Thursday, July 30, 2009

Solar Power for the Garden House - Light it Up!

Ok, this will be a long one. Here in the Pacific NorthWest, all kinds of alternative energy sources are used and abused. We just built a great Garden House and want power for lights out there. We'll run AC power out to it in a few years, but until then... how about SOLAR Power! Yeah!

We got a great deal on ebay for a 10W solar panel. Nice and sturdy.

We did have to wire the solar panel up... but it was pretty easy. We don't mind alittle hands-on with anything... in fact we usually tear something apart to see how it works.

The basic idea is to use the solar panel to continually charge a 12V car battery in the loft of the shop. When we need lights or radio, we simply use the car battery to power the lights.

To trickle-charge the battery by the solar panel, we built a simple "Shunt" charge circuit - it simply protects the battery and the panel from eachother and monitors the power output from the panel... if the voltage gets too low, it turns off the panel. While designing our own, we found this guy who has several we liked:
The only problem is... I hate to solder. Someday the kids will do it for me, but until then, I have to. I first started a circuit board using a perf board... but it took TOO many extra wires and drilling.
I've had this old "etch-a-PCB" kit and thought we'd give it a try! Besides, acids, permanent markers, drills, it all spells FUN!

First step was to convert the schematic (above) into a diagram to draw out on the copper plate. We then draw permanent marker on all the copper we want to STAY, and use acid to etch off the copper we DON'T want. Easy, right?

Here's our artwork. Yeah, it looks like the 5 year old did it... but she didn't...

Now was the fun part - ACID! Ouch - my eye! Did we mention that Dad's eye is inflammed, and he has it dilated and on medication every hour? Talk about flying blind...

Oh well - onward!

Being careful to use protective gear we doused the copper board with acid and watched it disolve away the unwanted copper. It took about 5 minutes. We rinsed the board in water, then touched up the marker and put it in acid another 5 minutes. Done!

Here is the finished board. A little solvent took off the marker and it was shiny. Last step for the board was drilling holes. Not many of those, so it was easy. Be sure to drill on the copper side.

Here are most of the components placed on the board prior to soldering. Can you see how we goofed? Yep, we layed out the board BACKWARDS! The copper and solder should be on the OPPOSITE side of the board from the components.

Oh well, no one will see it in our attic...

...good thing no one will see it, too. Look at those ugly solder joints! Look like my welds - gorilla! Ugly, but they'll hold.

Here is the finished board. Pretty simple in design and layout. About $5 in components from Digikey, half hour for making the PCB board, and another 15 minutes to solder it up.

But, does it work???

Yeah! It works pretty good. In the shade, the panel's output was about 18V, with 17.8V output from the board.
We covered up the panel, and output went down to 3V, and the shunt turned OFF. Good boy!

Here is the Garden House. Next step is to build a bracket to hold the panel to take in the most sunlight during the 1st half of the day. Even in the shade, out of the direct sunlight the output is more than 14V.

Now, with power available, its time to hookup lighting.

Two different sets of lights we'll be using - several of these LED light strips that run off 12V directly will be placed throughout the inside of the shed. A simple light switch will turn them off directly from the car battery.
A second set of LED lights we have purchased have PIR sensors on them and will be placed over the shed doors - so when we approach they will see us and turn on. Both sets of lights were purchased off ebay. The LED strips were about $9 per foot.

While we wait for the LEDs to arrive, we're doing more testing. We pulled the battery out of the back-hoe, and the solar panel will keep it charged and ready.
Here is the panel in the shade, and the battery charging. The initial charge on the battery was 11.91V. With the panel in the shade, the voltage increased to 11.97V in 1 hour. More data in the next few days of 100*F weather! Hot!
So far the project has run very smoothly. Total cost for the panel and circuit is $57, not counting the battery. Three LED strips and 1 PIR LED fixture cost a total of $38 on ebay, so we are at about $100 to add solar power out in the shed. We are feelin' green!