Recommended advanced AC power for US boats

[s/v Jedi]

120/240V US split phase AC diagram

This diagram looks very similar to the EU version but there are some differences:

The shore power is 3.6kW which is a 120V 30A outlet. That said, I recommend to use a 120/240V 50A outlet, connecting to 240V instead of 120V whenever possible. This halves the current for much cooler running, plus the 50A connector is much better than the 30A ones, preventing much trouble.

The shore power cord is a standard 120V 30A cord. You improve it by using a different inlet (SmartPlug) with a different connector on the boat side. You can further improve it by changing the shore side connector to a 120/240V 50A connector, wiring L to L1, N to L2 and gnd to gnd for a 240V feed. You do not need to have 6AWG conductors, 10AWG is good enough.

The isolation transformer requires configuration: the output neutral to ground jumper must be removed and the output jumpers must be set to 240V. For automatic input selection models that’s all that is needed but for manual ones you must set the input jumpers to either 120V or 240V depending on the shore power hookup you choose.

This means that the output from the isolation transformer becomes 240V at 15A, 3-wire configuration: L1, L2 and ground. There is no neutral at this point.

Next is the diesel generator, which also requires configuration: hopefully it supports 240V because that is what we need. Remove the Neutral to ground jumper and connect for 3-wire 240V similar to shore power.

The above measures drop the Neutral as used in split phase. This enforces perfect balancing of the split phase so that maximum power can be used. The price for this is paid later on in the diagram..;. for now we’re golden.

The transfer switch is manual for reasons explained in the EU version of the diagram.

Now we get to a part that is new for many who see this: we use EU versions of the Victron Multiplus 24/3000 inverter/chargers. These need to be reprogrammed: in the inverter section change the voltage to 240V and line frequency to 60Hz. Disable the ground relay. This converts them to US 3-wire 240V units so they match the inputs we created above.

The three output busses are exactly the same as described in the EU version diagram. This setup also allows the use of 60Hz aboard while connected to 50Hz shore power.

Now we get to the distribution part… here we pay the price for our perfectly balanced power because surely we need 120V in addition to 240V. This is further complicated by my criteria for redundancy, flexibility and future expansion which is why there are two distribution groups with each it’s own source selector. This is tackled by installing two 32A auto transformers.

There is an alternative: use one auto transformer with one 120/240V distribution group plus one 240V-only distribution group. You can even get a 100A auto transformer to put it all on one unit if you don’t care about redundancy. But we’re talking about $500 savings compared to the two 32A transformers. At PKYS the 32A units cost $550 each and the 100A unit costs $666.

With two units like in the diagram, the center taps of the transformers are used to create 120V just like a neutral. But these are kept floating and not connected to each other either.

Main points:

- Make sure that shore ground is not connected to ships AC ground
- Make sure isolation transformer output neutral to ground jumper is removed
- Make sure genset neutral to ground jumper is removed
- Make sure the Multiplus units are configured for 240V, 60Hz and ground relay disabled
- Make sure auto transformer ground relay isn’t used
- Make sure each distribution group has it’s own L1, N, L2 bus bars that are not interconnected .

[alaskanviking]

What do you have connected to your bus 2. that is only used for shore/external power only connection, for large loads you don't want on underway. like a water heater or AC unit. you have those type of loads on the panel though. is this just a redundancy thing?

what is the realities of connecting the multiplus in parallel? how difficult is it, do you have to reconfigure the software if your not running in paralel ie separating the charger and inverter functions or one unit dies ect.

i was planning on on one bigger unit a 5kw or 8kw due to the amperage requirements of the scuba compressor ~14amps. a 3000 is only putting out ~12-13amps. looks like Parallel units would work and give me ~26 amps. i originally set this up accounting for the starting surge amperage and probably need to recalculate everything - will be a large battery bank set up. the ability to separate charge and inverter functions are also very appealing. with the lithium bank it will double the charging ability as well which is very useful.

i am setting up to take on the full 240v 50 amps at the dock not just 30amps for the air conditioner. in theory it gives a little more flexibility for whatever power connection comes your way.

