The Solar Power Expert Blog

04/21/2011 Update on Free Charge Controller

by Chris - April 21st, 2011.
Filed under: Charge Controller. Tagged as: , .

I decided to post this email to my blog to prevent it from getting lost in the mailing list. I thought other people might have a similar question.

Hey Shiva,

I apologize for taking so long to reply.

Actually, both versions of the board use ceramic capacitors. The only difference between the two versions is the current (amp) sensor.

In v2, I tried to use a differential op-amp to output a voltage proportional to the current. Basically I tried to roll my own current sensor and it didn’t work too well. There are minor nuances that I was not aware of that effect the quality of the output of the op-amp. Check out the mailing list archives for details.

In v3, I decided to bite the bullet and use an IC to do the signal processing for proper current sensing instead of trying to roll my own. Unfortunately, I screwed up the package outline on the board, so the IC doesn’t sit on the board properly.

In regards to software, you can download the latest firmware from the SVN repository on source forge. I’ve written control software for most of the peripherals – including a SD card management and a basic terminal interface for manual control of the buck converter. It’s rough, but everything works. You’ll need to be proficient at C though to navigate it.

Let me know if you need more clarification on this.


Chris Troutner

—–Original Message—–
From: shiva
Sent: Tuesday, April 19, 2011 5:38 PM
To: Chris Troutner
Subject: Re: v2 Free Charge Controller Board

Hey Chris,

I was wondering what the main differences between the V2 and V3 board are. I see that the V3 board uses ceramic capacitors, as well as uses the maxim IC for the voltage sensing. I was just curious as to how you guys determined that these changes were significant. I also was a little confused about what it is that the voltage and current sensing circuit does.
As you can see i’m a beginner just trying to learn how this stuff works. Myself and a few other students from the University of Waterloo are trying to implement this open source board into use for charging lithium ion batteries. So as much information or guidance on how this dc-dc conversion is done can only help us. Also i was wondering as to the interface with the micro controller, is there some sort of software already available that we could load onto the ATMega or is that something we need to write as well.

Thanks for your time I apologize if these questions are a nuisance, its just we need all the help we can get.

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