Electrical Issues, Short or Open?

To the uninitiated, one electrical issue looks like the next.  'My lights quit working, can you fix it?' is a common question, or some variant thereof... I think its a short'.  I explain that I can't know until I check it over with test equipment, and ask the client if they did the basics and checked the fuses.  Usually that question gets a blank look for an answer...  

If you have never studied electricity, an automotive electrical system can look insanely complex with wires everywhere, switches in all sorts of places, various black boxes and connectors scattered everywhere, and to top it all off, nothing is labeled, which makes it even less friendly.  

All circuits in a car, motorcycle, RV or boat are all very similar.  You have a source of power- the battery or alternator or both, a fuse to protect the circuit, a switch, loads that are being powered (light, fan, etc...) and then the wires to connect it all up and conduct electricity from the source to the load and back.

All loads need two wires, one for the supply or negative side, one for the positive or return side.  Someone a long time ago screwed things up by saying that the positive side of a battery is the source of current, but that is nonsense and we need to kill that old confusing and useless paradigm.

Here comes the physics part of it... you have been warned.

Electrons form the outer, reactive shell of an atom of stuff, lets say metal in this case.  Those electrons, the source of the word electricity, carry a charge we arbitrarily call 'negative' while the inner portion of the atom carries a 'positive' charge.  It is these charges and the polarity difference that keeps atoms together, the positive and negative charges are pulled together by forces created by that polarity.  The weak electromagnetic force in physics is the direct result of these charges and  defines the interactions between those charged particles.

Extra electrons on the negative plates of a fully charged battery is what creates the negative charge on that terminal of the battery, and the lack of electrons is what creates the positive terminal.  Current physically flows from the negative side with excess electrons to the positive side with not enough electrons.  Voltage is considered to be the strength of the force created by the difference in the number of electrons stripped form the positive and dropped to the negative side during charging.  A discharged battery has the same number of electrons in both plates, therefore no voltage or current flow can happen.

A flow of electrons, bumped from one atom to the next on and on down the wire, is what we call electricity.  The voltage is the pressure driving the electrons down the wire, while current or number of amps is the actual measured number of electrons that are flowing in a given time past a given point.

In a standard circuit, the current flow is controlled by the resistance of the wires and load, and by the voltage pushing it down the line.  A fuse is rated for a specific flow of current through it, after which the wire inside melts and burns out stopping the flow of electrons through it.  If the resistance is too low in the circuit, the current goes up in direct proportion to the reduced resistance.  The same resistance can pass more current if the voltage is raised as well.  Either way, some safety device should be installed to prevent that over-current from damaging other components and wiring.

An open circuit is the simplest and most common form of failure.  It is also the hardest to track down.  An open circuit is simply one that no longer connects, thus current does not flow.  Somewhere in the circuit, something broke and no longer is connected and conducting.  It could be a switch that no longer switches, a burned out bulb or other component, or even as simple as an old fuse that finally blew from years of use near its limit.  Then there are the nightmare scenarios where there is a break in a wire somewhere in that massive bundle of wires and now we need to find it.  It could be broken in any of a thousand places along as much as 50 feet of wire in a bigger vehicle.  Like I said... nightmare scenario.  In these cases, I will often run a new wire with the old ones and power that load directly skipping the old wire entirely.

If two wires melt or rub through and touch metal to metal, the result is a connection that was not intended and usually results in over current.  This is a 'short circuit'  Literally, the circuit is too short to be healthy, it skips the load and has found a shorter path from one side of the battery back to the other side.  Hopefully the overloading of the circuit results in blowing a fuse, but if the circuit is one of the main power distribution wires, the fuse may be so high powered that it never blows, even while wires are smoking and catching fire.  

Replacing a blown fuse with one of a higher rating is always dangerous and stupid even for trained and experienced technicians running diagnostic tests.  Find the cause of the short, find it and fix it.  Then replace the fuse with the correct one and carry on.  Intentionally overloading a circuit by using a higher current fuse than the wire is designed for WILL result in a wiring fire.

A short circuit from improperly routed wires, or over-fused, under-wired circuits causing a fire is the biggest danger in self wired vehicles.  The car owner has the option to install stereo systems, additional lights and power sockets, inverters and appliances nowdays.  All these new and interesting electrical add-ons can be bought in the parts stores  or truckstops easily but have no decent instructions to educate the novice installer how to keep it safe.  

