Post by cowcharge on Sept 11, 2010 11:11:00 GMT -5
Hi! I'm in a rebuild on an old trailer that had no battery, no converter, and no water pump, so I've been looking up a lot of stuff about this.
If you're starting from scratch, I'd start by figuring out what maximum simultaneous load you plan to have. Are you gonna want to run a 30-inch flatscreen with surround sound while your wife keeps turning up the electric heaters and using the hair dryer while the kids microwave popcorn, make toast and use their X-Box? Or just a hot plate and a radio? Plan out a trip on paper, filling in what you expect to need electrically for a week's trip.
What load you need to be able to run all at once is the basis for all the math (if you want a system designed to your needs rather than adjusting your activities to the system's capacity), so start at the sharp end of the line, with the appliances and how you will use them, and work backward through the system to get to the battery bank size and the charging capacity you need to support your lifestyle. If you start somewhere else in the chain, say by getting a solar panel first, then everything else in the system will be determined by the output of that solar panel, including your usage of electricity or the length of your trips. It's much better to start your math with what you want to be able to do, and make the system bend to your will instead of the other way around, assuming you can afford the system needed. If the answer ends up being that you need to spend $20k on a 3-acre solar system to keep the batteries charged enough to run your life for a week, then you go back to the usage end, and see what you can live without to trim the amp hours used, until you end up with a good compromise between your usage and your bankbook. Something like "two hours less TV a day saves me X watts and therefore X amp hours per charge on the battery bank, which means I can stay off-grid another day with the cheaper 200 watt solar panels". Always start with what YOU want to do, not what one piece of equipment CAN do. That's if you have money, lol. Of course, if your budget's like mine, you'll find a cheap used battery somewhere and do the best you can to find something to charge it with, and tailor your electrical use to fit "until it goes dead".
From what I've read, it looks to me that charging capacity is really the hardest part of building a system that "never runs out". Inverters aren't that expensive, batteries are expensive but it's not hard to find big enough ones to supply what you need. You can outfit your camper with enough power and battery capacity to run an Aerosmith show if you want. But it's hard to find a solar system that will fit on a camper roof (or in a checkbook) that can generate enough juice to keep a large battery bank charged in a high-use system. If your trips are high-use electrically-speaking, your solar panels will probably be fighting a delaying action as the batteries discharge faster than the panels can keep up. You might have to run a generator a few hours a day to make up the difference, and only your planned needs can tell you that for sure.
I haven't gotten that far with my trailer yet, and I dunno if you'll find this useful in sort of getting a feel for what you might need for capacities, but I did a small unscientific power-consumption experiment while on a week-long road trip to Florida and back in my car. I ran my desktop computer with 17-inch CRT monitor all day while driving or stopping and half the night, with a simple 300-watt inverter running off the car battery. Never killed the battery or hit the inverter's low-voltage limit, even running engine-off for four or more hours a night. So a very simple system could be built for cheap, that would entail putting a small inverter in the camper, run off a 12v tap from the truck. I'm confident that if you were driving the truck daily or almost daily, that you could run quite a bit of useful gear at night and still keep up with the charging during the day. It's the things like microwaves, electric heating and cooling, and power tools that require larger systems and more charging.
Post by Gone Kayaking on Aug 22, 2011 22:45:42 GMT -5
Under the dinette bench (street side...would change to curbside if I were doing again) I have 2 AGM Group 24 batteries, a 450W modified sine wave inverter, a converter charger, and 2 15 Amp button fuses. It can be plugged in to shore power or run off the 12 v batteries. All the lights are 12 volt, as is the fan. Other uses for electricity are running the computer and stereo. We are able to boondock for 5-6 days during the summer without having to charge.
I paid to have it installed so that I wouldn't screw up...came to around 1000 including labor.
Next purchase will be solar panels for trickle charging and then the only reason we'll ever have to go an RV park is to do showers and laundry.
1956 Shasta 1500
Can't wait to go campin'
Folks sometimes confuse converters with inverters. Most travel trailers and "normal motorhomes" have converters. This makes 12 volts when you have either shore power or generator.
Inverters use d/c power to make a/c power or, just the opposite
In practicle terms normal campers using converters that your boondocking and without shore or gen the only accessories that are available to you are d/c powered.
If you have an inverter you can still use all the a/c powered stuff too. Having campers setup both ways I can assure you this makes the entire experiance much better all the way around.
Both converters and inverters may or may not have battery chargers.
If you want those a/c powered accessories when boondocking and you go with an inverter there are 2 types pure sine wave and modified sine wave. If you get a modified sine wave be sure to do your homework because there is no standards. Motors run hotter and lifespan will be reduced on anything powered from them. There are a few modified sine wave manufacturers Heart is one that comes to mind, but normally these should not be used for expensive electronics.
Going further even the absolute best pure sine wave inverter will have motors running hotter and diminished lifespan too, compared to plugging the same motor into the grid but it is insignificant enough to be a compramize willing to make. You can not say that with the ones of lesser quality. Cheep stuff like fans and inexpensive toasters or maybe a curling iron is about as much as I would be willing to risk on a "Pep Boys Special"
After reading through this thread, skipping all the theory, I just want to know what I need to buy to have one 12V outlet in my Compact to run a DC ice chest, and since I'll be on the road every day, I will want my tow vehicle to charge it, but have that device that shuts off the connection when I shut off my motor so that the car battery isn't drained. Do I need to go to the nasty little RV place to get this set up or is it pretty easy to do?
Post by universalexports on May 2, 2012 21:32:11 GMT -5
I believe they sell cigarette lighter plugs, with alligator clamps that just hook onto the battery, you would have to extend the cables probably to reach the back,
I would run a jumper cable from the car battery to teh camper battery with a battery isolator between them to keep from draining your car battery, a battery isolator only allows energy flow one way. then run the above mentioned lighter plug and gator clips to your cooler.
I bought one of these at radio shack, nice and heavy duty and simple, it converts 120 to 12 volt.
it has a standard plug in on the back that plugs into 120 volt, and a spot for a 12 volt cigarette lighter style plugin and a place to wire in a 12 volt 2 wire thing like a fantastic fan.
Hmm. That sounds almost simple enough except that I can't picture how I'd run the jumper cables from the front of my Astro, under the hood, to the battery that was, say, sitting on the tongue of the trailer, and have both those cables and the smaller alligator clips clipped to the same battery. ??
You need permanently-mounted wires to do that safely while driving. It's pretty simple to use ring connectors to attach multiple wires to the same battery posts, and you'd just need some sort of plug arrangement back at the battery for disconnecting the car from the camper. One + wire goes from battery to isolator switch (I screwed my isolator to an empty spot in the sheet metal in the engine compartment), then a long + wire from isolator switch to camper. The car frame is used for the ground, so you'd only need a short wire for the ground from car frame to camper battery. The isolator makes the car alternator start charging the 2nd battery as soon as the car battery is recharged from starting the engine (only a few minutes in my van). The only "hard" part is finding space for the isolator switch and crawling around underneath running the wire.