Tuesday, January 31, 2023


Why isn’t converter giving a full charge while driving?

RV Doctor

Dear Gary,
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 an older model 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.

Dear 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). 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.

gary-736Read more from Gary Bunzer at the RVdoctor.com. See Gary’s videos about RV repair and maintenance.



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Tommy Molnar
3 years ago

The Ad that shows up in this “RV Doctor” article shows five mice all caught in the old fashioned slam-tight, cut their heads off type mousetrap.
The ad reads “This Breakthrough Device uses ‘High-Frequency Sound’ to Repel Vermin…”.
Frankly, I’d much rather have a trap that catches five mice in it at once than some silly “High Frequency Sound”, mouse repeller. But maybe that’s just me. And yes, I know the picture is staged, but I LOVE it – ha.

3 years ago
Reply to  Tommy Molnar

There are two solutions — For the home that gets mice while you are away in the RV, Bird-X brand Transonic repellers really do keep the mice out. In the RV, there are live traps that work – Have-a-heart brand works well to catch a mouse without harm or suffering. You can let the mouse out into a forest as you travel, but not near where you are camped or they can return.

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