On Sun, 15 Oct 2017 04:20:19 -0400, rickman wrote:

> 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.


The particular range I mentioned (Romoss Sailing) can do that.  The
datasheet calls it "synchronous charging," and states explicitly that it
can charge itself and provide power to a load at the same time.  It
doesn't say whether there's an internal direct input to output bypass
circuit, but at these prices, do you care?

Disclaimer: I haven't tested one to verify how well it works in practice.

BTW, the sale's over now.

Allan

--- SoupGate-Win32 v1.05