Generator output oddity

[SeaEric]

The power was off on the dock today due to a high tide so I started up the Gen. It has 120V output to 2 legs of the panel. One leg was powered up at 120v and the meter on the other leg showed only about 60 to 65v. which I noticed when I turned on a very dim drop light. I immediately killed the power to that leg of the panel so as not to screw something up with low voltage.

Any idea what I should be looking at to diagnose this gremlin? I'm not a mechanic so I'm not going to tear into this myself. I am hoping to get an intelligent clue here so I can perhaps point a mechanic to a potential source.

BTW, its an 8kw Onan diesel, late 80's vintage.

 

[Boatsb]

If this is a new problem the windings may be bad. The generator has 2 opposite sets of windings that when turned at 1800 RPM make 60 cycles of 120 Volts in opposite phases therefore also allowing the ability to create the 220V from the hot side of each coil. If one coil is not working ( as you stated it was creating 60V) it may have something stuck preventing it from making full power. The fact that it has 60V makes me thing something in the winding either broke open or is not making contact.

 

[SeaEric]

This is a new problem. It worked fine the last time I ran it, 2 weeks ago.

 

[Brian Degulis]

See if you have 240V between the 2 hot legs. Cycle the breakers. try momentarily putting a big load on the low leg or a big 240V load.

Brian

 

[Beckytek]

Check the brushes on your generator. Ron

 

[SeaEric]

See if you have 240V between the 2 hot legs. Cycle the breakers. try momentarily putting a big load on the low leg or a big 240V load.

Brian

Thanks for the suggestion. I tried that, the voltage output diminished after hitting it with a load, and then stayed down. Sounds like I need a tech to take a look.

 

[67hat34c]

Check all connections at the gen and at the power panel or panels. Also chck connections on the AMP meter. Loose connections and or broken wires will cause voltage drop esp when any load is applied. ie. you may get 120 volts at the meter but when you turn on a light the volts drop.

 

[Genesis]

The bad news is that its probably a shorted winding.

The regulator will crank the voltage up when there is no load but as soon as you hit it with a load it can't excite the unit with enough flux to get the output and it sags.

It could also be bad brushes which will produce the same result (excitation under load fails to drive output as the excitation current is insufficient)

 

[SeaEric]

The bad news is that its probably a shorted winding.

With the caveat that I don't know anything about these units...are there separate "windings" for each output leg? As one is performing pefectly at 120v output and one is not. An what would you roughly estimate the cost to re-do the Gen end of an 8kw? The engine seems to run fine. It is a 20 yr old unit and before spending too much on it I would consider total replacement.

The regulator will crank the voltage up when there is no load but as soon as you hit it with a load it can't excite the unit with enough flux to get the output and it sags.

It could also be bad brushes which will produce the same result (excitation under load fails to drive output as the excitation current is insufficient)

I would assume brushes are easier and less $$ to replace? Hopefully a tech can reasonably determine which of these may be the issue.

 

[yachtsmanbill]

You lost the neutral on that leg. The ground is tying to pick up the difference. Hence, youre only getting half the load. ws

 

[Genesis]

Yeah, its pretty simple to figure out....

If its 20 years old its probably not worth rebuilding the generator end. You may get lucky and have something cheap to fix, but I wouldn't bet on it.

I had a similar failure on my old Onan and tossed it - for the cost of having the gen end overhauled I just couldn't justify it with that many hours on the unit.

 

[SeaEric]

I had a tech take a quick look today. He noticed enough other issues that may render this unit a take out unless the voltage problem is simple. He's going to get into it further in a day or so. In the meantime, it would appear that I can get a new 9kw Norpro in the mid-$6K range, with panel but no box. Tech said R&R on the back end of the old unit is almost as much labor as R&R on the Gen itself. New may be the way to move.

 

[krush]

From Hot to hot, do you have 240? Do zou have 240 with a load?

If yes to both, then like Bill said you got a problem in the neutral.


Im in europe...dont expect manz responses from me LOL