wrote:
On Sunday, 19 July 2020 23:17:07 UTC+1, Mike McLeod wrote:
On Sun, 19 Jul 2020 21:58:31 +0100, Chris Holford
wrote:

Although the inductance is probably not enough to worry about, the cold
resistance of the element will be less than the resistance at operating
temperature. This means that the initial current at switch-on will be
higher than the normal operating current.
Yup, I was aware of that and measured the current draw under warmed-up
running conditions.

what you need to know is cold resistance.


NT

Plug it into a Kill-o-Watt meter and watch the
power consumption from cold and see if it changes.

The Kill-o-Watt meter also has power factor, and the
PF should be 0.99 (indicating little in the way of
inductance). 1.00 would be purely resistive.

https://www.amazon.co.uk/YOUTHINK-El.../dp/B071NZ53WR

Power(W) === Mine has Watts and VA instead
Energy (kWh)
Voltage
Amps
Hertz
Power Factor === Old PC ATX about 0.65 (capacitive), light bulb 0.99 [ideal]
Minimum and Maximum power

These meters use sigma-delta converters operating at
500KHz to 1MHz or so, and are capable of TrueRMS readout.
(The same tech as whole-house digital power meters.)

Even for the idle current of an ATX power supply (which
is a severely distorted waveform), the meter gives
the right answer. That's why I like the instrument
for various purposes, as I can trust it to
"do the sums correctly". I have other instruments that
claim to do this and that, which are off by miles when
doing such measurements.

The only problem with the meter concept, is they use
a shunt resistor for current measurement. And if you
spend your day "measuring electric kettles", in the
past this made the shunt hot enough the solder inside
melts. A few of the meters have failed when used
for high power characterization.

It's a pretty nice instrument to add to a collection.
And mainly, because it actually works, and the thing
makes measurements for you. You may have to search
around to find just the right one, as some of them
have "junk functions" that are worthless. And you also
need the right "hole" on the front, for your typical
cords and plugs. There's no sense buying one for the
wrong country.

Paul