Filed under: Charge Controller. Tagged as: charge controller, charge controller schematic, free charge controller, open source hardware.
A member of the free charge controller mailing list pointed me toward Tim Nolan’s charge controller design. I took several days to really study his design. It incorporates the same design ideas as previous versions of the Free Charge Controller, but his design is much more simple and elegant. Not only is the design of the buck converter robust, it also solves many of the practical problems mentioned with earlier designs of the Free Charge Controller. To be more specific, it solves the following issues:
- The design is built on top of an Arduino, which means it can leverage the large user base and code base that the Arduino platform has built up over the years.
- The voltage and current monitoring circuitry and buck converter circuitry use a minimum number of components and are built on top of an Arduino protoboard ‘shield’. This means that an expensive, custom PCB is not nessessary. This further mitigates the problem in open source hardware projects by making it easier to get hardware into the hands of people who are interested in contributing
- Because a protoboard is used instead of a custom PCB, it’s easier for experimenters to try different hardware – such as different coils for different voltages, or bigger coils and MOSFETs in order to push more power through the system.
Developing a Kit
After finalizing the v2 design, I spent a few hundred dollars to have custom PCBs manufactured and purchased parts to build 10 kits to sell. I quickly realized that building kits is not a trivial process. It’s expensive, time consuming, and easy to mess up. Not only that, the process made me realize that I need to devote my efforts to the areas of the Free Charge Controller project where they are best used: namely design, documentation, and promotion. The functions of kitting, pricing, logistics, and customer interaction, while very important, are not areas that I am particularly proficient in or represent the best use of my time.
For that reason, I reached out to Jameco, a well known distributor of electronic components. They were very receptive to the idea of working with me to build a kit. There was a bit of work to convert Tim Nolan’s original design, which was based on Digikey parts, to find equivalent components out of their catalog. They were willing to stock parts they otherwise wouldn’t and were very flexible in working with me to develop a kit. Two weeks ago they sent me the first prototype kit and I have spent the time building and documenting the new design. We are collaboratively working through the final bugs introduced by the hardware changes.
v4.01 Free Charge Controller Schematic
As you can see from the schematic below, the design is very similar to Tim Nolan’s original design. The theory of operation from his hardware notes is completely the same. (Note: the component designations, like R1, in his notes refer to his schematic, not mine.)
You can also download a pdf copy of the charge controller schematic.
Plans From Here
The development kit that Jameco will soon have available for order is a huge step up from my original efforts to build a kit. For one thing, the elimination of the custom PCB and many components cuts the cost to about half. The cost of my original kit was around $120, and the kit from Jameco will be in the ballpark of $60 to $70. That’s almost a 50% decrease in price, which I think will prove a big difference in getting developmental hardware into the hands of contributors.
While my initial efforts at documenting the build process and creation of basic software will be a big help to those attempting to build it, I’m really looking forward to when ten people participating on the mailing list have built one. At that point, we’ll be able to discuss an optimal layout, building strategy, and write documentation around that. (While my personal build notes will be published here on my blog, the ‘official’ build instructions will reside at freechargecontroller.org so that everyone can participate in the documentation process.)
Another huge advantage the community can enjoy at that point will be fine-tuning the design. I envision the present design to be able to handle 12 volt solar panels on the order of 30 to 60 watts. Even if we can collaboratively improve the efficiency of the design, there will be physical limits in terms of voltage and current. I look forward to when we can begin to agree on the realistic specifications that we want to the design to meet. Once that is accomplished, we can then begin to finalize a printed circuit board (PCB) layout for the creation of an Arduino Shield – in order to make the assembly process even easier for people to build.
One reason I’m so excited about this development kit is that it will allow people to easily ‘hack’ the kit for customization. Do you need a charge controller that can pass 20 amps? Add bigger MOSFETs and a bigger coil. The development kit will be a perfect springboard for experimentation and expansion. I envision many different versions (forks) of the free charge controller will spring up from this design.