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Monday, October 19, 2009

High Voltage Generator

I have an Onan generator in an older Itasca Suncruiser. After testing I think I have proven that the generator is providing over-voltage; actually around 144-volts. It drops to 129-volts with both air conditioners running. Any help on how to correct the voltage output that is too high?
Norman,(Tionesta, PA)

Norman, oftentimes generators require a tune-up and set-up. If you are indeed measuring over 140-volts AC, do not use the generator until a proper set-up can be performed. There are three possible adjustable components on the typical RV generator and each component has multiple adjustments. Periodically, each of these adjustment points must be checked and set properly. The choke assembly may have one or two adjustments, the governor will have a couple and the typical gasoline carburetor will have three adjustments. Here's the drawback - each adjustment to the carburetor and the governor has a direct electrical result. In other words, every time someone turns a screwdriver or a wrench on those two components specifically, the voltage and the electrical frequency will be altered. The only way to correctly adjust the carburetor and the governor is by monitoring the output voltage and frequency at the same time a specific load is applied. That's why it's impossible to "tune a generator by ear" like we used to do with lawnmowers and other small gasoline engines. Many well-meaning handypersons have a habit of trying to adjust the RV generator to make it "run right." Unfortunately, this only results in a poor running machine and/or incorrect output voltage, etc.

There are a strict set of procedures whereby a generator is properly set up using a device called a load bank. Proper testing would also verify a faulty voltage regulator as well. Only qualified RV technicians should attempt to tune a generator. If your local RV center is not familiar with generator tune-ups, we have produced a professional technical training videotape detailing those exact procedures. If you or your shop is interesting in obtaining the tape, simply send us your mailing address and we'll send you the ordering instructions. I wish I had an easy fix for you, but measurements must be taken and the generator adjusted correctly before diagnostics can continue.


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