I recently purchased two Li-Ion batteries (2500mAh 3.7V each) and the USB charger https://www.adafruit.com/products/259. I would like to use them to power an autonomous vehicle with 4 DC motors, running off Adafruit Motor Shield V2 (pictured below).
Right now I am using 9 x 1.5V rechargeable batteries (so 12V total) to power the 4 DC motors connected to the shield, and 1 x 9V battery to power the board.
I have several possibly trivial questions regarding the "power" setup, and I apologize if they are super noobish. I am new to this whole hardware thing, although I've been doing software for decades.
- 1. The DC motors I have need 6-7V, so I was hoping to put the two batteries in a series to provide this voltage. But on your Li-Ion guide it says it's not "recommended", but then the explanation has some reference to imbalanced charging. I am not charging them, I am using them :) Both batteries are now at 4.1V exactly. And I plan to charge them one at a time using the supplied USB charger. Why can't I double the voltage by connecting the two batteries together and using them as one?
2. If I am powering Motor Shield with a separate 9V battery, do I need to worry about connecting the grounds of the two separate power sources, or does the shield takes care of that for me?
3. I would like the batteries to charge faster. I've been trying to understand the instructions and figure out exactly which resistor I need to solder over to get 1000mA charge (so 2X faster). In some places it says R4, and on the board diagram (when opened in Eagle) R4 seems to be the one marked "THERM", while some other instructions say the resistor to solder over is the "PROG" one. On the back of the board it says that charge rate is 1000/PROG so I decided that it's PROG, and then soldered a 2K Ohm resistor as seen on the picture. Did I do it correctly? How long should I expect it will take to charge batteries to full?
And here is the USB charger with soldered resistor:
Many thanks in advance for any feedback and help! I love your site :)