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prekursorius avatar image
prekursorius asked

Incorrect AC current smart meter readings

Hello,

we can't resolve a problem all the day. We have 3 phase system with Multiplus Cerbo and smart meter(first photo). The readings from the smart meter are incorrect; they differ by about twice compared to the readings from clamps on phase (3-phase clamps 4.1A and 2.3A in the app on second photo). We tried replacing the smart meter with another of the same model, but it didn't help. Both the phone and Cerbo show the same numbers, which are half of what the clamps indicate.

What could be wrong?


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4 Answers
ldoes (Victron Energy) avatar image
ldoes (Victron Energy) answered ·

Hi @Prekursorius, my first bet would be the configuration of your clamp multimeter. Can you set it to the lower range (60A) and make sure it is configured to measure AC (not AC/DC)?
Furthermore, it looks like there is quite a lot of distortion current (as indicated by low power factor) and your clamp multimeter might not play nicely with those nasty waveforms. Most meters that can handle this are marked as "True RMS" meters and yours doesn't seem to carry that label.

You can also hook all of the CTs over a single wire, and if all of them read the same current its a good indication that the VM-3P75CT is functioning normally.

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prekursorius avatar image prekursorius commented ·

Thank you for your answer.
As for the clamp settings, of course, I chose AC mode. And we're not talking about a difference in percentage; the discrepancy is in multiples. Check what the VRM shows (pay attention to the watts). The smart meter readings are clearly incorrect. I will try the test of hooking the CTs over a single wire.
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ldoes (Victron Energy) avatar image ldoes (Victron Energy) ♦♦ prekursorius commented ·

Hi @Prekursorius, the confusion between the power and current readings is due to a low power factor. See my answer to a related question here. This is either caused by non-resisitve loads in your system, or it might indicate that the CTs aren't hooked on the correct wires (L1 voltage port and L1 current port are measuring different phases).


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prekursorius avatar image prekursorius ldoes (Victron Energy) ♦♦ commented ·

Well, I am not talking about V*A ≠ W. Look at the general power balance: the load is using 2306 W, the battery provides 165 W, and the grid meter shows export. We don't have any generation yet, just the battery, load, and the grid meter. So, in my opinion, the meter readings are wrong, while my clamps show the correct values (if I recalculate everything to power, the numbers are approximately correct).

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ldoes (Victron Energy) avatar image ldoes (Victron Energy) ♦♦ prekursorius commented ·

Hi @Prekursorius, sorry I misunderstood your comment about power balance.
As you said, the meter shows export which shouldn't be possible at all in your system. Even though you have checked the connection of the CTs multiple times, I would suggest swapping the CT connections to the meter and checking if there is a configuration in which all phases show positive power.

Furthermore, please check if there isn't any dirt between or damage to the magnetic cores of the CTs. If the two halves of the core aren't perfectly flush, both the magnitude and the phase of the measured current is incorrect.

What were the results of the 3CTs 1 wire test?

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prekursorius avatar image prekursorius ldoes (Victron Energy) ♦♦ commented ·

What were the results of the 3CTs 1 wire test?

The place is 100 km away from us, so we want to prepare everything in advance. Installing Eastron's device is an option (we have used it in the past without any problems). Once we are there, I will provide the results of the CT test.

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prekursorius answered ·


Connected correctly, we've checked it several times


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prekursorius avatar image
prekursorius answered ·

Colors are corect


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prekursorius answered ·

This is not the first time we have installed a Victron meter, we didn't have this problem before. the impression is that the CT rotation is wrong

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