Voltcraft measuring device: reliably measure standby power consumption from 1,5 watts

Anyone who reads my test reports knows that I like to measure current and voltage or output power between technical devices and their power sources. With power banks, I do this with a small one USB multimeter from PortaPow. For 230 volt consumers, however, I was still missing a precise energy cost measuring device that would also provide low standby energy costs for economical consumers like the Apple HomePod can measure. Most devices that are placed in the socket only measure halfway reliably from a certain consumption and this is often over 10 watts, so that it is difficult to "measure" a HomePod that should only consume 7 watts. I have now found a solution with Voltcraft measuring devices.

Reliably measuring standby power consumption from 1,5 watts is possible with the TRMS Energy Logger devices from Voltcraft. Product images: Voltcraft / Conrad

Reliably measuring standby power consumption from 1,5 watts is possible with the TRMS Energy Logger devices from Voltcraft. Product images: Voltcraft / Conrad

Voltcraft meters for power consumption and energy costs

An example of the Voltcraft measuring devices is the Voltcraft Energy Logger 4000, which you can use for example buy from Conrad can. The offer there is cheaper than some Ads on Amazon. There is also the Voltcraft Energy Logger 4500 (here.). I tried such a measuring device for a test with my HomePod and came up with a value of 6,9 watts, which is very close to the 7 watts specified by Apple. I think Apple rounded up the value for the indication.

It is also important to note that the Voltcraft devices are TRMS measuring devices. This means that not only a standard value of the direct current is required, but the device takes the actual AC waveform into account (also deviating from sine). According to the product description, distorted phases are not a problem either:

Real effective value measurement (TrueRMS) for the most precise measurement results even with distorted phase positions

Voltcraft Energy Logger with data recording on SD card

The measuring devices record their results in order to keep an eye on consumption and costs and to check whether efforts to reduce costs are successful. That happens locally on one SD Memory Card. Which fits into the respective model can be found in the operating instructions. You can then read it out and draw your conclusions from it on the computer. But the software you need to read the data seems to be a disease.

I have not yet carried out my own test of the app - but if you look at the customer ratings of the device, they are very mixed. However, there is agreement that the device and the accuracy of the measurement results are very good, only the software is extremely difficult to understand and is therefore a reason for devaluation. Anyone who, like me, only wants to reliably measure standby values ​​from 1,5 watts (which do not change) only needs the display integrated in the device;)

Measure the conclusion on standby power consumption from 1,5 watts

If you are looking for a TRMS measuring device to check the standby consumption of your devices at home, in the office or in the whole company, which already works at 1,5 W, then I can recommend the Voltcraft models. Anyone who can dig into the software or who is satisfied with the consumption data on the display can also use the other functions. Compared to AVG or RMS meters, in addition to the AC sine curve and AC, other than sine, any DC influences are measured (AC = alternating current; DC = direct current). Further technical data and details can be found on the Conrad page linked above.


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  1. Norbert says:

    I have 2x pieces of the VOLTCRAFT SEM6000 on sale and with a voucher from a well-known electronics mail order company with di… .. bought for a total of just under 45, - €.

    You no longer have to crawl behind the cabinet to take measurements, you can read everything out via Bluetooth / app.

    You can also switch these things, even time-controlled (timer / schedule / random). The Bluetooth range is not extensive, but in my 50 square meter it is enough. It doesn't go down from the first floor.

    Power range: 0 - 4113 W.
    <1 W - tolerance: ± 0,23 W
    1 to 10 W ± tolerance: 1%

    • sir appleot says:

      Hello Norbert! Thanks for the tip. I'll test that thing too. However, I found other values ​​at Conrad.de:
      Effective range: 0,23 W to max. 3680 W.
      And tolerance: 1% (in the complete effective range).
      But the thing already makes a good impression ... there will be a test for it soon. : D

  2. Norbert says:


    I got the data from this PDF by Conrad:


    Strange that they give different values ​​...

    • sir appleot says:

      Ah, thanks to you for the link. I would rather trust your source (the PDF manual) than the naming of the data on the website. They are often not that precise ... from this point of view, the energy meter is actually an exciting thing!

  3. Joseph K says:

    The Energy Logger 4000 seems to be a good, solid measuring device for recording power consumption.
    As an additional highlight, data recording, export to SD memory card and post-analysis of recorded measurement data with Voltsoft are touted.

    I noticed the following deficiency:
    the energy consumption in kilowatt hours [kWh] calculated by Voltsoft and the consumption value [kWh] that can be read in the logger display "Consumption" are often completely different. The "forecast" values ​​for costs per month and costs per year are correspondingly different.
    The difference between the two kilowatt consumption values ​​cannot be explained with measurement tolerances at all.

