For nearly two years I have been trolling around the Internet looking for a Sun tracker circuit that may be worth following. I have also looked at many circuit books and never come up with anything that is precisely what I want.
I think I have found it at last and it was designed by Richard Gideon and can be found at http://www.phoenixnavigation.com/ptbc/home.htm
The article containing the circuit and explanation was posted in April 2005.
After looking at the circuit layout I asked a few questions in the Forum area.
I decided to go ahead and build it and quite early on I realised that so many capacitors and resistors would be a nightmare to wire up on a small board. I decided to do something that I have never done before which is to make up my own two sided printed circuit board after down loading software from PCB Express - http://www.expresspcb.com/
PCB Express offers a special deal for three printed circuit boards if one can fit the entire circuit on a board of their size. This I managed to do and after fiddling a bit I suddenly realised how wonderful a two sided board was for jumping connector lines up and down. I sent off the order on a Thursday and the three boards were in my hands the following Tuesday afternoon.
Whilst the boards were being manufactured I went shopping for all the parts plus sundry items such as weatherproof boxes, relays switches and so on. Time was on my side and I made up most of the 12 volt hardware side before the printed circuit boards arrived. In addition to the control circuits there are two other important items namely; the actuator and the light sensor.
The actuator is a Superjack 18 inch model with a 36 volt DC motor. I shall be running it on 12 volts DC so the slow drive is perfect. I checked the cam follower switches and found they were Normally Closed and my circuit required Normally Open types. I found some excellent replacements in an electrical shop which offers Japanese made models and include both Normally Open and Closed contacts, so this was a bonus. The dimensions of the new switch exactlty matched the old so the changeover was very simple.
The light sensor consists of two Light Dependant Resistors (LDR) in a weatherproof housing. On the outside I have glued on a shadow maker so that the movement of the sun causes a shadow over one of the LDR's. It's the same as a sundial. To make the LDR's more sensitive I have covered them with 15mm copper pipe pots with a peephole in the top.
The new boards arrived and I populated them in the usual way to ensure component values were in the right place. The centre of the electronics is based on a LM 339 chip - a comparator.
All the interfacing wires were connected and then the final moment came to connect up to a 12 volt battery. This was done and I am pleased to report that there was no magic smoke. The weather on the day of testing was rather heavy cloud with just the odd moment when the sun shone through. At the right moment I tweaked one of the variable resistors and lo and behold the system came to life and continued to track on and off throughout the day until the sun disappeared leaving the usual darkness effect. At a moment in time the system suddenly came to life again and the electronics returned the unit to face East ready for start up next day.
Needless to say I was quite pleased with all of my efforts, especially my first-time-ever with a double sided printed circuit board. I dare say some of you readers could make a better job of the layout and reduce its size, but I like having space to work in.
There are one or two interesting things about the circuit which have not been given an explanation in the circuit briefing written by the designer. Firstly, the printed circuit board operates on 9 volts from a 78L09 regulator while the rest of my board and the relays currently work from a 12 volt DC supply. If I was to change over to a 24 volt system the only items I need to change are the relays.
After the dish has `parked' in the East at night both LED 1 and 2 remain lighted and will do so until light appears the following morning when they extinguish themselves. The circuit design makes provision for an `optional' power supply switch so that the LED's could be turned off rather than being left to glow all night. At least that's my guess. As far as I can see the LED's remain lit due to the Light Dependent Resistors being saturated with `darkness'. I dare say some of the very experienced electronic experts on this site will better understand this better than I and come up with an idea to turn them off overnight - other than the optional switch that is. Despite remaining `on' however, no harm appears to have been done to the circuit.
The circuit also contains a delay in the form of a 3,300uF electrolytic capacitor which takes about four minutes to charge up. This absence of this feature would mean that the circuit was constantly motoring to follow the sun.
The light sensor module is interesting. I fitted it on top of the test bracket expecting everything to point directly at the sun, but it does not. I realised that this is due to the way in which the Light Dependant Resistors are set up in the module. The answer to correct alignment to the sun is to perform a trick with the mechanical part and adjust one against the other so that both are satisfied. The light sensor does its work and the metalwork points at the sun. This bit of fine tuning requires some fiddling between the azimuth and elevation of the sensor on the solar mounting, and the variable resistor controlling the sensitivity of the light dependant resistors. I have yet to master this, but it should not be a problem.
To help with this setting up process the main board also contains a toggle switch which takes 9 volts from the printed circuit board through a 4.7K resistor to the centre pin. The remaining two contacts on the switch are then wired to the base of each TIP 120 so that the actuator can be motored to the East or West. This is very useful for setting up.
Just to remind everyone this is a SUN tracker not a solar tracker. Allowing for the gradual change of the earth in relation to the sun in the next few months I am hoping to have my solar panels exposed to the sun for about eight hours each day.
So there we are, two years of my patience and a very good circuit. I hope you all like the article. Cost wise it has probably hinged around US$60 or less, but the future benefits outweigh the capital cost. I can now invest in some serious solar panels (I do things in reverse if I can - work out the control equipment then buy the parts).
If you want copies of my PCB Express files you will need to download the software and then ask me to mail them to you.
Next job on the list is to purchase some deep cycle batteries, but I am at least getting closer to opting for a 24 volt DC system in my home. More decisions!
David HK