Electronics > Projects, Designs, and Technical Stuff

USB Battery Bank Auto Shutoff

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engrguy42:
Well after some searching I found you can apparently use this simple modification to get adjustable duty cycle on a 555...

Peabody:
I keep having to remind myself, because I'm old, that the new way to deal with this kind of problem is to get a little 8-pin microcontroller like an ATTiny or PIC or MSP430 with its own internal oscillator, and program it to drive the mosfet with the exact pulse duration and interval you want.  That takes the place of all the 555 stuff, resistors, capacitors, pots, diodes, etc.  Cheaper, easier, more precise, fewer parts, less space, less power.

Anyway, I hope you'll report back with the final shortest, least frequent, lowest current, pulse you can get away with to keep the powerbank alive.  It may be that the total mAh penalty isn't all that great.

SilverSolder:

--- Quote from: Peabody on May 12, 2020, 02:43:26 pm ---
--- Quote from: SilverSolder on May 12, 2020, 02:35:57 pm ---
Some battery banks don't have the auto-shutoff feature.

I have an old 13000mAh power bank here where the cells are so worn out that the capacity is only around 1,000mAh now...   but it doesn't auto shut down, so is great for powering an Arduino etc. for several days!

--- End quote ---

Do you have a link to that one?  What I've found is that the circuits of these things have been "updated" over time to use new, cheaper, single-chip solutions that handle both charging and 5V output regulation, but that also include auto-off which can't be disabled.  So over time, they've pretty much all become auto-off even if they weren't that way a few  years ago.  Anyway, if you have a link to the one you have, I'd like to take a look at it.

--- End quote ---

Mine is a "SCUD P130" but the same item was sold under many names, apparently - "Huawei AP007 13000mAh Portable Power Bank" and "FREMO P130" look exactly the same, for example.

Might be hard to find these now, they are definitely an old model.  I only found one for sale, and it wasn't cheap.

SilverSolder:

--- Quote from: Peabody on May 12, 2020, 04:14:39 pm ---I keep having to remind myself, because I'm old, that the new way to deal with this kind of problem is to get a little 8-pin microcontroller like an ATTiny or PIC or MSP430 with its own internal oscillator, and program it to drive the mosfet with the exact pulse duration and interval you want.  That takes the place of all the 555 stuff, resistors, capacitors, pots, diodes, etc.  Cheaper, easier, more precise, fewer parts, less space, less power.

Anyway, I hope you'll report back with the final shortest, least frequent, lowest current, pulse you can get away with to keep the powerbank alive.  It may be that the total mAh penalty isn't all that great.

--- End quote ---

That is exactly what to do for this kind of project, I think.  I abandoned a 555 project and used a Pro Mini Arduino simply because the timing of the 555 was less accurate, and it didn't do exactly what I wanted, and ended up being a lot more work than knocking up the 3 lines of code needed...   Welcome to 2020!

engrguy42:
Wow that last circuit I posted seems to work !!! At least in LTSpice...

Just need to tweak a bit to bring the OFF time down a bit. Coolness...

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