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colin-jones avatar image

AC Couple Multiplus Compact PV Inverter Support Assistant

I am trying to repurpose an old processor Multi 24/1600 (firmware 196209) that has been running happily with Generator Start/Stop, AC Input Current Limit, Charge Current Limit Assistants. I want to add a 5 panels PV with an old Aurora inverter I have. Five panels in series are difficult for a DC MPPT and the cable run is long for 5 paralleled panels.

I added a 2nd Generator Start/Stop using General Flag to disable ACIN when Inverter load was low, and PV Inverter Support to manage the grid tie inverter.

When the grid tie inverter started (shore power disconnected) my VE Config display went from approx 50VA load to around zero, but the Multi started making a thuding noise every few seconds, like the transformer was banging on the case.

When shore power connected, INV load went to a very large number 15xxxxxx and the multi reset itself.

Have I missed something in the setup? I did try to read all the blog pages on Assistants, AC Coupled, and Solar.

Am I expecting too much from my old girl ?

Thanks for any assistance.


MultiPlus Quattro Inverter ChargerAssistantsac coupling
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5 Answers
Paul B avatar image
Paul B answered ·

Hi Colin,

The old 19XXXX processors have limited speed and memory sizes, so you are quite limited to what it can do with assistants.

I presume you have upgraded the firmware.


if it does not work then I think you may have to relegate it to another task. or replace the main CPU board with the newer version is another option

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Thanks Paul, the firmware is 1916209 which I installed a coupe of years ago. I thought all the newer firmware was for the later processors.

Yes thats the latest version (just checked)

JohnC avatar image
JohnC answered ·

Hi Col. Your 'thuding' noise is likely the transfer relay, indicating ACIN being either rejected or switched off deliberately.

Is the 5 panel string enough for your Aurora? Just a coupla clues..

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Thanks John, but the ACIN was disconnected at the breaker when it was thudding. Aurora was generating ~100W and AC load was ~50VA so maybe nothing left to actually charge, but VE Configure didnt show any DC current to battery.

The noise didnt sound like a relay switching, but certainly possible.

5 panels is a bit light for the Aurora longer term. It is starting but I expect very inefficient at 160v DC input. I will probably replace it with something smaller and more suited to the task if I can get the Multi working.


Paul B avatar image
Paul B answered ·

What assistants are you using to control the grid tie


I presume you have inserted one that controls the freq to turn the PV off if needed my example below uses a ess but there is a PV one as well


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Yes Paul, I added the PV Inverter Support assistant (last in list of assistants)

My understanding is it controls the battery charging in Inverter mode and will frequency shift to turn off the grid inverter if required.

I will delete the other assistants and test with just PV Inverter Support, and no ACIN and see if it is happy with that. The assistants aren't using all of the memory, but maybe it is too slow.

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Paul B avatar image
Paul B answered ·

Hi Colin

Is the Aurora responding to the freq shift keep a close eye on it,

My Grid tie (not Aurora) was not derating originally it was just going off so had to do some fine tuning. working well now.


also try the ess and see if that makes a difference


I also found that my unit when the mains was off was changing frequecy every 17 sec up and down to the settings in the ess. I moved the ESS from the number one spot down 2 spots and the problem went away. try the PV in number one then number 2 spot etc.


see if that helps

It was just trial and find the solution for me

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Thanks Paul,

It isn't getting far enough to freq shift. Barely starting the charge.

ESS requires the new processor I think. PV Inverter Support assistant was the predeccessor. Assistant notes say it must be the last assistant.

colin-jones avatar image
colin-jones answered ·

I tested again, with just the PV Inverter Support assistant installed, and AC IN disconnected.

Slightly less light to start so the Aurora output was <100W. Still a thudding noise coming from the Multi, but less concerning. The DC current went from -1 to 1 or 2A. As the Aurora output increased the voltage and frequency remained 240/50 in VE Config display. However, the Aurora display was showing voltage bouncing 230/248V and frequency 49/51. Once output was 150+W the Aurora shutdown with Grid out of range error. It reconnected but by the time output was 200W it shutdown immediately on reconnect.

I seems the Multi Compact mini grid wasn't strong enough to control the Aurora. Maybe it would be better with a different grid inverter, but it would be an expensive test if it behaved the same.

Looks like I will need to work on plan B.

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