115V AC to 230V? Is There a Reasonable Solution?

[Scott Berg]

We do this all the time. Best Practice for boat mostly in the US needing 240:

1) Upgrade boat inlet to a US type 125/250 3+1 inlet. We like to take that to a 15KVA Isolation Transformer. This means that the white (grounded neutral) won't come aboard, and the green (grounding) goes to the transformer shield

2) Take the hot legs of the secondary (with the transformer "neutral") to each current side of your breaker panel (upgrade the "main" breaker from 30 to 50 on each leg, and upgrade interior wiring from 10awg to 6awg)

3) Take the two hot legs (usually Black and Red) to a double breaker for each 240v circuit

If you intend to sail in europe you'll need a 2nd inlet with a rotary switch that permits you to take the 230amp 2+1 input wire where the 230 goes to the transformer and the ground to the shield. Form there nothing inside the boat needs to change.

NOTE: this will still give you 60hz power in the US/etc and 50hz most other places. That said, it will give you a safe system.

NOTE 2: I do this for a living, not asking to do yours! <grin>

[botanybay]

Originally Posted by Coquina

This is a pretty common wiring job. Standard dock outlets with two 30 amp 120 volt outlets should be on opposite legs of the shore transformer, giving you 240 volts between them.
This is not a hard job, but it isn't for a n00b either since getting it wrong can burn your boat down or kill you. A local competent marine electrical shop should be able to handle this. This does raise a question of why you have dual shore power connections now? What do they do now? A photo of your shore power inlets and main breaker panel for AC would go a long way
Also how many BTUs is the air conditioner?

One issue on US docks is the 2 110v connections can be any of
1) on two phases off a three phase shore transformer, the two "hot" wires will show 208v, neutral to either hot will show 110v. In this case the two phases are 120 degrees apart. Common in industrial lighting circuits and saves the marina about $500/slip when installing compared to the next option.
2) on a "split phase" shore transformer. This is like a home dryer circuit. It is two hot wires and a neutral half way between. The two hots will be 110v from neutral, the two hots are 180 degrees apart compared to neutral. Result is 220v (also called 240v, just as 110v and 120v are used interchangeably by many people)
3) if two seperate 110v plugs it may be that both plugs are on the same phase, thus hot to hot between the two plugs is 0v, neutral to hot is 110v for both plugs.

First look at the allowed voltage range of the AC unit. If it is designed to run on 208v and 240v then bringing shore power on board for 208/240v makes sense

Another option is an isolation transformer with step up (victron makes a nice 3600 watt unit which takes 110 and makes 220, 208 makes 208, and 240 makes 240. Plug in whatever and you get what you need with bonus of isolation.

An "auto transformer " provides step up without isolation and are less expensive and would potentially work.

[mcon12000]

We do this conversion on both shores daily for small loads. For the US to Euro scenario we use these..

https://www.amazon.com/Simran-AC-500...062807850&th=1

This units breaker will flip @10amps.

[GrowleyMonster]

First of all, the OP is on a U.S. wired boat and connects to U.S. standard shore power. Frequency is therefore not an issue, and so the appropriate transformer will work. Most isolation transformers can have their primaries (the shore side) connected to either 120 or 240 volt power. The primary winding generally has multiple taps and the winding can be used all in series or the two halves of it in parallel. Same for the secondary, the boat side of the transformer. You can have an output of 120 or 240. The connections could be changed by the user but only if he has a good understanding of how a transformer works and exactly what sort of power he is feeding it and wants to get from it. For the layman it is ESSENTIAL that a qualified electrician check the installation before going live!


While most shore power boxes having two 120v outlets do use opposite hot legs of a 240v feed and share the neutral between them, this is not necessarily always the case. You can test the outlets with a meter and know for sure, but if there is the slightest doubt in your competence to do so, again have an electrician check it out. Don't take someone's word for it.



American 220/240v appliances are meant to be connected to two hot legs and a neutral and ground. So in one sense, using two 120v shore power feeds having 240v between them would be okay. But in practice, it is not best practice. Where is the isolation?



It is common to find the dockside shore power box fitted with two 120v receptacles and also a 50a 240v receptacle. And so you could, if so equipped, install a 240v inlet on the boat and the appropriate isolation transformer wired 1:1, and purchase a 4 conductor shore power cable rated appropriately and with the appropriate ends on it. Then install an ELCI breaker and a single wired outlet for the AC unit. So one dedicated shore power circuit just for that. I believe given that option, that is the way I would go.



