Generator Discharge Troubleshooting

[Catbird]

My 82 Mainship MKI has its original OEM Onan MDJA 3KW genset. It starts and runs fine. The boat has 3 FLA batteries on a NOCO Gen3 charger. The batteries normally show 13.4-14V with the battery charger on, and the main panel shows 120V on either shorepower or generator power. I periodically exercise the generator under medium load for 30 minutes.

I ran the usual generator exercise routine about 10 days ago, with the reverse cycle a/c and battery charger on. I noticed battery voltage measured at the helm dropped to about 12.8V and the voltmeter on the main panel dropped to about 108V. I checked the ammeter on the generator and it was showing -2 Amp.

I started the generator again yesterday and with no load it showed 0 Amp output. I turned the a/c on, and the output immediately dropped to -2 Amp. I shut the gen down and aborted the exercise routine. I switched back to shorepower and everything returned to normal.

I have very little experience with electricity, and have only a digital multimeter. I don't know how to safely begin troubleshooting the issue. Any and all guidance will be greatly appreciated.

 

[Alaskan Sea-Duction]

My advise is to hire a generator tech to fix your issue.

With you very limited to non-existent experience around electricity, you could get hurt or worse kill yourself.....

 

[LaBomba]

My advise is to hire a generator tech to fix your issue.

With you very limited to non-existent experience around electricity, you could get hurt or worse kill yourself.....

I think this is sound advise. The only thing I might try is to check the fuses on the generator. I have two on mine on the control panel. Short of that call someone. It may be a simple solution but some training is required to find it safely.

 

[psneeld]

Do you have a manual with any troubleshooting in it?

If not, can you find one on the net?

Some forum sites have libraries to download manuals, there is manufacturer or dealer websites, there is boatdiesel.com to ask questions (pay site but usually worth it)

I do not consider simple troubleshooting by a manual to necessarily be life threatening....

 

[Ski in NC]

Those old MDJ series had external governor springs that get some corrosion on them and lose tension. If reading 108Vac under load, it could be as simple as low rpm. Get a meter that has Hz setting (frequency) or phototach the engine. Could be a simple adjustment. Should be 1800rpm under normal heavy load, about 1850 under no load.

 

[Catbird]

Thanks for all the responses. I can't argue with the warnings about electrical troubleshooting hazards. I've found some online links to a repair manual - was reluctant to subscribe to libraries like scribd.com because they require I provide credit card information (I've become averse to providing that info online). I'll look into getting a qualified tech to check the electrical side of the issue.
I'm also going to see about checking the actual rpm. Thanks again for all the responses.

 

[Alaskan Sea-Duction]

Please make sure you post your solution to not only close this thread out, but so the rest of us what your solution was. We also like pictures too.....Good Luck.

 

[Catbird]

I’ve got a generator tech coming out to the boat next week. I’ll circle back and update this thread when l know more.

 

[foggysail]

Those old MDJ series had external governor springs that get some corrosion on them and lose tension. If reading 108Vac under load, it could be as simple as low rpm. Get a meter that has Hz setting (frequency) or phototach the engine. Could be a simple adjustment. Should be 1800rpm under normal heavy load, about 1850 under no load.

My Kohler sometimes has trouble with lack of lubrication on the governor external connections. Spraying the control rod ends with a lub along with manually working the control rod back and forth while doing so might solve the OP’s headache. That maneuver is far less expensive than a genny tech who may approach the problem using a similar approach.

Do this of course with the genny not running

 

[Catbird]

Generator output back to normal. Mechanic needed about five minutes to confirm that the engine speed had dropped. He reset the governed speed and the generator went back to charging properly at normal 110v. I will be able to adjust the engine speed myself if needed in the future.