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Friday, October 30, 2009

"Smart" Battery Charging

I have a Holiday Rambler travel trailer which the local repair shop says needs a new power converter. Can this replacement job be done easily or should I have the dealer do it?
Steve, (South Bend, IN)

Steve, though some converter installations are relatively easy, especially if the new one is the same brand and model of the one you are replacing, I'd recommend you let a service center perform the replacement. It should take an experienced RV tech no more than an hour to an hour and a half to swap it out. 

But I'd get a second opinion to verify that your existing converter is indeed faulty. It just may have a poor battery charging function. Rarely do converters simply "go bad." Most are fine at converting AC to DC, but are ill-equipped to be an effective battery charger.

If you are serious about RVing, however, you might want to consider adding a multi-stage “smart” battery charger such as the Xantrex Truecharge 40 which uses charging criteria developed specifically for RV use. It optimizes the charging parameters by taking into account the battery temperature, the total amp-hour capacity of the battery bank and the type of electrolyte used. Here's a brief overview of how it operates. 

The multi-stage charge sequence begins with a bulk charge which basically pours all of the converter’s output into the depleted battery bank until the voltage approaches the gassing point, (around 14.2 – 14.4 volts). This bulk stage will bring the battery up to about 75 –80% capacity in the shortest amount of time. 

Next is the absorption stage. In this stage, the battery is charged at 14.4 volts until the current decreases to about 5-amps. At this point the battery bank is considered fully charged. Then it enters a maintenance type of charge sequence called the float stage. This float charge is commonly referred to as a "trickle charge." A constant voltage of about 13.3 to 13.5 volts is applied at a low current of about 1 – 3 amps. This is the point at which most other converters begin to boil the electrolyte. The Truecharge 40 eliminates this fear and most all RVs can be left plugged in indefinitely when equipped with this charger. The exception is when the battery bank consists of true deep cycle batteries such as two Trojan T-105, 6-volt golf cart batteries.

Most true deep cycle batteries are best utilized when charged and discharged deeply between charge cycles. They are not designed for prolonged periods of float charge. The Truecharge 40, however, considers this and allows you to choose a charging cycle sequence that only includes two steps – the bulk charge and absorption charge. A third, constant output voltage mode can also be selected if necessary. 

A fourth, equalization stage is also available. This equalization mode is simply a controlled overcharge designed to minimize or prevent sulfation from occurring in flooded batteries. During normal charge cycles, especially in the hotter climates, higher temperatures and impurities in the electrolyte may prevent some cells from attaining a full charge while allowing a higher degree of sulfating on the plates. Since not all batteries require a regular equalization charge, (most sealed, lead acid batteries in fact, do not), this feature is user-induced rather than automatic. 

Other advantages of the Truecharge include the ability to choose between gel, flooded or AGM battery types. Since each is constructed differently, the charging patterns should also be different. Over-temperature protection, overload protection and reverse polarity protection are additional benefits. And the good news is that it is quite simple to install. The 120-volt circuits of your existing panel will stay intact and only the battery charging function will be switched over to the Xantrex. 

In most every case, an upgrade to one of these highly efficient, "smart" power chargers is a wise investment and may very well eliminate or at least minimize the 12-volt battery charging woes so prevalent today.


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