question

jj-o-jj avatar image
jj-o-jj asked

AC consumption displays in part as DC consumption

400w AC load, no DC loads:

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177w - 201w ac - 91w dc = 115w total consumption, vrm shows 153w, 38W error.


Why would this be?



AC loads offde2.png


Same goes if disable "Has no DC system":

AC load on

de3load-on.png

AC load off (the only one that is almost without error)

de3load-off.png


Multiplus-IIVRM
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6 Answers
Alexandra avatar image
Alexandra answered ·

@JJ-O-JJ

If you are not using a shunt then it will be incorrect.

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jj-o-jj avatar image
jj-o-jj answered ·

I am using Smartshunt as battery monitor, DVCC on, SCS on.

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jj-o-jj avatar image
jj-o-jj answered ·

If i change battery monitor to MPII i get this result:

AC load, no DC loads:

de7.png

73w solar -201w ac load= -126W, not -238W as stated by MPII.


Same situation measured by Smart shunt as battery monitor:

de8.png

72w solar - 235w ac load -91W dc load (non existant in real life)= -254W consumption, not -295W as stated by VRM


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JohnC avatar image
JohnC answered ·

Hi @JJ-O-JJ

Much of the reason for this is the internal consumption of the Multiplus itself. The DcPower reading is derived by subtraction, so it will include this. I use a 5kVA Multi and it seems to usually settle at 30-40W internal usage.

But sometimes even settling is an issue. The sampling times don't coincide exactly for all the sources, and many ac loads have frequently switching power supplies which play havoc with the reported balance.

So it's difficult sometimes to see sensible figures at such a low usage. You could try viewing the VRM widget 'System - DCSystem' to see the variability it's dealing with. Even with the coarser sampling records of VRM.

This is quite normal, but understanding why it's happening may help ease the pain.

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jj-o-jj avatar image
jj-o-jj answered ·

That does not sound believable. Self consumption of MPII 3kva is 30-40W max, not 130W.

AC graph shows ac load is around 1,5 to 2 A so in accordance to the 400W nominal consumption of the load (dehumidifier).

de9.png

Why MPII displays this consumption as 200W ac + 91W dc i don't know, but this definitely IS NOT normal behavior in my book.

DC system graph: 500W DC consumption on a system with no DC loads? 90W constant consumption on a MPII with a self consumption of 30W? You sure this is "normal"?

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This is 1. consumption algorithm/programming error or 2. something related to the settings or 3. unknown. I am hoping it is something in the settings, so i can fix this.

Interestingly, with a different load (600w heater), power consumption is accurate.

AC 600w, dc 30W (i.e. correct MPII self consumption) = only 10W error, which is acceptable:

de10.png

Put differently , i never noticed these erroneous displays of consumption before i hooked up first load (humidifier), but i run compressor based loads also (fridge, AC).

Would it be possible for a specific load to trigger these incorrect consumption readings?


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JohnC avatar image JohnC ♦ commented ·

@JJ-O-JJ

Some loads may show more than others, but especially switching loads. VRM isn't great to show this consistently, but in this thread I found an example.. https://community.victronenergy.com/questions/157654/vrm-ac-output.html?childToView=157687#answer-157687

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jj-o-jj avatar image
jj-o-jj answered ·

391W=200W yes.

de12.png


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JohnC avatar image JohnC ♦ commented ·
@JJ-O-JJ

The 391 you've calculated here isn't W, it's VA. Your load has a nasty power factor.

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