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marekp asked

VRM DC current question

Can someone explain why DC current in advanced view is different from the dashboard view?

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Update.

Here is the situation from today.

This morning Sun was up and battery was discharged down to 30%.

Battery is being charged with 133A but Advanced view shows DC current at 76A

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After battery gets to 100%, Advanced view reports DC current of -65A but the actual current, measured by SmartShunt, is 8A

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I am not very confident in numbers I see on VRM.

Maybe someone from VRM team would care to explain what is happening.

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2 Answers
marekp avatar image
marekp answered ·

@Alexandra

If We look at the VE.Bus DC current numbers from the Inverter/charger point of view, than if DC current flows out of it, it is a positive value if DC current flows in to it, it is negative value.

At this moment:

Shunt DC current is 127.3A

screen-shot-2022-02-15-at-94006-am.png

MPPT DC current (battery side) is 34A + 19.2A = 53.2A
screen-shot-2022-02-15-at-94028-am.png

So, the VE.Bus DC current should be 127.3A - 53.2A = 74.1A.

Close enough. :)

VE.Bus DC current from Advanced view is +71.1A

screen-shot-2022-02-15-at-93952-am.png

Out of 127.3A, flowing into the battery,the Inverter/charger must supply 74.1A (from AC-out connected Fronius) This value is positive because current flows out of inverter/charger.

Concusion.

VE.Bus Summary in the Advanced view, is informing us about Inverter/charger situation on the AC and DC side.

It is not a bug than.


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Alexandra avatar image Alexandra ♦ commented ·
@MarekP

Neat. Learn something new everyday.

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Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

Hi @MarekP,

I think it's because advanced lags a little behind. It updates only every minute or so while the dashboard updates are almost in real time.

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marekp avatar image marekp commented ·

@Stefanie

Thank you your quick response.

I think it is not it.

Look at my 24 hour graph for battery volts and apms.

screen-shot-2022-02-13-at-21131-pm.png

The last time the current was so negatively high was about 20 hours ago.

At the moment this -66A were shown, battery was fully charged and PV was supplying power to the house and feeding to the grid.

Advanced view constantly showing DC current well below the actual one.

screen-shot-2022-02-13-at-22209-pm.png

At the same time SmartSunt is registering this:

screen-shot-2022-02-13-at-22547-pm.png

It looks like another VRM bug.

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ marekp commented ·
Not everything is a bug per se only because a behaviour cannot be explained.

Maybe there has been a load just for a short time and not long enough to be registered for the widget.

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marekp avatar image marekp Stefanie (Victron Energy Staff) ♦♦ commented ·

@Stefanie

This negative current in advanced view is constant.

There is no load, constant or short, that would explain this discrepancy.

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ marekp commented ·

What is the DC box and what's the source of it's values? Another BMV or SmartShunt configured as DC-Meter?

FWIW, as far as I know DC -39.9A means that there is a charger charging with 39.9A, where the charger is not known by the System and/or DVCC. It's not a negative current going out of the system/battery but into the battery. That's how it is working in my installations. But I think your DC box is the not the DC Power box like in my screenshot. Maybe a battery or another device?

Here is an example:

A Phoenix Smart Charger IP 43 currently charging. the Dashboard displays this as negative value, but it is accounted for (charge current minus loads) in the SmartShunt left to the DC box.

bildschirmfoto-2022-02-13-um-163929.png


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marekp avatar image marekp Stefanie (Victron Energy Staff) ♦♦ commented ·

@Stefanie 

What is the DC box and what's the source of it's values? Another BMV or SmartShunt configured as DC-Meter?

This is what I am asking from the beginning.

What is that DC current, in advanced view representing?

FWIW, as far as I know DC -39.9A means that there is a charger charging with 39.9A, where the charger is not known by the System and/or DVCC. It's not a negative current going out of the system/battery but into the battery. That's how it is working in my installations. But I think your DC box is the not the DC Power box like in my screenshot. Maybe a battery or another device?

OK, so how would you explain that now, with no PV production this DC current, more or less, matches the current taken from the battery?

screen-shot-2022-02-13-at-51021-pm.png

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It is still negative value as the current is coming out of the battery.

During the day this current in Advanced view was -40A when SmartShunt indicated -3.4A or -66A and -3.2A respectively.

Where those big negative values are coming from?

I do not have any chargers apart from 2x MPPT and 6x MP-II.