[s/v Jedi]

Originally Posted by alaskanviking

What do you have connected to your bus 2. that is only used for shore/external power only connection, for large loads you don't want on underway. like a water heater or AC unit. you have those type of loads on the panel though. is this just a redundancy thing?

what is the realities of connecting the multiplus in parallel? how difficult is it, do you have to reconfigure the software if your not running in paralel ie separating the charger and inverter functions or one unit dies ect.

i was planning on on one bigger unit a 5kw or 8kw due to the amperage requirements of the scuba compressor ~14amps. a 3000 is only putting out ~12-13amps. looks like Parallel units would work and give me ~26 amps. i originally set this up accounting for the starting surge amperage and probably need to recalculate everything - will be a large battery bank set up. the ability to separate charge and inverter functions are also very appealing. with the lithium bank it will double the charging ability as well which is very useful.

i am setting up to take on the full 240v 50 amps at the dock not just 30amps for the air conditioner. in theory it gives a little more flexibility for whatever power connection comes your way.

In parallel operation, which is my current setup, Bus 2 is exactly like the Multiplus OUT2, i.e. loads that should never discharge the battery, like water heater, A/C etc.

Bus 2 has a second function when you want independent operation of the two inverter/charger units, in which case it becomes the OUT1 of the second unit.

Please note that the Bypass breaker has similar functionality to the OUT2 bus when in parallel operation. There is no problem at all to have both distribution groups using Bus 1. The setup is pretty adaptable and based on my needs over the past 20 years... I just designed a setup that could do all the configurations I needed in the past.

I recommend two 3000 units over a single 5000 units. You get more power and redundancy. When configured for parallel operation, they appear just like a single 6000 unit. For wiring you need to keep everything the same length for either unit so it makes sense to mount them together. For configuration you need their USB Mk.3 adapter and the free software. It’s easy I think... but being an engineer I understand it may not be so easy for others. That said, the instructions are easy to understand and phone tech support is excellent.

When two units are in parallel operation and one fails, the complete system goes down. You should then open input- and output breakers, reconfigure for stand-alone operation and determine which unit has failed, continuing with the other at half capacity.

The attached picture shows the Cerbo GX reporting them as one unit, supplying 4kW

[alaskanviking]

I did a rough layout in 2019 after several discussions with techs from Bridgeport Magnetics and Victron. based off of one of SV Jedi's diagrams from a thread several years ago.

this uses the Bridgeport Magnetic isolation transformers which they would wind for this application. lets you use a switch to select input voltage from 120v, 208v, and 230-240. output is set for 240v floating with L1 & L2. you cold use only one transformer instead of the 2 i have here.

i was looking into different generator options then, now i have found a few sister boats with 4k-6k generators in the stern lazarette area and the weight doesn't affect the boat performance, so i will likely take that path now.

the soft start is for the isolation transformers. it allows the coils to slowly build up juice and magnetic field, instead of a huge inrush of current when you flip the switch. this can also be accomplished manually with a switch and resister.

goals at the time i created this document were not were not the same as SV Jedi put in this thread. primary goal was world wide power usage and ease of use. ie I wanted to flip a switch on the panel rather than crawling into the lazarrette to change a jumper wire on the Victron isolation transformer. note that there is an Victron auto-isolation transformer that automatically switches the input voltage however it doesn't adjust for 208v, its limited in amperage, and Victron said you cant parallel the unit like I'm doing here with the Bridgeport Magnetic transformers. having a large load like an AC would force you to use Victrons 100amp isolation transformer if i remember correctly. I couldn't get a decent diagram from Victron to convert the jumper cable set up to a switch for easier use like the auto-transformer.

I believe I will change some of this layout moving forward with my plans as I've learned a bit more and also prefer the redundancy of SV Jedi's layout. using two inverter chargers to gain the ability to separate the charge and invert functions is very interesting and adds on to my world wide power goals with regards to different power Frequencies. two inverter chargers doubles your charger amperage which is a significant advantage for anyone with a large lithium bank.

for anyone thinking of doing this keep in mind there may be a slight safety issue with this layout. if you don't set your switches correct before throwing switches it is possible to fry something. ie you have 120v input selected on the isolation transformer and have the sp/gen switched to the 240v generator as i have the generator input going through the isolation transformer in this document. at the time i was leaning more to using a Honda 2000 portable generator. using SV Jedi's layout is the correct way to use an installed generator ie not going through the isolation transformer but putting the gen/sp switch before the inverter chargers. i would change this attached layout to match Jedi's layout, removing the generator switch as i have it and just use an adapter cord from a 120v Honda 2000 to the shore power socket if one was used. i wouldn't use a separate shore power inlet for a Honda. you could but you would connect it to the L1, N, and G lines of the 240v inlet. easier to make an 240v 50a adapter since you have to have an adapter for the 30a shore power inlet anyway.

