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Friday, October 23, 2009

Sub-Par Battery Charging

Hello Doctor, I have a 34' Class A motorhome. My problem is that when using shore power my coach batteries do not stay charged. Just running a few interior lights for a few hours will drain them to where I have to start the engine and keep letting 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?
Ryan, (Little Rock, AR)


Ryan, the auxiliary battery bank, which powers all the interior 12-volt accouterments such as lighting, water pump, furnace fan, etc., receives a replenishing charge via many 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. The most common method of keeping the house batteries up to par is through the use of a charging inverter or converter. Many newer rigs come equipped with a state of the art battery charger integral to the AC to DC converter as well as the DC to AC inverter when plugged into shore power (or by running the generator). 

Back in the early 90’s, however, it was primarily the AC to DC converter that was relied upon to keep those batteries charged. Most charging converters of that era were of the automatic variety, as they all are today. In other words, when you plugged in the shoreline, the converter “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 converter convert, it also began automatically charging the battery bank. Usually an electro-mechanical relay (internal to the converter) was used to switch from battery power to converter power. Repeated use, higher and/or lower than normal voltages, dust and corrosion of the contacts internal to the relay would oftentimes cause the relay to fail. The result was that even though the motorhome was plugged in to campground power, the on-board batteries still provided the crucial DC current for the accessories. This sounds like your symptom. It could be a faulty relay in the converter or it may be a faulty charging module in the converter. 

In either case, it will be necessary to have that converter looked at by a professional service technician. Most RV shops, however, are not equipped to delve into internal converter 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 converters using old technology. 

Newer, lighter and more efficient charging converters are readily available today. It’s always been my advice to upgrade to one of the newer, solid state, microprocessor-controlled charging converters 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 converter 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 converters were not very good battery chargers; they were great converters, but the battery charging capability left something to be desired. If you like this rig and you are a serious RVer, consider an upgrade to the newer style.

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