AC Voltage Problem

[Bob Bradley]

In tracking down an unrelated issue, I discovered that the 120 ac on my boat is only 108 when plugged in to the dockside. It's a full 120 at the boat end of the cord, so I am getting good power from the dock, but the outlets are only 108. When I run the genny, they have the full 120v. Any suggestions?

 

[Pascal]

You need to narrow it down.

So you have 120v at the end of the cord... what do you have at the panel on the panel volt meter. Then measure voltage at the rotary switch.

Is it possible that when you are measuring voltage at the outlets you have loads which will cause voltage to drop compared to no load when you measure at the end of the cord ?

Do have inlet fuses? Do they get hot?

 

[SKYCHENEY]

Do you have isolation transformers? 208 will show 120v between any two legs at the cord, but the transformer will half the voltage so 208 will be 104 at the plugs on the boat.

The only fix is to wire the transformers with a boost switch.

 

[Bob Bradley]

How concerned should I be if that is the case?

 

[SKYCHENEY]

How concerned should I be if that is the case?

All of your 230v loads will be running at 208v and all of your 120v loads will be running at 104v. This creates more heat in compressors and motors and they draw more amps at lower voltage. It may be okay short term, but not ideal long term.

But the good news is if you have the OEM isolation transformers, you have the ability to boost the voltage 15% by rewiring them with boost switches.

 

[Bob Bradley]

How complicated is it to do? Electrician job or DIY?

 

[cww]

Based on observation (this boat is great for having separate volt and amp gauges for every leg of the connection so you can see what’s happening) my boat’s iso transformers will increase or decrease in an effort to get to +/- 240. I experienced some shitty dock power between N. VA and FL, the net result of the boat up converting voltage was less amps available and a barely audible buzzing sound, I had to shut down an ac unit to quit blowing the dock breaker. I think I was getting somewhere around 190V off the pedestal. But the transformer made it work.

Maybe I’m babbling about nothing, I have no idea what it does or doesn’t do on a 120 line. I know it’s theoretically possible but I’ve never tried to plug it into 120.

 

[SKYCHENEY]

How complicated is it to do? Electrician job or DIY?

I have converted several of them but its probably a job for an electrician. You have to move the incoming leads to the transformer and swap them with the output wires. You also have to add a switch and some wire from a couple of the terminals within the transformer.

Here is a thread that explains it:

https://www.samsmarine.com/forums/s...-mod&highlight=primary+secondary+boost+switch

 

[Bob Bradley]

Thanks, Sky. I'm sure that explains it, but just not to me. Fortunately, my fishing buddy Walter has been an electrician for the last 40 years or so, so I'll be referring him to that thread.

 

[SKYCHENEY]

Thanks, Sky. I'm sure that explains it, but just not to me. Fortunately, my fishing buddy Walter has been an electrician for the last 40 years or so, so I'll be referring him to that thread.

Just let me know if you need any other information. Its really not too difficult to set up.