I verified with the tech that incorrectly having 120v input to the 240 or 208 leads of the isolation transformer via an incorrect selection of the transformer voltage selection switch would be safe, and just give you an incorrect half voltage out of the transformer and to the inverter charger. the inverter charger would boost the voltage or fully switch to the inverter side due to the low voltage.

[s/v Jedi]

Originally Posted by alaskanviking

I did a rough layout in 2019 after several discussions with techs from Bridgeport Magnetics and Victron. based off of one of SV Jedi's diagrams from a thread several years ago.

this uses the Bridgeport Magnetic isolation transformers which they would wind for this application. lets you use a switch to select input voltage from 120v, 208v, and 230-240. output is set for 240v floating with L1 & L2. you cold use only one transformer instead of the 2 i have here.

i was looking into different generator options then, now i have found a few sister boats with 4k-6k generators in the stern lazarette area and the weight doesn't affect the boat performance, so i will likely take that path now.

the soft start is for the isolation transformers. it allows the coils to slowly build up juice and magnetic field, instead of a huge inrush of current when you flip the switch. this can also be accomplished manually with a switch and resister.

goals at the time i created this document were not were not the same as SV Jedi put in this thread. primary goal was world wide power usage and ease of use. ie I wanted to flip a switch on the panel rather than crawling into the lazarrette to change a jumper wire on the Victron isolation transformer. note that there is an Victron auto-isolation transformer that automatically switches the input voltage however it doesn't adjust for 208v, its limited in amperage, and Victron said you cant parallel the unit like I'm doing here with the Bridgeport Magnetic transformers. having a large load like an AC would force you to use Victrons 100amp isolation transformer if i remember correctly. I couldn't get a decent diagram from Victron to convert the jumper cable set up to a switch for easier use like the auto-transformer.

I believe I will change some of this layout moving forward with my plans as I've learned a bit more and also prefer the redundancy of SV Jedi's layout. using two inverter chargers to gain the ability to separate the charge and invert functions is very interesting and adds on to my world wide power goals with regards to different power Frequencies. two inverter chargers doubles your charger amperage which is a significant advantage for anyone with a large lithium bank.

for anyone thinking of doing this keep in mind there may be a slight safety issue with this layout. if you don't set your switches correct before throwing switches it is possible to fry something. ie you have 120v input selected on the isolation transformer and have the sp/gen switched to the 240v generator as i have the generator input going through the isolation transformer in this document. at the time i was leaning more to using a Honda 2000 portable generator. using SV Jedi's layout is the correct way to use an installed generator ie not going through the isolation transformer but putting the gen/sp switch before the inverter chargers. i would change this attached layout to match Jedi's layout, removing the generator switch as i have it and just use an adapter cord from a 120v Honda 2000 to the shore power socket if one was used. i wouldn't use a separate shore power inlet for a Honda. you could but you would connect it to the L1, N, and G lines of the 240v inlet. easier to make an 240v 50a adapter since you have to have an adapter for the 30a shore power inlet anyway.

I verified with the tech that incorrectly having 120v input to the 240 or 208 leads of the isolation transformer via an incorrect selection of the transformer voltage selection switch would be safe, and just give you an incorrect half voltage out of the transformer and to the inverter charger. the inverter charger would boost the voltage or fully switch to the inverter side due to the low voltage.

Yes, there are more options for isolation transformers. I will soon finish a new diagram that uses a 7kW Victron transformer and is suitable for 230V/50Hz as well as 240V/60Hz but not 120V or 208V.
So this doubles power but you loose 120V shore power ability.

About the power rating of the isolation transformer: it only needs to be enough for your average 24hr power consumption, not for peak times. The reason is that the inverter/chargers PowerAssist function will add power to the shore power. In this diagram with two Multiplus 3000’s and a 3.6kW isolation transformer, you can feed 9.6kW (kVA) to consumers as long as the battery allows it. During off-peak times the system takes any available shore power capacity to recharge the batteries.

Last but not least: the Victron isolation transformers have soft start built in so you don’t need a separate one