Test of the minimum power measurable by different wattmeter sockets

Various experiences made by members of the forums concerning in particular small household appliances and energy management.
Petrus
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Test of the minimum power measurable by different wattmeter sockets




by Petrus » 08/12/22, 20:26

Following the subject Hidden consumption washing machine: electricity-electronics-computer/hidden-consumption-washing-machine-t2429.html on measuring and eliminating standbys, I wanted to do a little test of my collection of different power meters, most of them bought at flea markets, just to see which ones are able to measure the low power of a standby.

1st test: a resistance of 100k Ohms (measured at 102k ohms) therefore 0,52W of consumption with a voltage of 230V:

The only one to display a result is a very simple little "Xavax" model EMG-7 meter which only displays the power, no current measurement function and power factor.
The power factor is still taken into account since the measurement is made by a specialized circuit. There is no marking on the integrated circuit but I was able to identify it as an AD71056, ADE7757 or equivalent.
xavax.JPG
xavax.JPG (245.29 KiB) Viewed 1312 times


Other meters do not take into account such a low power:
IDK.JPG
IDK.JPG (253.54 KiB) Viewed 1312 times

voltcraft.JPG
voltcraft.JPG (242.41 KiB) Viewed 1312 times

paget.JPG
paget.JPG (258.47 KiB) Viewed 1312 times

otax.JPG
otax.JPG (231.15 KiB) Viewed 1312 times

brennenstuhl.JPG
brennenstuhl.JPG (227.28 KiB) Viewed 1312 times


To see the minimum power measured by the different wattmeters, I therefore quickly made a standby simulator consisting of a USB charger connected to a variable load with a wattmeter between the two to see if the measured value is consistent.
charge_USB.JPG
charge_USB.JPG (234.65 KiB) Viewed 1312 times


results:
minimum power displayed:
Xavax EMG-7: 0,2W (power measured at charger output: 0W)
IDK MPM-70: 0,5W (power measured at charger output: 0,25W)
Voltcraft: 0,1W (power measured at charger output: 0,6W)
Paget trading No. 9149: 1W (power measured at charger output: 1,2W)
Otax: 6W (power measured at charger output: 5,5W)
Brennenstuhl PM230: 6,8W (power measured at charger output: 3W)

The most sensitive is therefore the Xavax EMG-7, the second and in my opinion the best power meter of the group, because offering the measurement of voltage, current and power factor is the IDK MPM-70

By the way, to do the test on the Brennenstuhl I had to repair it first, the voltage measurement was in the cabbage and the display almost invisible. The supply capacitor was out of order:
condo_brennenstuhl.JPG
condo_brennenstuhl.JPG (280.81 KiB) Viewed 1312 times

I had the same PB on a remote control socket of the same brand.
Now that it's dismantled, I'm thinking of modifying it to make it a special low-power wattmeter by changing the shunt and adding a fuse for safety.
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Christophe
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Re: Testing the minimum power measurable by different wattmeter sockets




by Christophe » 08/12/22, 23:16

Very good subject, of the kind that are rare!!

Thank you
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phil59
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Re: Testing the minimum power measurable by different wattmeter sockets




by phil59 » 08/12/22, 23:29

The best, does not indicate full power ...

Today, with the tempo option, it was red day, and I thought I was going to do a test with the inverter on battery, and when I measure, the box, the player, the TV, around 50 ", I arrive at an instantaneous consumption of the order of 70W, it seems weak to me, I would have thought to arrive in the range more than 100W.
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hmmmmm, hmmmmmmmmmmmmm, hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhmmmmmmmmm, huh, hmmmmmmmmmmmmm.

: Oops: : Cry: :( : Shock:
izentrop
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Re: Testing the minimum power measurable by different wattmeter sockets




by izentrop » 09/12/22, 00:36

Hi,
Petrus wrote:Brennenstuhl PM230: 6,8W (power measured at charger output: 3W)
I've owned the PM230, but I didn't find it faithful, neither did you, apparently. In addition, it needed a certain number of button batteries to operate.
Petrus wrote:Otax: 6W (power measured at charger output: 5,5W)
I also bought this model on sale. Quite faithful but internal battery HS, the energy measurement is not always reliable.

The one that can measure powers from 0.1 W has a range of 0-2400W, that must be the reason.

I had it for 6 € on ali, but the same currently are sold for 3680W. They must not have the same sensitivity of the blows although https://fr.aliexpress.com/item/1005004949474887.html
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Christophe
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Re: Testing the minimum power measurable by different wattmeter sockets




by Christophe » 09/12/22, 03:38

It's not true izy…the pm worked well except in low power (6W minimum) I still use it 15 years later…

The batteries were just for memory and display off socket.. Not obligatory in short…
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Christophe
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Re: Testing the minimum power measurable by different wattmeter sockets




by Christophe » 09/12/22, 03:41

Petrus, you are talking about the 1st test… I imagine that you have planned higher power tests then?
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izentrop
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Re: Testing the minimum power measurable by different wattmeter sockets




by izentrop » 09/12/22, 19:05

I had not done the test with the resistor alone:

100 kΩ displays 0.0 W
68 kΩ same //
47 KΩ displays 1.2 W calculation: 238 V X² / 47000 = 1,2 W, consistent result
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Exnihiloest
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Re: Testing the minimum power measurable by different wattmeter sockets




by Exnihiloest » 09/12/22, 19:38

Petrus wrote:...
The power factor is still taken into account since the measurement is made by a specialized circuit. There is no marking on the integrated circuit but I was able to identify it as an AD71056, ADE7757 or equivalent.
xavax.JPG
...

If I judge by the datasheets, these two circuits should easily provide a measurement at 0.1% accuracy, whatever the form factor. The calculation method is rigorous and the sampling frequency is sufficiently high:

"The real power calculation is derived from the instantaneous power signal. The instantaneous power signal is generated by a direct multiplication of the current and voltage signals. In order to extract the real power component (ie, the dc component), the instantaneous power signal is low-pass filtered. [] This scheme correctly calculates real power for sinusoidal current and voltage waveforms at all power factors."
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Petrus
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Re: Testing the minimum power measurable by different wattmeter sockets




by Petrus » 10/12/22, 20:01

Christophe wrote:Petrus, you are talking about the 1st test… I imagine that you have planned higher power tests then?

The 1st test was the resistance, the 2nd the USB power supply. I hadn't planned to do a test at high power, but if anyone is interested I can take out a blower to do a test at 1000 / 2000W.

Since the Brennenstuhl PM230 is the least sensitive of the meters with a minimum measured power of 6,8W I modified it to increase its sensitivity.
Originally the shunt is 3,5mohms:
PM230_origin.JPG
PM230_origine.JPG (264.6 KiB) Consulted 1143 times

I replaced it with another of 10x higher value:
PM230_modified.JPG
PM230_modifié.JPG (267.9 KiB) Viewed 1143 times

Then I had to redo a calibration by playing on the adjustable resistors:
Adjusting the current gain also changes the voltage measurement, so adjust the current measurement first and then the voltage.
settings.JPG
reglages.JPG (292.58 KiB) Viewed 1143 times

I also had to modify the two resistors R1 and R3 to have the correct setting in the adjustment range:
resistors.JPG
resistors.JPG (244.95 KiB) Viewed 1143 times

Once everything was properly adjusted, I also added a 4A fuse, since the new shunt will not take a current of 16A well like the original one.
PM230_mod.JPG
PM230_mod.JPG (240.56 KiB) Viewed 1143 times
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Christophe
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Re: Testing the minimum power measurable by different wattmeter sockets




by Christophe » 10/12/22, 20:31

Petrus wrote:
Christophe wrote:Petrus, you are talking about the 1st test… I imagine that you have planned higher power tests then?

The 1st test was the resistance, the 2nd the USB power supply. I hadn't planned to do a test at high power, but if anyone is interested I can take out a blower to do a test at 1000 / 2000W.


Yes it would be interesting since you have all the gear at hand! I think there will be fewer differences in high power...

If you can do a test around 100 to 200W that would be good too.

Hats off to the PM230 mod!! 8) 8) 8) : Shock: : Shock: : Shock:

And suddenly it is sensitive to how many W?
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