Allan Herriman wrote on 10/15/2017 3:42 AM:
> On Sat, 14 Oct 2017 20:18:36 -0400, rickman wrote:
>
>> I was looking for a Li-ion power source adapter and found this in the
>> process.
>>
>> http://www.ebay.com/itm/112419803835
>>
>> Looks like it would serve as a UPS for a rPi in many situations.  The
>> listing isn't big on specs, but they seem to show it will drive well
>> over an amp in a pass through mode.  They talk about a couple of amps on
>> each of two ports in power bank mode.
>>
>> I know this has been kicked around a bit here, but I  don't know if
>> anyone found an economical solution.  This unit is around $10 and a
>> Lithium battery will cost around another $4 or $5.  You can either use
>> the standard 18650 type or one of the Lithium polymer flat cells.  Both
>> seem to be available cheaply with about 3000 mAHr capacity running a
>> typical pi for around 2 hours.
>
> Looks ok to me, if all you want is a power bank controller that can
> charge and discharge at the same time.  You might find you can buy a
> complete power bank (including the Li cells) for about the same price if
> you shop around.  My local computer store was selling Romoss Sailing
> models on sale for ridiculously low prices recently.
>
> To be a useful, general purpose UPS though, it needs to be able to output
> a signal to tell the load (Pi) that it's about to run out of juice so
> that the Pi can shut down cleanly and go into a low(er) power state, all
> without corrupting the SD card.
>
> Assuming you can figure out how to derive such a signal (e.g. by
> monitoring cell voltage, or by starting a timer when the charging input
> fails), I guess you could try to couple it to something like this:
> https://shop.pimoroni.com/collections/raspberry-pi/products/onoff-shim
>
> "It watches the state of BCM pin 17 and, when pulled low (pressed), it
> initiates a clean shutdown. Last thing, just before your Pi shuts down,
> BCM pin 4 is pulled low to completely cut power to your Pi."

Perhaps you don't recall the difficulty people had finding a power bank that
would work like a UPS where it could provide power all the time and only
drain the battery when the power failed.

Ideally such a controller would actually be smart enough to periodically run
the batteries down a bit, but not all the time.  Still, this is pretty good
for a COTS board.

I have thought of a number of devices I would design if I could tap into the
whole manufacturing/sales thing you see on eBay.  I mean I don't touch the
units or even the orders.  I develop a manufacturable design and get a
royalty off the sales.  But I guess that just doesn't happen with eBay sort
of stuff.  I guess I could be in the loop somewhere, but I've yet to figure
out how to get access to the low cost manufacturing and get the devices sold
all without ever leaving Asia.

Anyway, this would be one of them.  Something that integrates well with the
rPi and doesn't cost as much as a rPi.  That's one of the sad parts of the
rPi, accessories cost more than the CPU board.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

--- SoupGate-Win32 v1.05