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We are saddened to announce the passing of Gary Bunzer on April 17, 2020. We hope the RV Doctor website will continue to provide helpful information for you. Thank you for your interest and support for the RV Doctor - Debbie, Heather and Gretchen

Thursday, August 4, 2011

No RV Battery Charging While Driving

I enjoyed your recent FMCA seminar about 12-volt battery systems. I have a converter that doesn't properly give a full charge while driving! I have a Dodge Sprinter chassis with the Mercedes  turbo. The converter is the 7300 series by Parallax Power Supply. The two 12-volt house batteries are new and I've only used the rig for less than four months. Is there a better converter that I should buy? Glenn C. (Eugene, OR)

Glenn, just to clarify, your Parallax converter/charger will not charge while actually driving down the road. It is powered by 120-volt AC electricity and should charge while plugged into shoreline power or when running the generator. The house batteries and the engine battery should receive a charge via the alternator on the engine while actually driving. It is plausible to run the generator while driving, but if the alternator is sized properly, both battery systems can be effectively charged while driving. Once you stop for the night, plug the coach into 120-volt AC park power and then the Parallax can top off the house batteries. (The Parallax will not charge the chassis battery).

If you're not getting a proper charging current to the batteries while driving, it will be necessary to evaluate the engine alternator and the battery isolator and all points between the alternator and battery bank. A proper setup will have the alternator output feeding into a dedicated dual battery separator or isolator.  The output amperage of the alternator is then split between the two battery systems, the house batteries and the chassis battery. 

One quick test you can make is to measure the voltage at the battery bank with the motorhome engine off. Note that voltage measurement, then start the engine. There should be a 2-3 volt rise in the voltage at the battery bank if the alternator is charging. If the voltage remains the same or goes down at all, it may be a faulty alternator, a faulty battery separator or faulty connections between point A and B.... meaning, further troubleshooting is in order. 

A Certified RV technician should be able to quickly diagnose which component(s) may be at fault and make the subsequent repair(s). In my RV Owner's Handbook, I give you the step-by-step procedures for testing the isolator and the wiring. But a quick voltage measurement with the engine off and then running will give you some indication of where the problem is originating. This, of course, is assuming the batteries themselves are in good condition. 



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If you are in doubt or do not feel comfortable about a procedure, do not continue. Simply call your local RV service facility and make an appointment with them. The advice, recommendations and procedures offered by the RV Doctor are solely those of Gary. They do not necessarily reflect the opinions, procedures and recommendations of our sponsors or advertisers.