Sunday, August 10, 2014

Solar Energy And Arduino: Solar Charge Controller

There's an intriguing microcontroller (MCU) project in an August 8 article on Design News titled "Gadget Freak Case #260: Arduino Solar Charge Controller." I have't read a lot about solar energy and Arduinos, or any other MCUs, so I took a closer look at the article.
Residential active solar energy system (from Wikipedia CC)

Many Humboldt County people seem interested in solar energy, although the often-foggy or cloudy climate of Arcata, Eureka, and other coastal communities isn't as well suited to solar energy collection as the climate of New Mexico or Arizona cities. However, it is still good to be experienced with technologies used outside the North Coast, and there are plenty parts of Humboldt County not immersed in marine fog banks or redwood forest mists. For this reason it would be useful for participants in the Humboldt Microcontrollers Group to know the basics of active solar energy systems and to have experience with the electronic components and operation of those systems. The topic of the Design News article above isn't an inexpensive basic active solar energy system, but I think I'll do some research regarding different types of inexpensive systems for a future group project.
Solar charge controller schematic from

The solar charge controller that is the topic of this post is located between the solar energy collection device and the energy storage system, usually a battery. The controller regulates both the voltage and the current going to the energy storage system from the energy collection device. The schematic at the right from shows the general concept (although that schematic is not from Gadget Freak project). The Design News article describes the function of the Arduino this way:
"This gadget uses Arduino to control the whole process and takes a voltage reading from the solar panel and the battery to be charged. Then, according to voltage levels on either side, it charges the battery using PWM control signal. Energy flow is driven with MOSFET transistors that ensure low energy loss. The charging controller is equipped with basic filters on both the battery side and the solar panel side. It is also equipped with things like overcurrent, overvoltage, PV panel reverse current, auto load disconnection, and overcharge protection."
Gadget Freak #260: solar charge controller (Design News PDF)
The solar charge controller build instruction PDF is linked to in the article, and seems like a good quality document. It has pictures, circuit drawings, Arduino code, and the type of helpful tips that many project documents do not include. An example of the helpful tips is where the project creator describes how to choose MOSFETs. For people who aren't already familiar with MOSFET properties and how they're used, he says this about drain source voltages for MOSFETs:
"When the MOSFET is turned off, the whole supply voltage will be measurable across it, so this rating should be larger than your supply voltage to provide sufficient protection so that the MOSFET does not fail. The maximum voltage a MOSFET can handle varies with temperature."
He also talks about whether to use an n or p channel MOSFET, continuous drain currents, thermal loss, gate threshold voltage and more. Tips like this are especially useful to people like me who are new to microcontrollers.

In months and years to come, it is my hope that the Humboldt Microcontrollers Group will build many MCU devices and systems. Nick's automated chicken coop door is the first one, as far as I know, and the Humboldt Laser Harp is the second, I think. It would be great if we can develop and put online as much information as possible about these MCU projects, assuming they're not going to be commercialized so they can earn us millions. Or even thousands. Anyway, part of gathering, organizing and publishing this MCU project information should be a good documentation format. There are many possible formats, but the Gadget Freak 'build instruction PDF' used in the solar charge controller project seems like a good place to start if someone in the MCU group doesn't have a different project information format they prefer.
Gadget Freak (from Design News and Allied Electronics)

This 'Gadget Freak' topic appears to be a regular feature of the Design News website. This solar charge controller is labelled #260. I don't know if that means there are 259 previous Gadget Freaks, but here are links to The Best of Gadget Freak Volume 1 and The Best of Gadget Freak Volume 2. Design News collaborates with Allied Electric, and they invite you to submit your electronics projects for publication. This is just one more way that people in the Humboldt MCU community can participate in the expanding world of microcontrollers and possible earn a few bucks. The Gadget Freak page on Allied Electric's site says:
"Are you a Gadget Freak? Allied Electronics and Design News would like to send you a check for $500 to spend at or anywhere you please! Submit your design for a gizmo or gadget that any Gadget Freak would appreciate, and you just might win! If your project is selected, you’ll receive a $500 check from Design News and will be featured in an upcoming issue of the magazine with your invention. In addition to the $500 awarded for being selected as a Gadget Freak, all selected gadgets...will be included in the Gadget Freak of the Year contest. Starting in November, the readers of Design News will then vote on the best gadget...The winning gadget will receive an additional $6,000 with two runners-up who will receive $2,000 each."
If you've built solar energy devices or systems with MCUs, it would be great if you came to one of the every other Thursday meetings the MCU group has. The next meeting will be on Thursday, August 24. If you can't make it to the meeting but would be interested in discussing your solar energy device or system, please email me at arcatabob (at) gmail {dott} com
. It would be great to meet you for coffee and a tech discussion, or possibly you'd be willing to show the MCU group your MCU in operation!


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