All current flowing to and from battery is measured by SmartShunt.

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ marekp commented ·

I may have misunderstood you there. But with the new screenshots it becomes more clear now.

The current shown in the VE.Bus Summary is a calculated value and is nowhere accurate nor can it be compared to values coming from a shunt. This is how it has been like forever and it's documented somewhere in the jungle of Victron documents. But I must admit that I've never seen such huge difference like in your system...

In a small system it more close to reality. Dashboard showing the MultiPlus with it's estimate of current. The voltage is correct. I have a energy meter which says that I'm actually using 30W and not 22W (calculated):

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marekp avatar image marekp Stefanie (Victron Energy Staff) ♦♦ commented ·
@Stefanie

Sorry if I made my question not clear.

I always assumed that the DC current value is the battery current since it is sitting next to the battery voltage.

Now I am not so sure, but I would like to know what is the intention of the VRM programmers for it to represent.

If there is no direct measuring equipment in the system, calculating that DC current might be OK, but if there is a SmartShunt or BMV present there is no point in calculating it. Just read it.

Now I am starting to second guess the numbers I see on the VRM portal.


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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ marekp commented ·

I only can guess here, but I think this for installations without BMV/SmartShunt. Maybe its a remnant of older days? And normally the calculation is not so far off except in your case.

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marekp avatar image marekp Stefanie (Victron Energy Staff) ♦♦ commented ·
@Stefanie

So maybe it is a high time to fix it.

After all it could be a bug. :)

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Alexandra avatar image Alexandra ♦ marekp commented ·

@MarekP

The widget in advanced view there is not the bmv reading, it it the system reading. (I could be corrected - but this is the conclusion I have alsways come to) Is that not the one from DC bus on multiplus that has no measurement of current? So more an assumption? If your system is ESS programmed then it could be power assist that is drawing from battery. I am guessing since obviously we are not seeing this real time. Dont forget each component is polled for information at different times and possibly at different rates.

The minute by minute logging is different to realtime viewing so it is possible that the graph is connecting dots and the bmv is showing the more transient power movements of power. And the update rates of each part of VRM is not the same, that combined with internet lag etc makes vrm monitoring more of an overview type thing. That is why local monitoring is needed.

And if you want to be more serious with monitoring and statistics use Grafana.

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marekp avatar image marekp Alexandra ♦ commented ·

@Alexandra

It is ESS.

Here is the graph of DC power and DC current for the 13/02/2022-14:02:10 from Graphana.

DC Power (49W)

dc-battery-power.jpg

DC current (0.2A)
dc-battery-current.jpg

Here is the DC values from Advanced view in VRM for the same moment (+/- 1 second)

screen-shot-2022-02-13-at-20209-pm.png

If there was a Power Assist it would be registered on the VE.Bus.State graph on VRM. There was none. My system fed the grid with almost 10kW when load was newer higher than 5kW, so there was no need for Power Assist.

screen-shot-2022-02-13-at-62007-pm.png

For the whole day I was seinig only large negative values for the "DC current" in Advanced view. It is statistically improbable to see only those "transient" values for DC current.

Still, I do not know what is this "DC current" in Advanced view showing.

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Alexandra avatar image Alexandra ♦ marekp commented ·

I do see what you are saying there. Not seen it as bad as what you have it on any of the systems I am monitoring at the moment, just been taking a look at them. But then it is not a system like yours.

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marekp avatar image marekp Alexandra ♦ commented ·

@Alexandra

I noticed that this problem is most visible when there is PV production.

Now, at night, the DC current, in Advanced view, is quite close to what SmartShunt is measuring.

I hope the problem is not caused by the "system like mine".

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Alexandra avatar image Alexandra ♦ marekp commented ·
;) i meant a three phase parellel with Fronius.

You have quite the setup there.


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marekp avatar image marekp Alexandra ♦ commented ·

@Alexandra

It is a hobby of mine. Others play with stamps or coins. I play with electrons. :)

Do you know why those two graphs are not identical throughout the whole day?

They are identical up until the Sun comes up.

screen-shot-2022-02-14-at-24739-pm.pngMaybe here is the answer to my original question.

I have a feeling that MPPT production is somehow influencing the VE.Bus DC current.

That sudden change in DC current (around 13:00) coincides with grid failure. Battery was full at that moment, so PV production had to be lowered to the load level.

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