct sunlight within their focus angle they produce a small current (micro-amps) and associated voltage which is compatible with TTL inputs. 

Tracking - the shadow vane and first row of west LEDs are used for tracking. The shadow alternately covers then exposes the first row of west LEDs. When the first row is exposed to the sun it outputs a small voltage... which turns on a DC motor via a TTL circuit which drives the tracker and sensor in a west direction casting a shadow over the first row of west LEDs causing the voltage to drop and turning off the DC motor. This process repeats about every 60 seconds.

Searching - when resetting in the morning or updating after a cloudy period all the rows of LEDs are used and the end result is a tracking condition as above. If the tracker ended the previous day facing west the rising sun will strike the east most row of LEDs and cause the east DC motor to turn on which will drive the tracker in a east direction ... the first row of east LEDs will drive the tracker about 45 degrees then hand off to the next row of east LEDs which will continue to the next then the final row of east LEDs which is next to the shadow vane... as the tracker continues to move east the vane cast a shadow over the last row of east LEDs causing the east DC motor to stop. The sun then creeps westward and after a few degrees of arc will expose the first row of west LEDs and tracking will begin. A interruption in tracking (cloudy period) will result in the same process as a morning reset but the west LEDs are involved rather than the east LEDs.

You can download the .pdf file with all the schematics and pictures that blogger for some reason won't let me post by going here: http://www.pdf-archive.com/2012/01/10/diy-solar-tracker-system/