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Alexander Bartash avatar image
Alexander Bartash asked

Quattro-II measured AC output power drops 150w while charging from grid with constant AC load

I have Quattro-II 48/5000/70-2x50 + BMV-702 + SmarSolar MPPT 450/200 + LiFePO4 48V.

The 220V grid is connected to Quattro's AC In-1 and all load is connected to AC-Out-1 for now. There is no AC load bypassing the Quattro's AC Out.

I noticed that whenever I charge my battery from grid (both scheduled & unscheduled charge), I see that measured AC output power in VRM drops about 150w.

Which means that:

  • If I have AC output power about 150w and start charging the battery from grid, the measured AC output current & power fluctuates below & above zero.
  • If have output power about 1000w it will drop to about 850w. Which means that the inverter is capable of measuring output AC power while charging, but it is 150w off.

And the actual load does not change. This is measurement or calculation error.

Is this expected behavior? I can reproduce this consistently during day & night.

Also on the screenshot below you can see that input power is 3232w battery power measured by BMV-702 is 2781w. 3232-2781=451w. Output power is shown 14w but I know that it is fluctuates at about 150w.

If we do the math 2781/(3232-150)=0.90233614536 charger efficiency.

I have AC in limit set to 16A and grid charge power is about 3kW.

I did not limit inverter's output power via configuration. If I enable heavy load like 2kW and start charging, it charges at about 1kW not exceeding 16A which looks correct to me.

High resolution: https://community.victronenergy.com/storage/attachments/46894-1674030416850.png

1674030416850.png

High resolution: https://community.victronenergy.com/storage/attachments/46895-1674030427023.png

1674030427023.png



MultiPlus Quattro Inverter Chargerbug report
1674030416850.png (679.6 KiB)
1674030427023.png (796.8 KiB)
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3 Answers
snoobler avatar image
snoobler answered ·

I'm not sure I'm following you, but I'll say this in case you're not aware...


An inverter/charger is both, but NEVER both at the same time, i.e., when charging, the inverter can't invert. When charging, all loads are powered by the AC-in source provided the AC input limit isn't exceeded. If AC input limit is exceeded and power assist is enabled, the inverter/charger starts inverting and stops charging to supplement the AC input to prevent overload.


That's why output power drops to near zero in your first chart and current drops to near 0 when charging in your second chart.


The difference in AC input power vs. Battery power is AC-DC conversion inefficiency and idle power consumption. That's the difference between the red and blue lines in your first chart.

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Bonhardt László avatar image Bonhardt László commented ·
I think in both case, the power comes from ac in (grid) -> ac out and in the same time ac in to battery as charge, so there is no DC-AC efficiency loss on AC out.
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Alexander Bartash avatar image Alexander Bartash commented ·

Thank you. That is what I also though initially but then I did another test

> If have output power about 1000w it will drop to about 850w. Which means that the inverter is capable of measuring output AC power while charging, but it is 150w off.

I understand that it is getting powered by AC-in but for some reason VRM shows load about 150w lower than it actually is while the inverter is charging the battery.

And in case of 150w output load it drops to 0 because measurement error happens to be about 150w. And if you look closely on the chart it is not 0, it acually fluctuates above and below 0 in the same manner as before the charger was turned on.

1674219109706.png

Which also means that the inverter is measuring output power but its measurements are 150w lower than real value.

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Bonhardt László avatar image
Bonhardt László answered ·

It seems you are not alone, i have 3x MultiPlus-II 48/5000/70-50 in a 3 phase ESS configuration and i noticed the same "issue".

having constant loads on "AC out" while charging the battery,
the measured output at "AC out" drops on all 3 multiplus.

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Alexandra avatar image
Alexandra answered ·

@Alexander Bartash

@Bonhardt László


See FAQ 10.6 or 6

Is is an effect of the capacitors in the inverter. So an interaction of components.

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Alexander Bartash avatar image Alexander Bartash commented ·

Thank you. But that question is about input current and my question is about output current and power. Also it mentions "Look at the Input power readings instead." but as you can see on my screenshots, output power has measurement error as well as current.


10.6. Q6: Optimize mode, no feed-in: The AC Input current fluctuates wildly - sometimes even going negative ...why is this?

This is normal. The current shown is the RMS current. Which does not represent real power, nor real energy being fed into the grid.

Especially around 0 W real power, you’ll see that the RMS current is very high. This is caused by the X-capacitors in the Multi.

Look at the Input power readings instead. They fluctuate a lot less, and are a more reliable indication of power and energy.

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