Generator to DC side of 3-phase grid connected system

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Karl Laasik asked Sep 12, '22

Generator to DC side of 3-phase grid connected system

Hi dear Victron community!

I have a grid connected three phase AC-out-coupled system with Multiplus-II, CerboGX, SmartShunt, Lynx distributor and battery balancers. Battery pack is 48V 600Ah made from 12 pcs of 12V lead acid GEL batteries (picture below).

I would like to connect a back-up generator for the wintertime to help the batteries when the electricity price is really high and the SOC is getting low. There is three possible solutions in my mind.

1. Generator and changover switch to AC in of MPII. That needs a very powerful 3-phase generator which is expensive and there are troubles with feed-in.

2. Generator and Skylla charger to the DC side. Not a big generator needed but there is no VE.bus communication with the system.

3. Generator and another Multiplus (preferred). This way I could have intelligent communication, more flexibility and even one extra 1 phase output from the extra Multiplus. Is it possible and logical this way? Red colour is for new equipment. Is there anything else I should add (generator auto start for sure)?

Any ideas, suggestions or examples are welcome...

Karl

Multiplus-II Generator grid AC PV Coupling multi phase

1663014953173.png (165.2 KiB)

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Answer 1 · 2022-09-13T05:18:19Z

Kevin Windrem answered · Sep 13, 2022 at 05:18 AM

The 4th MPII would not integrate into the GX control system. A single inverter/charger. A multi-phase and/or parallel configuration appears as one inverter/charger to the GX devices. The 4th MPII would appear in the device list but would not show on the overviews and would not integrate into DVCC .(at least I don't think it would.)

You could integrate a standalone charger into the system with an additional DC shunt programmed as a "charger". Not sure about DVCC integration but it would appear in the overviews (at least with GuiMods). I think there are also some Victron chargers that may integrate with the GX device.

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Answer 2 · 2022-09-13T06:52:10Z

bathnm answered · Sep 13, 2022 at 06:52 AM

You might be able to use this to get some control of the device

https://www.victronenergy.com/accessories/ve-bus-to-nmea2000-interface

Do your research however as it is not clear what capability you would get from this device when controlling the 4th inverter/charger

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Answer 3 · 2022-09-13T07:34:36Z

marekp answered · Sep 13, 2022 at 07:34 AM

@Karl Laasik

You can use this option:

2. Generator and Skylla charger to the DC side. Not a big generator needed but there is no VE.bus communication with the system.

and control the generator start and stop with assistant.

VE.bus communication is not needed.

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Answer 4 · 2022-09-13T12:08:00Z

Juha Tuomala answered · Sep 13, 2022 at 12:08 PM

First of all, I think you could have gone with Quattro from the start, but that's late now.

For option 1 - there is no need for huge generator, you can limit your charging power from ESS settings. Of course you need to decide fuel type, remote start feature and is it one or three pahse genset. Put couple of contactors between the inputs and MPII input. There are models that prevent them pulling at the same time. Control them with dc-relay that can handle 230V contactor-current. Works fine. You already have 3x70A chargers there, no need to get more of them. @Karl Laasik

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Juha Tuomala commented · Sep 13, 2022 at 12:10 PM

Also, problem with big capacity and especially lead batteries is that rest of the charging cycle takes long time and barely gives any load for the genset. Would make sense to use the genset at the same time for direct, reasonable loads through Multiplus switching. Just running the generator for absorbotion charging is waste of fuel imo if you cannot utilize the cooling heat.

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Karl Laasik commented · Sep 13, 2022 at 06:51 PM

I agree with the quattro part, would have been the right solution. But my father (it is his system) had limited budget (project). Things I am worried about with this solution is that the Multiplus might not accept the generator without changing the grid settings to compromise (lower efficiency) also on grid power. Also, the relays and contactors for switching off the grid are not as foolproof as manual changover switch.

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Karl Laasik Karl Laasik commented · Sep 13, 2022 at 06:56 PM

Generator auto start/stop gives quite a few options to also turn off the generator when the load is not enough. So, the generator is only started when it is really needed, and the battery is getting empty. There are plenty of loads at all times and the generator will not be used for only charging. Of course, there would be a possibility to make the battery bank bigger, but then it will be more difficult to keep it balanced and as I read from the Victron instructions this amount of lead batteries is quite on the limit already.

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Juha Tuomala Karl Laasik commented · Sep 13, 2022 at 08:23 PM

Maybe get some lead acid balancer? I will get lithium next, no more lead batteries.

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Juha Tuomala Karl Laasik commented · Sep 13, 2022 at 08:20 PM

It’s true that Quattro is picky of its juice. Especially the frequency, your genset should have an electric governor to keep the rpms stable under load.

I use contactors, there are models that can be mechanically locked together and prevent them pulling at the same time. Switchover wont even crash desktop computer. Only lights flicker a bit.

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Answer 5 · 2022-09-13T20:30:21Z

Juha Tuomala answered · Sep 13, 2022 at 08:30 PM

You could also get a DC 48v generator. Those are used in telco environments. Some have controllable voltage regulators. That would be an effective charger.

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