Re: Backup power supply

On 14/03/2024 18:11, bp@www.zefox.net wrote:

Mike Scott <usenet.16@scottsonline.org.uk.invalid> wrote:

On 14/03/2024 15:51, Joe wrote:

I'm using a cheap APC, I believe 650 or 750, with USB monitoring hookup.  Also have my router connected (with VOIP) to keep
communication possible for a little while (runtime abt 30 minutes).  Battery replaced once, I believe it was some 7 years old.

>
Somehow that makes no sense to me..... current 650 is 227 pounds (maybe plus
VAT) on the APC website. 5 times the cost of the Pi. I'm sure it's a
very nice UPS, but.... ???
>

 Sense or not, it seems to be a fact of life. The inverter/charger/transfer units
I used have vanished from Amazon, replace by units with four times the power and
double the price. Battery prices seem to have dropped very slightly, but are
still a whisker over $200/kWH.
 A 12 volt to 5 volt stepdown converter appears to be less than $10, small 12 volt
batteries range from $20-100 in the few AH range, a 12 volt 5 amp charger ranges
from $11 to $50. The charger would be the iffy part, since a smart charger on a
loaded battery is apt to get confused by what looks like high self-discharge..
 Something reliable for less than $100 will take both luck and ingenuity. One
possibility is finding a used UPS unit in e-waste and replacing the battery.
 bob prohaska

Seems the rechargeable bit is the issue. For my part, and purely to use as a short-term standby for the Pi until mains resumes or the system can shut down cleanly - I'd be happy with something with a bundle of AA cells or similar. I doubt a clean switchover circuit would be difficult to design, but my electronics knowledge is decades out of date :-{
--
Mike Scott
Harlow, England