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ralf-ct avatar image
ralf-ct asked

Understanding VRM 'Advanced' Widgets, why is my voltage changing?

I cannot seem to find any information explaining the readings shown by the individual 'System', 'VE.Bus System' and 'Battery Monitor' widgets,

i.e. the voltage on VE. Bus System 'AC Input Voltage and Current' is identical to 'AC Output Voltage and Current'.

Am I correct in assuming 'Input Voltage' is the voltage coming from Grid, and 'Output Voltage' is the voltage being supplied to the consumers by the inverter?

Should the inverter not 'clean up' the supply and provide a steady voltage?

48v-3000-multiplus-ii-vrm-portal-2023-06-12-090748.png

48v-3000-multiplus-ii-vrm-portal-2023-06-12-090812.png

Our electricity supply is irregular due to daily loadshedding throughout the country, the constant on/off does not make for a reliable system.

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3 Answers
pwfarnell avatar image
pwfarnell answered ·

When the grid is supplying all the ac loads, the inverter is doing nothing, the input is merely "passing through" to the output. It is only when the input current is not enough for your loads that the inverter starts doing any work to help if you have power assist enabled and a maximum input current set but in this case the inverter will still follow the grid voltage and frequency, it is just boosting the current. It is only when the grid fails that the inverter takes over and controls the output voltage. The grid is a much larger power source / power sink so the small inverter can not control your ac output voltage when it is connected to the grid. Look in the manual for the diagram, I habe added a link but it might not bevthe right inverter for you. The inverter has a relay which connects ac input direct to the ac output so the inverter follows the grid. You are incorrectly thinking that the ac input goes into the inverter workings and then to the output, this is wrong, the inverter workings are bypassed by the ac input.

https://www.victronenergy.com/media/pg/MultiPlus-II_GX/en/appendix.html#UUID-d72390fd-6b27-0612-e003-f786387486eb

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nickdb avatar image
nickdb answered ·

In an ESS the multi synchronises to the grid within upper and lower limits set on the inverter itself, beyond which it will reject grid and just invert.

The output voltage and frequency will always match the input voltages for this reason, whether or not you are supplying power from grid, battery or both as a typical ESS does.

To add, with the state of the grid in SA, voltages fluctuate wildly especially after loadshedding, mine goes as low as 199V, and will drop under loads that you generate as well as from other users on the grid. I have shuffled phases to try improve mine but it is just the way it is.


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ralf-ct avatar image ralf-ct commented ·

"The output voltage and frequency will always match the input voltages for this reason, whether or not you are supplying power from grid, battery or both as a typical ESS does." But if the grid is down during loadshedding, should the inverter not provide 'clean' power, later syncing to grid once the power returns?

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pwfarnell avatar image pwfarnell ralf-ct commented ·

I would expect that when the grid is down your voltage should be relatively stable, but can still fluctuate as your loads change. I do not have ESS but a boat, today I pulled the shore power and left the marina, which has a voltage right at the upper limit. Chart shows more stable voltage once the inverter is inverting in isolation.

screenshot-20230615-221307-kindlephoto-1923260092.png

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ralf-ct avatar image ralf-ct pwfarnell commented ·
That's a 25+ Volt difference!
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pwfarnell avatar image pwfarnell ralf-ct commented ·
In Uk we are nominally 230V with range of 216V to 253V, my marina is st max limit plus I have an isolation transformer which steps up at low load.
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nickdb avatar image nickdb ♦♦ ralf-ct commented ·
Yes, once grid is dropped it will provide a steady 230V and 50Hz.
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Alexandra avatar image
Alexandra answered ·

@Ralf_CT

The statement should the inverter not clean up the supply...the Victron is not an AVR.... It is an inverter that synchronises to grid as was mentioned.

When you are inverting it will be stable as it can then determine its own voltage and frequency.

We have also got an unstable grid and have found it it best to self disconnect where possible.

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ralf-ct avatar image ralf-ct commented ·

I probably missed something before, our voltage does seem to stabilize while on inverter. Last night we were off from just after 22h00 to 23h30, the voltages were a lot better than on AC.

48v-3000-multiplus-ii-vrm-portal-2023-06-16-110444.png

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Alexandra avatar image Alexandra ♦ ralf-ct commented ·
When you are inverting and see spiles it can be cause by triac based appliances. I have a hair dryer that does some interesting things to the voltage.

If in erting and it really dips then usually the DC side is not readily supplying the needed power.

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