Convert from 240 VAC to 120 VAC

[dpeel]

Wow!
Thanks for a great response!
The boat is a 2005 vessel built by Sweden Yachts. I am hoping that the wire size will be suitable for 120 Vac.
The boat will be based in the US permanently (with some distance cruising also) and therefore probably makes most sense to convert since only the battery charger and hot water heater are on 240V (apart from outlets). Hot water heater should be simply a new element.
I will investigate further when I get back on the boat in a few weeks time.
I do like the thought of using an inverter also - this gives more options.
Thank you for all your thoughts and suggestions - I will need to think these all through! I did check out the previous threads referenced and it certainly sounds like same debate
Thanks all!

[boatbod]

A single 30A/120V shore power connection requires 10AWG wiring to the main breaker, then you can go down to smaller wire sizes to individual appliances/outlets based on the ampacity of the circuit and breaker size. Typically outlets are going to be 14AWG.

[john61ct]

Maybe just focus on high-amp shore charging 24V, and get a big 24V-240AC inverter if that's cheaper than replacing the few AC loads (switches, wiring)?

[Dave22q]

Generally reducing the voltage proportionally increase the amperage. You boat may need extensive rewiring. My understanding is that step transformers are not the easy solutions they seem to be but I would urge you to talk with a certified marine electrician before doing anything.

[KP44]

Originally Posted by a64pilot

Your right, but as an aside note the current and or power will be cut in half, that was why I was trying to get across, it may not be safe to run a hair drier, toaster or other high power appliances, or it may be, depending of course what was available. 1500 watts or there about is about all you can normally pull out of a single circuit, usually I think?

The wires will carry a set amount of current, measured as amps. Your breakers or fuses protect the wires from too much current. A 15 amp breaker protects 14 ga wire. Running 15 amps at 120 volts is somewhat over 1500 watts, and that's about the limit of a 15 amp circuit. (There is an inherent loss caused by AC.) Look at your breakers / fuses to see what your capacity is - and do not change the breakers unless you retrofit with properly sized wire for the new breaker(s).

[mikecambrai]

I have just done the conversion the other way. I bought an American yacht with 110v. I had to replace the inverter charger anyway so I opted for a 230 volt one, and changed everything to 230v. This was not cost effective to do with the generator so I bought a 110/230v 3kva transformer on ebay and took the generator output to this transformer. If I had to go from 230v to 110v I would therefore use a simple transformer perhaps restricting the input to the rating of the transformer.
As far as generating current is concerned I would always go for solar. Your biggest load is probably the fridge. 4 x 100w panels should cover this and most else. The biggest other load that you might have would be aircon, but you either need shorepower or generator power to cover this load wherever you are. For redundancy a wind generator would be the alternative.

[camel2012]

Was a bit concerned about a few earlier posts...

Power draw is dictated by the load device. Typically the same regardless of voltage. French and American coffee pots all draw the sane watts for the same performance.

Power = Volts * Amps... therefore...

Amps = Power / Volts

Therefore less volts = more Amps proportionally.

Usually fuses and breakers protect cable/wire and not necessarily load devices.

As already mentioned, you need to check the wire and cable sizes versus ABYC recommendations and the new expected current draws. Wires may be good and breakers may need replacing... or worse yet both. I'm assuming the issue is both the dock side and to plug in loads? A lot of devices are now universal voltage but not everything here in the states is...

A large 120V charger and inverter for 240v may work ok if 120v only loads is not a requirement , but you would lose a lot in the 2 conversion steps.

[SVNeko]

Originally Posted by dpeel

I am bringing a sailboat back from the UK to the US.
The current shore power is 240 VAC and I need to convert to 120 VAC since the boat will primarily be in 120 VAC area.
The boat system is 24 VDC and there are few 240 V items - battery charger and hot water heater.
Can anyone provide advice on best way to proceed? I do not know the cable size for the current system and whether this will be suitable for higher amps.
Also, any recommendations for charging batteries off-shore other that a generator?
Appreciate any help.
Dave

I don't see why you don't just run it on 240/60 US AC. The water heater is just resistive - it doesn't care. Most 220v stand alone chargers can accept either frequency. So you may not need to do anything. If you need to add AC later, you can find units that accept 50 and 60 hz. This way if you go back to a 50hz location, you can still plug right in. A 110/60 inverter can power your plugs. You may need to upsize the wires going to outlets if you use the existing sockets.

