Generator Voltage Problem Again

[RTyler]

Last fall my MDJE 7.5 started producing +/-160 volts and would trip the field circuit breaker on the VR, and then drop to about +/-45 volts. Sent the VR to Flight Systems, and re-soldering some connections fixed the problem resulting in 120 volts dead on. Last week it started doing the same thing again. Sent the VR back to Flight Systems but this time their telling me that it bench tests ok. I'm thinking maybe I have a bad wire or connection from the VR to the stator causing the VR to sense no or low input voltage resulting in the field voltage spiking and thereby running up the output voltage. BTW engine rpms are ok. Any thoughts?

Robert

 

[REBrueckner]

Your suggestion about a loose connection is a good one if the symptoms of your problem were the same before and after the voltage regulator was sent away.

On the other hand, if the genny produced proper voltage for a period of time, say several hours, suggesting everything was normal after the voltage regulator was returned to you, I'd suspect a broken/loose solder connection in the voltage regulator itself....something they "fixed" subsequently failed.....Maybe it tests ok for a minute or two...and/or maybe vibration from your genny causes the contact break....

 

[RTyler]

When I got the voltage regulator back from Flight Systems last time I remotely mounted it from the underside of the salon floor to isolate it from engine vibrations, so I don't think vibrations are the issue. I spoke to FS at length this morning and they sound pretty confident that the VR is not the problem. I'm just hoping that it's nothing in the genset itself, anything else I think I can handle. Given the symptoms and the fact that it can produce 165 volts I'm thinking its just not communicating properly with the regulator.

Robert

 

[Nick]

I have an electronic copy of the service manual for the MDJE. Send me your email address in a PM and I'll send it to you.

 

[REBrueckner]

So did the same symptoms pattern appear after repair of the VR as before or was the pattern different? Did the voltage regulator actually have a problem the first time you sent it out?? Did Flight Systems offer any suggestions??

You have to provide us specifics if you hope to get good suggestions in return.

Otherwise, start by using the wiring schematic of your genny to trace all the wires and connections you can find between the VR and other components. So far it sounds like a control/regulation issue rather than a generation issue.

 

[RTyler]

The first time Flight Systems looked at the VR they found cracked solders and fixed them which took care of the problem. It worked perfectly for 6 months, and then began the same symptoms. I have since spoken with a very knowledgeable Onan tech and he says the order of likely possibilities are:

1. Problem on VR circuit board ( Flight Systems has ruled this out )
2. Problem with VR transformer T21 ( Flight Systems says this is ok also )
3. There are 2 jumper wires on the VR board that could be bad. ( Flight Systems says they remove these during testing and therefore they could be bad)
4. A short in the F1 or F2 wiring to the stator. ( Very unlikely, but possible )

Tech said it is not rotating rectifiers or other problems within the genset based on the fact that it is producing high voltage before the field breaker trips. Heading to the boat tomorrow to check these things out, I'll keep everyone posted.

Robert

 

[REBrueckner]

Post #6 is great..and provides you the route to a solution....

I'd guess in a heart beat, or less, another broken solder connection in the VR except with your mounting it separately off the generator , that is less likely...unless you stressed/bent it while mounting????? Rubber washers are a good way to isolate such compent from unwanted movement....one under the circuit board and one over it between the circuit board and the mounting screw....

With six mos between similar symptoms, I know what I'd do after checking and finding nothing: order another circuit board and try it....

 

[RTyler]

If these things don't work I'm thinking about going with a whole new VR. Advanced Services and Parts sells a VR648 Universal Voltage Regulator that they say will work, and its only $179. It has to be wired to the genset end slightly differently but I don't see that as a big problem.

Robert