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Friday, October 23, 2009

Conniving Charging Converter

I have a year and a half old RV. I store it inside a metal building. It sat for about six months and when I went to use it the battery was dead. After pulling the caps the battery looked like it had been boiled to death from over charging. I usually leave it plugged in thinking the charger would stop charging. I have a Magnetek 7345 Converter. Did I damage the charger by leaving it plugged in all the time? Would I be better off disabling the Magnetek converter and buying an external charger designed to be plugged in all the time like the one on my boat? Should I just charge the battery a couple of days before a trip? I thought you should keep the battery charged. Is this correct on deep cycle batteries? Is there a way to check where the problem might be with the charger? All fuses that I can find are good and no breakers are flipped except the hot water heater I leave it off unless we are camping.
Paul, (Waco, TX)


Paul, there are differing views concerning leaving the RV hooked up to constant shore power, as well as a plethora of misconceptions that attempt to validate each view. It is my opinion a lot depends on the type of converter/charger that is equipped on your motorhome. For a generic, stock answer, I usually recommend not leaving the coach plugged in unless you are available to constantly check on the battery system, especially if your batteries are of the standard, wet cell lead-acid type. Many, run-of-the-mill converter/chargers have the propensity to overcharge the batteries when energized full-time. Most continue to charge well past the relative gassing voltage, thereby shortening the life of the batteries and creating a hazardous situation. I'm not sure which model Magnetek you have, so consult your product literature to verify if yours is a multi-step charger.

Multi-step converter/chargers do allow unsupervised, continuous connection to the shore power. But older chargers simply did not have the technology available to allow multiple charging algorithms. Some had a “trickle” charging feature, but overcharging can still occur at any current rating once the battery voltage has reached 14.3 volts DC. 

In addition, the absorbed glass mat, (AGM) battery has increased the RVers electrical hope. Because AGM battery technology permits more positive plate material to be saturated by the absorbed mats in each cell, there is an automatic increase in the battery’s capacity in virtually every area. More life cycles, reduced internal resistances, higher amp hour rating, more reserve capacity and deeper depth of discharge cycles are some of the improvements over other types of lead-acid batteries. AGM batteries are less susceptible to damage caused by overcharging, but unless your rig is equipped with one of those multi-stage, “smart charger,” or unless you are readily available to check the specific gravity manually every four hours or so, I would not recommend leaving the unit plugged in all the time. A highly recommended, though somewhat costly, upgrade includes AGM batteries coupled with a multi-stage charging converter. The configuration I favor finds the existing converter left in place as the actual converter with the new multi-stage smart charger installed solely as the battery charger. Costly, but optimum.

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