On Thu, 14 Jan 2021 10:18:57 +0000, Ahem A Rivet's Shot wrote:

> On 13 Jan 2021 23:37:18 +0000 (GMT)
> Theo  wrote:
>
>> Joe  wrote:
>> > Lithium cells have a linear-ish discharge curve, from 4.2V down to
>> > around 3V. Any sensibly designed lithium battery will cut off its
>> > output at the chosen lower bound, because if it completely
>> > discharges, it's dead forever. Not a 'steep' decline, a 'fall off the
>> > wall' decline.
>> >
>> > It's a good idea to have some independent means of anticipating this
>> > point.
>>
>> But lithium ion cells don't work for this application.  We need 5V.
>> One cell is too little, two cells is too much.
>
>  One cell and a DC-DC converter to give you a regulated supply,
> monitor the cell so you can shut down (well) before there's too little
> to run the converter.

The Powerboost 1000C from Adafruit does that - has 5v input an is
connected to an RPi and a single cell LiPO cell, so is a a postage-stamp
sized 1 amp UPS.

It can run the attached RPi while charging the LiPO from the 5v supply
and continue to run the RPi off the LoPO in the 5v feed is turned off.

Needs some soldering: it comes with all the connectors that can be
attached to it, but not soldered in. The idea is that you only install
the ones you need.

Note I have one, but haven't yet found the round tuit I need to get it
and a Pi Zero up and running using it. When the project is complete I'll
what will be effectively a pocketable system TFT touch screen and built-
in charger.


--
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Martin    | martin at
Gregorie  | gregorie dot org

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