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Old 28-01-2017, 13:39   #1
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Convert from 240 VAC to 120 VAC

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
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Old 28-01-2017, 14:18   #2
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Convert from 240 VAC to 120 VAC

When you convert to 120 VAC of course the amps you can safely carry on each circuit will be cut in half.
I think before I did that, I would investigate a 120 to 220 transformer and convert the shore power and not the boat.
Offshore battery charging without a generator, Solar seems preferable, but wind, towed generators and fuel cells are of course options, just seems Solar is less expensive and more reliable. Have to have a place to mount panels of course and deal with the appearance and windage
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Old 28-01-2017, 15:01   #3
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Re: Convert from 240 VAC to 120 VAC

If you've only got a few 240v appliances it may be cheaper to replace them rather than install a step up transformer.
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Old 28-01-2017, 15:32   #4
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Re: Convert from 240 VAC to 120 VAC

If you are EVER thinking/considering world-cruising with this boat, you'd be money and effort ahead running a separate 115 system parallel (in my experience- anyway). As you think about it, you'd be surprised how few drops you need to add. Many appliances (no-motors, however) are 90-250v 50/60Hz. Tools overseas are cheap as chips, getting 110 gear serviced - forget it. We specifically ran the 220 setup separate, battery charger, inverter, and refer/freezer modules don't care which stub they're on. TV/PC-laptop doesn't mind, and who uses DVDs any more?
Galley equipment is a challenge, blender (Margaritas), and mixers are the headache. Chances are the hot water cylinder is 240 - so run it shore side anyway.

Just one sailors opinion.

Cheers, Jim

BTW be sure and get a pile of the goofy UK plugs!
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Old 28-01-2017, 15:34   #5
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Re: Convert from 240 VAC to 120 VAC

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Originally Posted by a64pilot View Post
When you convert to 120 VAC of course the amps you can safely carry on each circuit will be cut in half.
NO, the Amps you can carry will be the same. The Watts will be cut in half.
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Old 28-01-2017, 15:58   #6
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Convert from 240 VAC to 120 VAC

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Originally Posted by StuM View Post
NO, the Amps you can carry will be the same. The Watts will be cut in half.


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?
If so and you cut the voltage in half, you can now only safely pull 750 watts, and a hair drier I think exceeds that?
Transformers like we used when I was in the Army to run our US 120 VAC stuff are not that expensive.
I brought a Germany Army Hatz Diesel 4 or 5 KW generator back with me, used a big transformer to run things and it was fine, got to think what would be different about a boat?
Plus why change anything to the boat is you don't have to? Don't have to change all the receptacles etc.

I would get another transformer with the idea of placing it on the dock inline with the shore power cord, I don't think I would want it in the boat.
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Old 28-01-2017, 16:16   #7
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Re: Convert from 240 VAC to 120 VAC

Dave, is this a reasonably modern standard built boat by a major manufacturer? If so you may find that since they want to export to the US the wiring is already sized for you and only the sockets on the end varying depending on which country the boat is going to. Certainly my Sterling battery charger will run on 110 - 230v. The immersion heater might be a problem but that is just an element assuming they have the same thread.

You might also want to investigate the earths. UK boats tend to have both 230v and 12v earths tied together to a ground (anode). I have a feeling the US do things differently. StuM is quite knowledgeable on this stuff.

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Old 28-01-2017, 16:18   #8
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Re: Convert from 240 VAC to 120 VAC

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Originally Posted by a64pilot View Post
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?
If so and you cut the voltage in half, you can now only safely pull 750 watts, and a hair drier I think exceeds that?
Transformers like we used when I was in the Army to run our US 120 VAC stuff are not that expensive.
I brought a Germany Army Hatz Diesel 4 or 5 KW generator back with me, used a big transformer to run things and it was fine, got to think what would be different about a boat?
Plus why change anything to the boat is you don't have to? Don't have to change all the receptacles etc.

I would get another transformer with the idea of placing it on the dock inline with the shore power cord, I don't think I would want it in the boat.
No, as Stu already stated, only the power is cut in half.

It's not clear what you are recommending wrt to a transformer. Are you suggesting the OP only use EU appliances?