The same size AC unit wired for 120VAC would draw twice the current of the 240VAC version. And there is starting current to deal with, which can be quite significantly higher than run current! IOW, you may find that a unit the same size or even a smaller unit that you think would be enough, would trip your typical 30a breaker. There are some workarounds for soft starting the AC but consult your electrician. Consult your electrician, anyway, on your Air Conditioner choice and your power setup. Do it right once instead of doing it wrong three times.


If your boat is much over 40 feet then a 240v circuit is an appropriate addition to your electrical system. For a small boat, say under 32 feet, it would seem to be maybe not so essential. Your biggest load will be for climate control. Heating and cooling that 27' Catalina isn't the same as heating and cooling a 45' trawler. By a cubed factor.



Simply having a 240V inverter and keeping the batteries charged is fine for smaller loads but be VERY sure of your power ratings and add your own hefty safety factor before trying to use it to power a large air conditioner. A lot of things can go wrong, especially if your boat is unattended for hours or days at a time. Modern sine wave inverters are pretty sailor proof, with low voltage cutoff, etc, and something like a couple of lightbulbs and a small fridge, I would certainly be okay doing that on my boat, but easier to have 120V applicances and devices in the first place. The only reason to prefer a 240v product in 120V land is to be compatible with the shoreside breakers and stuff.


When installing anything, make sure your wire is big enough, rated for the current. Back in parrot mode now... CONSULT AN ELECTRICIAN and if you do the work yourself, have him check it out before you go live. An actual practicing Marine Electrician, that is. There are some fundamental differences between house wiring and boat wiring.


I won't even start on all the excellent books on boat wiring and electricity that you ought to have and study. The more you learn, the less you will doubt your electrician's recommendations and the more sensible they will be to you. And the safer you and your boat and your guests will be.


Yes, you could learn to do all this yourself and make informed, knowledgeable decisions on your boats electrical system. Just remember the path to true knowledge is usually filled with MISTAKES. Mistakes with 120 or 240 volts can kill, or cause a lot of property damage, even destruction. Not saying you can't DIY this. Not necessarily saying you shouldn't. But weigh the risks, known and unknown, and you will probably end up agreeing that for major electrical refits like this, a professional is worth what you will have to pay him. Your insurance company would cheerfully agree, too.

[Steve DAntonio]

Others have correctly noted that you can derive 240 VAC from two isolated 120 VAC inlets, provided they are not on the same phase. While many boats use this arrangement, two 120 VAC, 30 amp cords, none that are wired in compliance with ABYC Standards, utilize 240 VAC gear, because there is no guarantee both legs will be energized, and there is no guarantee they will be out of phase, as they must be to generate 240 VAC.

In a single 240 VAC cord the likelihood of having out of phase legs, or only one leg available, is very low, it would occur if the dock were wired incorrectly, or there was a fault in the cord or one of its ends, otherwise you'll always get split phase 120/240 VAC power from a common 240 VAC cord.

If you plug into two 120 VAC dock outlets that are in phase, the HVAC unit will receive the hot legs of the 120 VAC circuit, I'm not sure what would happen, it might be damaged, but it won't work. There is no way of knowing if shore outlets are in or out of phase without measuring the voltage with a multimeter.

The panel does not have a main 240 VAC breaker. The vessel's panel would also not be able to measure the incoming 240 voltage with a panel meter, another ABYC violation.

ABYC E-11.5.3.4 specifies that, "In AC circuits, all current-carrying conductors and the grounding conductor shall be run together in the same cable, bundle, or raceway." If you use two separate 120 VAC cords to derive 240 VAC you would violate this guideline.

Also, 240 VAC circuits must utilize two pole, simultaneous trip breakers. If a cord supplies each leg, one primary or dock breaker could trip while the other remains energized, which would leave the unit exposed to a single 120 VAC leg. It would not work.

You could jury rig this to make it work by tying the two 120 VAC shore supplies together to derive 240 VAC, but it won't be right, or compliant. I would either get a 120 VAC HVAC unit, or install a transformer; it doesn't need to be an isolation transformer, it could be an auto-transformer, they are common and less costly.