[SVNeko]

I don't agree with this.

Originally Posted by valhalla360

1) This is incorrect. A large percentage of marinas do not have both. We are 240/60 and have not met a SINGLE marina that could not accomodate us. For that rare bird, we have a dual 15amp cord that combines legs to make 240. Haven't had to use it in 4 years.
2) 240v is typically reserved for larger slips which come with higher prices...assuming they will even give you the bigger slip. Again, not our experience at all.
3) 240v-60hz is still different from 240v-50hz. So?
4) Still need an adapter and need to make sure, the plug is wired properly. For some locations, yes, but it is an easy DIY thing.

If it's short term:
- Get a large battery charger (120v to 12/24v) to feed the batteries and a 240v inverter fed off the batteries. You get correct voltage and hertz and there is nothing else you need to do to the existing 240v system. Nice benefit that it acts as a power conditioner so brown outs and other shore power issues have at least partial protection. Many battery chargers will take a range of voltages and frequencies allowing use in many locations.

If it's long term, you run into the problem that service and replacement of the 240v-50hz appliances becomes problematic. When the blender goes, you can't get another 240v-50hz blender and your power system doesn't want to run the 120v-60hz blender. It may be worth doing a full conversion. These minor things is what an inverter is for.
- A parallel system must be well thought out to make sure everything get's the correct power and you can't accidentally short across systems.
- Google wire size for amperage and there are tables with recommended wire size based on the amperage. Going from 240v to 120v will double the amperage for the same power. If you are lucky, the manufacturer sized the wiring for 120v and used the same wires regardless of where the boat was sold. If not, it can be a substantial project to convert over as the entire electrical system will need to be replaced.
- If you are lucky and the wires can handle the amps, it should be simpler changing out the circuit breakers, outlets and the shore power inlet (plus any appliances that can't handle 120v-60hz).

[pjhagbard]

Easy and clever solution: Install an Isolation Transformer. Gives a lot of other advantages + what you are asking for.

Good exampel as I have experience from:

https://www.victronenergy.com/isolat...-3600va-7000va

[oleman]

There are many very good reasons for using a transformer for doing any AC voltage conversion.
You get 100% isolation from the pier power.
You do not have to do any rewiring except in front of the transformer.
When you go someplace where the pier is 220 volts, you will need no conversion.
Only downside I see is you will need to purchase the correct size transformer and will require a place to install it.
Every commercial vessel I was ever a crew member on used multi-tap isolation transformers on pier power circuits.
We normally used 3000A 3% 480V from the pier.
Use a certified professional electrical contractor!

[pjhagbard]

With a isolation transformer you will have 230V in the yacht - you don't have to think about cables / dimensions...

[Latetonite1]

Please...this is basic stuff guys. The Wattage will be the same. Simplified., Volts x Amps. So the amps will have to double to get the same Wattage, or power if you like, from a system delivering half the Voltage.

[DotDun]

An isolation transformer won't fix the frequency. If the current shorepower charger only operates on 50hz, it won't work behind an IT on 60hz.

Although I am a fan of isolation transformers, this won't fix the OP's issue. He wants to use US appliances on his boat! This is going to require at the very least, changing the shorepower circuit and the receps. He may have to change the branch circuits (wire and breaker) if the existing ones are inadequate to support the desired appliances.

[buzzstar]

Originally Posted by a64pilot

I had apparently incorrectly assumed he was coming over for a short time, not permanent.
I would also assume ( there is that word again) that an EU manufacturer if they sold boats for the US market would size the wire for the lower voltage, and if the boat was an EU boat, then it just got heavier wire than it required? Would seem to make sense. I toured the Porsche factory many years ago and when I asked about US specs I was told they build a world car, meaning it met all specs, not several different cars for different parts of the world

Yes, but the Porsche automobiles do not float long enough for the wiring to to become a problem. Really strange responses abound this go around on the subject.

In a broad sense, wiring designed for 240 volts has less amperage capacity than wiring designed for 120 (or 110) volts. It will not necessarily overload or overheat, but the risk is greater. Check the wire diameter/gage for the alternating current system, and then determine if it is appropriate for the anticipated amperage and length of the wire run. Your breaker or fuse system may also present problems. The amount of caution is between you and your vessel,, but may well include your insurer, your guests, your neighbors, your marina, and the local fire brigade.