VM3P75CT Counters do not match

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emilleopold asked Mar 23, '24

VM3P75CT Counters do not match

We have build an ESS System like "20240124ms_ESS_Konzepte.pdf". Just now there are 3 flats (OG, EG, UG) which have separate GRID counters. At the end the OG and UG should be supplied from the ESS system in EG. For test reasons we compare the values from the VM devices with the values from the GRID meters. And there we have found a big difference at the OG values (app. 80%).

Also the consumption value from the VRM is very different to the grid meter values.

VM_OG, VM_EG and VM_UG are configured as AC-LOADS. Do they come into the calculation of the VRM values ?

Any idea what can be the problem ?

Thanks for support.

20240124ms_ESS_Konzepte.pdf

ESS

microsoft-excel-20240323ms-smart-meter-2024-03-23.png (129.8 KiB)

20240124ms-ess-konzepte.pdf (243.6 KiB)

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Answer 1 · 2024-04-02T07:42:16Z

ldoes (Victron Energy) answered · Apr 02 at 07:42 AM

Hi @emilleopold, as you might have guessed those differences are much larger than what you should expect from the VM-3P75CT. The first thing that springs to my mind is a difference in the method of energy registration between the VM-3P75CT and your grid meters.
VM-3P75CT uses so called "vector-registration" in which the individual phase energies are summed and then the net result is either added to the total forward energy register (if sum is positive) or total reverse energy register (if sum is negative).
If your grid meters uses a different method of total energy registration, such as "arithmetic-registration", then the resulting total forward energy register is different than that of the VM-3P75CT. You can learn more about this at https://clouglobal.com/calculation-methods-for-energy/

If this is the case, you can compare the two meters by summing the total forward energy and total reverse energy registers.

As for VRM and energy meters configured as AC-load, they are only for monitoring, not used for calculations: https://www.victronenergy.com/media/pg/Cerbo_GX/en/connecting-victron-products.html#UUID-219a875a-5193-e157-a2a6-c822c1521a4c

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Answer 2 · 2024-04-02T10:37:40Z

prein answered · Apr 02 at 10:37 AM

Maybe related: I find the power readings quite accurate, but the current readings are a mess..

1,5A for 194Watts, etc..

I believe this is a bug, since the power readings are very accurate..

img-2256.png (189.3 KiB)

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ldoes (Victron Energy) ♦♦ commented · Apr 02 at 11:07 AM

Hi @Prein, I believe this is unrelated and is most likely the result of low power factor / current distortion. Please see my answer to related thread here.

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