ESS scheduled charging issue with high grid load on grid parallel setup (EV Charging / Time of Use Tariff)

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fjj asked May 3, '22

ESS scheduled charging issue with high grid load on grid parallel setup (EV Charging / Time of Use Tariff)

Hi,

I have a grid parallel setup with ESS working perfectly, apart from when there is high grid load during a scheduled charging window.

Setup is as follows:

Multiplus-II (48/3000-35-32) inverter AC In connected to Grid, no connections to AC outs, with AC coupled PV on input side. CT clamp on meter tail connected to Multiplus-II for grid consumption monitoring.
Cerbo GX setup with ESS (With Batterylife Optimisation on) with scheduled charging setup to take advantage on my low rate overnight time of use tariff.
Batteries are 3 x Pylontech US2000C

Scheduled charging works fine until my EV charger kicks in (same window) and suddenly grid load is ~9.5kW with charger, baseload and EV 7.2kW charger, the charging then stops and the batteries start to discharge even though this is a scheduled charging window.

Is this expected behaviour? Surely the inverter should realise this is not current following through the inverter itself, just the AC side of the setup?

My idea for a 'quick' fix is to relocate the CT to my distribution board, as my EV charger is supplied from a separate DB directly from a distribution bus before the main DB, however the cables are tricky to access so keen to know if this will work before making access.

Any advice appreciated!

Thanks.

Multiplus-II ESS grid parallel

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Answer 1 · 2022-05-03T17:35:21Z

lackland answered · May 03, 2022 at 05:35 PM

One thing to check is 'Input current limit' in the inverter settings (Cerbo – Device List – Multiplus-II).

At first I thought this was some kind of protection for the inverter or its AC circuit, but in fact it's the maximum allowed to be drawn from a weak grid connection (such as a "shore" connection at a dock or campsite). If this is set at, say, 32A, as soon as the draw goes over 8kW the inverter will begin to supply power to prevent any higher demand on the grid. This has priority over scheduled charging because the top priority is to avoid tripping or overheating the grid connection.

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fjj commented · May 03, 2022 at 07:27 PM

Thanks for this - I had a look and it is indeed set to 32A, although that is the maximum which it can be set to. I have a 100A incoming service, but I guess as the inverter is rated at 32A this may be the reason, however it isn't relevant to the high loads as they are not going through the inverter - everything is 'AC side' on AC In.

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Answer 2 · 2022-05-04T10:28:07Z

fjj answered · May 04, 2022 at 10:28 AM

FYI - for anyone else with similar issues, moving the CT clamp to the main DB, effectively moving it behind the EV charger, has resolved the issue. Both car and battery charged fine last night.

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Answer 3 · 2022-05-04T17:04:20Z

lackland answered · May 04, 2022 at 05:04 PM

Good to hear your workaround worked.

On my 48/5000, although the default for 'AC input current limit' is 50A (as stated in the manual), I can adjust it as far as 100A. Possibly you have Power Assist enabled, or a setting somewhere which makes the inverter think its AC output(s) are in use.

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