Also, while discussing twin 120 VAC inlet systems, the neutrals for those systems must always remain isolated from each other.

[skenn_ie]

I recommend an isolation transformer with twin primaries and twin secondaries. That way, you have galvanic isolation/protection and the option to configure for step up, same voltage, or step down.

[wingssail]

For us the simple solution was to purchase and plug in a step up/step down transformer. (originally we needed a step down from 240 to 110, when entering French Polynesia, later we upgraded to a more capable unit).

Over the years and through out our circumnavigation we supplied 110v to our 110v boat in countries with 220-240v using the higher quality (5kva) transformer (Chinese).

There were times when we used an 8000BTU AC unit which needed 240v while the boat needed 110v. We plugged the AC directly into the shore power and used the transformer to stepdown to 110v for the rest of the vessel's AC wiring.

More recently when in 110v land we plugged the 110v shore power directly into the boat's system and used the step-up feature of the transformer to supply 240v to the 8000BTU ac unit which we had brought along from 240v land.

The transformer has jumpers on the front to allow a multitude of transformations. (any voltage in, any voltage out)

None of these connections required any electrician intervention.

[chris_maica]

If going to Europe you could consider getting s site transformer when you arrived. A sturdy bit of professional kit from the building trade. Usually 230/110v, 3kva. Has a couple of outlets. You might want to check the dimensions. They are quite heavy.
The following company would deliver to a marina I think,order online.
Not the first few items returned. It's quite s chunky yellow box.

screwfix.com/search?search=transformer

[ranger58sb]

Originally Posted by Madehn

is there a simple way to get 230V AC from my 115V shore power connections- i have one AC which i have been waiting to install that needs 230V. I have dual 30 amp 115 volt shore power plugs currently. This is the only piece of the boat that needs this voltage- am i better of to just go get a different AC unit. ( i got a great deal on the unit which i thought was a 115v unit at the time. My fault for not looking closer now trying to rectify my

Easiest is to sell the 230V unit, buy the correct 115V unit, get on with life...

All that electrical work just to correct one little purchasing error isn't necessary.

-Chris

[GrowleyMonster]

Originally Posted by ranger42c

Easiest is to sell the 230V unit, buy the correct 115V unit, get on with life...

All that electrical work just to correct one little purchasing error isn't necessary.

-Chris

That is an option, IF it is available in 120VAC, and IF it doesn't trip the circuit breaker or the main breaker. Current draw will double. Run current will probably not be an issue, but startup current MIGHT. So it is not a clear choice. Some research or consultation will be needed. The "buy and try" method I would not feel entirely comfortable in recommending.


I think maybe at this time the OP might reveal the size and type or make of the boat, and the size in BTU and the type of the AC unit, and any data available on power required for start and also for run. Buy and Try would be a better approach, if more data could be considered.


<EDIT> And another question is how or IF the AC will be powered while away from shore power. Of particular interest would be the rating of any generator present.

[skenn_ie]

A transformer can easily be wired so that it can take it's input from an inverter OR shore power. I have an inverter ta has an output socket on the front. I plug the boat electrics into it when I want that, or into shore power or generator when I want to use THAT. It plugs into an unconnected socket for safety when other sources are in play. That system prevents inadvertent connection to two sources. For isolation purposes, make sure that you don't get an Auto-transformer, as often used on building sites. Those DON'T provide isolation.

[smac999]

Originally Posted by GrowleyMonster

That is an option, IF it is available in 120VAC, and IF it doesn't trip the circuit breaker or the main breaker. Current draw will double. Run current will probably not be an issue, but startup current MIGHT. So it is not a clear choice.

The 120v model would draw less current then The 240v model running through a transformer from 120. As transformers are not 100% eff.

The op still has not come back to awswer if the unit is 50 or 60 hz.

[GrowleyMonster]

Originally Posted by smac999

The 120v model would draw less current then The 240v model running through a transformer from 120. As transformers are not 100% eff.

The op still has not come back to awswer if the unit is 50 or 60 hz.

Uh, no. Twice the current to do the same work if you half the voltage. Talking about the secondary side of the transformer. I am not talking about the primary side of an isolation transformer, or a Chinese portable type transformer. Those things have a habit of melting down. The ratings are not to be trusted.


I believe the OP was in the U.S. and so the AC is msot likely 60hz. The boat is in the U.S. so it is getting 60Hz shore power.