NY wrote:
"jon" wrote in message ...
On Fri, 31 Jul 2020 11:24:31 +0100, Pamela wrote:

Is this sort of plug-in power meter suitable for measuring a desktop PC
with a switched mode power supply?

I bought something similar a long time ago but found it was giving
misleading readings. Are these better now?

https://www.amazon.co.uk/Consumption.../dp/B07FZZ17ZY


Switchmode power supplies don't seem to adversely affect the supply
electricity meter, but I am sure a large inductive load with a directly
chopped supply would affect everyone up the road.

I have a meter (from Maplin) which measures power in both W and VA, one
assuming that current and voltage are in phase and the other taking into
account the fact that they are not. Real power [W] = apparent power [VA]
* power factor.

I presume it is the real power that an electricity meter registers and
that you want a plug-in meter to read.

You would like the meter to measure W and VA, so that
when picking a UPS (uninterruptable power supply), you
measure both quantities and pick a UPS which deals
with the more taxing one.

Sometimes the loads have more W, sometimes more VA
(relative to the ratio of W to VA the UPS offers).

https://www.amazon.ca/Batterie-secou.../dp/B06VY6FXMM

1500VA / 900W UPS === example of a typical ratio of capacities

You can hang a power bar off the front of the meter,
and put your entire computer room on the meter, to get
total W and total VA, then the numbers can be used when
picking a UPS (which has both a W and a VA spec).

On a modern computer room, W is approx equal to VA,
due to the use of Active PFC on the ATX supplies. On
older computer rooms, the PF is 0.7. There was no Active PFC
in the old days, and more heat also came out of the supply
cooling hole. The new supplies are much better on
efficiency.

Paul