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Old 11-28-2006, 07:45 AM   #1
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What is an INVERTER

I have a new AS but it did not come with an inverter. I still do not know the purpose of an inverter or if I should purchase one as an add on.I asked the dealer this question but it was not answered in ameaningful manner. Am I missing something that is essential?
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Old 11-28-2006, 07:52 AM   #2
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Hi - there is a really nice tutorial on the Airstream website about this.

Don't confuse converter and inverter.
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Old 11-28-2006, 08:16 AM   #3
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The CONverter in your new Airstream converts 120VAC from the power company, to run 12VDC appliances and CHARGES the batteries.

An INverter converts 12VDC from the batteries to run 120VAC appliances when you aren't near 120VAC power. It DISCHARGES the batteries, often at a very high rate, because it takes approximately 12 times the amount of current from the batteries as it's supplying to the 120VAC appliance (it isn't 100% efficient, so that's why 12 times instead of just 10).

At its rated output, even a small 500W inverter can drain two fully charged Group 24 batteries to dead in 2 hours or two Group 27 in 3 hours. If you want longer life from your batteries, you'll not discharge them below 50%, nowhere near dead.

It's best to limit inverter usage to only that absolutely necessary.

- Never use one to generate heat, when propane can do the job. Besides space heating, that includes making coffee and cooking.

- Whenever possible, use 12VDC versions of appliances. This often eliminates two inefficiencies, the inverter's and that of a transformer that's going to power the appliances with a lower voltage.

- Note that many appliances, electronics, etc. use a 120VAC wall transformer to supply 12-14VDC to the appliance. You can replace the transformer and cord with a cigarette lighter plug and cord and eliminate two inefficiencies, that of the inverter and that of the wall wart.

- Things like cell phones, handheld radios or GPS units, iPods, etc often have 12VDC chargers available for them. Use them if possible.

- Most notebook computers use DC voltage greater than the 12 supplied by your batteries. Rather than use an inverter for them, you can use a 12VDC notebook computer power supply that uses a DC-DC converter that's less inefficient.

- Many LCD TVs that have an external power supply also use a higher DC voltage, and you haven't much choice but to use an inverter. Just keep in mind, a 100W TV powered by an inverter will be drawing 5 amps out of each of two batteries, and can take them from 100% to 50% charge in only 10 hours.

- The cigarette lighter plugs on the Winegard antenna connection plates are only rated at 8 amps. You shouldn't use more than an 80W inverter in these, even though there are larger inverters with higher wattage (volts x amps = watts) that have lighter plugs.

- Larger inverters should be wired directly to the batteries (through an appropriate fuse) using a heavy gauge wire as recommended by the inverter manufacturer, and it should be as short as possible. Inverters are sensitive to low battery voltage and longer wire runs lower voltage.

Hope this helps,
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Old 11-28-2006, 09:07 AM   #4
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Current from outlets

Thanks for your explanation of inverters; it actually made sense to me, an absolute neophyte to onboard electronics. What I've been wondering is when your AS is NOT connected to shore power, what current, if any, is flowing from the three-prong (120 volt?) outlets in the coach? Are they dead, or does the system provide 12 volt current from the outlet under these circumstances? Second, where can I get a cigarette lighter plug and cord that plugs into one of these outlets?
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Old 11-28-2006, 09:30 AM   #5
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Current from outlets

I can't speak for Moe, he did an excellent job of covering the old inverter question, by the way.
But, my experience has been that IF the SHORE POWER is not plugged into an AC current source, the 115 volt style outlets have no AC current.
UNLESS, of course, you have an on-board AC motor generator and it is running.
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Old 11-28-2006, 09:35 AM   #6
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Without an inverter, there should be NO energy flowing in the 120 VAC outlets when not connected to shore power. They are two independent systems( or should be) If any current flows in the 120 ac circuit when on the road, there's a serious problem in the wiring.
Hope that helps.
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Old 11-28-2006, 09:49 AM   #7
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When you aren't plugged into shore power, your 120VAC outlets in the trailer are dead, 0 volts, unless as we and many others do, you have the trailer plugged into a Honda EU2000 (or similar) portable inverter/generator. There's no way I'd run one in the morning unless we were the only ones camping there, and even then, as quiet as they are, I'd prefer not to.

A 12 volt outlet looks like those in your tow vehicle, one of which may have a cigarette lighter plugged into it. Not all 12 volt outlets are rated to supply the power for, or can stand the heat of, a cigarette lighter. The only 12 volt outlets in our 34 are the ones on the Winegard antenna connector plates. One is over the credenza behind the curtain, and the other next to the fold-down mirror/TV shelf in the bedroom.

You can get the plugs/cords at Radio Shack. Note that the appliance end may have different tips, and that the + side isn't always in the center. Make sure you match the cord tip with the one on your appliance's wall wart.

Don't be worried about being a neophyte. The first time we stayed in our Airstream was in the middle of a pasture. My wife got up and plugged the coffeemaker into the outlet and nothing. I told her we didn't have power. So she said she'd just heat the water in the microwave. I just shook my head. I heated water in a pan on the stove and poured it through the coffeemaker basket into the pot.

For what it's worth, 12VDC appliances are often not a reasonable alternative to 120VAC ones, especially when it comes to heat. Those 12VDC coffeemakers can take 45 minutes to an hour to brew a pot of coffee, and still take quite a bit of battery power.

Many boondockers and boaters heat water on the stove and pour it through a Melitta coffeemaker. We now use (especially on the boat) a 33 ounce GSI JavaPress and two 16 ounce wide base stainless steel travel mugs. Being coffee lovers, we also grind beans with a GSI Coffee Grinder.
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Old 11-28-2006, 11:37 AM   #8
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Electrical memory aid

Originally Posted by woodedareas
I have a new AS but it did not come with an inverter. I still do not know the purpose of an inverter or if I should purchase one as an add on.I asked the dealer this question but it was not answered in ameaningful manner. Am I missing something that is essential?
A simple mnemonic: An inverter INcreases 12 volts dc to 120 volts ac, and a converter CONtracts 120 volts ac to 12 volts dc, all by electrical magic!
Fred Coldwell, WBCCI #1510, AIR #2675
Denver, Colorado - WBCCI Unit 24
Airstream Life "Old Aluminum"
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"From the Archives"
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