Helping your mechanic diagnose electrical problems starts by properly describing the problem.  If you can tell your mechanic that the windshield wipers have an open circuit and don't work, its very different from saying it has a short circuit in which the fuse blows every time and you smell burning plastic.  Correctly stating the problem is the first step to your mechanic not spending hours to determine what kind of fault is happening.  

Hope that clarifies a few things for ya... til next time...

MW outta here :-)




 

More Magnets and Machinery...

In the last tech article on magnets and machines, I described how any piece of iron bearing metal can be made magnetic and can act just the same as any other magnet simply by wrapping that chunk of metal with insulated wire and applying an electric current to it.  Lets explore more of the capabilities of these wonderful devices, electromagnets, and what they can do for us.  

Alternators and generators are machines that transform mechanical energy into electrical energy.  They do this by spinning a magnet inside of multiple coils of wire. 

OK- time to backtrack?  Cool, back to basics. So one of the fundamentals of physics, and more specifically, electromagnetism, is that a moving magnet can induce an electric current in a wire.  When a magnet is passed over even a single strand of wire, the magnetic field knocks electrons loose from the atoms of the metal and pushes them into the next atom.  This bumping of electrons from one atom to the next one near it is the transference of energy from the magnet to the wire.  

Electrons move from one atomic cloud to the next and we call that electric current: the flow of electrons in a conductor.  That electronic flow is what we use to do various types of work in toasters and microwaves, electric tools and computers, cell phones and satellites. Creating that electron flow in a wire is now considered basic physics, but 150 years ago, it was unheard of and unknown to most people.  Experimenters like Maxwell, Faraday, Edison, Tesla and a myriad of others all contributed to our knowledge of how electric current could be created and utilized. 
  
Most of the electricity that powers our homes and businesses comes from the burning of coal or natural gas, or from nuclear plants, but they all do it the same way- heat water, boil it to steam under high pressure, then release the pressure and allow the steam to expand and cool as it moves through the turbine.  As the superheated steam passes through the turbine unit, it cools and transfers its energy to the turbine blades attached to the shaft, then to a generator/ alternator.  As the steam passes through the turbine,  most of the energy in the compressed superheated steam gets used to spin the turbine at very high speeds.  The turbine is connected via a common shaft to the generator or alternator head usually.

In a car, the alternator is spun at high speeds by a belt on a small pulley driven from the crankshaft pulley.  Usually these days a large, flat belt (serpentine belt) is responsible for turning the alternator in a car along with all the other accessories that need spun (A/C, power steering, water pump...) Regardless of how they are spun, an alternator is an interesting piece of equipment.   Inside an alternator, there is is the inner core (rotor) anchored directly to the spinning shaft.  This rotor is simply a coil of wire that is charged with a small electric current to become a magnet.  That magnetic coil in the rotor has ends and center made of iron, (steel) and thusly as current is applied to the coil in the rotor, the magnetic flux in the rotor core increases proportionally to the current flow.  These steel ends are brought around to the sides of the rotor to create a series of alternating North and South magnetic poles around the circumference of the rotor.  It is the constantly changing magnetic flux, switching rapidly from North to South that induces a current tin the stator coils. 

Controlling an alternator to put out specific voltage or current is simple in some ways.  A separate, or integrated voltage regulator controls output power by varying the small current that flows through the rotor.  Surrounding the rotor are the stator coils that are excited as the magnetic rotor spins inside them.  This creates a tremendous voltage and current in the stator with only a small current flowing through the rotor.  Its the input current that controls the output current.  For this reason, this design of alternator has become the standard for almost all equipment that must produce electrical power.  

So, again, heres to magnets and the ability to create all sorts of machines using them.  Magnets can be used to make speakers that spread sound through the room, or they can be used for detecting the position of something tiny and in need of perfect calibration.  Magnets are everywhere, and where they are not, we can make them using steel and wire to create electromagnets.  These electromagnets can be easily controlled with tiny amounts of power, thus the output of an alternator is also easy to adjust and control.  

Heres to long lived machines and healthy, happy people too,

             Again soon, MW

Nothings Shocking Now: An Electrical Primer (Part 1)

Electricity seems to many people some great mystery who go through life  happily flipping switches and expecting the lights to come on, and feeling helpless when they do not, feeling betrayed by every ideal of technological persistence and reliability.  I promise it is neither mystery nor given right.  It is science, tried, tested, and true.  Electricity powers our lives- its good to have some basic knowledge about it. These basics, what electricity is, how to determine the type of fault, and what can be done about it, are all basic skills that I can pass in fairly directly over the course of a few articles.