Keeping the starting batteries topped off means your motorhome’s always ready to go.
If your motorhome is a modern unit built within the last decade, it may have come from the factory with a chassis-battery charger/maintainer. When plugged into 120-volt AC shorepower, this charger keeps your motorhome’s chassis (engine-starting) batteries topped off. Most of the factory-installed chassis-battery chargers are very small models that only deliver about 1 amp of current. While this may be enough to keep the starting batteries topped off in a perfect world, often you may need more current than they can deliver. Many motorhome systems such as slideouts, electric leveling jacks and engine starting rely on the chassis starting batteries, so keeping them properly charged is very important.
When your motorhome is in storage and connected to shorepower, most of us assume that the batteries are not being used and that the built-in 1-amp charger is enough to keep things topped off. However, unless you are using the main disconnect switches to cut off all parasitic drains, the batteries may still be under a small load. That small drain may be enough to prevent the batteries from being fully charged due to the low current that the typical chassis-battery charger provides. And, if your motorhome is a bit older, or is an entry-level model, it may not have a chassis-battery maintainer installed at all.
A good solution is one of the high-amp chargers on the market today that uses a different method of handling its charging duties. This type of charger connects to your house batteries and “steals” some power from them (when 120-volt AC power is available or a solar system is used to charge the house batteries) to provide up to 15 amps of charging current to the chassis batteries.
Since your house batteries are usually the highest-capacity battery bank in the motorhome and are often charged by a sophisticated three-stage, built-in high-amp inverter/charging system, this makes them an ideal source to power this relatively new type of charger. Another advantage is that in most motorhomes both battery banks are stored in the same bay, making installation of this type of charger easy.
Two of the most popular chargers of this type are the Xantrex Echo Charger and the LSL Products AMP-L-START. For our purposes, we selected the AMP-L-START due to its lower price ($64.95 versus $129.99) and its widespread use in the motorhome market. LSL calls this a “diversion charger” because it steals a little of the charging energy from the house-battery bank and diverts it to the chassis batteries. This type of charger can be used in gas and diesel motorhomes and is designed to work on dual or single starting batteries; the house-battery bank can be of any size. LSL says the AMP-L-START can be used with all types of batteries, even if the house batteries and the chassis batteries are different types. In fact, the motorhome we used for the installation has mixed battery types, and the AMP-L-START has worked great for us.
When the AMP-L-START senses voltages greater than 13.2 volts on the house batteries, it starts charging the chassis batteries. (The house batteries can be receiving voltage from solar panels, or the built-in inverter/charger.) This 13.2 volts is higher than resting voltage, and it serves as the trigger to activate the chassis-battery charger we installed. Once the house-battery voltage drops below this level, the charger goes off and does not add a parasitic load of its own to the battery bank.
This charger also has an overvoltage protection circuit that shuts it down during battery equalization, and it emits an audible alarm if the chassis-battery voltage drops below 11.9 volts. The device features an easy-to-see LED panel to advise you of its charging mode, as well as lights to indicate improper wiring.
Once connected, the AMP-L-START is a fully automatic system, and we have used it for several months with great results. According to the manufacturer, the AMP-L-START uses a tapered charge rate that is optimized to prevent electrolyte loss in the battery bank. Although it is a very easy charger to install, we have included a pictorial of the steps to remove your motorhome’s old charger (if equipped) and to install the new one. With only three wires to connect, the AMP-L-START is one of the easiest upgrades you will ever perform.
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