    Based on my analyzes, I find that only the measurement results are within
    the measurement tolerances are correct, which can be read in the logger display, i.e. active power consumption [kWh], cost [€ / m], cost [€ / Y].
    Based on the recorded measurement data, the calculated results of Voltsoft apparent power, real power, energy consumption [kWh)] are mostly more or less wrong.

    What actually takes place in the Logger 4000 in terms of measurement and numerical technology?
    1. Voltage [V], current [A] and the power factor CosPHI are updated in the display approximately every second.
    The real power = voltage * current * CosPHI is also updated about every second. The logger adds up the active power consumption approximately every second, which can be read off in the logger display "Consumption" in kilowatt hours [kWh].

    2. Every minute the Logger 4000 saves the mean value of the voltage, mean value of the current and (fundamental error) the minute mean value of the CosPHI of the last minute.
    These minute mean values ​​are available in the recorded logger data, from which Voltsoft calculates the consumed apparent power [VA] = mean value voltage [V] * mean value current [A] and the consumed active power [W] = mean value voltage [V] * mean value current [A] * mean value CosPHI per minute.

    A follow-up analysis of minute mean values ​​and the kilowatt hours calculated from them are wrong - and seriously wrong if the load is changing in terms of output.
    It is just not generally possible from the recorded minute data
    determine an active power consumption in kilowatt hours,
    which corresponds to the consumption information on the display.

    If you have a Logger 4000, you can make the following two attempts:
    - fill a (simple) kettle (known to be a purely ohmic consumer) with cold water,
    - Plug in the logger and connect the stove,
    - Delete logger memory, mode button until display "Consumption",
    Press the Mode button for 5 seconds until - - - - -.
    - Switch on the stove, observe voltage, current and especially CosPHI!
    The CosPHI value will be constant at 0.99 (1.00), because the stove is a purely ohmic consumer.
    - When the stove has switched off, read the active power consumption in the "Consumption" display and write it down,
    - Copy logger data to SD card, analyze with Voltsoft.

    Result: the course of the active power and the apparent power is practically identical,
    because CosPHI = 0.99
    and please compare the calculated consumption of the kilowatt hours
    with the value from the logger display Consumption!

    - fill the kettle again with cold water,
    - Delete logger memory, mode button until display "Consumption",
    Press the Mode button for 5 seconds until - - - - -
    - Switch on the stove, observe voltage, current and especially CosPHI!
    - Sporadically switch off the stove every 30 to 45 seconds and switch it on again after 15 to 20 seconds!
    It was clear that the water would start to boil later and that the stove would take longer to switch off.
    - When the stove has switched off, read off the active power consumption in the "Consumption" display and write it down
    - Copy logger data to SD card, analyze with Voltsoft.

    Result: the course of real power and apparent power diverge,
    and please compare the calculated consumption of the kWh display with kWh-Voltsoft!

    Voltsoft lists date, time, current [A], CosPHI, active power [W], apparent power [VA]
    Why is the voltage [V] not also listed ?!
    Real power, apparent power are calculated by Voltsoft from voltage, current, CosPHI.
    The listed CosPHI minute averages are absurd, because the kettle is
    an ohmic consumer at every switched-on time (CosPHI = 1.0).

    Voltsoft cannot calculate anything correctly from the recorded logger data with regard to energy consumption. With changing load situations such as (modern) coffee machines, irons, steam ironing stations, Voltsoft will always determine different, mostly much lower active power consumption compared to the consumption values ​​in the logger display "Consumption".
    Accordingly, the costs calculated by Voltsoft per month and costs per year are also incorrect.

    Based on the recognized relationships and observations, I consider it to be a major conceptual error in the firmware of the Energy Logger 4000 that minute mean values ​​of voltage, current, CosPHI are saved every minute and should be used for subsequent analysis.

    Instead of voltage, current, CosPHI, the logger should generate the
    Save mean values ​​of active power and apparent power of the last minute
    for a follow-up analysis.

    At the end...
    Only the measurement results are correct within the measurement tolerances,
    which can be read in the logger display.
    Voltsoft can calculate voltage, current, CosPHI
    do not re-determine the active power consumption [kWh], which is congruent
    with the indication in the logger display is "Consumption".

    • Jen Kleinholz says:

      Hello, Josef! Thank you for your comprehensive report on the Energy Logger 4000. I have already read that the Voltsoft software still has weaknesses, but I only use the logger for measuring without logging. But I think your hints will be helpful for people who want to do more with the Energy Logger.

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