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Basic Electricity 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
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Basic Electricity - Page 2
Basic electricity for boat builders, boat repairers and owners. What you need to know about the electrical systems on your boat. Generation of electricity, grounding electrical circuits.
So where does electricity come from, or rather, how do we make electricity? What are the sources?
The first and most obvious is the electrochemical process I described as a battery. Dissimilar metals in an electrolyte form a cell from which electrons will flow between the metal plates. But what about when the battery gets too low (discharged) and we need to recharge it? Where does that electricity come from? And where do we get this Alternating Current?
That comes from a different process call electromagnetic induction. Many
hundreds of years ago people discovered magnets. They also
discovered that if you float a magnet in a liquid it points to magnetic
north, the north pole. This led to the magnetic compass. But it wasn't
until the last few hundred years that scientists determined why. Our
earth has a magnetic field. This field radiates along lines of magnetic
flux that flow north and south. Every magnet also has a
magnetic field around it with these same lines of magnetic flux.
Then someone discovered that if you move a wire (a complete circuit, not just a short piece of wire) through a magnetic field it causes electrons to flow in the wire. You are creating electricity. As the wire moves through the lines of magnetic flux around the magnet, the electrons in the wire get all excited and start dashing about.
So after much experimentation it was discovered that if you rotate a coil of wire on a shaft (a rotor or armature), inside a magnetic field, electricity is generated in the coil. This is a DC generator.
If you are much
over 40 years old you may remember that cars had generators, not alternators, up
until the 1970's. For the most part, the devices that make
electricity are still called generators, even though they are now mostly
alternators. So what's the difference? A generator puts out DC,
and an alternator puts out AC.
As I said on the previous page, DC loses a lot of
voltage when transmitted over long distances due to resistance in the
wires, and a thing called voltage drop. Someone discovered that AC did not
lose a lot of voltage this
way. So until recently power plants have all put out AC from very
large Alternators. In recent years methods have been discovered to
transmit DC over long distances as well, but power plants are still mostly
AC. In generators, if you wind half of the
coil, (the armature) one direction, and the other half the opposite direction, as the rotor turns the electrons go one way
in one half and the opposite way in the other half. That gives you
alternating current. If you spin this rotor at 60 revolutions per second
you get 60 cycle AC.
So, power plants put out AC. Car generators put out AC. Generators
on your boat, whether on the engine, or a separate generator, all put out
AC. This is then "rectified", that is, converted to DC and
used to charge your batteries and run equipment.
In the USA and around the world, there are thousands of plants generating
electricity by using steam to turn the generators, water to turn the
generators, wind turbines, tides, and even nuclear power. The plants
are all connected to a power grid. In North America, the USA and Canada
are both hooked up to the same power grid. This grid is divided up
into many little grids and separate power sources, but by throwing
switches the power you get in your home can come from almost anywhere in
North America. This power can then be used by you to not only power all of
your electric appliances, but also to charge your batteries.
Usually, the batteries in your boat are recharged by the generator on your engine, but if hooked up to shore power, you can use a charger to do this. You can also put what is called a converter on your boat, convert the AC to 12 V DC and use it directly to run all of your DC equipment, as well as charge the batteries. A typical marine alternator.
Also, there are alternative methods to generate electricity. The best
known is solar power. Certain types of silicon, when exposed to sunlight,
put out a small amount of electric current. By connecting hundreds of
these solar cells together, large amounts of current can be generated.
Many boats used for long distance cruising use solar cells to recharge
Some cruisers also use wind powered generators to charge their batteries.
Also see http://newboatbuilders.com/pages/electricity16.html on solar power and wind turbines.
One of the most important concepts when dealing with electricity is the
AC uses three wires. A black wire which is
considered the hot side, a white wire which is considered the neutral, or
grounded side, and a third green wire which is a safety wire, or grounding
wire. If you go to your local substation you will see such a ground. Even
your house has a ground. If you look at the wiring in
your house you will see that it is made up of three wires bundled in a
cable. They are black, white, and green. If you have 220 or 440 there will
be a fourth wire which is red. Both the white and the green are connected
to ground. This is an important point, because on shore side systems the
white and green are connected. But on a boat they are not. That is why the distinction
between the grounded wire and grounding wire is so important.
In DC systems, ground is usually established by using the negative side as the ground. However, some DC systems do use a third wire. The positive wire is red, the negative wire is black or yellow, and the third wire is green.
All wiring on boats is color coded. That is, for each type of equipment
and for main power circuits there is a specific color used for the
positive wire. The negative is always black or yellow.
Another important point is that there should be only one ground point in any system. This goes for both DC and AC. Both are grounded at the engine block. This is the only point on the boat where the two systems are connected.
© newboatbuilders.com 2007 All rights reserved. revised 12/30/2016
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