Living with 12v

We have designed a number of projects to help those wanting to take on an alternate life-style. 
Two projects are:
A Solar Charger.  A circuit designed to convert the voltage and current from any number of solar cells to charge a 12v battery. 
A 12v Fluorescent Lamp Driver - drives one or two 20watt tubes from a 12v supply.

Living with 12v has its advantages and its drawbacks. This article will present a brief picture of what it is like, generating and living with a low-voltage supply.
Many families are turning their back on the rat-race of city life and settling into the pleasures of tranquil country living. Apart from the savings, the freedom and peace of mind, country living has a pleasantness that has to be experienced to be believed.
It's a life away from the bombardment of television, traffic, pollution, junk-mail, phone - and lots of other things that wear you down mentally.
Moreover you escape the products that you dread so much - junk food, movies, magazines, newspapers, junk from garage sales and so much more.
In the past few decades many city-dwellers have packed up and moved to the back blocks - to a life many would call harsh and uninviting. But these adventurers are not uninformed - they know what they are doing. They have made a clear decision to trade the ease of city life for a more rewarding life style. A life style that takes a certain type of person to appreciate.
Many prominent figures have told us of the virtues of the "alternate life style."  People like Dr Jim Cairns and "Peter Pedals" have painted a glowing picture of the potential it has to offer. But the great majority of us have done little more than listen to what they have to say, then promptly forgot.
In this article I want to cover some of the differences that remote living brings, with respect to energy consumption.

ENERGY
Many experimental communes of the '80's still survive today and the community groups they set up have thrived and expanded. 
Simple luxuries as a hot shower or running water take on a different meaning when you have to supply the wherewithal to make it happen yourself.
No longer can you flick a switch or turn on a gas jet without firstly having to install the infrastructure yourself.
No longer do you measure your consumption in kilolitres of water or kilowatts or power or mega joules of heat but everything is worked out in base quantities. This means gallons of water, watts of electricity and "how long a bottle of gas will last."
The only thing you may have in plentiful supply is timber and running water but no one has thought to go back 100 years and use these resources to their fullest. One hundred years ago the average house or farm used only a fraction of the energy we use today, but some had enormous supplies of energy available in the form of running water and timber and some took advantage of these and set themselves up very comfortably indeed.
We have seen pictures of farms with water wheels to grind wheat into flour or windmills to raise water and pump it hundreds of meters up hill. Others had self-contained generating plants sufficient for the needs of a small township. You must remember, farms of old were quite often totally self-contained. They couldn't rush to the shops for a loaf of bread or an extra piece of timber to complete a project. And they couldn't tap into the 240v or the water main, as these utilities simply weren't developed.
If a farm required power for milking machinery, shearing equipment or wood sawing, they had to install their own power plant. This was usually a stationary steam engine, commonly called a "donkey engine."
This was simply a boiler and single or double piston steam engine with a power take-off (drive shaft) so that with the use of belts and pulleys, a shed or workshop could be powered with equipment such as lathes for wood turning, shears for shearing, wheels for sharpening and revolving stones for grinding or milling. There could even be power enough for generating electricity, although electricity generation came later.
The only problem with a steam engine is it requires constant attention. It must be regularly oiled and fuelled. And one of the drawbacks is the noise it produces. Escaping steam is music to an enthusiast but an annoyance to others. Steam engines also consume water - lots of water. But the cost of running a steam plant is virtually nil; using off-cuts of timber.
You also get endless amounts of hot water if you tap off the condensate.
But sadly the skills and knowledge of producing such remarkable pieces of machinery has died with our fore≠fathers and few of us know about the mechanics of steam engines.
The only area I am familiar with is electrics and electronics.
If you want to duplicate the power of a donkey engine with modern technology, you would have quite a challenge. They were capable of delivering 10 Horsepower or more, depending on size and even a 5HP model will be almost impossible to duplicate in other forms. Let's see why.
One Horse-power is equivalent to 746 watts. But what can you do with 746 watts? A Kettle consumes 2400 watts, a fan heater needs 2200 watts, a power drill consumes 550 watts and a washing machine takes 500 watts while globes are 60 to 100 watts each.
