120VAC 15A powering 220VAC 50A circuit

[Guidon]

For a 2006 Mainship 400 with a 120/240VAC 60Hz AC panel - has anyone found an adapter to connect the 50 amp shore power input to a standard 120VAC NEMA 5-15 female plug (extension chord) to energize the 120VAC circuits during the off season (decommissioning/recommissioning)? I understand the legs need to be bridged so both are hot and I found an adapter which was internally bridged it didn’t energize the panel circuits. Looking for a solution that actually works on a MS400.
Thank you

 

[O C Diver]

If you have a 240 volt panel, it will only energize if each leg has 120 volts but not the same phase. The sine wave alternating voltage must peak at opposing points or atleast off by 120 degrees. Long story short, it won't work by tying both positive circuits to one singular positive power.

Ted

 

[Bacchus]

I thought all of that type tied both hot leads of 240V side to the single hot of the 120V side. I dont know how the MS 400 panel is configured but AFAIK these are the only ones available for that use.
Marinco 115A | Fisheries Supply
Do you have any info / documentation on your inlet. & panel?
Do you have any 240V appliances/circuits or is everything 120V?

 

[SteveK]

A 240V line would have 2-120v out of phase hots and a neutral. If you found a bridge device for the two hots, it should work, but did not.
Where does the bridging occur, at pedestal or boat?
Do you have an isolation transformer?

 

[mml2112]

I use a 50 amp to twin 30 amp Marinco y-adapter. Then I use (2) separate 30 amp to 15 amp adapters with extension cords to two different 15 amp circuits in the storage building. The 15 amp circuits need to provide different legs so you can’t have them on the same circuit. I have a isolation transformer and that does not pose a problem.

 

[Guidon]

Thank you very much for the replies and detailed information.
To answer a few of the questions- the bridging occurred in the adapter I pitched (bench verified the 50a legs of the adapter were bridged). There is an isolation transformer installed and there are 220vac circuits (ac, battery charger, stove, bridge stove).
I think OC Diver and Steve K hit the nail on the head and unfortunately where my boat is on the hard, I don’t have access to two separated 120vac circuits. I don’t suppose the Marinco adapter would “shift” the bridged inputs so they are out of phase(that would justify the cost).

 

[Bacchus]

I have a friend with 240V 50A inlet that uses one of these 15A 120V adapters for power on the hard. His only 240V appliances are 3 ACs and the AC water pump. I'm assuming, but haven't dug into the details, that his panel has 2 -120V busses that are in phase when using the adapter and opposite phasing when power by a 240V pedestal. He obviously can't run any 240V devices but his 120V circuits work and he needs to manage loads. He basically uses it for his 120V batty charger to maintain his battys. I font believe he has isolation xfmr(s) and really don't know how ac240V isolation xfmr is configured? Wondering if that is your issue?

 

[SteveK]

Thank you very much for the replies and detailed information.
To answer a few of the questions- the bridging occurred in the adapter I pitched (bench verified the 50a legs of the adapter were bridged). There is an isolation transformer installed and there are 220vac circuits (ac, battery charger, stove, bridge stove).
I think OC Diver and Steve K hit the nail on the head and unfortunately where my boat is on the hard, I don’t have access to two separated 120vac circuits. I don’t suppose the Marinco adapter would “shift” the bridged inputs so they are out of phase(that would justify the cost).

I do not know much about isolation transformers, so this is a WAG.
The IT is expecting out of phase input of two 120V lines but with the bridging is only seeing one 120V on both inputs. It may not be able to transfer to the AC panel this way. I see @twistedtree is posting, maybe he can chime in.

 

[tiltrider1]

There is what's possible and there is what's most likely.

Most likely, your IT is looking for out of phase 125v and has no neutral. If that is true then you are done. You will never be able to make a single 125v circuit power your boat unless you bypass the IT.

It is possible that you have two IT's in series using both the hots and the neutrals in which case you could get 125v to one side but not the second side.

It is also possible to by pass the IT and wire in a 125v socket that feeds power and neutral to both panels. This is not a 5 minute project, would require an expensive rotary switch and require some electrical knowledge.

 

[Guidon]

Thank you for all of the replies, very educational to say the least. I suspect the IT is looking for out of phase input. I plan to access the IT to understand what IT i have and how it is wired. From there i should be able to determine if there may be a solution. That said, as powering the boats 120vac circuits is more of a convenience, I certainly don’t expect I’ll go down the path of a step-up transformer.

 

[Greg QS]

My boat is 220v 50 amp and will not power up unless 220. Try 2- 110 leads on different phases. It takes trial and error but normally you can find it. Most marinas stagger there 110 outlets, 2 extension cords into separate phase 110 receptacles and you can energize. Just keep you consumption low. You can get a y adapter to 2 110 receptacles.

You can request at hall out that you are placed with 22o available .

 

[l00smarble]

There is what's possible and there is what's most likely.

Most likely, your IT is looking for out of phase 125v and has no neutral. If that is true then you are done. You will never be able to make a single 125v circuit power your boat unless you bypass the IT.

It is possible that you have two IT's in series using both the hots and the neutrals in which case you could get 125v to one side but not the second side.

It is also possible to by pass the IT and wire in a 125v socket that feeds power and neutral to both panels. This is not a 5 minute project, would require an expensive rotary switch and require some electrical knowledge.

This is the correct answer.

There is one work around though if you want to go through the expense and trouble. We use them all the time for service work on boats on the hard.

You can buy a "portable" 2kva transformer and rig it with a 15a/120 male pigtail on the primary side and wire it to step up voltage to 240v/7.5a on the secondary side with a 50a 120/240 female pigtail. We rigged a 15a breaker on the primary side.

You deploy this transfomer next to the 15a receptacle. It will give the on board transformer the voltage it wants but limited current. You will be limited to about 1500w total continuous load (the limit of the 15a receptacle).

I don't ahve an image of the ones we built but they are ACME transformers and look something like this: