I saw in the Framework Launch Event video that there were plans for an external battery pack that can reuse the old battery (the FrameBank). Then I read in this thread that those plans were going to be eventually put on GitHub, but will not be sold by Framework. Given that this is probably a pretty low priority project for them, I was considering how I could build my own.
However, I am having a hard time actually finding out how to do this. 99% of DIY battery pack tutorials use the 18650 batteries. The pinouts for the framework battery are a little confusing as there are 3 power, 3 ground, and 4 data/management pins. How many of those pins are needed for power delivery or battery management? Is there a simple one package solution like this board. This thing was designed for cell batteries like the 18650, so can it be used for a flat battery? GreatScott had some great information on USB PD and DIY stuff. But there are so many questions that I don’t know where to start.
My background is in Aerospace so dealing with buck converters, IC chips, battery management systems, or power management, seems like a daunting task for a newbie like me. There are so many things to consider and I’m afraid of frying my electronics. So I guess my question is, is there a simple solution to making a battery bank that I am overlooking or will this require a custom designed DIY PCB board and components?
Well, if you are asking about the multiple pwr and gnd pins, all of them really. Unless you’re soldering directly. When multiple pins are used for power it’s normally to increase current handling capacity. Contacts introduce resistance.
For the data / SMBus pins, you might not need to use it, but you should, for safety sake. Any proper large battery pack has temperature monitoring. The SMBus is for the Smart battery system wikipedia and through that you access the temperature monitoring.
I’ve been curious about the battery enclosure as well. Hoped it was a real thing.
Interfacing with a battery can be fairly easy, or fairly more hard/problematic, depending on how much of the logic is built into the battery package, vs. what’s implemented on the board. They can look similar just looking at the connector.
I’ve not looked into what Framework uses, and if the design is still in the concept phase, it’s definitely something that would be first to check-out before thinking about designing anything else. Depending on where the BMS/cell monitoring lives, it’d dictate the design of the PCB that interfaces with the battery. I highly suspect, though, that the battery package itself contains the BMS and protection logic - so the pack itself can also contain serial, capacity history, etc., for making battery replacements & accurate “fuel gage” possible.
Really, from there, it just depends on how cheaply you want to build it - do you want an interface to show remaining SOC%? How about a little OLED to display watts, volts, capacity, lifetime? Or just cheap and dirty? These things would be relatively simple to implement, but implementing a simple interface would be surprisingly easy (as long as you have good power-management to keep it from bleeding the battery dry while it’s stored in a drawer for 6 months at a time).
Design considerations would include:
- How much of a user-interface do you want - nerdy, basic, or nonexistent
- What capabilities do you want on the output - 60W USB-PD? Quick Charge (5v/9v/12v)? Or just basic 5v?
- Keeping the pack safe when not in use