Since several people have voiced interest in setting up there own Solar Powered Led home lighting in my 2 Solar Powered LED home Lighting threads Part1 and Part2, I thought I would wright up a little bit of information on the VW Solar panels. If someone wants to purchase some real Solar panels, a charge controller, and some deep cycle batteries then by all means go for it I don't think you will regret such a decision. Just be prepared to spend several hundred dollars. If someone is just a bit curious about the idea and wants something to play and experiment with and doesn't want to make that kind of financial commitment then this thread is for you. I will be discussing the VW Solar panels which can bu used to build a small PV system which is well suited for running a few home lighting LED's and should have a complete build cost of well below $100.
Volkswagen started suction cup mounting small PV (Photo voltaic) panels inside the windshield of there cars so that the batteries would not go dead while being shipped to the dealer. There now seems to be no shortage of these panels on Ebay try searching for VW Solar.
There are 2 different types of VW panels the older ones were made of Polly Crystalin PV cells (Blue cells) and are rated at 3.2 Watts. In direct sunlight they are specked to charge a 12V battery with about 170mA though of 4 I have played with all have slightly surpassed this speck with the best one put out up to 230mA in the Arizona sun.
A charge controller is an important part of a PV system and for some reason people sometimes think they can do without one. I used to think this as well when I first started playing with PV panels a few years ago. I had a nice sized 75 amp hour deep cycle battery and thought that one panel would not damage by battery especially if I was continually using power out of it on a daily basis. Well I destroyed my battery within a few months and bought a new battery and charge controller shortly ther after. Maybe Volkswagen learned the same lesson because the first Polly Crystalin panels plugged into the cigarette lighter with no charge controller. They lated added a small charge controller circuit inside the cigarette lighter plug. Of the 4 panels I have played with 2 had charge controllers and 2 didn't. All 4 panels were identical on the exterior with no visible way to tell which had a charge controller and which didn't.
The only possible way to tell without taking the plug apart is perhaps by the manufacturing date stamped on the back. The oldest one that did have a controller was stamped Dec 30th 2004 So I am going to predict that if you get one with manufactured in 2005 or later it should have a charge controller in the cigarette lighter plug. There also appears to be a version of this panel that plugs into the cars OBD2 diagnostic port and it came out sometime in 2006. I have never played with this particular panel so I can't say if it has a controller or not but I would hope so.
The newer panels are produced by ICP solar and are made of a thin film on glass (Amorphous) panel. They appear brown/burgundy in color and are rated at 4 watts. I just acquired one of these newer panels a few hours ago and although I have not experience with them long term as I have the older models I think I can still give some insight on them. You can probably expect them to charge a battery at 275ma in peek sunlight. They have a small box in like with the cord which is the charge controller and they plug into to OBD2 diagnostic port.
The real advantage that the VW panels have over your average solar battery maintainer that you would find in a automotive or department store is the included charge controller circuit and they have higher power output than most other battery maintainers I have seen in the store.
Now to talk about how to improve the charge controllers. I like it when things give me feedback and let me know what they are doing. Most charge controllers tell you when the battery is fully charged or how close it is to being charged. The older panels controllers had a place on the PCB for an LED which was not installed but can be easily added. You can see the white wires I added which go to a remote LED you will also need to add a resistor to the spot on the PCB marked R10. I used a 4.7K ohm but you can probably use anything between 1K to 7K ohms, just remember you want to be able to see the LED but dot have it suck up much of your valuable power. I added extra wire to the input and output of the controller and screwed the cigarette lighter case back together and allowed it to still act as a housing. One added feature of this board is that it used a .5A PTC resettable fuse for protection. If it ever gets tripped just remove power for a few seconds and it will reset. I am assuming this means it is good for controlling up to a max of .5A or current. I have ran 2 of the older panels on one charge controller and it all seemed to work fine.
The newer ICP charge controller is a much simpler design but from my brief testing it seemed to work well. It has a .5A glass fuse for protection which will need to be replaced if something goes wrong. The main power transistor is a large TO220 and appears to be rated for 3 amps but as it is the design does not have the heat sinking which would be necessary for that kind of current. There is also a pass through diode which is likely only rated for 1Amp. So if the diode was improved upon and some heat sinking was added to the transistor this charge controller could likely be used for up to 3 amps. You probably will need to lower the value of R4 to something like 200 ohms for it to work at these currents. I added an indicator led by soldering a resistor (same choice criteria as the other controller) to the ground connection and connecting the other side to the cathode of a LED. The anode (+) of the led is connected to the side of the large 500 ohm resistor (R4) that is loser to the legs of the transistor.
These indicator LED's will be illuminated when the battery is being charged. When the battery is near full the led will begin to flash, the duty cycle will reflect the state of charge, the longer it is off the more charged the battery will be.
In the past I did a small experimental system using one of these older panels I used the 12V 7Amp hour SLA battery out of my Thore spot lite. Small 12V lead acid batteries should be easy to come by, just make sure it is a good one and not the fried one out of that old UPS in the scrap pile.
As far as LED's are concerned you should have a whole pile of candidates waiting to be put to good use with all the Cree (or whatever the LED of the month currently is) upgrades going on. Those old LED's will work great. Just wire 3 in series with an appropriate current limiting resistor. I used a switch box with several different resistor values I could switch in to give me different drive currents. I ran my test setup with these parts for several weeks and it worked great. My charge controller indicator LED was showing my battery was reaching a full charge almost every day. I got ambitious and hoked up my Rayovac battery cooker (charger) to the system and used it to charge a couple NiMH cells. It probably was not a great idea because the battery did not reach a full charge again before I took the system down probably less than a week later. So be realistic and don't expect a 3.2 watt panel to run your computer and refrigerator, well you get the idea. It is a lot of fun trying to be as efficient as possible and seeing how much you can get done with as little resources as possible.