You’ve Got The Power
Generators are an RV life source off the grid, so when something goes wrong, it’s an urgent fix — but not always an easy fix.
RV generators are an integral part of an off-grid system. However, when a generator goes haywire, it’s not just inconvenient, it also can be difficult and expensive to troubleshoot and repair. Not all RV repair facilities service generators, and those that do often employ technicians who lack anything beyond basic generator troubleshooting and repair skills. Even maintaining or adjusting a generator requires specialized equipment and training, so advanced troubleshooting often trips up an RV technician. Take, for instance, this letter from a reader:
We have a Sprinter Era 70A. We recently had the generator (Onan) serviced by Cummins. The generator will start but not hold a load. The Cummins facility hooked it up to a separate propane supply and it holds a load with no issue. Next, the two-stage regulator was replaced, and the propane lines were cleaned — and still the generator will not hold a load. Are we missing something basic like a reset switch, or is this a bigger issue?
We can glean much information from the email. The first thing we can determine is the generator in question is propane fueled, as opposed to diesel or gasoline powered. From this, we can define the system boundaries within which we can troubleshoot the problem. A propane RV generator consists of the following high-level operational systems: propane supply, regulator, propane plumbing, battery, alternator, fuel filter, engine (power plant), and control system, along with several other subsystems. Notice that I have separated the alternator from the engine. The engine output shaft is connected to the alternator shaft and produces the rotation of the alternator rotor, allowing the system to generate power. In most cases, it’s important to consider these components separately to assist with following the fault tree.
Let’s define the problem statement: Generator starts but will not maintain output voltage. There are obviously many ways to write the problem statement, but it needs to be accurate, to the point, and to clearly define the problem. Otherwise, the troubleshooting can go off-track.
Now, let’s examine what we know, which will allow us to rule out what is NOT the cause. First, since the generator starts, we can rule out the battery as the problem. Second, Cummins connected a separate propane system to the generator, and it worked fine. Therefore, we can rule out the engine, control system, fuel filter (replacing the fuel filter at manufacturer-recommended intervals is always a good idea), and alternator as root causes. We have now eliminated many of the high-level operational systems as the cause of the issue.
It is important to note that in some cases, there may be an intermittent fault, multiple causes, or faults not seemingly related to the root cause. In these cases, advanced troubleshooting skill is required. However, we should always start with the basics, as most issues can be traced to a single logical root cause.
We are left with the fuel subsystem, which consists of the propane tank, regulator, and plumbing. Here again, the email provides us with a clue: Cummins replaced the two-stage regulator with no change. Unless the new regulator was faulty out of the box, we can rule out the regulator as the cause. While it is possible the replacement regulator was bad, this should not initially be assumed unless there is good reason, such as problematic history of the same part.
Could the issue be related to a batch of bad propane? The author did not mention any concerns related to the other propane appliances, so for the moment, let’s assume that is not the case. There is also the question of whether the tank contains enough propane. We can revisit these later if we don’t find the cause on the first pass.
What remains is the propane plumbing. To simplify, let’s review basic mechanics and energy. As the engine does more work, it requires more fuel. Ignoring losses, the engine is converting potential chemical energy (propane) into thermal energy (combustion in the engine), then mechanical energy (rotation of the rotor), and finally electrical energy (current). As the demand for current increases, there must be an increase in propane flow. This increase must be supported by the regulator and plumbing supply lines.
We previously determined that the regulator is not likely the cause of the issue. Interestingly, there was no mention of whether the regulator was properly adjusted prior to installation. Regulators are not always properly preset at the factory, and installers don’t always adjust them. In this case, a poorly adjusted regulator would not likely cause outright stalling of the generator; so, this, too, can be ignored for the moment. That leaves the likely root cause to be the plumbing supply lines. If the problem can’t be identified there, additional advanced diagnostics will be required.
At this point, we have ruled out (at least on the first pass) the propane itself, as well as the regulator, and we believe the issue lies with the fuel line between the regulator and the generator. In most cases, this line is neoprene, so it can become kinked easily if it is improperly installed, too long, too short, etc. A kinked line is not able to carry the increased flow rates required when the generator is supporting an electrical load.
When I formulated my response to the author, I suggested a few things that might resolve the issue, including a kinked propane line. The author responded that the root cause was, indeed, a kinked line. By using our brains, we can prepare the diagnostic process efficiently and often without unnecessarily pulling things apart.
While technical knowledge can be taught, it is very difficult to teach the art of troubleshooting. Whenever I offer technical training, it quickly becomes apparent which students will be more successful, as they are the ones with better critical thinking skills. If you possess these abilities, and you have even a smattering of technical acumen, I recommend learning as much as you can about your RV. A little knowledge goes a long way and can save you a lot of money. Just be aware of your own limitations and ask for help when you need it.
Send your troubleshooting questions to Steve Froese at techtalk@fmca.com. The volume of correspondence may preclude personal replies. Not all responses will apply in every instance. Some situations may require a visual inspection and hands-on testing. If you choose to follow any procedures outlined in this column, first satisfy yourself that neither personal nor product safety will be jeopardized. If you feel uncomfortable about a procedure, stop and make an appointment with an RV service facility.
You may also want to consult the FMCA Forums (https://community.fmca.com) to see whether your question has already been addressed or, if not, to post it.