In article , NY wrote:
"charles" wrote in message
...
In article , Martin Brown
wrote:
On 27/10/2020 16:41, David wrote:
Just doing my winter disaster planning.

One item was to be able to run a small generator to keep the freezer
going in the event of a short power cut.

For a short powercut you really just need to keep the freezer door
closed and then put it on superfreeze for a bit when power is restored.

After the first day it is worth rigging up local power. Most power
cuts are usually shorter than that unless something goes very badly
wrong.


about 6 years ago there was a cable fault in out road. An emergency
generator was brought in and coupled up to our house at about 1am. had
it for 4 days.

When the electricity company were doing some work on high voltage feeds
to various substations in the area, they brought in loads of huge
generators (they moved them from one village to another as the work
progressed) and fed groups of houses from the genny. The constant
throbbing of the diesel engines, day and night, was a real problem. I
think our power was on local feed for about a week.


I've wondered about getting a UPS for electronic equipment that reboots
at the slightest interruption. We went through a phase last year of
getting brief ( 1 second) power breaks every few days - or maybe a
sequence of them every 30 seconds or so. The electricity company had not
been going round pruning overhanging trees near HV lines, and when one
touched a wire (eg in stronger than normal wind) a circuit breaker would
trip and reconnect.

How good are UPSs at providing mains that is sufficiently glitch-free,
when switching to and from battery, that computers don't notice? The
only UPS I've tried to use was one that my wife bought at the same time
as her big PC, but we never got round to trying for a couple of years -
and when we did, the battery would not provide mains, even with
negligible load, for more than about a second. The battery was either
dead on arrival or else had failed through lack of use (maybe through
being stored with no charge). So I've never seen how seamless the
changeover is from mains to battery. I presume they are more
sophisticated than a relay, where contact bounce, even if mains cycles
match, may cause problems. Do most UPSs run the inverter all the time
(without taking power from it) so it is ready at a moment's notice,
locked to mains frequency and phase for instant switchover. I presume the
big problem with a UPS is when the supply is switched back to mains,
because the inverter will have been running off a free-running
oscillator that will be a different frequency so there will be a
discontinuity at the point of switchover. Or do UPSs stay on battery
after the mains has returned, tweaking the local frequency and phase
gradually until they are locked to mains and then switch without a
discontinuity.

This was a cheap consumer 700 VA APC UPS, so probably one that switched
over, rather than one that was always running off battery and inverter,
with the battery kept charged by the mains but with no direct connection
from input to output.

I originally got a UPS because we suffered from 'brownouts' at night which
locked up my, then, modem. There have been the occasional loss of mains
since then and both my Acer Windows machine and my ARMX6 ( RISC OS) have
happily carried on working. an APC UPS

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle