Two wattmeters: 0W and 25W, which one is true?

[r-p]

See the picture. What is attached is a 0-30V 0-10A switch mode power supply from the early 90's (I think).
One wattmeter claims it uses no power at all (which is what I expect, as it is switched OFF), the other claims >25W.

I haven't measured inside, but the only explanation I can come up with is that the capacitor is before the powerswitch and that the cosine phi messes up the measurement.
Not sure how, but that is the best I can come up with.

Any ideas?

I don't really understand PCF (power correction factor?), but does that have anything to do with it?

The second pic is with the SMPS switched on without a load.
The number under the powermeasurement on the Silvercrest is the powerfactor.






Edit: in case it isn't obvious, the two powermeters are stacked, so the Silvercrest is measuring the SMPS and the second watt meter, the second watt meter is only measuring the SMPS. If the Silvercrest is only measuring the SMPS, it shows a similar result, which is why I tried this in the first place.

[budm]

Re: Two wattmeters: 0W and 25W, which one is true?

The CAP across the AC line before switch will show current draw but will show close to 0 power (W) due to capacitive reactance.
What readings do you get form both meters if you check the Wattage, Current, PF, VA using light bulb as the load?
The meter that shows 28W, what does it show on VA and the current draw? AC line filter cap will not cause the meter to show 28W.

[stj]

Re: Two wattmeters: 0W and 25W, which one is true?

the capacitor across the power inlet often has a discharge resistor in parallel actually.
but no way will it pull 25w, it's usually only a .4w resistor.

and i wouldnt put much trust into something you got from LiDL btw.
i'm refering to the "silvercrest" kit.

[r-p]

Re: Two wattmeters: 0W and 25W, which one is true?

The CAP across the AC line before switch will show current draw but will show close to 0 power (W) due to capacitive reactance.
What readings do you get form both meters if you check the Wattage, Current, PF, VA using light bulb as the load?
The meter that shows 28W, what does it show on VA and the current draw? AC line filter cap will not cause the meter to show 28W.

25W lightbulb, the front shows 24.6W (no V and A reading available), the Silvercrest 25.9W (about 0.118A and 229V equals 27W but might have read this a few seconds before the wattage measurement).
Taking into account that the front meter adds to the draw measured by the Silvercrest, they are even closer (forgot to measure the draw of the lightbulb ONLY on the Silvercrest, but the wattage kept creeping down during the first minute, so that would add a measurement inaccuracy anyway).

PF was 0.98 or so.

The A measurement with the SMPS was 0.213A @229V with a PF of 0.60 and 29W (all values from the display). While only half plugging the 230V plug into the back of the SMPS while it is OFF, I can clearly hear arcing, so there is definately something going on before the powerswitch. New idea about this is that they have chosen this option because it has some remote control option.
Here's the PDF for the powersupply, I am reading it now to see if that gives some moree clues.

[ben7]

Re: Two wattmeters: 0W and 25W, which one is true?

I wonder. Maybe the one meter (not the silvercrest, the other meter!) uses a capacitor voltage dropping power supply. Might make it have horrible PFC, and the silvercrest shows it taking a lot of power (even though it actually isn't)

[r-p]

Re: Two wattmeters: 0W and 25W, which one is true?

If the Silvercrest is only measuring the SMPS, it shows a similar result, which is why I tried this in the first place.

This line was hidden somewhere in the back of my first, very long post

[r-p]

Re: Two wattmeters: 0W and 25W, which one is true?

Sorry for the slow answer, but I have since chalked this up to the Silvercrest being a piece of crap.