Intelligent use120 vac Appliances in the Inverter Powered Home Jerry Fetterman One of the major developments in the alternative energy home market over the last 5 years has been efficient AC inverters. No longer is it necessary to 1) modify the circuitry or motors of products to run them on DC or 2) buy sometimes inferior quality, high-priced DC products. Now you can go down to the local discount store and purchase off-the-shelf appliances just like the folks who use commercial power. While most commercial 120vac products will run on an inverter, some intelligent decisions about what appliances to buy can save you hassles and significant amounts of power. INVERTER RULE #1: Let your inverter return to standby In standby mode, your inverter uses minimal power. Using products that are on 24 hours a day, such as clocks or devices with clocks in them, causes your inverter to be "on" all the time. Most inverters use less than 1 watt in the standby mode and upwards of 20-30 watts powering such minimal loads. While 20 to 30 watts does not seem that much, running such a load 24 hours a day takes 1 to 3 PV panels. To eliminate or minimize such loads 1) use quartz battery operated clocks, 2) do not use appliances with built-in clocks, 3) use appliances such as battery chargers, cordless telephones, and answering machines with DC inputs, and/or 4) use such appliances on AC only during periods of power surplus. Some appliances which appear to be turned off still may consume enough power to keep your inverter on. This is generally a result of the manufacturer installing the switch on the secondary of the transformer rather than the primary. It also can be a result of circuitry that stays on all the time such as in instant-on" TV's or remote controlled appliances. One way to trace a "phantom load" is to monitor the sound of your inverter; know what it sounds like in standby mode and in the "on" mode. If your inverter does not return to standby when all appliances are off, start unplugging appliances until you find the offender. If the inverter powers an extensively wired house, then the inverter may stay "on" because of the wiring. The inverter sees the capacitance of the wiring as a load and remains "on". If this is the case, adjust the standby level of the inverter. If the standby level of the inverter is not adjustable, then remove portions of the wiring by flipping their circuit breakers "off" at the mains panel. INVERTER RULE #2: Smaller can be better. This rule pertains primarily to use of AC water pumps and motors. In general, pump people will recommend pumps/motors that are larger than actually needed. A small pump/motor might take longer to do the job, but will take less surge to start and less power to run. Since, your inverter capacity is limited it is often better to save the capacity for other loads and go with a smaller pump/motor. Special Appliance Recommendations Color TVs: Many color TVs have either remote control and/or instant-on circuitry. This tricks you into believing that the appliance is off when you push the remote control. In reality, however, it is only partially off and is consuming power as it waits for you to use the remote control. In contrast, a TV set with a switch and an analog dial is off when you switch it off. If the couch potato in you likes to zap ad audio from your couch, one way is to install a switch or switched extension before the TV. Microwaves: Microwaves come with analog and digital controls. The analog type has a rotary timer and is off when not in use and is recommended. The digital types have displays/clocks which are on all day and are not recommended. Automatic Clothes Washers: Clothes washers are one of the most difficult loads for an inverter. While many will run from a 1200 watt inverter, others require a minimum of 2000 watts. This is due to the surge requirements. The washers requiring the least from your inverter pump the wash/rinse water prior to spinning, like Whirlpool and most Kenmore washers. Spinning with a full load is hard work for the motor and requires large surges. Gas Stoves and Ovens: A stove/oven with pilot lights requires no inverter power. To eliminate wasting gas by pilot lights, you can turn them off and start the burners with a hand held ignitor. Avoid gas stoves and ovens with built-in clocks. While some stoves/ovens with pilotless ignition work well with inverters, some use a heat element to trigger a solenoid before turning on the burner. These take a considerable amount of energy. Fluorescent Lights: Compact fluorescent lights with electronic ballasts work well on inverters. In contrast, fluorescent lights with coil ballasts produce a 60 cycle buzz. This buzz is audible on some fixtures and not on others. Find out if you can return the fixture if it is noisy before buying it. The rare incompatibility problems While modified sine-wave inverters run most equipment, you might find an appliance which does not operate correctly on inverters. This is usually the result of using edge-triggered power semiconductors. It occurs primarily in electronic equipment with mechanical parts. We have had personal trouble with a copy machine and a computer printer and have heard of problems with an electronic typewriter. This problem is NOT inherent to all products, just to specific models of machines and inverters. Before buying a high-cost appliance see if you can try it on your inverter. Access Jerry Fetterman is co-owner of Yellow Jacket Solar. Yellow Jacket Solar supplies remote home PV systems and water pumping systems to their local SW Colorado neighbors and has a mail-order catalog. The owners have lived with photovoltaic power since 1981.