Normal circuits in the EU are 10a or 16a, delivering 2300w or 3680w. Hence, using the same wiring/breaker @ 120v yields 1200w or 1920w.
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Old 28-01-2017, 16:28   #9
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Convert from 240 VAC to 120 VAC

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Originally Posted by DotDun View Post
No, as Stu already stated, only the power is cut in half.



It's not clear what you are recommending wrt to a transformer. Are you suggesting the OP only use EU appliances?



Normal circuits in the EU are 10a or 16a, delivering 2300w or 3680w. Hence, using the same wiring/breaker @ 120v yields 1200w or 1920w.


Yes, that is what I am saying, he would only use 220 V appliances as the boat would of course be 220 V.
Depending on gauge of wire of course, I think I may pull new wires if I were converting to 120 VAC myself. Or as was suggested run parallel circuits.
My preference for 120 VAC wiring for normal household type of circuits is 12 GA. I think European standard is smaller than 14?
My one experience with European wiring was the house I lived in in Germany and when I was installing outlets and lights I remember being astonished at how small the wiring was, of course it didn't need to be bigger due to the voltage.
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Old 28-01-2017, 17:02   #10
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Re: Convert from 240 VAC to 120 VAC

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Originally Posted by a64pilot View Post
Yes, that is what I am saying, he would only use 220 V appliances as the boat would of course be 220 V.
Depending on gauge of wire of course, I think I may pull new wires if I were converting to 120 VAC myself. Or as was suggested run parallel circuits.
My preference for 120 VAC wiring for normal household type of circuits is 12 GA. I think European standard is smaller than 14?
My one experience with European wiring was the house I lived in in Germany and when I was installing outlets and lights I remember being astonished at how small the wiring was, of course it didn't need to be bigger due to the voltage.
They were probably the equivalent of 14 AWG for lighting circuits , 12 AWG for GPOs.

Going to 110/120VAC, I'd go one size up for "normal household circuits" if you are including GPOs. (12 AWG may be a bit light there for heavier duty appliances)

Reasonable guidelines:
1.5 mm2 - 15 amp - 14 AWG
2.5 mm2 - 20 amp - 12 AWG
4 mm2 - 25 amp - 10 AWG
6 mm2 - 32 amp - 8 AWG
10 mm2 - 40 amp - 6 AWG
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Old 28-01-2017, 17:21   #11
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Re: Convert from 240 VAC to 120 VAC

Wow...... Flash backs to 6 months ago with even the same amp/current/watts debates!

Same question in this thread for reference.

Converting from 220 volts to 110
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Old 28-01-2017, 17:35   #12
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Re: Convert from 240 VAC to 120 VAC

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
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Old 28-01-2017, 18:03   #13
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Re: Convert from 240 VAC to 120 VAC

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Originally Posted by a64pilot View Post
Yes, that is what I am saying, he would only use 220 V appliances as the boat would of course be 220 V.
Depending on gauge of wire of course, I think I may pull new wires if I were converting to 120 VAC myself. Or as was suggested run parallel circuits.
My preference for 120 VAC wiring for normal household type of circuits is 12 GA. I think European standard is smaller than 14?
My one experience with European wiring was the house I lived in in Germany and when I was installing outlets and lights I remember being astonished at how small the wiring was, of course it didn't need to be bigger due to the voltage.
Rest assured, the EU knows how to protect the wire. If the breaker is 16a, the wire is sufficient to handle 16a (2.5mm2 = ~13awg). Hence, changing the voltage to 120v, the wire will still be protected. If the requirements are for more power than 1920va(w) on that circuit, then replacing the wire and breaker is necessary.
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Old 28-01-2017, 19:42   #14
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Re: Convert from 240 VAC to 120 VAC

Almost every marina now has both 120 and 240 power; why not just run the boat @ 240 and use a step down transformer for a few appliances? That's what we do
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Old 29-01-2017, 02:56   #15
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Re: Convert from 240 VAC to 120 VAC

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Almost every marina now has both 120 and 240 power; why not just run the boat @ 240 and use a step down transformer for a few appliances? That's what we do
1) This is incorrect. A large percentage of marinas do not have both.
2) 240v is typically reserved for larger slips which come with higher prices...assuming they will even give you the bigger slip.
3) 240v-60hz is still different from 240v-50hz.
4) Still need an adapter and need to make sure, the plug is wired properly.

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.

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.
- 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).
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