House Calls with the RV Doctor
By Gary Bunzer
Dear RV Doctor:
I have a 34-foot 1990 type A motorhome. My problem is that when I have the coach hooked to shore power, my coach batteries do not stay charged. Just running a few interior lights for a few hours will drain them to the point that I have to start the engine and have the engine alternator charge the batteries. The three coach batteries are only a few months old, but sitting in the driveway with shore power (and even solar panels) connected, I can’t keep the batteries charged for very long. Could this be related to the battery isolator?
Little Rock, Arkansas
RV Doctor: Ryan, the auxiliary battery bank, which powers all the interior 12-volt accoutrements (such as lighting, water pump, furnace fan, etc.), receives a replenishing charge via several different methods. Since we use motorhomes to live in, it stands to reason that there be more than one method typically employed for the house circuits.
The engine cranking battery, on the other hand, exists for one sole purpose: cranking the engine and powering the engine/chassis-related 12-volt components. Typically, the alternator supplies a steady charging current to both types of battery systems. This segment of your charging system apparently is still doing its job, so that rules out the battery isolator as the culprit.
Another method of charging is through solar panels and a sophisticated charge controller. Your solar array simply may not be large enough to handle the capacity of three batteries.
Even though the three batteries are new, the first thing to do is separate them and test each one individually “” even a new battery could be bad. Next, check the actual output voltage “” if it is above 13.5 volts, the charging circuit is okay. If the charging voltage is below 13.5 volts, replace the charge controller.
The most common method of keeping the house batteries up to par is through the use of a charging inverter or convertor. Many newer RVs come equipped with a state-of-the-art battery charger integral to the AC-to-DC convertor, as well as the DC-to-AC inverter, when plugged into shore power (or by running the generator). Back in the early 1990s, however, it was primarily the AC-to-DC convertor that was relied upon to keep those batteries charged. Most charging convertors of that era were of the automatic variety, as they all are today. In other words, when you plugged in the shoreline, the convertor “automatically” switched the source of the DC current from the batteries and took on that job as its primary task. Parallel (no pun intended) with that task, a charging module was automatically activated and not only did the convertor convert, it also began to automatically charge the battery bank.
Usually an electromechanical relay (internal to the convertor) was used to switch from battery power to convertor power. Repeated use, higher and/or lower than normal voltages, dust, and corrosion of the contacts internal to the relay often would cause the relay to fail. The result was that even though the motorhome was plugged into campground power, the onboard batteries still provided the crucial DC current for the accessories. This sounds like your symptom. It could be a faulty relay in the convertor or it may be a faulty charging module in the convertor.
In either case, it will be necessary to have that convertor looked at by a professional service technician. Most RV shops, however, are not equipped to delve into internal convertor repairs, but there are specialty shops around the country that do just that. In many cases, however, it’s a wise decision to forego internal repairs to antiquated charging convertors using old technology. Newer, lighter, and more efficient charging convertors are readily available today. It’s always been my advice to upgrade to one of the solid-state, microprocessor-controlled charging convertors employing three- or four-step charging algorithms when it’s time to repair or replace that old unit. But, specialty companies do stand ready to repair your old charging convertor if you so desire.
The newer technology will come with a larger price tag, but the payoff will yield many years of quality battery charging. In all honesty, the older-style charging convertors were not very good battery chargers; they were great convertors, but the battery-charging capability left something to be desired. If you like this coach and you are a serious RVer, consider an upgrade to the newer style.