question

cobraphil avatar image
cobraphil asked

Still struggling to get AC-IN to connect.

Newly installed MultiPlus-II 5000 has been running great for several weeks now except for one nagging problem. I use Node-Red in ESS mode 1 to turn the inverter to Invert Mode at night time, then allow the batteries to charge in the morning. When the batteries are fully charged I switch the inverter back to ON mode to allow feed-in. Sometimes the AC-IN will connect within a matter of seconds, sometimes it takes hours. AC-IN is connected to stable grid-power at 50.4-50.6 Hz. Even at a stable 50.4 HZ for a sustained period of time it will not connect. Without changing anything, if the grid frequency drops to 50.1Hz or 50.2Hz for a minute, it will connect. Otherwise I have waited for up to 8 hours before it will connect.

Accept wide frequency range is enabled. I have tried all of the various other settings: weak AC, UPS Function, Conditional A/C Input Connection is disabled, etc.

I had mentioned this in a previous post, but it was a smaller issue that what I was facing at the time. So I decided to make it it's own post. Thanks.

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Multiplus-IIfrequency
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shaneyake avatar image shaneyake commented ·
Can you post screenshots of VRM? so we can see input vs output frequency over time?


In your screenshot above you can see that the output and input frequencies are not the same. The contacts won't close till the inverter is synced with the grid. It is possible that the grid is changing frequency too fast for the multi to sync and then the grid stabilises and then it connects.

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Kevin Windrem avatar image Kevin Windrem shaneyake commented ·

On my Multi Compact the input and output frequencies are different by between 0.2 and 0.4 Hz even when locked and accepting shore power. I assumed it was a measurement error since the input and output are connected together.screen-shot-2021-08-28-at-10654-pm.png

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screen-shot-2021-08-28-at-10654-pm.png (40.5 KiB)
shaneyake avatar image shaneyake Kevin Windrem commented ·
Yeah, I have that measurement error too, only 0.2hz for me normally.

That's why I asked for VRM data to see if it more than that or it just happened to be the case when the screenshot was taken. I have had issues with Multiplus-ii locking to grid when the change in frequency is high. This for me tipical at sites with bad connections and big loads. It does a similar behaviour where you just leave it and eventually it connects.

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1 Answer
basil katakuzinos avatar image
basil katakuzinos answered ·

I have no clue why it is doing this. Might be worth contacting your distributor. Do you know you can use the ESS settings to avoid having to disconnect from the grid at night?

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basil katakuzinos avatar image basil katakuzinos commented ·

No need to use node red for this

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shaneyake avatar image shaneyake commented ·
They are using 2 grid meters to prevent feedback from the campus. So not a standard ESS setup, however They can just set the Grid setpoint to 0W at night instead of disconnecting.
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cobraphil avatar image cobraphil shaneyake commented ·
Due to the continued issue with connecting with AC-IN, I am currently letting it stay connected and using PV Power, AC Loads, L1 Current to calculate my Grid Setpoint via node-Red. So if there is no PV Power, Grid Setpoint is zero at night time as shaneyake pointed out.

I will try to get screenshot later today or tomorrow. Thanks.

Once it is connected, it will stay connected through the frequency swings. I thought the wide input frequency range would allow it to connect even if the frequencies did not match. I guess that is not the case.

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Kevin Windrem avatar image Kevin Windrem cobraphil commented ·
The AC input and output frequencies must match (more accurately, the phases must match) at the instant the AC input relay closes otherwise there would be a huge current spike through the relay. The result could be an inverter overload or damage to the relay.

If the input frequency is changing faster than the inverter frequency can chase it, then there will never be an in frequency/in phase condition. (The voltage must match also.) We are speculating that this is the cause of the delayed connection but it seems logical. Selecting wide frequency would permit acceptance of an off frequency AC input, but this may not be speeding up the inverter syncing to the input.


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cobraphil avatar image cobraphil Kevin Windrem commented ·
Thanks Kevin for your input. This is the conclusion that I have come to also. When the grid frequency does come down to 50.1Hz for a period of 10-30 seconds, then it does connect. I am located in Papua New Guinea where I know the grid is not clean and stable much of the time. It is clear now that the wide input frequency range is only for after the connection is made.
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Related Resources

MultiPlus-II Product page 

MultiPlus-II Manual

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VE.Bus Error codes

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