In article l.net,
Dave Liquorice wrote:
On Thu, 29 Oct 2020 10:19:10 +0000, Martin Brown wrote:

Despite the ring circuit being correctly wired and being quite
short,
and there being little load on it...when I switch on the laser
printer, the UPS shifts taps to compensate for the voltage drop -
it
is clearly audible.

That sort of surprises me, there will be an inrush as the filter
capacitor and PSU capacitors charge but wouldn't expect that to be
greatly different to a PC.

Laser printers are a brutal load to get the fuser element that melts
the toner onto the paper up to temperature quickly is a brief but very
high surge current from cold. Easily enough to trip a UPS out.

Ah, I read "switch on the laser printer" as powering up, rather than
sending something to print. Can't see why the fuser has to be heated
on power up.

so that you don't have to wait for ages when you press Print.

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