Message-ID: <65f36ffb@news.ausics.net>
From: not@telling.you.invalid (Computer Nerd Kev)
Subject: Re: Backup power supply
Newsgroups: comp.sys.raspberry-pi
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Date: 15 Mar 2024 07:45:32 +1000
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Andriy D <usenet@dolik.dev> wrote:
> The Natural Philosopher <tnp@invalid.invalid> wrote:
>> On 14/03/2024 07:57, Andriy D wrote:
>>> This is exactly my concern - I want this think up&running 24/7/365 and I don't want
>>> it to burn my house down :)
>>> I guess this is where you'd say 'risk' and 'price' are in a inverse relationship ;)
>>> -- 
>> It is entirely possible to trickle charge a lithium cell at uber low 
>> risk, Essentially you want to current limit the supply at at one tenth 
>> of the hourly capacity so e,g a 2200mAh celll would need to be charged 
>> at no more than 220mA, and voltage limit the charge at 4.2V.
> Majority of the schemes I've found so far suggest use of NiMH cells as 
> they are less 'combustive'.

Indeed, but if the power requirements are low (a Pi Zero without any
power-hungry USB/HDMI connections) then supercaps might be an easier
option. Since then you don't need to worry about over-charging,
which will still wear out NiMH, even if it doesn't then burn your
house down.

Here's one project that came up in a quick search:
https://hackaday.com/2020/11/05/a-super-ups-for-the-pi/

> However cheap AliExpress devices do use Li-ion cells. Confusing :)

Confusing? Not at all, those Chinese sellers know you're not going
to be able to sue them if their junk burns your house down. If you
buy a mains powered device from them I think you're lucky if the
secondary doesn't short right through to the mains and kill you
when you touch it - it's happened before with phone chargers. It
was recently in the news here in Aus that Li-Ion batteries had
caused over 1,000 fires in the past year. I'm highly suspicious
even of cheap locally-distributed Li-Ion products and wouldn't
consider buying one from an unaccountable AliExpress seller unless
I was prepared to sit near it the whole time it charges on a
fire-proof surface.

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