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Output of mains current monitor

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We need an AC Mains current monitor to monitor the AC current going into our 3.8kw, 230VAC battery charger.

I found the HMS 05-P:
**broken link removed**

…But it look like it gives a voltage out which is just an offset sine wave with a 2.5V DC offset. (The datasheet isn’t terribly clear about this).
So we would also need an ideal diode peak detector to go with it, giving us a DC voltage representing the peak. Do you know of a mains current monitor which just puts out a steady DC voltage which is representative of the mains current?

We wont be able to put one of those in the power supply, as we need something through hole or surface mountable.
I now believe that we will have to use the HMS 05-P current monitor, but then put its output into an LTC1966 RMS to DC converter chip.
We should do this because as you know, the mains is not a true sinusoid, but is “flat-topped” due to distortion.


Like the following…somewhat unfortunate though since the RMS to DC converter (LTC1966) costs £5
(LTspice and schem attached)
Can you think of a cheaper way than this?


  • rms to dc converter.pdf
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  • rms to dc converter.txt
    1.8 KB · Views: 51


We used LEM devices many times.
Yes the offset is 2.5V. And the input waveform is transferred to the output.
At nominal input voltage you will see 0.625V output voltage.

Instead of using dedicated RMS to DC converters, we used a microcontroller for 8 channels true RMS calculation.

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