Stand-by power usage of z-wave modules

[mhorst]

Are there any numbers on the stand-by power usage of z-wave modules, specifically the shutter switch modules from Düwi ?

I have seen some websites specify that it is below 1W, but I cannot find anything about it in the official documentation from Düwi.
Furthermore, my own experiment indicates it is something like 11-12W.

I did my experiment because I recently got a Velux window with a shutter, and wanted to connect it to my z-wave system. The official Velux system does not support this, and reportedly uses 22W in standby (http://www.domoticaforum.eu/viewtopic.php?t=3562). So I made my own system using 24V power source, some relays and a Düwi window shutter module. To see how much power I would save, I hooked the components up to my multi-meter. It turns out that the z-wave module alone (without all the other components) draws 51mA when doing nothing. At 230VAC that is almost 12W.
That module has the new Z-wave.ME firmware, I also tried one of the older modules in my home, with the regular Düwi firmware, and that came in at 49mA, i.e. a bit over 11W.
I think that's a lot, and it worries me because I already have 5 modules installed in my home (I believed the 1W mentioned on the websites, never bothered to check otherwise until now).

So I was wondering what other people's experiences are w.r.t. stand-by power usage of their z-wave modules.
I saw, for example, that the Fibaro modules claim (in the official documentation) a standby power of less than 0.25W. If this is true, I'll probably replace my Düwi modules for Fibaro modules.

[mhn]

I usually measure my Z-Wave devices before I install them.

I don't have a Duwi, but my Z-Waves devices use around 1W. A little more or a little less.

Regards
Morten

[mfb]

The problem is the way the power usage is calculated. Calculating the power by using "Voltage * Current" gives VA and not Watt.
To reduce the voltage in small embedded systems often a capacitor is used. This gives a bad power factor and a current that is not in sync with the voltage.
The used power in such a system is much lower than the calculated VA, so the used power can be < 1W even if the system is using 11VA.

[mhorst]

Ah, thanks. I just spend an interesting hour reading about Power factor on wikipedia and related articles.
I think they skipped this subject during my high-school physics class.

I attached a energy meter instead of my multi-meter. It shows that the Düwi module draws approx. 45mA, but indeed uses less than 1W of power. So that is a lot more reasonable

Interestingly, the energy meter reports cos rho as being 1.00. My guess is that the voltage and/or current is no longer a nice sine wave and that the (cheap) meter has problems determining the power factor.

Also I managed to measure the stand-by usage of a Fibaro dual-switch with my multi-meter, it uses 3.8 mA. So that is below 1 VA, meaning that it is below 1 W even before correcting for the power factor.
(I didn't attach the energy meter, since it is not accurate enough to register these kinds of levels.)