Another transformer question

[madhatter1]

I don’t want to hijack the other thread but one thing I can’t wrap my head around is how the transformer can take 120 30A cord and make 240V. I thought the selector switch on the panel was running the 120v through a second transformer with 2 sets of coils, therefore 2 120v outputs with one leg of each bonded and grounded to create the neutral. But in a drawing provided on an old thread by Dottieshusband and it shows one transformer and selector switches for input voltage.

I can see how it makes one 120 leg and a neutral but don’t see foe the other leg windings get input voltage. Now I have a damn headache trying to figure out how it works. I can’t find anything on the internet that shows dual voltage inputs to a single transformer. So right now it’s black box magic to me and I just know that it works. It is pretty cool to have because I have needed it twice. Once on a temporary dock while mine was being worked on and another time at a marina that had no 50’s working near us and the 30A got us through the night.

 

[SKYCHENEY]

Here is the schematic:

https://www.samsmarine.com/forums/attachment.php?attachmentid=10759&d=1318429410

What happens is that the 120v input is split between two windings in the transformer. That powers each side of the 240v on the output side. Think of it as just making half of that feed 180 degrees out of phase to produce the 240. Reversing the phasing of the primary side of the transformer will reverse the phasing of the secondary. It all happens by powering different parts of the windings via the different taps and switches. So your 30 amp cord is running one winding in the transfromer clockwise and another winding counter-clockwise.

 

[madhatter1]

Response and diagram is much appreciated. With X being the output side the shore 240 goes to H-1 and H-6 and 120 goes to H-1 and H-6?
The location of the H taps confuse me. Are they purely symbolic and location on the diagram meaningless except position in relation to each other? Thanks for the help. I did spend a good part of the day researching this and keep coming up empty.

 

[SKYCHENEY]

The way Hatteras installed these was using the primary as the secondary and the secondary winding as the primary. They reversed it for their application. So, X1 and X4 is where the 240v input from shore comes in. IF you only feed a 120v input then you separate it so it independently feeds both X1 and X2 as well as X3 and X4.

If you want to use them to boost, you have to go back to using H1 and H6 as the input terminals, thus reversing it back to its factory default configuration. You will then need a switch to either connect H3 and H4 together or H2 and H5 together for boost.