Ask the RV Doctor
Thunder and Lighting Q. I have a 1982 Cobra 24-foot motorhome with a water heater problem. When I turn on the ignitor, it explodes when igniting the propane. I can hear the ignitor clicking before it lights. And when it finally does light, it’s with a loud boom. Can you give me some suggestions? It seems to be the worst when it is a little cold outside. Dan Roberts
Tucson, Ariz. A. It’s my hunch your unit may have a partial blockage in the curved mixing tube. Plus, I would venture your water heater is in need of what is commonly referred to as a “clean and service.” All LP appliances require yearly preventive maintenance in order to remain at optimum operating efficiency. Performed each season, this set of specific maintenance procedures will minimize, if not virtually eliminate, all appliance operation failures. Too lengthy to list comprehensively in the column, some of the steps include setting the incoming LP line pressure, cleaning soot and carbon build-up from probes and sensors and checking/adjusting the appropriate gap spacing. In addition, cleaning electrical contacts, checking circuit board functions, etc. are all items mandated by virtually all appliance manufacturers. Specifically, I would check the LP-gas pressure at the water heater and the adjustment of the primary air shutter. Misalignment of the burner tube could also lead to your symptoms, but I would look close for a blockage of sorts in the burner tube itself, impeding or disrupting the normal flow of incoming LP as it is mixed with the primary air. Ho Hum Q. I have a 2001 Bounder diesel pusher and I’m on my second battery charger for the coach batteries. Unfortunately I continue to hear a very large humming noise from the charger. Also, the charger is located just under the bed and this creates quite a problem with sleep. Is this humming normal and, if so, can it be moved away from ear distance for sleeping? Jack Brown
Toledo, Ohio A. Jack, what you are hearing is an audible mechanical resonance created by a harmonic distortion in the converter/charger. I know that sounds like double-speak, but the phenomenon is somewhat technical. I’ll try to explain the happenings. Most AC electrical loads are linear, meaning the current is proportional to the AC voltage. Examples include regular AC lighting and simple motors. Linear devices rarely vary in frequency. Non-linear electrical loads, such as your AC/DC converter, can produce electrical waveforms that are multiples of the normal 60 hertz sine wave associated with the 120-volt AC electrical system in the RV. These multiple waves, called harmonics, are actually superimposed over the original sine wave. The original, fundamental sine wave combined with any of the overlaying harmonics will result in a non-sinusoidal wave form of an entirely different shape. This is very similar to the harmonics associated with stringed musical instruments. (I could demonstrate this easier on my guitar!) This new waveform then, has the ability to create a mechanical resonance within the transformer section of the converter. Overheating of the transformer, additionally, can lead to increased levels of harmonic A distortion which usually manifests itself as an audible hum via the mechanical resonance. (Hang on, we’re almost there!) The laminated steel plates that make up the transformer literally begin to vibrate at a frequency that is able to be heard. Unfortunately, there’s not much you can do to eliminate this resonance, short of redesigning the converter to include special notch filters to block out or eliminate the offending frequencies. Sound baffles can be placed between you and the converter, but care must be taken to avoid any build up of heat in the converter area. The best cure is to simply upgrade to one of the newer, high frequency converter/chargers. They are engineered with devices that can cancel out the harmonics and allow the waveform to maintain the 60 hertz necessary. Another benefit of upgrading is the optimum battery chargi