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mswoboda asked

Design of a split phase system 120/240V 60Hz with Victron Quattros

Hi to the community!

We want to build a split phase system 240/240V 60Hz (located in Panama) with Victron Quattros of at least 30kW.

My question is which Quattros I should choose and if an Autotransformer makes sense.

I have to explain what the system should be able to do:
We want to run a wooden dry chamber (theoretic maximum of 20kW) consists of different devices. Most of the time its should not exceed 13kW, but theoretical 20kW are possible for a short term. All devices are 240V/60Hz

Furthermore there will be a small carpenter workshop, with different machines. The machines (all of them are 240V) in the workshop won’t run at the same time. The maximum of one machine is 4kW on 240V.

For the 120V will be the light and maybe small tools like a drill machine, but again, not many machines at the same time. So I think, not more than 1200W.

Initially we wanted to take two of the 15kW Quattros split phase (30kW) but I noticed in the beginning that the 15kW model is only in 240V available. (Later on I noticed in the manual that it is possible to order a model 15kW with 120V, I have to find out if I can get this model).

So I have three options for the topology:

1. Suppose I get the 15kW model with 120V, I would have two of them as a split phase system. I don’t think that I run into a balancing troubles (between the 120V phases), because the heavy loads run on 240V.

2. If I don’t get the Quattro 15kW 120V model, I have to take 4 of the Quattro 8kW models. Two in parallel and split phase. So I would have 32kW power at the maximum. Of course more expensive and more work with AC cable wiring!


3. Suppose I take two of the 15kW 240V Quattros and I will use a Victron Autotransformer (100A) and still most of the most loads are 240V, will the Autotransformer be the right solution? I mean, the Autotransformer makes it possible to use the 240V Quattros and is balancing the two 120V phases (if I understand the function of an Autotransformer in the right way).

The rest of the system (beside the inverters) will be the following:

- 55 kWP module power with a few MPPT RS (I have to do the calculation with the Victron Excel, if I have the data sheet of the modules)

- 176kWh LiFePo4 batteries (15 pieces in parallel with 48V/230Ah connected with copper busbar)

- Lynx system, Cerbo, all connected via VE.Can
- ESS, the system should be capable to feedback electricity if the dry chamber/workshop is not used

- A generator (have to think about the size) if there is a power outage and the batteries will deplete


I am a technical engineer and I build up a three phase system in Austria (3x220/50Hz) with 3xMultis 5kW, 15kWP and a self built LiFePo4 battery (560Ah@48V). So I am new to split phase and electricity in general here in America.

I am happy about your recommendations or comments!

Michael



MultiPlus Quattro Inverter ChargerAutotransformersplit phase
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3 Answers
shaneyake avatar image
shaneyake answered ·

If you have to have 2 inverters anyway, you might as well do 2x 120V in split phase config.
If those 15kva 120V inverters are not easily available in your area I would run the 230V inverters with a single autotransformer as your 120V loads are small.

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mswoboda avatar image
mswoboda answered ·

Thank you.
The 15kVA/120V are not a common product at all. In the manual is written that you can make a request to order some. So I have to ask my distributor.

Suppose I get one, do you know: If I use your suggested topology with the 2x15kV split phase and add one Autotransformer(100A), what is the maximum Ampere/kW I can use at the same time with 220V, and what is the maximum I can use with 110V?
That's what I don't really understand...

Furthermore I need the full power, i.e. also the heavy loads if there is an grid outage, so I can use only one AC out.

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shaneyake avatar image shaneyake commented ·
I would rather go with a 230V unit if you can't get a 120V. You never know what might happen in the future and you might need a replacement.


If you use 2x 120V then the 240V max 30kva with 15kva per 120V phase.

If you use 2x 230V then the 240V max with be 30kva and 23kva per 120V phase with a max imbalance of 28A.

In the 2x240V config you 240V loads are directly connected to the inverter via breakers of course but aren't feed from the auto transformer. I would have a separate panel for these 240V loads.

This panel would then also feed the autotransformer with which can do a max of 100A passthrough and 28A imbalance between the 2 120V phases, it can handle pretty big peak currents but the imbalance is still limited to 3360va. This isn't really a problem unless you have big 120V loads. If you are saying all you need to run is a few 120V tools, lights, etc, it shouldn't be hard to keep that below 28A imbalance on average.

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mswoboda avatar image mswoboda shaneyake commented ·

Thank you for your answer.


Yes, the argument, that we don't get a replacement is a good one...

What do you mean with "separate panel"? Do you mean a panel for the breakers?

One thing I don't understand, or I am not sure about it: In your suggested configuration: Is the direct 240V connection on the output AC-OUT2? If yes, we cannot use it, because we want to use the system also if there is a power outage.
Look at the attached pic of Victron. Maybe I am wrong...
1671578789549.png




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mswoboda avatar image
mswoboda answered ·

Ok, thank you. That is the way I thought it is working.
What is the problem with grounding when disconnected from the grid?

And again my question: So I can do this only using the AC-OUT 1 (ie. this runs if its disconnected from the grid).

You wrote:
"If you use 2x 230V then the 240V max with be 30kva and 23kva per 120V phase with a max imbalance of 28A."

So you calculate 100A for the 120V, but I think the 100A is just for the 240V.
Look at this:
1672189132346.png


Thank you!



1672189132346.png (359.8 KiB)
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shaneyake avatar image shaneyake commented ·

You need to keep in mind that when the 120V phases are balanced like in this image there is no current on the neutral and therefore no current in the transformer. The transformer basically sees it as a 240V load. Therefrom you can draw up to 100A.diagrams-1.pngNow if there is an imbalance in loads the current will have to flow through the transformer and that is limited to 28A. In this example is there is more load on L1 then the difference and only the difference between L1 and L2 will flow on the Neutral in Blue. If there is more load on L2 then it will flow on the purple path.
diagrams-9.pngGreen and Red paths are limited to 100A, Blue and Purple paths are limited to 28A.

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