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johnmc Senior Member Joined: 21/01/2011 Location: AustraliaPosts: 282
Posted: 08:50pm 02 Feb 2014
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Good Day All,
I am in the process of building a single axis solar tracker and would prefer to use a timed tracking control.
The problem is, that while I would be able to use timers and limit switches, a
picaxe solution appeals to me.
It would be much appreciated if there is a of the shelf timed tracker unit or
information that includes the required programs to make one.
Best wishes to all Johnmcjohnmc
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 09:18pm 02 Feb 2014
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I dont know of a off the shelf item to suit your requirement, although im sure you could buy prototype boards and wire it all together.
Its really a matter of what you want to acheive.
Here is a couple of photos of one i built for Amack, although i dont have the time to build you one.
Pete.
Sometimes it just works
johnmc Senior Member Joined: 21/01/2011 Location: AustraliaPosts: 282
Posted: 10:49pm 02 Feb 2014
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Good day Downwind,
Thanks Pete for your reply,that is the type of tracker control that I would like to
build.
I have built the odd board years ago but it was nearly always with discreet
components,the main problem that has to be faced is my lack of programming skills.
John
johnmc
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 11:53pm 02 Feb 2014
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Have you ever used a picaxe chip, as that might help to understand your electronic skills.
Dont be shy, because a program can be written and emailed or posted on the forum, that you can just download to the chip.
BUT, its a matter of are you able to program a chip, or even understand how a picaxe can be used for this application, tell us more.
The basic requirement of parts is, a picaxe chip, i would suggest something like a 20m2, a RTC (real tine clock) like a DS1307, (lots on fleabay) a display, a LCD would be easier than a led 7 seg display like i used.
Keypad is optional, although it can make setup easier, but if you dont mind changing the program and reloading the chip, no keypad needed.
Pete.
Sometimes it just works
johnmc Senior Member Joined: 21/01/2011 Location: AustraliaPosts: 282
Posted: 12:15am 03 Feb 2014
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Thanks again Downwind
No Pete I have not programed a picaxe but have written to memory chips on cnc controls
also written PLC programs when I retrofitted controllers to a cnc mill and also to a mazak lathe I have a basic understanding of picaxe but am willing to learn if pointed in the right direction.I completed 2 years of industrial electronics about forty years ago I have also setup a selectronic inverter on my boat
.
johnjohnmc
MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819
Posted: 12:24am 03 Feb 2014
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Hello John,
It sounds like you are well over half way there. Programming a Picaxe or a MaxiMite is little different to programming a PLC. Most of the electronics is in the Picaxe (etc) but you might have to hook up a relay or two. That's about the extent of it.Edited by MOBI 2014-02-04David M.
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 03:49am 03 Feb 2014
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I have been running 3 timed solar trackers (2 axis) for over a year now.
Yes, you could complicate what is basically a very simple electro-mechanical solution with microprocessor electronics to archive the same result.
But is it going to be more reliable? I dunno.
More fun to build? Could be.
But you will require some kind of positional feedback to tell the microprocessor where the tracker is aimed, this will require extra wiring.
My tracker has just 2 control wires to supply it with 12V for one minute, at the timed interval. All positioning is done by a notched plate & micro switches, including parking it horizontal over night.
Klaus
MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819
Posted: 11:53am 03 Feb 2014
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My system was made for two axis tracking but only found the need for single axis. I had a reed relay at either end of the travel for "end of arc" detection and divided the arc up into a number of fixed intervals.
The system has a real time clock which tells the system when to return to start of day position.
The tilt control was never really needed and these days with the price of slar as cheap as it is, I would simply fit an extra 20% more panels and leave it fixed at north with the tilt determined by latitude. That way you don't have things to go wrong (and they do). 20% is about the extra you get by tracking.
However, don't let me stop you from building it - it is fun to get it working.David M.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 12:30pm 03 Feb 2014
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I am putting together a single axis timed tracker right now.
It could not be simpler.
Basically a hardware store digital on/off appliance timer, and two limit switches on the tracker gearbox.
The tracker gearbox is driven by a stepper motor to have exactly 180 degrees rotation in exactly 12 hours, the stepper is driven from 50 Hz mains frequency digitally divided.
The control logic is very simple.
The timer is set to come on at 6:16 am and go off at 6:16 pm (7:16 am and 7:16 pm daylight saving time). The extra 16 minutes corrects for the longitude of Melbourne within the Eastern Standard Time zone.
If you are located east of Melbourne, less than 16 minutes, west of Melbourne maybe a bit more.
The stepper tracks forwards for 12 hours, and reverse for 12 hours, determined by the time switch.
If it hits a travel limit switch before the timer reverses the motor, the motor stops an waits for the timer to switch.
So it always reverses and starts travelling the opposite way at 6:16 am and 6:16 pm.
This is a very simple way to synchronise the motor to the correct solar time, and it will stay synchronised, and correct itself automatically if it gets lost, say due to a short power interruption.
You don't really need a microcontroller.
And a $12.00 digital timer works better, has its own internal battery backup, and costs less than building something totally from scratch.
You just need a few logic gates to stop and reverse the stepper when a limit switch or the timer activates.
