Solar Charger for 12V SLA Batteries
Guenther Daubach
Posts: 1,321
Hi all,
as indicated in the http://forums.parallax.com/showthread.php?p=884828 thread, I'm working on a solar charger project for Parallax. Ken has asked me to share this project with you guys here in the forum.
This charger should be easily assembled by DIY'ers, work without adjustments in most cases, and it also should self-protect against disasters like wrong polarities, shorts, and dead batteries.
Beyond this KISS approach, I was challenged to add some bells and whistles:
With three additional pushbuttons, and the always existing three status LEDs, it is possible to configure some of the charger's parameters, like the maximum charge current, the boost voltage, and the flat voltage.
By adding a three-pin header, and a Parallax serial LCD display (2 x 16), you can upgrade the charger to the "de-luxe version". The LCD display normally shows, the charger status. In configuration mode, together with the pushbuttons, the LCD display makes it easy to setup the various parameters. Such parameters are stored in the microcontroller's EEPROM section for future power-ups.
Too bad that my "special friend", the SX microcontroller has entered its end-of-life phase - I had really preferred using an SX for this project. As an alternative, I have choosen the ATtiny26 controller instead.
In the attached ZIP archive, you can find the preliminary schematic, the PCB design, and a short description of how the charger works.
Please feel free to post any hints, ideas, wishes, suggestions, .....
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Greetings from Germany,
G
as indicated in the http://forums.parallax.com/showthread.php?p=884828 thread, I'm working on a solar charger project for Parallax. Ken has asked me to share this project with you guys here in the forum.
This charger should be easily assembled by DIY'ers, work without adjustments in most cases, and it also should self-protect against disasters like wrong polarities, shorts, and dead batteries.
Beyond this KISS approach, I was challenged to add some bells and whistles:
With three additional pushbuttons, and the always existing three status LEDs, it is possible to configure some of the charger's parameters, like the maximum charge current, the boost voltage, and the flat voltage.
By adding a three-pin header, and a Parallax serial LCD display (2 x 16), you can upgrade the charger to the "de-luxe version". The LCD display normally shows, the charger status. In configuration mode, together with the pushbuttons, the LCD display makes it easy to setup the various parameters. Such parameters are stored in the microcontroller's EEPROM section for future power-ups.
Too bad that my "special friend", the SX microcontroller has entered its end-of-life phase - I had really preferred using an SX for this project. As an alternative, I have choosen the ATtiny26 controller instead.
In the attached ZIP archive, you can find the preliminary schematic, the PCB design, and a short description of how the charger works.
Please feel free to post any hints, ideas, wishes, suggestions, .....
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Greetings from Germany,
G
Comments
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Check out the Propeller Wiki·and contribute if you can.
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Check out the Propeller Wiki·and contribute if you can.
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-MH
The new Parallax Solar panel is only 6 volts. Do you need three of them for this charger ? That would be a lot of money ($450).
I was thinking it would be a boost circuit so you could charge a 12V battery with one of the solar panels.
If this is NOT designed for the parallax solar panel, then these are mute points.
Bean.
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Use BASIC on the Propeller with the speed of assembly language.
PropBASIC thread http://forums.parallax.com/showthread.php?p=867134
March 2010 Nuts and Volts article·http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/prop/col/nvp5.pdf
·
I do understand the purpose of MPPT
why would you not use it, and thus not make maximum use of the energy generated ?
Linear tech have a suitable MPPT chip, so why not just use that.
Of course, if this controller has an LCD for info, then fine, use a micro, but why not also implement MPPT in software.
Mike
There really wasn't an effort to design the Panel to be compatible with the Solar Charger for a couple of reasons, one of which is that we wanted to keep the cost of the Panel down to something reasonable, and using commercial grade cells to generate 18 volts (that's thirty six cells!), would have nearly trippled the cost of the Panel...Which, to me, would have been completely unacceptable.· The Panels, of course can be "daisy-chained" to up the required voltage.· And another thing was that the spec that Guenther was·working from,·was out well before the Panel was a "photon in anyone's eye" ;-)
That being said, the prospect of making them somewhat compatible (through the form of a dc/dc converter) probably looms on the horizon·
One of the original thoughts was that this might be an opportunity to put together a Panel that is reasonably priced, has real power (30 watts), and can be assembled on your kitchen table with a soldering iron, some flux, and patience.· Then, if desired, a second or third or nth panel can be added to your "system" over time, gradually allowing an ever-increasing amount of power to come forth.
One of the frustrating things for me was that the idea of "building your own solar panel"·almost always resulted in something that looked like a "wind-chime" that's been glued to a sheet of plywood, with very low repeatablity panel to panel, and overall *crushing disappointment*.· We wanted something that, after successful assembly, would generate power, look somewhat cool, and last for a long time...at least that's the intent!
The "6volt" level seemed to be the most logical "building block" (think "lego") to start with.
