Two Multi 12/3000, two shore power inputs, one Cerbo GX

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Ed Jones asked Jun 8, '23

Two Multi 12/3000, two shore power inputs, one Cerbo GX

I have a customer telling me the following is possible, but I'm not seeing how it's possible...

This is in the USA.

Customer has a circa 1989 house boat with two 30A shore power inputs. He has a generator that outputs 120V/240V. One shore power input and one leg of the generator go into a single manual transfer switch. The output of the transfer switch feeds an AC load center that powers one half of the boat (the front). The second shore power input and second leg of the generator feed a second manual transfer switch, which feeds a second AC load center that powers the other half of the boat (the rear).

Forget the generator for a moment...

This customer says he has a friend who has two Multis, two shore power connections, and ONE Cerbo GX with his house boat with two 30A shore power inputs, one feeding each MultiPlus.

Questions:

1. Can I feed each Multi with two different 120V 30A inputs that might be in phase or out of phase, and when on shore power have each Multi pass it through to its respective AC load center AND be controlled with a single Cerbo? This doesn't appear to work when I test it in the shop with the Multis configured in single phase / parallel.

2. If I configure them in split-phase (2 phase 120 or 2 phase 180), then I could feed each AC load center from one of the phases, but since I don't know what the phases will be coming from the two independent shore power connections, I don't think this will work either.

I've told the customer we can do what he wants and pass-thru both shore power connections but he's going to need two Cerbo GXs since the inverters will act independently.

Is there a way to do what he wants using just one Cerbo? I maintain he can't (reliably) do this and will need two separate systems. Am I just missing something?

Thank you in advance for your thoughts.

multiple inverters

2 |3000

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Answer 1 · 2023-06-08T18:10:23Z

derrick thomas answered · Jun 08, 2023 at 06:10 PM

Yes and no, lol. Easiest would probably be to wire them in split phase and disable "switch as group" in veconfig. That will enable them to function when connected to split phase or single phase shore connection.

The other option is to connect them separately to each side of the panel as you have indicated, but one of the multis will be connected to the cerbo via Vebus, and the other one via mk3 adapter. This will lose some of the functionality as far as controls but to what extent I am not entirely sure. Connecting the second multi via mk3 will however enable you to be able to monitor it on the cerbo.

Perhaps a better solution would be a 2x120, or 2 2x120 in parallel if more capacity is needed. They are designed specifically for North American split phase mobile applications as long as there are no split phase appliances. (The 2x120 are designed to automatically deal with switching between split phase and single phase shore connections as are common throughout North America.

2 |3000

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Answer 2 · 2023-06-09T13:14:45Z

Ed Jones answered · Jun 09, 2023 at 01:14 PM

Some added color...he had already purchased a MultiPlus 12/3000 and then decided he wanted to add a second one. And I have them configured in parallel (you said series but I think you meant parallel) and have switch as group turned off. But, I don't think that automatically allows you to feed separate shore power inputs, especially not knowing if the two 30A inputs are in phase (from the same leg of the marina's power), 180 degrees out, or 120 degrees out if they have three phase power feeding the main distribution panel at the marina.

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derrick thomas commented · Jun 09, 2023 at 05:48 PM

Couple of things...

1.Parallel means sharing the load evenly on one leg or single phase input @120v

2.Split phase means 2 inverters(in this case) with each inverter feeding a separate phase of the input/output. What you are describing sounds like a split phase configuration.

3.You need to know the phase separation of the shore connection or you will have problems. Is it 180 split phase? Or 120 star 3 phase? The inverters need to be configured accordingly.

4.Having switches as group disabled will allow you to feed in with the 2 shore connections regardless if they are in phase or opposite phases. The difference is that when they are in phase one inverter will passthrough and the other one will not. The inverters will see the dual shore connections as a single input but will look for wether or not the 2 legs are in phase or not.

Given the special situation you have here, if the customer wants to be able to run both sides of the panel from a single phase set of shore inputs, you really have no choice but to keep them separate and not run them in parallel or split phase. Only other option here since you already have the inverters is a transformer.

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jjbond derrick thomas commented · Jun 10, 2023 at 06:53 AM

(2.Series means 2 inverters(in this case) with each inverter feeding a separate phase of the input/output. What you are describing sounds like a series split phase configuration.)

Wowza, remind me to never have you do any electrical for me, you need a refresher on the difference between series and parallel. There is not even an application called series when it comes to inverters, it's split or parallel.. What are you implying someone does, take the 12v into one, the 120 out of it into the 12v of the next one hoping 240 comes out the output of the second one?

Please take advantage of Victron's free training before you burn someone's house down.

https://www.victronenergy.com/live/ve.bus:manual_parallel_and_three_phase_systems

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derrick thomas jjbond commented · Jun 10, 2023 at 05:43 PM

@jjbond My bad, you are absolutely correct. Don't know why I put series instead of split phase. Total brain fart. I assure you I absolutely do know the difference. If you read the rest of that post you can clearly see I have referenced split phase and not series. Dealing with several different discussions at once and mistakes were made. I will change my previous post so as not to provide false information to anyone reading this thread later on. I feel like a total moron now.

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jjbond derrick thomas commented · Jun 10, 2023 at 07:23 PM

LOL.. no problem, we all have brain fades now and then, the difference is that with these systems and newbies, any guidance given could cause serious damage and/or fire to the newbie taking our advice... but all good... I really only wanted to see the video of you putting the 120 into the 12V input into the second one, that would have been worth the popcorn and soda.. LOL.... thanks for being cool about my smart arse reply, you have a good sense of humor, thank you.

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derrick thomas jjbond commented · Jun 10, 2023 at 05:57 PM

" There is not even an application called series when it comes to inverters, it's split or parallel.. What are you implying someone does, take the 12v into one, the 120 out of it into the 12v of the next one hoping 240 comes out the output of the second one?"

Not at all, that would just be moronic. As I posted just a moment ago in response to your post, corrections were made in regards to my 'brain fart'.

On another note however, there absolutely IS an application called 'series' when it comes to inverters and it comes up on here actually quite frequently. This refers to taking the ac output from one inverter and feeding the ac input of a second inverter to boost total output capacity. Though this is not a 'victron approved' method it certainly has been done successfully.

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