It could not be simpler or more straightforward.Edited by Warpspeed 2014-02-04Cheers, Tony.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 10:48am 08 Feb 2014
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Some thoughts on putting together a suitable motor and gearbox......
I think most of us will be using either 1Hz divided down from from a quartz watch crystal, or 50/60 Hz from the power grid as the primary frequency source for a timed tracker.
In my case, I decided to use the 50Hz grid as my frequency reference, simply because it is constantly being corrected, there being zero cumulative long term time drift.
The trick to this is working out all the factors of the total overall time/frequency division, and how to obtain those same factors as easily as possible with a practical combination of electronics, stepper motor, and gearbox ratios.
So we start off with our requirement, and break that down to factors:
50Hz grid to one second x50 (5 x 5 x 2)
Seconds to one minute x60 (5 x 3 x 4)
Minutes in one hour x60 (5 x 3 x 4)
Hours to track x12 (3 x 4)
Total x 2,160,000
There are many types of stepper motor with various numbers of steps per revolution available, but these days the most common type by far, is the 1.8 degree, 200 steps per revolution type commonly used for CNC and robotic applications.
200 steps per revolution x200 (5 x 5 x 8)
Add a 25:1 gearbox x25 (5 x 5)
Add a 27:1 gearbox x27 (3 x 3 x 3)
Four stage counter x16 (4 x 4)
Total x 2,160,000
Getting more or fewer factors of two is pretty simple with a digital counter.
So our 25:1 gearbox could be a 100:1 or 50:1 or even 12.5:1 which are all common ratios.
The 27:1 gearbox could also be 54:1
In my case I already had a 200 steps per revolution stepper, and a suitably large 54:1 gearbox. I then bought a small 50:1 gearbox off e-bay.
That, plus a divide by four counter running off 50 Hz to drive the stepper thould keep perfect time.
Just google "gearbox 25:1" for example, there is plenty of stuff out there to do the job. Cheers, Tony.
AMACK Senior Member Joined: 31/05/2009 Location: AustraliaPosts: 184
Posted: 02:50pm 02 Jun 2014
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Hi John, The tracker that I use is the one Pete and I put together a while ago. It has been working well for over three years now and the only think I have had to do is replace the small motor that runs the reduction box's. It came from Jay*** and was only $25. It puts out more power than fixed panels as you would expect. I think that it is well worth the effort and the out put will pay for the out lays. I used a holden car diff to move the panels and where I live the wind is so strong at time I have had a chook lay the same egg twice. The diff has not moved but some nights when the wind is blowing like mad I expect to get up in the morning and find it gone but it is still there. I have 6 250 watt panels on it and that is one big sail to catch the wind..
Amack
P.S there are a few early photos on the Australian pixaxe forum..*Note to self
1. Make it thick
2.Make it heavy.
3.Make it stronger than it should be.
4. Don't rush the first job as the second job will cost more and take mor
johnmc Senior Member Joined: 21/01/2011 Location: AustraliaPosts: 282
Posted: 01:16am 03 Jun 2014
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Good day All,
Firstly I would like to thank all the people who posted advice,which is most generous of your time and knowledge.
Also the people behind the Back shed forum.
I have just finished building my solar tracker which is controlled by off the shelf digital timers, limit switch and a partial index wheel and linear actuator.
The array consist of 8, 250w panels that sit on a grid of 75x50x3mm RHS for the backbone and 65x35x2mm RHS for the bearers (the picaxe solution is yet to happen).
At present I do not know how to post photos on this forum and would appreciate some
advice on the method used to post photos and drawings.
cheers john johnmc
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 02:32am 03 Jun 2014
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Use the forum image upload button at the top of the reply window.
It will appear in your post reply as a text string and not a photo.
use the "Preview Post" button at bottom of screen to view the photo prior to "post reply" to see what it looks like.
It will take some time for the photo file to upload to the forum so expect some delay while it uploads.
Pete.Sometimes it just works
johnmc Senior Member Joined: 21/01/2011 Location: AustraliaPosts: 282
Posted: 02:16am 04 Jun 2014
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Good Day to all,
The following photos are of my 2kw tracking array with no sun light.
This photo shows the limit switch and part index wheel which allows a total
movement of 90 degrees in 15 degree steps. The RHS sections
have been bolted together which allow easy fitting of the solar panels
and no weld induced stress on the RHS sections.
All mounting plates and index wheel was plasma cut.
The main backbone of the array runs on sealed bearings to help reduce the load on
the linear actuator.
These stainless steel clips attached and stop galvanic action between the steel RHS section and the solar panel.
General view of panels when at maximum west facing position.
The control box of the tracking array which allow the array to move in 15 degree steps from east to west facing and also allow horizontal parking at night.
As the linear actuator was to fast for the one minute times I have had to run 0 t0 60 second timers in series with the minute times as it requires only about 10 seconds to
close the limit switch
Cheers john
johnmc
johnmc Senior Member Joined: 21/01/2011 Location: AustraliaPosts: 282
Posted: 02:24am 04 Jun 2014
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Good day
Thanks again Downwind for your advice on uploading files to the forum .
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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The diff has not moved but some nights when the wind is blowing like mad I expect to get up in the morning and find it gone but it is still there. I have 6 250 watt panels on it and that is one big sail to catch the wind..
