question

ttbb avatar image
ttbb asked

DC consumption not logging on VRM?

I have just set up a Raspberry Pi running Venus OS

System: 2x 75/15s + Pi / 7s Lithium NMC / DC only setup with all loads via the load outputs.

So the VRM dashboard shows 'live' consumption at last update, the advanced widget 'System Overview - DC system' does a good job of allowing me to see watts used at any point in time.

Load out data from the MPPTs clearly exists. Why then is there no DC consumption logged on the dashboard like solar power produced?

https://vrm.victronenergy.com/installation/50299/share/e844d84d


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Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @TTbb

there is, but not as 'DC power' that is only available with a battery monitor.


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ttbb avatar image ttbb commented ·

Hi @Daniël thank you for the reply . I am not so interested monitoring the individual outputs at any point in time, although its useful and nice. Totals over a time period in watts is what i am after.

If all the data is already available and clearly it is because consumed watts are logged within the controller history, live consumed watts are being shown in the VRM dashboard. 'System Overview - DC system' can be used to track back what was used at any point in time. Why is a battery monitor needed just to log this data to present it like the PV watts generated? That seems to make no logical sense!

I thought i would give the VRM a go and set up the Pi because the MPPTs are functionally compromised by the lack of an internal clock. Without a new day starting at a consistent set time and a useful time such as midnight the logging in history is not really that useful.

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JohnC avatar image JohnC ♦ ttbb commented ·

Hi TT. I don't know if this is what you want, but if you set Dashboard to 'Last 7 Days' and hover over the bar you want, you'll get daily summaries.

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ttbb avatar image ttbb JohnC ♦ commented ·

Hi @JohnC yes that is exactly what i am after and it works wonderfully for solar but the issue is consumption is not logged. :(


@Daniël is suggesting it can only be done with a battery monitor. As is probably clear form my response I can't quite wrap my head around that one. The data already exists form the MPPTs and is presented in 'advanced' where it can be tracked back. To show on the graph would surely just be taking the total between two points in time, what am i missing? Maybe i am missing something but is that not exactly what is happening with the solar logging??



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JohnC avatar image JohnC ♦ ttbb commented ·

In the VRM Dashboard, have you tried all selections in the System Overview box?

If you have 'Has DC System' checked in Venus, try with it unchecked.


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ttbb avatar image ttbb JohnC ♦ commented ·

When Has DC System is on live consumption is shown under system status but not logged. when it is off it does not show. The whole DC power logging seems a mess form what i can see.

@Daniël is contradicted by the victron VRM faq

"The calculated value for 'DC Power' is not used in any way by the GX, beyond just being displayed 'on screen'. In particular it is not logged on the VRM portal and it is not included in system calculation and it does not appear as part of the recorded Solar Yield."

That is saying it cant log at all evern with a battery monitor. but then @Markus writes something in an earlier post that contradicts that.

" I have read the requirements and I am a little confused. What does "Currently the calculated value for 'DC Power' is not used in any way by the GX, beyond just being displayed 'on screen'. In particular it is not logged on the VRM portal" mean? When I have DC consumption, which I have most, it is displayed and logged in the VRM graphs."

So maybe markus can give more clarity on what makes it work / what is required.

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JohnC avatar image JohnC ♦ ttbb commented ·

I wish I could test this for you, but don't have suitable kit on hand.

When 'Has DC System' is checked, the system expects to see a BMV to measure it and include as one of the data inputs. With no BMV, it will "calculate" it, usually from the difference between mppt input and inverter output. That 'calculated' figure is often a little 'unstable' due to varying sample times and other things. So that is likely what the literature is referencing. Not much point in using it for further analysis because it's a made-up figure anyway.

In your case, the mppt must know the difference between it's total solar output and what it's delivering to the batts, and the 'DC system' is calculating it rather than it coming directly from Load output measurements. If you compare the headings on Daniel's and your widgets, you'll see the different sources stated clearly.

It's why I suggested turning off that 'DC System' tile and watching the Consumption tab on Dashboard. Might need some time to gather enough data to see how that works though.

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ttbb avatar image ttbb JohnC ♦ commented ·

@Markus thank you for confirming this.

@JohnC Thanks for your response. I can fully appreciate those reasons for needing a battery monitor. . What you said makes sense, I understand the concept of power factor and inverter conversion efficiency not being consistent across all loads and temps. The calculated value makes a lot of sense in that respect.

Shame it can't work with the kit i have. Another thing to add to the shopping list lol.

I did turn off 'Has DC System' and left it off to see what happened. This is what does happen.


DC system stops logging and current on 'system - battery voltage and current' starts logging where it was not before.

I took a look to see if there was any difference between the yield reported in the MPPT history and the VRM


There is a 10Wh difference but interestingly the day prior when Has DC was on it was spot on the same 250Wh. I have turned it back on now and will cycle it on and off for a few consecutive days to see what the outcome is. It could be total chance.


While looking at the MPPTs history i also noticed the Pi is not even registering as a load. Solar yield is so low right now i put the load form that one MPPT onto mains before setting up the Pi. I thought it would be a good opportunity to see how much power it was going to consume.

I could see form the VRM it was below 0.1a and not showing. i thought it might be totalling up and get show in the MPPT history . Clearly not so that is the limitation of the MPPTs load output, below 0.1a and it goes unaccounted. Admittedly i don't know how accurate any such meter is.

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markus avatar image markus ♦♦ ttbb commented ·

@TTbb Hi,

DC consumption on VRM overview graph, is only available when using a BMV battery monitor.

Regards,

Markus

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