Sunny Buddy Resistors to vary charging voltage

Other
1

In my lab I have a bunch of old sunny buddies that a previous manager modified to charge to 7.1 volts. No documentation was made about how this was done. I need to modify a new batch of sunny buddies for my students that also charge to 7.1 V because the students break them and wear them out over time. I read all the documentation on the sparkfun website (datasheet and schematic and hookup guide) and it is shown how to calculate which resistors are needed, but there is no picture that unambiguously relates the schematic or datasheet to the actual, physical board.

In short, I need to know which three resistors on the actual sunny buddy are the ones discussed in the datasheet for adjusting float voltage. I can make a pretty good guess, but the traces are hard to see and the resistors are not labeled and I am not absolutely sure. If sparkfun could produce a picture labeling the resistors in question, that would make this pretty simple.

Thanks very much,

Justin

2

This took me a while to figure out, but I believe you’ll be messing with these 3

image
image541×541 120 KB

These are the values I calculated (1% tolerance):

R6: 536kΩ or 540kΩ
R2: 464kΩ or 470kΩ
R3: not needed

3

Dear Russel,

Thank you very much for your help. Those were the values I calculated as well, but even though I RTFM, as your icon recommends, I couldn’t figure out with certainty which resistor went where. If you don’t mind saying, how did you go about figuring it out? You said it took a while; did you have to disassemble one to test it? I am curious about the method. Have a great day!

Justin

4

I imported the Eagle files from the product page into KiCAD which has labels for the components :wink:
I had R6 figured out based on the schematic but couldn’t tell the rest from photos with certainty