For a normal household, 746 watts doesn't go very far and yet the production of even 1000 watts is the absolute maximum you can produce from natural resources on a budget of about $3,000.
Obviously the use of some high-wattage electrical items is completely out of the question if you are reliant on generated power, and you would have to boil water on a gas or wood stove and make toast in the fire. But if you wanted to use a washing machine, you would fully consume the electricity from a 1HP generator.
Commercial electricity is produced in such enormous quantities that we tend to overlook the difficulty in producing it.
A normal household consumes about 24 kilowatt-hours of electricity per day. This is equivalent to the constant use of 1kw, or one radiator bar, EVERY HOUR OF THE DAY.
But we consume electricity in short bursts of 5kw and more, and this is called peak demand.
This is the problem you face when producing your own electricity. It you want to cater for peak demand, you will have to install 5kw equipment.
This is a very expensive consideration and thatís why you have to look at the situation completely differently.
Even to generate peaks of 1kw from natural resources such as wind, sun and water would be a challenge.
Surprisingly, the only way you could get close to 1kw is with a water generator or water turbine.
If you want to get a constant 1kw with wind you will need a 3kW generator as wind is generally only available for less than 30% of the time. The same applies to solar power and this will involve a $3000 budget.
But with a fast-flowing stream and plenty of head water, you can generate 1kw from a turbine and have constant power, 24 hours a day.
The advantage of a water turbine is its ability to generate 240v and/or a lower voltage so you can use the electricity as it is being produced or store it in batteries for those occasions when you have high demand.
The main problem with wind generation is waiting for wind speed high enough to start the generator producing a worthwhile output. At low RPM a generator produces only 10% - 20% of its rating. It requires a fairly strong wind to get up to 90% of rated output. The same applies with solar generation.
The thing that most brochures leave out is the fact that solar panels only produce the rated output when the sun is shining at full brightness directly over the panel. All other conditions produce about 10% to 40%. Then you have to consider the number of cloudy days. City areas have a high number of days with cloud coverage whereas country areas are considerably freer. This makes solar panels very inefficient in and around major cities.
Using our 24 kilowatt-hours per day example, we can say that this is the consumption of a fairly large city household using kettles, tumble dryers, dishwashers, TV's and lights.
When you change to an energy efficient situation, this consumption has to fall to the range 50 to 200 watts. Out goes the kettle, dishwasher, iron, radiator, toaster etc and the only things left will be energy-efficient lighting, TV, washing machine, vacuum cleaner and power tools.
Obviously the washing machine, vacuum cleaner and power tools will be used for very short periods of time. Small TV's are ok as they consume less than 20 watts and lighting can be reduced to 20 watts per room by the use of high efficiency lights such as fluorescent tubes and compact lamps. The only dis≠advantage with compact lamps is the need to run them on 240v and some of the energy is wasted in the converter in the base of the lamp.
See the index for a project to drive a 20 watt fluorescent tube from a 12v supply. You must remember, with normal 20 watt fluoro's, 20 watts is lost in the lamp and another 10 watts is lost in the ballast. So a 20 watt fluoro really consumes 30 wafts! Our project consumes about 22 watts TOTAL to drive two 20 watt tubes to slightly less than full rated brightness.
Once you work out your requirement and find it is somewhere around 200 watts average, you are in a situation that can be managed with a solar panel and/or wind generation.
A low voltage system also means a low energy system as the limiting factor is the current.
If you have a mains operated washing machine drawing 500 watts, the current will be about 2 amps.
If you have the same item operating on a 12v supply, the current would be nearly 42 amps! Normal wiring can handle up to 15 amps so you can see everything would need to be three times larger. This type of cable is not readily available. The same would apply to the on/off switch, with a special type being needed.
But the real limiting factor is the voltage drop in the wiring. At a current flow of 40 amps, even thick cable would produce a voltage drop of 2-3v on say a 5 metre run. This means the 12v supply becomes 9-10v at the appliance. This will cause the appliance to draw less current and the power of the motor in the example above will drop from 500 watts to 270 watts. That's down to nearly half power with just a 3v drop!
