On 29/10/2020 09:24, Dave Liquorice wrote:
On 29 Oct 2020 00:44:08 GMT, Bob Eager 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. Think I'd be looking to see if the UPS is
a bit "sensitive" or what the volt drop drop is on that ring when
loaded. May be indicating a slightly iffy joint somewhere.

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.

Inkjet printers are fine though.

--
Regards,
Martin Brown