Inverter AC1-5.0-E-G2 making occasional loud 'buzzing' sound when batteries at 100%
Posted: Mon Jun 16, 2025 10:07 am
Hello! I have a AC1-5.0-E-G2 inverter connected to an EP11 battery. There's no solar PV attached to this AC1 inverter, it's just for the battery. There's a zero export limitation on this AC1 inverter agreed by the DNO.
Separately I've got a 7kW PV arrary with 7kW export agreed with the DNO.
On the AC1, when the battery max SOC is set to 100%, once the batteries are at 100% charge, the inverter stops charging and goes through is usual 60sec checking cycle repeatedly... all good... I'm then occasionally hearing a few seconds of buzzing/arcing sound from the AC1. Only when the batteries are at 100% and the separate PV is generating more than the house is consuming and there's a few kWs exporting.
If I set the battery max SOC to 95% I don't experience this at all.
My working thought is:
1. The AC1 doesn't know the PV is allowed to export; it only knows it has an export limit of zero.
2. When the batteries are at 100%, and there's excess energy exporting from the separate PV, the AC1 tries to dump this excess as it has an export limitation, and that's the sound I'm hearing.
3. If I have the max SOC at 95%, then the AC1 inverter can always push some of what it sees as 'excess' (and not allowed to export) into the battery.
And keeping the max SOC to 90-95% is a reasonable thing to do to manage this.
Would be great if the AC1 could know it's not allowed to export from the batteries, but that it's okay that there's an export going on. But that doesn't seem possible with the current software/firmware.
Anyone have thoughts on this?
(FOX support has already replaced the AC1 under warranty, but the replacement behaves the same; they've offered to replace the EP11... but I really don't think that's the fix here)
Separately I've got a 7kW PV arrary with 7kW export agreed with the DNO.
On the AC1, when the battery max SOC is set to 100%, once the batteries are at 100% charge, the inverter stops charging and goes through is usual 60sec checking cycle repeatedly... all good... I'm then occasionally hearing a few seconds of buzzing/arcing sound from the AC1. Only when the batteries are at 100% and the separate PV is generating more than the house is consuming and there's a few kWs exporting.
If I set the battery max SOC to 95% I don't experience this at all.
My working thought is:
1. The AC1 doesn't know the PV is allowed to export; it only knows it has an export limit of zero.
2. When the batteries are at 100%, and there's excess energy exporting from the separate PV, the AC1 tries to dump this excess as it has an export limitation, and that's the sound I'm hearing.
3. If I have the max SOC at 95%, then the AC1 inverter can always push some of what it sees as 'excess' (and not allowed to export) into the battery.
And keeping the max SOC to 90-95% is a reasonable thing to do to manage this.
Would be great if the AC1 could know it's not allowed to export from the batteries, but that it's okay that there's an export going on. But that doesn't seem possible with the current software/firmware.
Anyone have thoughts on this?
(FOX support has already replaced the AC1 under warranty, but the replacement behaves the same; they've offered to replace the EP11... but I really don't think that's the fix here)