High efficiency solar charger circuit tops off those lead-acid batteries

Make your next project solar-powered with this charging circuit. It’s completely through-hole, and there are no microcontrollers that need to be flashed. If you can source parts and are handy with a soldering iron building this will be a breeze.

Both the maximum system voltage and the low voltage drop out are configurable. After assembly, you just need to attach a regulated power supply to the load terminals. Tune the power supply to the max voltage and turn a potentiometer until an LED comes on, then repeat the process for the drop out voltage. Board artwork for the two-sided PCB and a schematic are available from the page linked at the top. If you’re not into etching your own circuit boards you can buy one for around $10.

[Thanks Murray]

Building a solar power heliostat

[Frits] has been working on an solar panel heliostat (in Dutch, check out the translated page here).

The heliostat uses a small PICAXE to control the motor, along with an DS1307 real-time clock to make sure the motors start at dawn. Instead of using optical encoders or magnetic sensors, the angle of the heliostat is measure with a pot attached to the drive shaft. [Frits] did a lot of data collection to figure out that this method is accurate to about 1 degree – just fine for something that doesn’t need to be exact.

According to [Frits] this heliostat will put out 12 to 50 percent more electricity than a fixed panel. Although the build does seem a little bulky, putting it on a  house with a roof pitch of 23.5° would greatly reduce the horizontal profile.

A video of a solar panel rotating at 15 degrees/hour isn’t that interesting, so [Frits] posted a clip of 6 mirrors slewing around fairly fast to demonstrate his system. Check it out after the break.

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Selective solar sintering with sand

[Markus Kayser] built an amazing solar powered SLS printer, but instead of using lasers and powdered plastics his machine uses the power of the sun to heat sand into complex shapes.

[Markus]‘ printer uses the same concept as his earlier solar cutter – burning things with a magnifying glass. Interestingly, the printer isn’t controlled with stepper motors and reprap electronics – it’s completely cam driven. The solar panels only power the motor attached to the frame moving on bearings made from skateboard wheels.

We’d guess that [Markus] is using a little more than 2 square meters of Fresnel lenses in his project. Since solar irradiance is about 120 W/m² (PDF warning), [Markus] is concentrating a lot of energy onto a point the size of a quarter, which would be necessary to heat up sand to its 1500° C melting point. The resolution isn’t what you could get with a laser, but [Markus] was able to print an amazing bowl along with other complex 3d shapes.

Check out [Markus]‘ video of the solar sinter printer after the break. There’s also a video of his previous experiment with the solar cutter.

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25C3: Solar-powering your gear


The 25th Chaos Communication Congress is underway in Berlin. One of the first talks we dropped in on was [script]‘s Solar-powering your Geek Gear. While there are quite a few portable solar products on the market, we haven’t seen much in the way of real world experience until now.

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LED sensor solar tracker

More of my EV kick coming through. A solar tracker is used rotate a solar panel to get optimum energy from the sun. This one uses LEDs as the light sensor and mosfets to drive the output to rotate on a single axis. He even reduced the duty cycle on the fets so no heatsink is needed. Mounting in a peanut butter jar keeps the circuit dry and allows the sun to shine through. (The designer sells these, but has circuits up on the site)