16 September 2011


Yes it’s a very technical entry – but these notes have been somehow helpful to make my decision: why not share it? But let me be clear: I’m not an electrician and strongly advise to seek professional help as soon it comes to work on any electrical system!

The Problem
A boat has normally two setups: firstly 12V or 24V from the batteries and secondly a high power system (where the voltage is the same as in your house) as soon you plug into shore power (or run a generator). The first is called DC (Direct Current) and the second AC (Alternate Current)

Our boat has a US shore power connection which runs with 120V/60Hz, but the rest of the world is mainly running with 240V/50Hz. So as soon you’re leaving US Territory you may get 240V/50Hz from the dock. Plugging your 120V plug into 240V may burn down the electrical system or worse the boat - so we need a solution. Without the ability of getting shore power we would miss a lot of comfort.

The difference between the norms is the Voltage 120 vs. 240V and the frequency, 50 vs.60 Hz. Changing the Voltage has to be planned carefully as you have different power running trough your electric “pipes”: 2000 Watt at 120V is not the same as 2000 Watt at 240 Volt! As higher the Voltage as lower the A to get the same “juice” or Watt. So 2000 Watt on 240 Volt are 8,3 Ampere but on 120 Volt its double the amount 16,6 Ampere. This means 120 Volt needs much stronger (thicker) cables. So you would be able to use the 120V cable for 240V as they are built for higher Ampere. But not vice versa as the 240V cables could burn if overheated with to many Amps.

So how do you bring the different electricity into the boat?

Option 1 - Multi AC Battery Charger only
Of course you just have to think about this whole power change if you intend to use AC power while on the dock – if you just rely on 12 Volt appliances on board there is a very easy way to migrate: Just buy a Battery Charger which is capable to handle all AC input (normally 90V–250V & 50- 60 Hz). So if you hook up on shore power your Battery’s get charged and you are setup for the whole world! And if you have a decent sized Inverter (a tool which makes out of 12V DC Battery electricity 120 or 240V AC) you can even run normal stuff from the Inverter. Nice and easy setup but limited to the Inverter Power, in our case 1000 Watt at 120V. And this means no Air-condition and no hot water. Costs are about 800 USD.

Option 2 - Transformer
A step down transformer will change power from 240V/50Hz to 110V/50Hz or the other way around (a transformer cannot change the frequency). This means we have to ensure that all the appliances on board are running with 50Hz and 60Hz which is used in the US. Some can handle both, some not or at least with 17,5% efficiency loss. In our case were fine, the only piece running just 60 Hz is the Microwave!

You have basically two choices with a transformer: A cheap China made transformer which you wire between 240V & 120V. Its cheap and stays on deck while in use (not really safe on a boat in the water). Or buy a dedicated Marine Transformer installed below deck and hard wired to you system. Additional this is adding a significant safety feature to the boat’s electrical system as it isolates the boat’s AC complete from the shore connection.

Est. Price
Philmore Stepdown transformer ST-5000 W
By far the cheapest solution with a bit of a hassle to store and setup as it is heavy – tempting with the power
Max: 41 A
Cont: 33 A
44 lb / 20kg

300 USD +
+ 150.- Material
+ High Power, Cheap
- Heavy, Stays in cockpit, lot of cables, Parts / safety question
Victron Energy 3,6 VA
Great Company, secure system
50 lb / 23kg
1’000 USD
+ Isolation 110 & 240V from Shore
+ fix mounting, Softstart included
- lower output, price
Mastervolt IVET-D16A, 3,5kVA –MT
Cool Transformer but pricy
50lb / 23kg
1’600 USD
+ Isolation 110 & 240V from Shore
+ fix mounting, Softstart included,
- price
Charles Industry 93–IXFMR3/8I–A
Hard wired for Voltage, switch needed to change 110V to 240V.
30 A
60lbs /
1’000 USD
+ 500.- Material

+ Isolation 110 & 240V from Shore
+ fix mounting, No Softstart
- Complicated to change power

Option 3 – Changing complete to 240V
We may consider this if we intend to keep the boat in Europe – 240V is anyway the better system. If we install a Marine Transformer as above we can keep it for the protection – great thing anyway. But a lot of stuff will be needed to get changed (Thanks God not the wiring). See our estimation:

Inverter 240V
Battery Charger
New Aircon Water Pump
Outlets, Cables, Breaker
Water Heater

Our Conclusion = Option 2
We currently install the Victron Transformer. Keep you posted as soon up and running!

1 comment:

  1. Hi Marco, would have been also my decision. Sounds good, what you are doing. And I studied electrical engineering, at least some 2 years or so within my technical computer science studies. :)) Cheerz, Sven