PROBING THE MYSTERIES OF THE INVERTER: PART II

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and the lower ones at 12 volts. You'll quickly notice that the permissible lengths at 12 volts are one-tenth those possible at 120 ... and that the wattage being delivered is also reduced by the same factor. All told, the losses at 12 volts are 100 times as great as those at 120.

Because the voltage on the input side of the inverter is almost always lower than that on the output, it's important to minimize the losses on the low voltage side by placing the inverter as close to the main power source as possible. And, in practice, the inverter is usually located with the battery bank.

REMOTE SWITCHING

Unfortunately, locating the inverter in the battery compartment presents its own set of problems. When the unit is in use, power is drawn from the source and efficiently transformed into AC. But when the load is removed, the inverter will still demand a certain amount of standby power in order to keep its internal circuits active.

This tare energy (which was discussed at some length in the article in issue 80) slowly sucks power from the storage system without doing any useful work. The obvious answer is to shut down the inverter when it isn't needed ... but when it's located in the battery compartment, this is no simple chore. And, when it has to be done several times per day, the procedure can become pretty frustrating.

It is possible to purchase inverters with built-in load-sensing circuits that will detect an AC load on the output and switch the unit on. This feature is available, though, only on mediumand high-capacity models ... and it's impractical (and inefficient) to use a 2.5-KW inverter when you need, say, only 500 watts.

Another way to approach the problem is to install a remote switch. Some inverters come with remote cutoffs, and Fig. 2 shows how such a device can be wired into a system that's not so equipped. The relay is placed in line with the inverter's input, and the coil can then be switched on or off . The relay's contacts must be capable of handling the full input current value, though, and the coil volt age must match that of the input. Heavy-duty relays of this sort are often used in electric vehicles, and several sources of these com ponents advertise their wares in MOTHER's pages.

MORE POWER

Many people who are just starting to develop alternative energy systems begin with small setups and then expand them as more funds become available. Most often, such upgrading involves raising the power output of the original setup ... however, it isn't always easy to make your inverter's capability "grow" with the rest of the system.

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