PowerBoost Charger - Low Voltage Cutoff?

[greggorievich]

Hey there! First post here, though I've bought several things from Adafruit before and have built a number of little projects.

I'm looking at building a (or a few) phone chargers using some PowerBoost boards. I'm not yet sure whether I want to use the PowerBoost 1000C, or a PowerBoost 1000 basic and something like a TP4056 board to charge the pack. (The latter would probably be advantageous, as I understand that the 1000 basic can output more current, meaning a faster phone charge).

The issue I'm running into is that rather than buying cells/battery packs for the project, I was hoping to use recycled 18650 cells from laptop batteries, which means they don't include a protection board.

I know some variants of the TP4056 have a protection circuit and Load+ and Load- pins, however these all seem to be limited to 1.2A from the battery which would be insufficient current for my needs, so that idea won't work.

I did notice that the PowerBoost Circuits have an ENable pin that will cut the output if it's shorted to ground, and also a LBO low battery output pin that drops to 0v when the battery hits 3.2v. Is there possibly some way I could connect these together so that instead of getting a low battery warning at 3.2v, it just shorts the ENable pin and cuts off the output? Ideally, this would work alongside a power switch for the charger to disable output when not in use (that is, so that either a physical switch or the low battery cutoff would be able to short the ENable pin to ground).

Failing this, does anyone have any suggestions around creating a small/inexpensive low battery cutoff circuit that would still be able to handle the ~4A of current from the batteries to the PowerBoost?

For a bit of context about my skills, I can read simpler schematics and circuit diagrams and I know a fair amount of the basics about working with electricity and circuits, but I'm by no means an engineer.

Thanks in advance for any thoughts or suggestions!

[adafruit_support_mike]

The PowerBoost is designed so you can connect the LBO to EN and have the boost circuit shut off automatically when the battery goes low.

[greggorievich]

Thanks, Mike! I wasn't able to find it that explicitly in any of the documentation, but it seemed to be implied.

I'm thinking of using an SPDT switch to control this - have the "Off" side of the switch short the ENable pin right to ground, and have the "On" side of the switch short the ENable pin to the LBO pin. Obviously I intend to test this out, but off the top of your head do you see any issues with this setup?

[adafruit_support_mike]

Yeah, that's a common way of doing it. Should work without any problems.