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From: nospam.Vincent.Coen@f1.n250.z2.fidonet.org (Vincent Coen)
Newsgroups: comp.sys.raspberry-pi
Subject: Backup power supply
Date: Fri, 15 Mar 2024 14:10:58 +1300
Organization: Agency HUB, Dunedin - New Zealand
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Hello Ahem!

Friday March 15 2024 10:51, you wrote to me:

 > On Thu, 14 Mar 2024 21:00:49 +1300
 > nospam.Vincent.Coen@f1.n250.z2.fidonet.org (Vincent Coen) wrote:

 >> Assuming it is fully charged which would be normal (assuming no
 >> outage in the preceding 2 - 3 hours 95% or better.
 >>
 >> Otherwise do you mean the estimated run time if so then system under
 >> power in watts per
 >> hour

 >     You have units confusion. Watt is a unit of power, a rate of
 > movement of energy. Watt-Hours and similar units are units of energy.
 > Watts per hour is meaningless.

 >> under the rated size - 25%  so lets say :

 >     Assuming you are talking about an APC SMT750I or similar they are
 > rated for a power output of 750VA or 500W. At full power the battery
 > is good for about five minutes.

 >> 750 w
 >> ----  = 150 = long time :)
 >> 5 w

 >     Make that 5 minutes * 500W/5W or 500 minutes which is indeed a
 > long time but a lot shorter than the 150 hours you were expecting.

 >> Also e.g., my desktop / server system with an estimated consumption
 >> of 250w (and it is lower as using modular PSU, 85% eff or better )
 >> would be around 3 hours but that assumes there is nothing else under
 >> load and

 >     No it would be maybe 15 minutes.

The time specified in my post was based on ACTUAL power on time using battery
only.

No I will admit it is also based on some other kit being turned off / shutdown
if needed such as the monitor (keyboard / mouse are battery powered).
Hub is very low, router low with no secondary kit being connected to the UPS
such as printers as not required for normal operation.
The primary system uses a modular PSU and secondary DASD are stopped if not 
use
after 2 minutes - they are rarely used other than back ups and secondary
systems / O/S, etc.

Likewise on receipt of a power cut and after a predefined number of minutes 
not
needed applications are shut down although there is no many.

Average time before the system will shutdown is 75 - 90 minutes on a 1000Kva
UPS and with a newish battery.  The UPS is connected directly to supply so is
always being under charge or at least being topped up if needed.

Real live cycle of the UPS battery depends totally on the number of times the
UPS is used when the mains power goes down and since moving from a village to 
town property, power cuts are rare and normally short.

I do not have a way of working out exactly the power requirements are of the
main system although I can look at the loading of the UPS via a direct web
location going by memory as it has been years since I tried it and that
assumes it was the APC model I currently use as I down sized our UPS's after
down sizing our home when the mobo's failed on the 2200Kva units.
The cost of the current kit, new, was around 300 each and they have had a 
least
one change of batteries each.

Not all computer around the house has them such as the media recording system
(using MythTV under Ubuntu) does not.

One powered kit in the village was the C.H. (Gas boiler and controls) but now 
just use an extension lead to connect it if needed and only in the cold winter
period, I seem to recall, maybe once.

Vincent