Instructor: Mike Hirata, Director of RV Sales, Heart Interface

Many new inverter/chargers have a built in "equalizer" feature. It applies only to wet cell batteries. Any time batteries are left for a long time in storage, sulfates will build up on the plates and impair battery performance. Equalization is a "planned overcharge" which will slough off the particles which have built up on the battery plates. This is an important step to maintain the condition of your batteries. Do it only after it's in the float stage, and after making sure the battery water is full. You should be present during the equalization period (usually about 8 hours) to monitor the process. If one battery is getting excessively hot, you may have a bad battery. Should that occur, terminate the equalization process by unplugging from shore power. An equalizing charge will typically be approximately 16 volts; therefore it's import to shut off all DC appliances, because some may not be protected against such high voltage.

Most appliances run more efficiently on AC than DC. Also, the selection of AC appliances is much broader than in DC appliances, which is one reason demand for inverters in RVs is growing. For example, there is very little choice of larger TVs which will run on DC; and those which you find are likely to be more expensive.

Caution: be certain to select an inverter with high efficiency. Heart Interface advertises 90% efficiency for its units. High 80% to low 90% is good. Avoid units which don't specify the efficiency, or which fall below 80%. In selecting a unit, be certain that the specs are accurate. Reliability and warranty are important. A two year warranty is a good indication of product confidence. Safety is another consideration. Look for the "UL" bug on the product.

There are some things we can do to maximize inverter systems. For example, we can take steps to ensure the batteries are being charged properly. If you can get 4-5 years out of a battery bank, rather than 1-2, the savings can be considerable. Available steps include three stage charging from the alternator; the use of solar panels to keep the batteries topped off; and proper maintenance -- the use of 3 stage inverter/charging devices to ensure the "float" charge is low enough to avoid gassing (see notes from yesterday's class).

It's important to understand battery capacity and cycle life. Avoid excessive discharges. When using the inverter, stay within the "50% rule" (see yesterday's notes). Precision amp hour meters can be extremely helpful in accomplishing this. Amp hour meters will actually track the status of your battery. The user inputs the total capacity (e.g. 440 amp hours in a battery bank). The unit will monitor the amps consumed on a digital display. As the batteries are charged, it will keep track of amp hours coming back in -- thus tracking the exact status of the battery bank.

It will also show voltage status and amp flow at any point in time. Many of these units track historical information as well. The number of cycles can be called up, as well as the average number of amp hours consumed per cycle. All of this can be displayed on the meter's digital readout. [Note: we have such a device "(Link 10" meter)-- a Heart product -- in our RV, and it is VERY helpful].

Some of the things to look for in a good system: The ability to manage up to 8 circuits; digital monitoring of volts and amps; user friendly selectable settings; inverter charger compatibility (if you're plugged into a 30 amp source, and both roof air conditioners are going, the ability to manage where the AC input goes. If the battery needs charging, it should have a priority.

Note tip offered by Greg Holder: The typical vehicle alternator stops charging as soon as the vehicle battery is fully charged. At that point the regulator shuts down the current. At that point, the house batteries are no longer getting a charge. A quick solution is to turn on the headlights. That will cause the regulator to allow the current to flow again, and the house batteries will be recharged. A complete solution would involve installing an after market three stage regulator.

The most important element of inverter systems is the battery capacity. It's quite easy to calculate the amp hours required for every appliance in the RV. Make an inventory, and estimate how many hours per day they will be used for your RVing lifestyle. Add them up to find your daily "need". That will be the basis for determining the size inverter you'll need; and also will help you determine the amp hours needed in the battery bank. The instructor seems to imply that a "normal" battery bank would be in the range of four 110 amp hour batteries. But many RVers will be able to get by with less, and others will want to have more -- all based on lifestyle needs.