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Gather literature from manufacturers and dealers. Use the 800 numbers in ads (and see later). Check particularly "Trace," "Heart Interface," "PowerStar" and "STATPOWER" brands for RV use. There are other excellent inverters also, but these state-of-the-art inverters are those against which others are measured. Contact RV Solar Electric for copies of technical reports on these inverters by recognized authorities. In any case, COMPARE:
Output Power-- In watts. You'll need to get an inverter capable of more than the max watts you'll use at one time. For how long? This figure may be hard to find. Use the manufacturer's 800#. Anyone that can't give an answer should be eliminated. Good companies will show, for example, that their 1,500 Watt inverter might operate at maximum power for 15 minutes and at 1,100 Watts continuously. If their inverter actually does run continuously at its rated power, that should be the only number--but you'd better quiz 'em and make sure.
Surge Power-- Should range from about 2 times output power to 6 times output power. You need this to start heavy loads, capacitor-start motors and the like. For how long? Most manufacturers don't commonly list this figure. It's short, usually 2 minutes or a few more. Nothing wrong with that because that's all that's needed. If it lasted much longer, it would just get hot and ruin itself
Idle Current or No Load Power Drain-- An important figure if you'll leave it turned on (idling) so that it automatically delivers full power when an appliance is turned on. This can equal nearly 20 watts of 12-volt power in some brands. (20W at 12V = 1.7Amps). You certainly don't want an idling/standby inverter to constantly drain over an amp-and-a half from your battery. Quality inverters draw only a fraction of an amp (as little as a tenth, or much less, of an amp) at idle.
Efficiency-- Is a critical figure. It should exceed 90% overall in [most] inverters (excepting true sine-wave inverters -- see later). It should not vary much from partial to full loads. Beware of inverters that advertise 90+% overall efficiency but may drop to less than 50% at some load levels.
The above are the key comparison figures. Others, such as output voltage and frequency regulation should also be compared but will be similar in high-quality inverters. Note that top quality inverters will regulate voltage, for example, to within 2% of the rated 120VAC. This is better than your power company, which usually regulates voltage to only 5%!
Cost-- is the final comparison. As when buying anything else, just make sure you don't mix apples and oranges.
Mixing apples and oranges is common when shopping for inverters. It's complicated because of the brands and models within brands that can vary widely in capacity and quality of components. Even though they look alike, they may not be alike. Many inverter manufacturers make top-of-the-line models for reliability, maximum performance and durability. They'll then make a similar model intended for light or intermittent use (sometimes called a "consumer" version). There's nothing wrong with this. The "lighter" model will work well if used as intended and can often be 50% or so cheaper. What you have to remember is TANSTAAFL (There Ain't No Such Thing As A Free Lunch). If you're a serious RVer, you'll be demanding the maximum from an inverter. Get the top model with the capacity you need. If you're just going to watch a bit of TV or similar, you might be satisfied with the light-duty version. I get lots of mail saying, "I was going to buy an XYZ inverter for $800 but I found the same one in a truck stop for $300." No they didn't! The look alike and may have had the same or similar brand name, different model name and was rated at lesser watts. BIG difference. (It may also have been a pirated phoney copy from who-knows-where--and probably was in the above example--because of the ridiculous difference in price.)
phred Tinseth © 1998-2000 Reproduction Permitted