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

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.

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

I don't think they are particularly sophisticated (and I have a couple
that look exactly like that) and may have difficulty reading much
other than a near resistive load with any real / absolute accuracy.

However, I find them fine as a general indicator of power consumption,
especially when comparing like with like (SMPSU powering a Raspberry
Pi or a PC etc).

I can't think if I've ever measured something that was actually rated
that didn't also have variables / additions that could have impacted
the result or if I have, I didn't note that it was far away from what
was stated (suggesting they were accurate and the meter also
reasonably so).

I think the last things I measured / compared were a RPi NAS, a
slimline Shuttle PC running as a NAS, a Synology NAS and a Buffalo
Terastation NAS and the results were about what I expected. As
mentioned though, you often had to take several readings with the HDD
idle, unit sleeping etc.

Cheers, T i m

"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.

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

When a similar design is used for time-of-day whole-house power,
it's likely to be 1% or better on measurements. Whereas this
cheap meter might be 3% or so. The circuit relies on a shunt resistor,
and a likeness of a shunt resistor is shown in the following advert.
A shunt resistor has low ohms value, plus it has a low tempco and
is stable when it gets hot (Manganin or Zeronel 50ppm or so).

https://www.amazon.co.uk/MICTUNING-M.../dp/B01JOUZELG

The shunt resistor gets hot when run at "max rating" 10A all the time.
On the North American version, it would get hot enough, the solder
would melt and the component could shift.

With these meters, you look for "reports of a burning smell".
And the reviews on your meter, have such a report.

The shunt resistor could be gauged to get less warm, but
to do that, the sensitivity of the meter portion has to be
turned up. Which can degrade the accuracy.

The measurement is done with dual sigma-delta converters,
at around 500KHz or so. One converter for voltage, one
converter for current. Deriving quantities like Power Factor
PF is done with a microprocessor. Arithmetic calculations
are carried out continuously at high speed.

THe meter is capable of giving reasonable values. Here
are some examples:

1) My ATX PC "meets EUP spec of 0.5W when OFF". If you select
shutdown on the PC, the soft power is supposed to drop to
0.5W. My supply, which is not EUP, is 1.3W or so. Even plugging
in a USB stick, you can see that reflected in the power.

2) Now, place the computer in S3 Sleep. The green LED on the case
will start to blink indicating sleep.

The meter will read "5 watts" for four sticks of DDR2 RAM.
The meter will read "7.5 watts" for eight sticks of DDR3 RAM.

The more modern the memory standard, generally the lower
the power becomes per stick.

3) If you're charging your iPad on there, the meter might read
10W to 15W when the computer is not otherwise in usage. Like,
sleep the computer, and try and charge the iPad. You will
be getting close to the 5V @ 3A limit on +5VSB in such a case.
If the PC doesn't have a charge port, the iPad might only
draw 5W (plus the sleep power of 5W).

Conventional meters, bad measurement methods, will tell you
the PC draws 100W when sleeping. Which is patently false,
and easy to figure out when +5VSB only delivers at most, 3A.
As long as the new meter shows the low values I've shown
above, like an EUP number if the PC is EUP compatible,
and low numbers for S3 sleep, then you have a good idea that
the meter is working.

Modern ATX have PF = 0.99 .

Old ATX have PF = 0.65 to 0.7 or so.

Old ATX are inefficient, and a lot of heat pours out
of the PSU fan. Newer ATX are 80+ efficient, and waste
heat is a lot lower.

The meter you're buying, is not quite as accurate from
a resistor tolerance point of view, as other meters you
own. But... the measurement method is light years ahead
of some other crude attempts to do this. There's a
big difference between a realistic S3 sleep power of 5W,
and a dead-wrong 100W value you got from other instruments.

Thus, the readout says

Real value = 5W

Meter reads 5W +3% downto 5W -3%, or 5.15W to 4.85W
(digits displayed... 5.2 to 4.9 W)

It's the prevalence of the meter burning, that gives some
idea how desirable the model is. And you check the reviews
for that and decide whether the people are abusing the
meter or not.

Paul

I can remember when I worked at a factory which made tvs back in the valve
days, they used an autotransformer, so chassis was live and a half wave
rectifier. They ran soak tests on the sets in huge banks, and got a visit
from the Electric company about them squashing the half phase they wre on
they had to have a three phase supply fitted and run some off of each phase.
What I never quite got was that most makers at the time did the same thing
so out in homes these sets were all doing this, surely?
Brian

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"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.

On Friday, 31 July 2020 16:44:58 UTC+1, Brian Gaff (Sofa) wrote:
I can remember when I worked at a factory which made tvs back in the valve
days, they used an autotransformer, so chassis was live and a half wave
rectifier. They ran soak tests on the sets in huge banks, and got a visit
from the Electric company about them squashing the half phase they wre on
they had to have a three phase supply fitted and run some off of each phase.
What I never quite got was that most makers at the time did the same thing
so out in homes these sets were all doing this, surely?
Brian

Yup. I'm guessing about half the sets used one polarity, half the other, at least for HT. The heaters used both.


NT

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

You are unlikely to save that much by using one even if it works perfectly.

