- by Pete Snidal (C)1988
Being as we are. citizens of the plugged-in generation (no pun intended), it is inevitable that we're going to want some electricity-eating conveniences. These start out simple - lights and music are the first, and can get more involved with time. You'll likely find your basic needs are, or become:
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Where to Get The Juice?
12V or 120?
Every electrical item in you bus will be a consumer of either 12V DC or 120V AC. (Battery power or "house current." Many people figure it's best to avoid duplication and stick with 12V lights and accessories, and do with as little 120 stuff as possible. You can buy 12V light bulbs that look just like ordinary house bulbs - they fit fine in ordinary table lamps. You can also buy a myriad of lighting fixtures designed for 12V operation, using bulbs from automotive turn signal or domelight bulbs to radio pilot lamps.
As for radio, TV, and stereo gear, there is every bit as much available in 12V as there is in 120. If you want a radio, get a good quality automotive AM/FM radio, if you want power, buy an automotive power amp. Same for CD players - all built to operate on 12V. Speakers, fortunately, don't care - all that matters for speakers is impedance - 4, 8, or 16 ohms. You can use your speakers from your home stereo system if you have the room.
For appliances, just remember that heat is very difficult to make with 12V, motors are a little easier to run. 12V hair dryers, curlers, or toasters, won't be around for awhile - they'd draw a ton of current. Blenders are available, and maybe coffee grinders and other frivolities. But don't forget to check out the possibilities for hand power for motor-involved appliances. Electric can openers, blenders, etc. can be duplicated by hand. Power tools can be replaced by cordless models, such as drills, sanders, etc., and it is possible to charge them with your bus electrical system, especially if their batteries are of a voltage lower than 12V. There are lots of toast-making devices which run on a propane burner. As for electric shavers, there used to be 12V electric shavers - I used one for my first few weeks of live-aboard bussing, then one morning I decided that I was (at least semi-)retired, and didn't have to shave any more. So I threw it in the first trash can we came across, and I haven't shaved since. That was in 1972! The moral to this story is that there are many things you can do on 12V, many things you can switch to doing manually, and many things you don't have to do at all - the very best way to adapt!
Summing up, it will be best if all your on-board electrical equipment is 12V. Then you have only one voltage you need to supply for all your gear. When you're running, there will be no problem at all - all your power will come from the vehicle's regular electrical system.
Most people don't build a live-aboard to drive around in 24 hours a day. You may be merely overnighting between drives, or you may be parked for months at a time.
Basically, the electric power you consume while parked will come from your batteries. As they are drawn from, the batteries need to be replenished. Batteries get charged in a variety of ways:
Some Engineering Basics
It may be a good time to discuss some basic electrical concepts. Such as AC, DC, Volts, Amps, Amp-Hours, and Watts. Taking a little effort to understand these terms now can save you a ton of bother later. So let's do it. If you already understand these, you can just skim them over.
Alternating Current - AC: electricity produced by alternators. The flow of electricity from an alternator actually reverses direction twice or more in each turn of the alternator. Electricity travels fast, so it's not a problem. But AC won't charge batteries - suck/blow/suck/blow won't blow up a balloon. So for battery charging, you need Fortunately, AC can be changed to DC using a Rectifier. And AC voltage can be changed by using a Transformer. A battery charger is just a transformer (120V:18V) and a Rectifier (AC:DC) (Don't ask!)
Direct Current - DC - electricity produced by rectifying AC, or by a DC Generator, or by a discharging battery. DC is necessary to charge batteries, but won't drive any equipments which require AC - such as anything that needs to change the voltage in a power supply, using transformers. Fortunately, DC can be changed to AC using a Multivibrator, and the resultant AC can then be brough to any desired AC voltage using a Transformer. An Inverter is just a Multivibrator/Tranformer/Voltage Regulatorystem in a box. You can buy them in power ranges from 200W to Many KW. Handy little gadgets for such things as computers or record turntables.
Efficiency: Conversion from AC to DC, or even between AC Voltages, always involves a problem with efficiency - you never get out all of what you put in. Sort of like exchanging money at the bank - the bank always takes a slice. Now, let's have a look at the basic quantities in which we find DC:
Voltage: Described in every textbook as Electrical Pressure. The higher the voltage, the more dangerous it is. 120V will kill you. 12V won't. 7.2KV is the voltage at the top of your power poles. See how big those ceramic insulators have to be so the power won't jump across them? 12V needs only a millimetre or so of plastic. Actually, it won't even jump through a piece of paper.
Amperes: or amps. The rate of flow of electricity - how fast it's moving through the wire. If a wire becomes overloaded, trying to carry too much power, it actually heats up. If it maxes out, it can LIGHT UP and set your HOUSE AFIRE. Fortunately, we have a safety device, called a Fuse, or a Circuit Breaker. The rating of the safety device must be determined by the thickness , and length, of the wire - not, as many people believe, by the amount of current required by the load. Your breaker or fuse must let go before the wire starts to melt it's insulation and light things on fire. Trust me. (Don't ask how I know!)
Amount: Your battery(ies) is (are) your gas tank. Gallons are Amp-Hrs. Put 25 Amps in a battery for 2 hours, that's 50 Amp-Hrs. Unfortuately, Efficiency rears its ugly head here, and the best battery will only give back a portion of this. Call it a brokerage fee. Bottom line: always have the best battery/s you can find. If you're charging off shore power, or when you're running, it's not as important as when you're charging from solar power or motor generator, since shore power is relatively much cheaper. But solar power is limited, and motor generators burn fuel.
Power: If you're trying to do a given job, you need a certain amount of power. Power comes in Watts. If an electric drill runs on 120V, it will use considerably less Amps, than if it is running on 12V, drilling the same hole. Fortunately, power is easily calculated, since it is defined as volt-amp product. So 6 Volts at 10 Amps is the same amount of Power as 12 Volts at 5 amps.
Avoid temptation to run both 12V and 120V systems. The duplication factor is a big waste. I've met people with 120V gensets who try to charge their batteries while running the big mother so they can make toast and run the drier, and it seldom works worth a damn. Big multi-Kilowatt generators are expensive to run, heavy, and usually have much more capacity than you'll ever really use. Sort of like swatting flies with a sledge hammer. Exceptions are runing heavy appliances like water heaters, toasters, big power tools, arc welders, washers, and God Help Us, Driers. (Some of the big Barfs actually run washers, driers, and electric ranges on electricity. They're built to be plugged into shore power at the golf course/trailer park/marina, and the generator is just popped in there in case of such dire emergencies as actually finding yourself in a trailer park without shore power.)
Summary: My personal preference is to build a system in which everything is 12Volt battery powered, and shore power is just another way of keeping the batteries charged, with a battery charger. The charger is preferably filtered to avoid getting AC ripple into the more sensitive appliances, such as TV and Radio gear. The batteries also charge from solar panel(s), vehicle charging system, and 12V motor generator.
Lastly - Isolating Your House System from the Vehicle Battery
You want your house system to be connected with the vehicle charging system when the engine is running, but not when you're parked. The simplest way to ensure that your house won't run down your vehicle battery when parked is to use some sort of automatic isolation switch. The simplest of these is probably the best. Just use a Ford-type starter solenoid. Energize the solenoid from an accessory output from the vehicle ignition switch. When you turn the key, the Solenoid connects to your vehicle electrical system. When you switch off, it's off. Works for me.
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