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From: The Natural Philosopher <tnp@invalid.invalid>
Newsgroups: comp.sys.raspberry-pi
Subject: Re: Backup power supply
Date: Sat, 16 Mar 2024 23:53:28 +0000
Organization: A little, after lunch
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On 16/03/2024 17:56, bp@www.zefox.net wrote:
> bp@www.zefox.net wrote:
>> side, you could put it all downstream of the Pi power supply
>> and skip line detection entirely. That's a big advantage.
>>   
> On second thought, this is probably wrong. If one connects
> to a Pi a 5 volt supply in parallel with a blocking diode
> and a 6 volt battery, the diode is still forward biased
> and will drain the battery eventually. Some kind of switch
> is needed, controlled by line detection.
> 
> Maybe a three terminal regulator set for 5 volts out powered
> by a 9 (or higher) volt battery pack could be substituted.
> Still, one has to consider the idle draw of the regulator.
> TI's LM340 takes 6 mA roughly. Still, that's a smallish
> supply for a Pi. You'll likely want something larger.
> 
> Apologies for the red herring!
> 
> bob prohaska
>   
I think the chances of finding an 'ideal' battery are relatively slender.
You are likely forced into some sort of 5v switched mode regulator - and 
its probably wisests at least for a single Pi - to have that permanently 
delivering power and just have the battery on permanent mild charge
-- 
The New Left are the people they warned you about.