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robincg asked

Incorrect Grid Input Measurement

Hi all, I have a Multiplus II gx 5vka with 2x MPPT 150/60s and a FreedomWon 20/15 LifeP04 battery in an ESS configuration,

My issue is I have noticed that the grid input measurement shows that it is accurately trying to maintain my chosen grid set point of 50W however when I measure the current from the grid to the Multiplus II with an ameter i see that the power from grid to the inverter is actually around 350-400 watts. Is this a known issue with the Multiplus 2 units? is my unit just badly inaccurate?

Multiplus-IIESSVenus OS
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Are you using the AC in to record the grid energy use or do you have a CT sensor on the incoming supply or a connected energy meter? Asking as I did have a similar situation but it appears to have gone away before I had a change to investigate further. I am currently using the Victron 100A CT sensor to record grid energy used as I have other loads connected to AC in.
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You can't measure power in AC circuits with the Ampmeter. The current could also be due to REACTIVE power.

With alternating current, you could have 2 Amps RMS of current in the wire and only 20W of active power.


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1 Answer
marekp avatar image
marekp answered ·

@RobinCG

Grid set point is the value the system is trying to maintain but is not possible to keep it exactly.

The actual value of power transfer varies sometimes widely because system has to take data from many points and based on this info decides on its settings.

To make maters worse data needed for calculation does not come at the same time and calculations also take time.

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My concern comes from my previous setup of 5kva multiplus with a Venus GX which was pretty much accurate within 10-20 watts or so on the VRM or Remote console displays.

But yeah the discrepancy on my current system raised some alarms for me. I remember a forum post where it was mentioned that the multiplus II units might have an issue with the current sense plug which caused the displayed grid wattage to be wildly inaccurate, but alas I cannot for the life of me find that post again to confirm if it is similar to what i am experiencing.

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@RobinCG

Do you have a power meter at AC-in?

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So i have a fairly basic wireless AC meter but it doesnt take voltage shifts into account so is not accurate for more than a rough idea of power usage. I use a hand held AC amp meter on the AC line to the inverter input to more accurately work out wattage at a glance.



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@RobinCG

Do I understand it correctly that this wireless AC meter is not connected to your GX device.

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Correct, I am comparing against the AC in measurement provided by the multiplus and by what I can see on my hand held ac amp clamp. the cheap ac wireless ac sensor and the amp clamp measure very close but the multiplus seems to be under reporting Grid usage by around 300 watts or so. So vrm displays between 20-90 watts on average when in reality it is closer to 300-400 watts.
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@RobinCG

Is your load connected only to AC-out of MP-II?

Are you sure there are no other loads between your AC meter and MP-II?

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Yes my load is connected to the AC-OUT1, and I am certain that there are no other loads in between that could be fouling up the measurements.


Side note I would like to get an ET112 Energy Meters ET112, ET340 & EM24 - Victron Energy

to eliminate the cheap wireless ac meter and integrate the whole thing with vrm but where I am based availability is special order only and I have not yet gotten around to it.

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@RobinCG

For 1 phase system ET112 is enough.

I have 3 phase system with EM24 but even that is not assuring the same power transfer numbers.

Below two numbers from the same moment.

1. EM24

2. Independent meter

difference.jpg

As you can see there is no way for those numbers to be the same. :)

When load and production is more stable the numbers get closer.

difference-3ph.jpg


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difference.jpg (28.3 KiB)
difference-3ph.jpg (90.7 KiB)

SO I finally found the document that outlines something similar to what I am suffering. I have not been able to take my system offline as of yet to test their suggested fix as there is really no downside other than downtime to try it.


https://community.victronenergy.com/storage/attachments/28254-2021-12-mpii-esii-quaii-current-sense-socket-issue.pdf


Do you think in your experience that this could be my issue?


Robin

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@RobinCG

I never used internal or external current sensor, so I cannot say how big influence this have on the accuracy of the power measurements.

Their explanation sounds plausible.

I have EM24 power meter.

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