Re: Backup power supply

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 ;)
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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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