Jedi AC power diagram: updated version 3

[s/v Jedi]

Originally Posted by RaymondR

I could be wrong, I learned a lot of this stuff a long time ago and my memory is not what it once was.

You can have a transformer with centre taps on either primary or secondary coils with them still fully isolated from each other. My understanding of whats known as an autotransformer is one in which the primary and secondary share a coil and therefor there is no isolation possible.

However if you have a separate isolation transformer between the shore power transformer and an autotransformer in the boats circuits then you will have isolation between shore and vessel power and the presence of the autotransformer would not introduce DC to the shore power circuit or trip the RCD.

When you look at my diagram, you find the auto transformers (I use two) all the way at the right, where the distribution breakers are. Everything that is to the left of it, is 240V only, without any Neutral. This makes for a simple, powerful setup.

Attached a diagram of these Victron auto transformers. L1 and L2 are the inputs as well as outputs. There is one winding with a center tap, which becomes the Neutral. There is a grounding relay in case one needs a grounded Neutral.

The beauty of this setup is that when at the distribution panel loads are balanced over L1 and L2, the transformer does nothing, carries no current. Only when an imbalance occurs, the transformer handles it and of course L1 and L2 fed into it are always perfectly balanced, optimizing inverter and genset capacity. The transformers I use are rated for 32A.

All the way in the left side of the diagram you see the shore power input, which uses an isolation transformer.

[newhaul]

Originally Posted by s/v Jedi

You mean like this: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Same ones are sold by Blue Sea Systems for much more $$$ but they probably are better quality. I have been using the cheaper ones and they work fine, although I don’t switch much, maybe two times a year (leave marina to go cruising, then come back in marina from cruising)

I have 3 inputs so a bigger switch that I couldn’t find on Amazon, so my next source is eBay or AliExpress (often the same sellers).

That will do exactly what I need and the price is great thank you

[s/v Jedi]

Now that this thread became active again, let me update it. I already posted the latest diagram above, which is basically the same as in the OP but much nicer done after I got the software for it.

Attached here are the two panels that I designed to go with it. First is the main panel, which holds the input selector switch and the breakers for the inverter/chargers as well as the bypass breaker. I also added power monitors for each input. These also count kWh so you can check the marina bill

The second panel is for the distribution breakers. As you can see, I ended up with only two distribution groups. Each group can select input independently from the other with the rotary switches.

Note how I aligned breakers and used colors to make it easy to work with. Also note how I divided loads over the groups. Remember that these groups, when they support 120V, needs separate auto transformers.

The reason that I have separate panels is that I am limited to a maximum of 8” height for them.

[shimari]

Originally Posted by s/v Jedi

Now that this thread became active again, let me update it. I already posted the latest diagram above, which is basically the same as in the OP but much nicer done after I got the software for it.

Attached here are the two panels that I designed to go with it. First is the main panel, which holds the input selector switch and the breakers for the inverter/chargers as well as the bypass breaker. I also added power monitors for each input. These also count kWh so you can check the marina bill

The second panel is for the distribution breakers. As you can see, I ended up with only two distribution groups. Each group can select input independently from the other with the rotary switches.

Note how I aligned breakers and used colors to make it easy to work with. Also note how I divided loads over the groups. Remember that these groups, when they support 120V, needs separate auto transformers.

The reason that I have separate panels is that I am limited to a maximum of 8” height for them.

Where did you get the panels made?

[Alex A]

Do you use GFCI outlets for the 120v/240v distribution, and do they work?
Are you able to detect L1 to equipment case ground faults in the loads after the 120v/240v distribution?

I'm asking as you have an AC ground for the cases of the IT/Inverters/AT but I imagine that the ground is not physically linked to the AT neutrals.

[s/v Jedi]

Originally Posted by shimari

Where did you get the panels made?

Front Panel Express (Google them for link). You design the panels yourself using their free CAD software, send the files in and they send you the panels in a couple of days

[bdgWesternMass]

Originally Posted by s/v Jedi

The beauty of this setup is that when at the distribution panel loads are balanced over L1 and L2, the transformer does nothing, carries no current. Only when an imbalance occurs, the transformer handles it and of course L1 and L2 fed into it are always perfectly balanced, optimizing inverter and genset capacity. The transformers I use are rated for 32A.

Could I restate this as?

only when L1 and L2 are carrying alternating current does the transformer kick-in

[s/v Jedi]

Originally Posted by bdgWesternMass

Could I restate this as?

only when L1 and L2 are carrying alternating current does the transformer kick-in

No, only when the current on L1 is different from the current on L2, then (only) the difference is handled by the transformer.

So when L1 does 20A and L2 does 22A then the auto transformer sees 2A.

[s/v Jedi]

Originally Posted by Alex A

Do you use GFCI outlets for the 120v/240v distribution, and do they work?
Are you able to detect L1 to equipment case ground faults in the loads after the 120v/240v distribution?

I'm asking as you have an AC ground for the cases of the IT/Inverters/AT but I imagine that the ground is not physically linked to the AT neutrals.

Being behind an isolation transformer, one can use double pole breakers and do away with all ground conductors. But this brings in the case ground faults:

When one appliance develops a case ground fault, the metal housing becomes energized by one of the two poles. This is not a problem because it is what is done on purpose with a grounded neutral. The difference is when another appliance also develops a ground fault but from the other pole. In theory one can touch one appliance with one hand and the other appliance with the other hand and be electrocuted.

This is why I recommend to install the ground conductor to all outlets, inverters etc. Even though it would be of near zero possibility, with the ground conductor installed, you simply trigger the breaker as soon as the second case ground fault occurs and this problem is eliminated.

The only reasons for alarming on the first ground fault is for applications where power supply is a critical necessity, like hospitals, navy ships etc. When they are able to detect the first case ground fault, they can fix that, which improves power availability. For sailboats the DC power is used for all critical systems like bilge pumps, autopilot etc. so we don’t need this.

For detecting the first case ground fault, additional equipment is required.

GFCI outlets will work as regular outlets but don’t provide any benefit over regular outlets because the danger from ground as a return path is eliminated because the ground return oath has been eliminated. Without that danger, you don’t need the safety anymore.
But when the boat is hauled out and connected to shore power, it stops being a boat and may require a grounded neutral, in which case the isolation transformer comes with a jumper to provide that and you have gfci outlets etc.

[Alex A]

Sorry, another question: Do you have a connection between your AC ground and DC system?

[s/v Jedi]

Originally Posted by Alex A

Sorry, another question: Do you have a connection between your AC ground and DC system?

No, AC ground is exactly as shown in the diagram.