ESS/Genset AC out 1/2

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Jonne Holmberg asked Dec 22, '23

ESS/Genset AC out 1/2

Can Multiplus II (5000VA) know if the energy is coming from grid or genset?
I mean, during grid blackout, the feed goes to critical loads, energy taken from batteries.

When the capacity from batteries goes low, Cerbo will set the genset on.

This leads to problem, because the mains (Ac out 2) becomes active as the AC in feed gets electricity into the unit. The mains load exceeds the capacity of the genset. The genset is only for critical loads.

So, my question is, can Cerbo or the energy meter hold the relay open on AC out 2 when the feed is from genset? And close the relay when the feed is from grid?

ESS ac out 2 generator auto start

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Jason - UK answered · Dec 22, 2023 at 12:05 PM

@Jonne Holmberg Yes via the use of assistants and a means of grid detection controlling the contactor on the AC-OUT2.

Using the Programmable Relay assistant, you can set AC-Out2 to off on the 'open' of another input like AUX1 or AUX2, and that input connected to a relay that opens on grid failure.

https://uk.rs-online.com/web/p/power-relays/0348762

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Answer 1 · 2023-12-22T10:57:45Z

Jason - UK answered · Dec 22, 2023 at 10:57 AM

@Jonne Holmberg As far as I am aware you cant do this, if anything you risk damage to the generator and the MPII because you will have 2 AC generating frequencies fighting each other combined with the MPII having no way to automatically disconnect from the generator.

You need to have a auto-change over switch on the AC-IN side of the MPII, so when the grid fails, the auto-change over switch automatically switches to the generator, and the MPII sends the run signal to the generator to run. When the generator is up to speed and is generating sufficient voltage, the MPII will then sync with the generator. When the grid supply is reconnected, the auto-changeover switches back over to the grid supply, and you have a interlock that stops the generator.

As a side note, its good practice to have the generator run for a minimum run time to prevent short cycling, and allow it to reach operating temperature before shutting down. This prevents premature failure of the generator.

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Answer 2 · 2023-12-22T11:53:10Z

Jonne Holmberg answered · Dec 22, 2023 at 11:53 AM

Thank you Jason, but I was clearly a bit unclear.
We have an auto-change over switch.
My question is, can I adjust the MPII (or cerbo) so, that it feeds with genset only AC out 1 (critical loads) and both AC out 1 and 2 when grid is avaliable?

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Answer 3 · 2023-12-22T12:18:14Z

Jonne Holmberg answered · Dec 22, 2023 at 12:18 PM

Thanks!

Just one thing, will the AC out 2 relay close if the genset changes to grid?
My point is, the genset is suitable for only critical loads (AC out 1), not all loads, and it starts if the capacity of batteries run out.

So, the AC out 2 inactive with genset, active with grid.

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Jason - UK commented · Dec 22, 2023 at 12:39 PM

@Jonne Holmberg If the mains supply switches from the genset to grid, the AC-Out2 will become active again, providing the small relay as mentioned above is powered by the grid only.

Also, you might want a delay set into the assistant so when the grid comes back online again, you might want the AC-OUT2 to wait say 10 seconds just in case the grid fails seconds after coming back online, or you get a 'grey out' (grid live but not fully energised / or low voltage)

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