Onan Generator Emerald BGE/NHE Spec A-C

 First off, if you have not already checked out this awesome website on troubleshooting go here: 

https://www.flightsystems.com/troubleshoot

There, you can find tons of information on gensets for onans. Also, these guys repair a lot of controllers for onan and make replacement boards as well. 

This will be a short post with some simple things you can check. 

Most, not all, of technical calls I get are the same exact thing: "When I press the start button, it runs, but when I let go of the button, its turns off" 

There are many ways this can happen. So Lets think about the "brains" of these gensets. 

First The controller. The main control board is usually at the switch or attached to the switch in the genset(generator set) . The main function of the board, is to start and stop the genset. Your press the start button, relays close putting either power OR a ground to external things that makes your genset run. 

Usually the main board is not seeing something it needs to see to stay running. this could be ac voltage, oil pressure etc. 

In this generators case, there is a bridge rectifier system on these. 

see controller and bridge: https://www.flightsystems.com/56-2784-00-replacement-control-board-for-onan-300-2784-300-2943.html

So lets look at the ac windings and do some resistance checks. First check resistance at the circuit breaker wires.  these are your stator windings. they should be .3 to .5 ohms measuring across them. 

Then we can test the field. on the bridge you will find a postive sign and a negative sign. lift the wires off those, and measure across the wires. these should be 7 to 10 ohms. 

Usually the bridge is bad if the readings are correct, or, the field is wayyy off and the slip rings will need to be cleaned.