Quattro Overcurrent with no load attached

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ceriw asked Nov 23, '20

Quattro Overcurrent with no load attached

Good morning all,

I had several overcurrent shutdowns on my system last night. System is 2x Quattro 8k in parallel, Venus GX, REC BMS. System was running in "inverter only" mode.

the first at 00:20. We were all in bed so there was very little power usage (around 250W). I reset the system and it went into overcurrent shutdown again at around 04:25. This time, when I reset the inverters, I put the house onto grid bypass, so there was zero load on the output of the units.

With no load on the units, they went into overcurrent shutdown again at around 06:35.

We never see overcurrent on this system during the day, when we can have some quite high power usage (it's not unusual to have the dishwasher, washing machine, induction cooker etc all on at the same time)

Anyone got any ideas?

MultiPlus Quattro Inverter Charger

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Answer 1 · 2020-11-23T11:28:40Z

Guy Stewart (Victron Community Manager) answered · Nov 23, 2020 at 11:28 AM

Hi @ceriw

The most likely cause of this is an issue with the AC input supply connection.

There is a lot more explained (including how to confirm, and what can be done in this specific Loss of Mains "LOM" detection manual).

Basically, the Quattros are testing the grid is there by trying to shift the AC input frequency. The grid should hold the frequency steady, and then the Quattros know the grid is still attached.

If the grid is not attached, the frequency will shift with the Quattro, and the grid will be considered 'disconnected' and the AC input transfer switch will open.

But there is another possibility, the grid is still there, but the Quattro is also able to shift the frequency slightly because they are more powerful than the AC input (bad connection, wire run too run long or skinny, etc). This creates a differential between the grid voltage and current sine wave and the Quattros voltage and current sinewave, and that differential allows current to flow, and potentially overload the Quattros.

This is an issue unique to ESS systems where grid codes are selected that require LOM protections, are you using those features? Removing the ESS assistant, and the local grid code will very likely resolve it, if that is possible for your situation. Easier than physical inspection and potential upgrade of AC wiring too.

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ceriw commented · Nov 23, 2020 at 11:39 AM

Hi Guy, thanks for coming back to me. Last night during all 3 of these events, the Quattros were set to "inverter only", so the grid was not connected. Under this condition, would the grid code settings still take effect?

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Guy Stewart (Victron Community Manager) ♦♦ ceriw commented · Nov 23, 2020 at 11:44 AM

Can you physically isolate the grid by switching off the AC supply so that the AC input terminals of the Quattros show 0V?

That should isolate this as a potential cause of your issue (if it still occurs).

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ceriw Guy Stewart (Victron Community Manager) ♦♦ commented · Nov 23, 2020 at 12:16 PM

Hi Guy, ok, i will try that tonight and see if it behaves any differently.

Many thanks for your suggestion

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ceriw Guy Stewart (Victron Community Manager) ♦♦ commented · Dec 08, 2020 at 10:40 AM

Hi Guy,

I've been trying various scenarios to build up a picture of what causes the overload error and what doesn't. The common denominator running through all of them is it only throws an error when the system is delivering less than 300W.

One of the most useful grabs happened last night. There were no loads attached to the units and there was no grid supply connected, so ruling out anything upstream or downstream on the AC side.

I've attached screenshots below of this.

Any idea where I go from here?

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Answer 2 · 2020-12-09T09:38:02Z

ceriw answered · Dec 09, 2020 at 09:38 AM

Last night was the worst the system has been - shutting itself down a lot.

One thing that did come to mind is the possibility that the master and slave units are somehow going out of sync with each other.

With the AC inputs individually isolated and the AC outputs isolated after the master and slave units link, the only place that any AC current could go would be from the output of one unit to the output of the other. Just before the system shuts down with an overload error, you can hear the transformers in them humming like the unit is under heavy load. There is not a corresponding high power draw from the battery at this time either, which may again point towards power shunting between Quattros.

Is this possible?

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Guy Stewart (Victron Community Manager) ♦♦ commented · Dec 09, 2020 at 11:29 AM

That is a definite possibility. Low load overloads can be caused by an AC sine wave that is out of phase between units (or the grid). A reactive current, this will not show up as a power reading from the battery, or on the units themselves.

Replace the communications cables,

Check all cable connections. Confirm that AC out cables are equal length to the common AC bus, with sufficient AC length (at least 2 M, and as small wire as possible for AC).

Confirm DC cables are equal length between DC bus and battery terminals for both units.

Remove parallel programming, reset to stand alone and reprogram.

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ceriw Guy Stewart (Victron Community Manager) ♦♦ commented · Dec 09, 2020 at 11:40 AM

Thanks Guy,

I will replace the coms cables. At the moment, they are UTP cable, is this recommended or should I move to FTP or STP?

AC out cables are 3.1M long (within 2cm of each other lengthwise) , 10mm CSA.

8x 1.5M 50mm CSA battery cables are all the same length.

On your last point, are you recommending reprogramming tham back up as master slave, or to disconnect 1 unit and run the other as a standalone to see if the issue goes?

Many thanks for your support on this

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Guy Stewart (Victron Community Manager) ♦♦ ceriw commented · Dec 09, 2020 at 12:06 PM

For the comms cables, use a factory made Unshielded Twisted Pair cat5/6 at least 10 cm from any power cable runs, and crossing at 90 degrees where it must.

I would disconnect the units from each other, ideally run them as isolated individuals, one at a time, if it's possible they can power the circuits without both.

That will help to further isolate the fault.

If you can't reproduce the fault as individual units, then reconnect them and reprogram again as the parallel pair (after updating to the latest firmware).

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