An Overview Of Generators

By Gary Motley Master Certified RV Technician

Subjects for this series of articles are sometimes hard to choose. I always try to choose subjects that will be of interest to all RVíers . Generators are not in all RVís but I have had two people ask me to write about Gensets. Some of the subjects I am writing about are as a result of concerns I see in my shop on a regular basis.

Presently there are 3 major manufacturers of Gensets for RVís. They are Onan, Generac or Guardian and Power Tech. Onan presently has the largest portion of the RV Market.

Gensets produce electricity mechanically using a coil of wire, a magnetic field and motion. Magnetic lines of force from the magnetic field cut through the coil of wire producing the flow of current. The speed or number of RPM is what causes the proper frequency. The frequency in North America is 60 cycles per second. This is accomplished at 1800 RPM in most Gensets. 60 cycles per second times 60 seconds per minute is equal to 3,600. Single pole generators which have only one magnet on the rotating part (rotor) are 3,600 RPM generators. These are generally louder and less desirable. Gensets with 2 poles or 2 magnets on the rotor are 1,800 RPM Gensets (3,600/2=1,800). These are pretty much standard in most RVís today. There are variable speed generators which use an inverter or a PC board to create cycles or hertz.

There are 3 ways to increase the Output Voltage of a Genset:

1. Increase the electromagnetic field into the rotor. This is done through the use of a Voltage Regulator which constantly reads the Output Voltage and increases the amount of current flowing into the electromagnetic field to increase the Outage Voltage or reduces the Input Voltage to reduce the Output Voltage. The desired Outage Voltage is 120VAC plus or minus 10%. The load will vary the Output Voltage while the Voltage regulator will seek the proper Output Voltage of 120VAC. This is the most common practice of voltage regulation.

2. Increase the size of the wire in the coils or the number of coils. It is not practical to increase these while the Genset is running. This must be done when the coil is built.

3. Increase the speed of the Genset. Increasing the speed increases the Voltage Output. As you can quickly see, increasing the speed of the Genset also increases the frequency. This has already been covered.

The Governor is what controls the speed of the generator. Anytime you have your Genset serviced, part of that should be a governor adjustment. Some Gensets use a PC board and other electrical components to control the speed.

Do not ever let anyone increase the Voltage Output of you Genset by increasing the speed. The increased speed also increases the frequency which can damage many of the products that run on 120VAC in your RV. Enough about making electricity with a Genset.

Here are several bullet points about how to get the most from your Genset.

1. Before starting your Genset, Check for the following: Proper oil level; air inlets clear, clean air filter, clear exhaust, and tight connections.

2. Never start a Genset with a heavy load. To do so may cause damage to the major Genset component. It could also damage the appliances due to low voltage or frequency. Air conditionaers must be off before starting or stopping the generator.

3. Always take the loads off the Genset for 3 to 5 minutes before shutting it down. This will allow for a cool-down period.

4. Always allow a warm up period before a load is applied to a Genset. 5. Before purchasing a Genset, hear it run and satisfy yourself that the noise level is acceptable.

6. To Try to explain in detail the Power Ratings versus the appliances to be run would be much too lengthy. Be Sure to the Genset you purchase has the capacity to meet your needs.

7. Gensets have circuit breakers built into them. You should know where these are and always check them before seeking professional help.

8. If you ever have a Genset installed, you should insist that you get the installation instructions and inspect the installation before accepting the completed job. Some of the specific instructions for proper installation are: ventilation; fuel line routing, vapor tight to the interior, 12V DC hook-up; 110V AC wiring; exhaust termination; proper mounting and tying fuel lines in. This is a partial list but you can get the idea of the importance and safety of proper installation.

9. At my shop, I have seen some very unsafe installations. I cannot stress enough the importance of a correct and safe installation.

10. Gensets have 3 sources for fuel. Gasoline, diesel, or propane.

11. Newer RVs have either of two ways to connect the Genset power to the coach 120VAC distribution system. One is manual where the shore cord is plugged into a socket with Genset power, generally inside the shore cord storage area. The other is an automatic transfer switch which uses the 120VAC output from the Genset to close a switch which sends the Genset output to the distribution system.

12. Gensets can be air cooled or liquid cooled. Most are air cooled.

13. Genset power decreases 3.5% for each 1,000 feet above an altitude of 500 feet.

14. Power decreases in extreme temperatures by 1% for each 10į F above 85į F.

15. To prevent fuel varnishing in a gasoline powered Genset, you should run your Genset at least once every 4 weeks under half load. A long two hour exercise period is preferred over several short periods.

16. To prevent surging, exercise your Genset, keep your fuel and air filters clean, use fuel system stabilizer and cleaners.

17. Check your owners manual for periodic maintenance details.

18. An hour meter should be used to record the hours for maintenance.

19. For proper cooling, some Onan generators require that the cover be on while running. These are the Microlite, Microquiet and a Campmate.

20. Always use proper oil of the correct viscosity when your oil is changed. I like Onan oil because it is specifically made by Onan for generators.

21. As you always should with any accessory for your RV, be certain you get the installation instructions and check that your accessory was installed as per the instructions. Read the user instructions as well as your warranty information and respond properly.

Some fundamental safety rules include:

1. Check all exhaust system connections regularly for leaks and tighten them as necessary. Do NOT operate the generator with a faulty exhaust system.

2. The tail pipe must extend past the edge of the vehicle at least 2 inches.

 3. Always operate the generator in an area where the wind will carry away the exhaust fumes.

4. Never sleep with the generator running unless the RV is equipped with an operating carbon monoxide detector.

5. DonĻt store anything, especially gas, oil, rags or other flammable materials in the generator compartment.

6. Keep the exhaust and air intake free from obstructions such as clothing, furniture or other material.

7. Perform all service and maintenance work with the generator engine off and the positive battery cable disconnected.

8. A restricted spark arrestor can greatly affect performance. Have this serviced periodically. Certain campground require installation of a spark arrestor screen.

Thank you for reading this article. I have attempted to give you some information to help you enjoy your RV Genset while not being too technical.

Thanks again,


Article as published in October, 2004, issue of Oklahoma RV News.

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