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January 03, 2007



In "RV-speak", where motorhomes and many travel-trailers have AC/DC systems, the "inverter" refers to a system or device for producing AC from DC; a "converter" - or "converter-charger" as it is sometimes called - produces DC from AC "shore-power" for operating the RV's low-voltage systems (lights, water pump, ignition voltages for refrigerator, furnace, and water-heater propane burners, blower voltage for furnace, sensor voltage for system-health management monitors, and ventalator fans) and the required charging voltage for the "house" batteries.

The most common converter-chargers are rated between 35 and 65 amps and can comfortably handle all the DC load of the RV for which they were spec'ed - while providing a modest output to charge the deep-cycle marine batteries used to power the RV while not "hooked up."

Due to the voltage/current relationship and DC-to-AC ineffeciencies inherit in voltage inversion, operating high-current/power consumption appliances still remains problematic. Most RV's have addressed this by equipping the RV with a generator rated for the high-consumption appliances.

In terms of power budget, RV's combine the best of both worlds: systems or devices with large current/power requirements are typically non-essentials and are powered by shore-power or generator, the two best sources for high-voltage/high current power. Under most conditions, people can live without TVs, VCR's, microwave ovens, and air conditioners; things like RV refrigerators, furnaces and water heaters by necessity are designed to be very effecient and to operate from low-voltage sources (house batteries) and gas when AC is not available.

Chris Byrne

I wrote some about this a few months back in relation so solar power, and a couple times a few more months back; once for camping power, and once jsut on generators.

I'm actualy saving in the fund for the eu2000i; both for emergency home power, and bugout power (only 43lbs); as well as general ouitdoor power needs. Quiet (relatively), clean, and efficient, but yeah not cheap.

Anyway, in the plan for us, is a large battery setup (I'm thinking a bank of large marine storage batteries), wired in to a solar system (living in Arizona it'd be silly not to), and with leads for the generator setup to act as backup and surge power. I figure 6-8 or so of the long reserve yacht batteries, or solar accumulator batteries will do us pretty good; serving our emergency household loads for several days at least, for about $2000-2500, plus another $1000-$1500 or so for the charger, inverter, wiring, and cutover switch (Depending on how the new solar technologies pan out, we may wire in the system as part of our normal household electric as well).

If the budget allows, I'm going to pick up both an eu2000i, and a larger generator (probably not the 3000. Though it is excellent, it's also a lot more expensive than comparable power rated gensets from other major manufacturers) for fixed site power; dedicate the 2000 just to mobile power.

Actually first step here though, is to pick up a large deep freezer; somethign I've been meaning to do for a year now. With a deep freezer and a goodly supply of ice, that's a fair bit of your power load reduce already.


In dealing with power emergencies, one has to remember that appliances like air conditioners, freezers, and refrigerators have one common characteristic: all have high-current-starting motors in the refrigeration compressors. Although you may have an inverter rated for the current draw listed on a freezer or fridge's electrical rating plate, the >surge< current of the motor starting up must also be taken into account.


Great comments, people.

JT brings up something that I haven't thought about before: the possibility of buying an AC/DC/LPG refrigerator/freezer for permanent home use. It might be considerably more expensive to buy, and might not be as efficient when run as an AC-only model, but wouldn't it be great to just have a bottle of propane and a small 12VDC battery to ignite the flame and not even have to worry about that load or it's surge-start problem?

The other thing I've been thinking of is to look into having a couple of big bottles of CNG, although it would take a very serious type of SHTF situation to end NG gas supply, the usual severe storm doesn't affect it.

Chris, you're right about solar, and in the PHX area, wind also. My daughter's sailboat which she lived and cruised on for 3 years was equipped with both, a 64 square foot solar array and a wind generator. The solar array could be counted on for almost 10 amps output (and it was 1st generation), and the wind generator would put out 18-20 in a strong breeze, and 5-6 if it was turning at all. Since the boat had only one long-term load, a cold-plate refrigeration system, and one occasional one, the autopilot, the two sets of golf-cart batteries would last for weeks without any sort of A/C input.

There is one caveat to off-grid in the SouthWest, and that is cooling. If living off-grid, you simply have to give up air conditioning and maybe even swamp cooling, you just can't supply that may kilowatts. That calls for personal cooling (wearing cotton clothing and misting water and making breezes on yourself).


I seem to remember that one type of battery needs to be stored at 50% charge for long term storage. That's not lead-acid, correct?


Anon, I don't know about any storage battery with such a requirement. When some lead-acid models are sold, they have no acid in them, and must be filled at the dealer, then charged. I know of no such requirements for LIon, Ni-Cad, Gel or AGM batteries.

You may be thinking of self-discharge rate. Lithium Ion will discharge at almost 30% per month, but the others self-discharge at no more than 5% per month.

I have a lot of LIon batteries, and I must say it is definitely a pain in the patoot to remember to charge them on a calendar basis, but I put up with it, because where else can you get a AA cell with 2.8 amp-hours capacity? I have a marine walkie-talkie that I replaced it's Ni-Cad battery with LIon, and now the radio will operate three times as long as with a NEW Ni-Cad.

Normand a Kerr

I was looking to buy a food slicer, and then I noticed it sayed It had a D.C. motor. Does that mean I have to run it off a battery? Or maybe a converter? The info. on the appliance, witch is on the internet, does not give any info????


You may be thinking of self-discharge rate. Lithium Ion will discharge at almost 30% per month, but the others self-discharge at no more than 5% per month.

Harold Galley

i am interested in building a power system that could handle all applainces that ia use in my house.


i like to use the inverter in my car, that battery is 12volts, and if i do attach the inverter to my car battery in car then can it be possible that i can play the ac appliances in the car, for example home theater system or any lights,,,,that we use in home.i want to generate the dc power to ac. so i need some assistance to do that,and if u help me i will really be obiliged.please to assist me what r the equipments i need and how to do,,,i heard from some one that if the car will be in running condition then will i be able to use the power of the battery to use for ac current or only when i switch off the engine i will be able to get the power....?

ED NOTE: You can do this, Sanjeeb, but remember the numbers. The average car battery is about 60 ampere-hours or less, and a moderate load will drain that battery in minutes. Also, if you are using the accessory plug in the car to power the inverter with, you cannot use more than a 120-watt load through them, or you blow the fuse. You best way to go is to put in a second battery of the deep-cycle variety, then use a battery isolator to connect it to the primary battery. The load will always be on the secondary battery, and your car will still start and run properly on it's primary battery. If you get a Group 31 deep-cycle battery of 115 amp-hours, you can drain it at 25 amps (300 watts) for almost 3 hours without recharging and without risking damage to the battery (the 50% drainage rule). Don't forget the capacity of your car's charging system. It has to be up to the task of putting all those amp-hours back into the battery, which usually means long engine runs to do it. If you can, use an AC battery charger and plug the car in to it to recharge. Don't forget that you will need at least 4-guage copper cables to hook up a set-up like this.

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