On 31/07/2020 11:24, 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

Big Clive review

https://www.youtube.com/watch?v=fRGKilvExMo&t

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On 31/07/2020 15:00, T i m wrote:
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

I don't think they are particularly sophisticated

According to Big Clive it has a dedicated power analyser chip with a 100
page data sheet.


--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

"Brian Gaff (Sofa)" wrote in message
...
I can remember when I worked at a factory which made tvs back in the valve
days, they used an autotransformer, so chassis was live and a half wave
rectifier. They ran soak tests on the sets in huge banks, and got a visit
from the Electric company about them squashing the half phase they wre on
they had to have a three phase supply fitted and run some off of each
phase.

What I never quite got was that most makers at the time did the same thing
so out in homes these sets were all doing this, surely?

Yes, but by definition the ones in homes would be randomly
spread across the phases in the streets, not all on the one phase.

"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.

On Sat, 1 Aug 2020 04:14:08 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH the trolling senile pest's latest troll**** unread

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"Rod speed is not a Brexiteer. He is an Australian troll and arsehole."
Message-ID:

On Sat, 1 Aug 2020 03:37:56 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH the trolling senile asshole's latest troll**** unread

03:37??? Is it trolling time already, you disgusting Australian piece of
senile ****?

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MID:

On Fri, 31 Jul 2020 19:00:16 +0100, alan_m
wrote:

On 31/07/2020 15:00, T i m wrote:
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

I don't think they are particularly sophisticated

According to Big Clive it has a dedicated power analyser chip with a 100
page data sheet.

Cool.

I guess what I meant was 'I don't think they are particularly
sophisticated' ... compared with professional and more sophisticated
kit that costs many times more and probably comes with a 100 page
instruction book and a certificate of calibration ...'. ;-)

If they were as good for that price that would be nice to know.

Because the 'cheap stuff' is made down to a price rather than up to a
spec (or a much higher price g), they often fail / become less
accurate at the extremes, or when measuring the more awkward stuff.
All down to the laws of diminishing returns on the cheaper gear.

Cheers, T i m

Brian Gaff (Sofa) wrote :
They ran soak tests on the sets in huge banks, and got a visit from the
Electric company about them squashing the half phase they wre on they had to
have a three phase supply fitted and run some off of each phase.

In an home environment, they would be randomly spread across the three
phases. There would still be the issues of drawing current on one half
of the cycle though.

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

T i m wrote:
On Fri, 31 Jul 2020 19:00:16 +0100, alan_m
wrote:

On 31/07/2020 15:00, T i m wrote:
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
I don't think they are particularly sophisticated
According to Big Clive it has a dedicated power analyser chip with a 100
page data sheet.

Cool.

I guess what I meant was 'I don't think they are particularly
sophisticated' ... compared with professional and more sophisticated
kit that costs many times more and probably comes with a 100 page
instruction book and a certificate of calibration ...'. ;-)

If they were as good for that price that would be nice to know.

Because the 'cheap stuff' is made down to a price rather than up to a
spec (or a much higher price g), they often fail / become less
accurate at the extremes, or when measuring the more awkward stuff.
All down to the laws of diminishing returns on the cheaper gear.

Cheers, T i m

They typically use dual sigma-delta converters, with maths
in firmware. And the maths in firmware, have been slightly
tweaked over the years for better accuracy. (This is what
happens when your privately held maths are exposed to
public scrutiny.)

Yes, the meter is good, and fit for intended purpose.
With better quality analog components used inside,
the accuracy might be improved slightly. But not in
a way that affects the gross improvement these meters
bring (7W reading on the above meter, versus 100W
approximate reading with separate regular meters).

Using an ordinary digital meter to do volts,
a digital meter to do amps, the calculation of VA resulting,
the 100W, is dead wrong. You can validate the 7W number,
against the known loads inside the (sleeping) PC at the time.

Vetting a PC in S0 run state, that's harder to do.
That's why I recommend checking PC in sleep state,
then compare to any other method you want to cook up
for sleep state, to do the same task.

The refresh power for DRAM chips is known and on the
datasheet. You can compare that load, to what the
meter indicates.

You can also apply DC loads to USB ports, then figure out
roughly what kind of efficiency exists in the +5VSB converter
(a separate converter, separated from the main converter).
In the old days, +5VSB was only 50% efficient (terrible).

Paul

On 18:48 31 Jul 2020, alan_m said:
On 31/07/2020 11:24, 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

Big Clive review

https://www.youtube.com/watch?v=fRGKilvExMo&t

Very useful. Thank you.

Clive says at the end: "It's actually really well made. It's accurate and
works surprisingly well". (25 min) That's all I need to know.

Mind you I did once follow Clive recipe for porridge which wasn't a total
success. Using raisins was okay but his suggestion to add Coffee Mate didn't
work for me.

On Friday, 31 July 2020 15:10:51 UTC+1, NY wrote:
"jon" wrote in message ...

I have a meter (from Maplin) which measures power in both W and VA,

No. Power is Watts, and VA is not Watts.

Power is the rate of delivering energy, and one Watt is needed to accelerate one kilogram by one metre per second per second.

Electrically, average Power W is the average of instantaneous (Voltage x Current); and VA is Root-Mean-Square Voltage x Root-Mean-Square Current. Power Factor is the ratio of those two, W / 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

That is NOT what it registers. It registers real Energy, in real kilowatt hours.

and that
you want a plug-in meter to read.


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