That's why a high voltage was chosen for household distribution. Even if all the appliances in the home are turned on at the one time, the current flow will be less that 40 amps and thus the voltage drop between the meter box and the appliances will be less than 5v. Five volts drop for a 240v appliance is negligible.
But with a 12v supply, things are totally different and so you have to consider and realise that a 12v system is very limited.
Most plugs, sockets, switches and wiring is designed for a current of 10 amps. Some are designed for 15 amps but nothing is designed for a higher current. If we are using 240v AC (mains voltage) we can draw up to 2400 watts. But if we have a 12v system, we can only draw 120 watts.
Special 12v appliances are available including washing machines, vacuum cleaners, food mixers and power tools, but most have a maximum rating of 200 watts and this makes some of them very "feeble" in comparison to the general "modern-day" product. Battery operated power tools are the best solution as these have the battery fitted near the motor so the voltage drop is not noticeable. But they are also very slow performers and operate for only a short time before needing to be recharged.
One of the solutions to solving the voltage drop problem was the introduction of a 32 volt system, some years ago. At 32 volts there was no possibility of a "tingle" or shock from the wiring and therefore the user could wire up his house without the need for a licensed tradesman.
A small petrol-driven generator was used to charge a bank of car batteries and the system was totally automatic. As the voltage on the cells dropped to below 28 volts, the generator cut in and charged them up again.
A whole range of 32 volt appliances was invented for this system including lights, fridges, washing machines, radios and power tools. It is actually a better system than the 12v arrangement as it can be distributed around the home or farm without the voltage-drop problem. But many of the 32 volt devices are no longer available.
No matter what voltage you choose, the current is limited to about 10 amps. If we go to 15 amps, we create fairly hot conditions in the wiring and you start to get the smell of warm insulation. Anything over 20 amps requires very expensive wiring and most of the components such as switches etc are unavailable.
The only solution is to change everything to gas. You can readily buy a gas fridge, but when will they invent a gas television set?

GAS COMPARISONS
Gas jets are rated in Mega joules, but to an electronics person this does not have any meaning. We need to convert to watts.
The smallest burner on a gas stove is rated at 3.5 mega joules. This is equivalent to 1,000 watts.
The next burner is rated at 6.6 Mega joules. This is equivalent to 1.8kilowatts and a 9.5cm diameter burner is equivalent to 3.1kw. You can see that cooking consumes an enormous amount of energy. Cooking is one of then most inefficient transfers of energy you can get. Even boiling water on a gas stove is only 70% efficient. The remainder of the heat is lost around the sides of the container. You can feel the lost heat above anything you are cooking. The oven is the most inefficient. It consume over 3kw and yet takes an hour to cook a meat pie!
By comparison, an electric kettle is nearly 100% efficient except for the time when it produces steam, just before it turns off.
But the highest efficiency cooking is the microwave oven (really only about 50% as half the energy is lost in the magnetron and associated electronics).
A 600watt (consumption 1200 watts) microwave oven will cook a bowl of peas (heat the frozen variety) in 2 minutes. This is more efficient than conventional cooking as the temperature-gradient from the heat-source to the object being heated is less. The only problem with microwave cooking is the slight change in taste when compared with conventional cooking and for this reason it did not take off to the extend it was envisioned. 
This is the general picture. You need to combine three forms of energy to get total coverage. Firstly you need gas for cooking and heating water, solar pre-heating of water and heating the house, wood stove or fire for heating and/or cooking and some form of solar or wind generation for a 12 volt supply.
You will then need a 200 watt or 1kw inverter to change the 12v to 240v to power.
At the moment our projects cover the bottom end of the scale.  
Our Solar charger is one of the smallest chargers available. 
It allows any number of cells to be used to charge a 12v battery. Normally you need at least 15-18v from a set of cells to charge a 12v battery as the voltage from the cells falls as soon as the sunlight is reduced. 
With a charged 12v battery you can use our Fluorescent Lamp Driver project. 
This is the starting point.