Shore Power for the XPM78

The availability of shore power is both a blessing and a curse. It is convenient to be able to supplement systems when in a marina or harbor. At the same time, the plethora of voltages, frequencies, and capacities can be very confusing. Vanguard is built to cruise worldwide and should encompass the flexibility to maximize what is achievable, but that's easier said than done. This is the story of how we understood the issues and our solution. 

Firstly let us discuss the problem. Our XPM-78 explorer yacht, Vanguard, has some relatively unique machinery installed. It has a hybrid drive and very large power batteries. Let us start by summing up just what is on the yacht*. 

• 230 VAC 50Hz Single phase
• 415 VAC 50Hz Three-phase plus neutral
• 24VDC (with the occasional 12VDC for Comms and Nav gear)

These feed into systems containing

• 20 kWh of LiPO house batteries at 24VDC
• 120 kWh of LiPO power batteries ar 600 VDC

In turn, the available power sources are:

• 6 kW of solar panels at peak capacity
• 2 by 90Kw alternators (hybrid drives operated decoupled from the propellers and at full engine speed)
• Shore power at a single or three-phase.

Now let us have a quick look at just what is available as shore power

Single Phase:

• 120 VAC 60 HZ 30 amps approx
• 240 VAC 60HZ split phase (2 phase and neutral) 50 amps
• 230 VAC 50 HZ 50/100 amps

Three-phase

• 280 VAC 60 HZ Three-phase 100 amps
• 415 VAC 50 HZ Three-phase 100 amps

One last complication in the mix is that we need galvanic protection in the form of an Isolation Transformer. This stops earth currents from circulating between ship and shore (for safety and to limit corrosion). We need to avoid the larger and more expensive yacht berths that commonly have three phases available at the pedestal for cost reasons.

Have you ever seen a circus trick known as plate spinning? Lots of moving pieces in the air at the same time? Well, that is how this felt at the time! 

When faced with a multifaceted problem, a good point to start is by simplifying the issues into bite-sized prices. So we started with the supply frequency. 50 and 60 Hz systems are incompatible at the AC level. Also an isolation transformer will not change the frequency. It was sensible to have all single-phase power input through the same dual frequency Victron isolation transformer and charging system and to feed the house batteries. This was a slight increase in conversion losses, but we felt that was worthwhile in pursuing simplicity. 6kW peak of Solar power infeed is also charging the house batteries. 

This left the problem of three-phase. We wanted to maximize the advantage of a beefed-up power source to charge the power batteries. We can convert everything to 50Hz three-phase AC or 600VDC to charge the power batteries and also provide for galvanic isolation irrespective of the infeed. 

We have three choices here - 

• to create a hybrid solution with 50Hz supply dropping to the three-phase bus bars and 60Hz supply is converted to DC and charging the batteries (house or power bank).  
• to install a universal shore power supply that will produce clean three-phase power voltage stabilized with input from both single and three-phase shore power, 50 or 60Hz. These are available from several suppliers, Magnus Marine, ASEA, and ANG, just three of them. We found all the vendors helpful but again ran into issues. The physical size was the first problem as we have a cramped engine room. We solved this by reducing the capacity from 25 KVA to 12KVA. Still a powerful charger but at a much smaller physical size. We also needed to limit the infeed current so as not to trip the shore power breaker. That feature was not (yet) available in the size we needed.  
• Use the same inverter setup to control the hybrid drives and create our own DC charging system. The hybrid drive used both large 25KVA three-phase transformers and powerful AC/DC inverters. Inverters are bi-direction in that you can feed both AC or DC to receive the opposite at the outlet end. 

In conclusion, there is no simple, all-encompassing answer to shore power connection. 

• relying on a single frequency is a viable strategy if your cruising limited to the Americas, or the rest of the world.
• If you have a high power requirement and a worldwide cruising scope, things become more complicated. 
• Conversion single-phase to DC avoids this frequency issue at some penalty in transmission losses. 
• For larger installations, consider a shore power converter or if you have the battery capacity then convert everything to DC. Still, even these also have a cost and size penalty in comparison to more simplistic systems.

- all voltages quoted are approximate and may vary a little in reality. 

Victron Skylla Inverter Charger for single phase to 24VDC

Praxis HP Inverter for 3 phase to 600 VDC

Magnus Marine Universal Shore Power Inverter