Troubleshooting the control system in your RV generator looks and sounds complicated. It can be if you look at the total system concept. It is fairly simple if you look at the board and the system as a collection of simple circuits.
Get your trusty/rusty printer fired up and print RV Generator Control Systems, Part 12 and Troubleshooting Part 18a. These are the basic concepts that you will use. You will also need a multi-meter to take the readings. You NEED the Schematic and Wiring Diagrams of the control system you will be troubleshooting. The Schematic tells you how the system components interact and function. The Wiring Diagram shows you how the board internal and external wiring is arranged and gives you the actual location of the wires or components you are checking. When in doubt, read the Theory of Operation of the control in the Service and Overhaul Manual for your generator. You did get one didn’t you? The guy or gal fixing the genset at the dealer will usually charge around $100.00 an hour. The book costs about $20.00.
Let’s see if we can solve the control problem. Symptoms: The generator starter rotates the engine, it won’t start and the fuse blows after a few seconds. There are no obvious burned places on the board. Nobody has worked on the unit and no maintenance has been done since the last good operation.
Deductions — The battery and battery connections are good. The start button works along with the start solenoid and the starter. This takes care of most of the first two function statements in part 12.
Get a supply of the appropriate size fuses and we will continue. Let’s check for spark like we did in 18a. YES we have spark but its weak and the fuse still blows.
Deduction — The ignition and plugs are probably OK. There are only two or three circuits that will pop a fuse in the control. Let’s check them.
The fuel pump, electric choke and the field flash circuits are the only ones in use at this time that draw enough current, if shorted, to blow a fuse. The easiest one to check is the fuel pump. Unplug it and try again. If the fuse doesn’t blow, you have a bad fuel pump. Go get a new (low pressure) one. If the pump checks OK, unplug BOTH wires from the electric choke heater coil and try again. If that checks good, it gets a little complicated. Field flash only functions during starting and only sends a 12 volt DC signal to the positive brush on the generator rotor. Uncover the slip ring and brush assembly and determine which one is positive. Connect your multi-meter from the positive brush wire to the frame of the generator. You should have 12 volts DC during starting.
If all three of these parts check ok, then we have a real problem. You most likely have a skinned wire somewhere on the generator set. Look for wires going over a sharp edge or wires that might vibrate during operation and rub on metal. That can be fun to find.
If the generator starts and runs as long as you hold the start button, we have a totally different set of problems. Deduction — The battery, starter, fuel pump, choke and ignition are functioning.
According to function statements 3 and 4, we must have a voltage/frequency signal from the generator to shift the control from external power (start switch) to internal power (let go of start switch). This 120 volt ac signal can be checked at the output circuit breaker/s. If no signal, you may need either a brush and slip ring cleaning or a new voltage regulator OR BOTH. Don’t even think about a new rotor or stator – yet.
If you get a voltage signal then function statement 4 comes into play. The safety circuit on an RV genset normally consists of a Low Oil Pressure/Level switch and possibly a Temperature switch to sense either cylinder head or oil temperature. Check your diagram, these switches are usually normally open during operation, and close their contacts if a malfunction occurs to shut the unit down. Check the oil level and then check your manual to find the location of the offending switch/s. If the switch shows an incorrect reading, replace it.
If you get this far and the little monster still doesn’t run, I recommend you take it to an RV generator dealer. Your trailer dealer may or MAY NOT have a qualified technician. If he doesn’t, he may swap parts until it works ($$$$) or farm the job out to an RV generator tech OR BOTH. Check the Yellow Pages under Generators, Electric or go on the internet to the manufacturer and they will normally have a list of dealers by City or Zip Code. Dealers not only have trained technicians, they also have factory furnished test equipment and the knowledge that only comes with experience when dealing with generator controls.
You gave it a good try. Knowing when to get help is a VERY important part of troubleshooting. You have probably also increased your vocabulary by a few new words.
I don’t know what I’m going to talk about next week, any suggestions?? How about brush and slip ring troubleshooting and cleaning? I do know that for our golden wedding anniversary on May 3rd, I took my darling spouse to the Golden Arches (Mickey D’s) and I’m still alive to talk about it. How lucky can a guy get?
Generator Jim
Jim Latour