So, once I get one of Guenther's magical little chargers,·Yes!, I'm gonna put three Panels in series and see what pops! er...(poor choice of words)...see what happens!
As things unfold here, I'll keep you up on what may/might be next: dc/dc converter, mppt, etc.
And your suggestions/input are critical· - keep 'em comin'!
-Matt
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Matt Gilliland
-- it should support the possibility of MPPT, simply because of the coolness and education factors.
-- The Propeller should control something like a SEPIC chip that can work from a wide range of input voltages and produce a wide range of output voltages. (SEPIC can step voltage either up or down) With the appropriate control algorithm, it can charge any battery chemistry from any input source. For example, the LT1517 constant current/constant voltage SEPIC battery charger chip is an 8-pin DIP and can control up to 1 amp with its internal switch.
-- The Prop would control two feedback loops via the shutdown pin on the SEPIC chip, the primary loop for battery, dependent on its chemistry dependent charging algorithm, and the secondary loop on the input side to regulate the MPPT when the power is called for by the primary loop.
-- The Prop can monitor all the voltages and currents and temperatures and times involved in the algorithm, plus manage a host of bells and whistles.
I use a linear float charger for all my 12v SLA systems, but I'd really like one that can be quickly repurposed to charge Li-ion or NiMH batteries.
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Tracy Allen
www.emesystems.com
Roy:
Adding a USB connector to bring out the 5V is pretty easy. Let me see if there is enough real estate on the PCB for a USB-A connector.
mikestefoy:
Well, it could be kinda MPPT controller. The hardware allows to determine the solar panel voltage as well as the battery voltage, and the charging current. So, it is up to the software to implement MPPT charging. So far, I have finished a first version of a simple software, and as soon as I have the PCBs here for the prototypes, I'll test and enhance it.
Shmoopy:
I've been using the SX for many of my commercial projects with good success. Now that the SXes will vanish one day, I'm forced to use other controllers for new projects. Whenever it makes sense, I plan using the Propeller but I often have smaller projects (like the SLA solar charger) where the Propeller's power really is an overkill. Therefore, I looked for another family of cost-effective and powerful controllers. My favorite candidates were the AVR or the PIC controllers. Although some PICs and the SXes have some similarities, I finally decided to go for the ATMEL AVR controllers because I had already used them for some projects where the customer's specs requested AVRs.
Yes, the code for this project will be published, and I'll be using assembly.
Bean:
Well, I got the specs for "my" solar charger from Parallax as a separate project with no intention to combine it with the Parallax Solar Panel. Nevertheless, a special charger for the Parallax panel with some kind of a boost circuit would be another interesting project.
Matt:
Thank you for clearing up some points, and congratulations to your fine solar panel design!
I agree, there are many more interesting applications around solar power, so let's keep discussing this topic.
Tracy:
The project specs I got from Parallax ask for a simple, cost-effective charger that can be assembled by hobbyists with a minimum of soldering experience. Sure, using a Propeller instead of an ATTiny would add a lot more "horsepower" to the charger, allowing the implementation of MPPT charging, or SEPIC technology (with or without a special chip like the LT1517).
All:
Some readers may wonder what MPPT and SEPIC means:
MPPT means "Maximum Power Point Tracking". This is a technique to optimize the charge process by monitoring the panel's momentary output voltage, and the momentary battery voltage. Those two results are used to determine the optimum charge current that "transfers" as much solar power into the battery as possible.
SEPIC means "Single-Ended Primary Inductance Converter". Such circuits allow to charge batteries from an input voltage, lower or higher than the required battery charging voltage. To make this possible the circuits can act as step-up converters but also as step-down converters. SEPIC circuits require inductors, fast switching diodes, and a special controller, like the LT1517 Tracy had mentioned. IMO, the functionality of such special controller could be realized with the Propeller as well. Maybe, this becomes the next Parallax Solar Charger project.
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Greetings from Germany,
G
http://forums.parallax.com/showthread.php?p=889596
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
article on "Designing a Solar Cell Battery Charger" by Jim Drew
It might help you
http://www.linear.com/ltmagazine/LTMag_V19N4_Dec09.pdf
Mike
thanks for your info - I had a quick look at the article. Seems to me that it contains useful information, so I'll definitely have a closer look at it later.
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Greetings from Germany,
G
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Tracy Allen
www.emesystems.com
John
Size and cost?
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You only ever need two tools in life. If it moves and it shouldn't use Duct Tape. If it does not move and it should use WD40.
the specs I received from Parallax for this project ask for an easy-to-assemble, low-priced design.
Without the End-Of-Life announcement for the SX controller, I would not have selected any other controller but the SX for this project, and an SX28 would be a really good choice.
On the other hand, the Propeller would be a real overkill for the project, size- and cost-wise. Therefore, I had to look for a device "outside" of Parallax.
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Greetings from Germany,
G