Because
one cannot see billions of electrons flowing through a wire at the speed
of light, electricity is usually an area that most of us shy away from,
Unlike cleaning a carburetor, changing a flat tire or bolting accessories
onto your bike, electricity is a truly cerebral endeavor. It is difficult
to watch someone who knows what they are doing diagnosing an electrical
problem, and learn enough to repeat the process at a later date when confronted
with your own electrical nightmare. lithe like the Prince of Darkness takes
up residence in one's motorcycle, we either guess at what's wrong and start
replacing parts or take it to a shop where the hope is that the mechanics
won't do the same.
Figure
1
Circuits
Everything
that is electrical on a bike is part of a circuit. Circuits are just the
layout or design of how an electrical component will be powered and contolled
(figure I). Three things are required for a circuit to operate. While this
may seem obvious at first, it's far less so when looking at a complex wiring
diagram and the actual wiring harness on a motorcycle. When something electrical
doesn't work, see if one of these three items is missing. Here they are: The
Power SourceA
motorcycle's battery and/or alternator are usually the power source for
a circuit. This includes any wires that make connections between the power
source and various electrical components. The power source of a circuit
provides electrons to power the entire circuit. The power source is also
known as the "power" or "positive" side of a circuit. A
Load Device A
load device is anything that uses voltage or has resistance to electrical
flow. Most load devices amount to various lengths and sizes of wire that
take on different forms. For example; motors, relays, lights, solenoids,
coils, spark plugs and computers are all load devices. Most load devices
perform some type of work, Another kind of load device is one that you
can do without. Bad connectors or frayed sections of wire also have resistance
to electron flow and act as unwanted load devices. The
Ground ReturnThe
ground side of a circuit provides a way for the electrons to return back
to the power source. Ground returns complete circuits. Also known as the
"ground" or "negative side of a circuit, ground returns can be wires, the
engine, transmission or the frame of a motorcycle. A
simple circuit requires a source of power, a load and a path to connect
them from positive to negative. A motorcycle's chassis provides the majority
of the ground side's conductor path. Basic
Terms When
a circuit operates, the battery acts much like a water tank with an internal
pump. Water is pumped out of the tank, does some form of work, and returns
back. For ease of explanation, all of the drawings we will use show electricity,
or electrons, moving from Positive (+) to Negative (-). This is called
"conventional" electron theory. In reality, the electrons flow from negative
to positive in a direct current circuit. To understand how a circuit works
you need to know how voltage, amperage and resistance interact together. Voltage
is the "pressure" used to push electricity from positive to negative. Voltage
is a lot like pressure that an air compressor produces and stores in a
tank. When you use an air tool, air is pushed from the tank, through the
air hose and into the tool where it will do work. The higher the air pressure
the more work the air tool can do. The more voltage, or electrical pressure
pre sent,
the harder the electrons are pushed along a wire and through the load device.
There is only 12V worth of "push" inmost motorcycle batteries. With the
engine running the alternator raises battery voltage to around 14V. An
ignition system will raise the voltage to over 40,OOOV. If you have ever
been "zapped" by a plug wire, you know what that "push" feels like. Amperage,
or current, is the amount of electricity or electrons moving through a
wire or load device. If someone tells you that a starter motor uses high
amperage (180A
for a Harley), what he really means is that lots of electrons have to travel
from the battery, through the Starter and back to the battery for the Starter
to turn the engine over. The wires going to the starter have to be large
so there is low resiStance to current flow in the starter circuit. This
low resistance to flow will allow high amperage to reach the Starter. A
load device like a taillight will use low amperage. The taillight does
not have to do as much work as the starter and, therefore, will use only
about lA. Because of the low amperage, the wires going to the taillight
can he smaller than the wires going to the Starter.
The resistance in the smaller wires does not slow down the electrons needed
to produce lA, the energy needed to light up the taillight. Resistance
in a circuit slows down the flow of electrons and is measured in ohms.
All load devices by definition have some resistance to electron flow. For
example, a turn signal may have a high resistance of 12 ohms, and only
use a small amount of current or amperage. A starter, by contrast, will
have low resistance to current flow and only measure 0.06 ohms. The low
resistance in the starter circuit will allow a high amperage draw from
the battery. The relationship between voltage, amperage and resistance
was figured out about 170 years ago by a German dude named George Simon
Ohm, hence "Ohms" law. Simply put, it says that one volt of pressure will
push one amp of current flow past one ohm of resistance. It
is often expressed by this circular formula in Figure Two. To find the
value of any unit in a system, simply blot it out of the formula and supply
the known values of the other two units
W Where
p is power in watts, I Is current in amps, and E is electromotive force
in volts, then: P=IxE l=P/E E=P/l If
you were going to design electrical circuits for a motorcycle, you would
need to figure out bow much power was required to run all the electrical
accessories. These calculations would determine things such as: How many
watts or amps the alternator needed to output, the size (electrically Speaking)
of the battery, the rating of fuses and circuit breakers, and what gauge
wire was needed for each circuit. The relationship between power in watts,
current in amps, and electromotive force in volts is easily expressed in
another circular formula that is used the same way (Figure 3). This
is useful if you are thinking about adding electrical accessories to your
motorcycle. For example, you want to add a 100W headlight, an electric
vest and a loud, obnoxious horn. First you need to find out how much power
all this stuff will take to operate. The headlight is easy because it's
rated at 100W. The instructions that came with your vest tell you that,
if turned all the way up, it will consume 75W. The horn is rated in amps,
so you'll need to convert its rating into watts. The SA horn will be powered
by the alternator, which outputs 14V at 2000 rpm. Five times 14 equals
70W. All the accessories added together come to a total of 245W. Your alternator's
maximum output is 38A or 532W (38 amps x 14 volts). Now look in your service
or owner's manual to find out how much the stock electrical equipment uses.
The lights use 12A and the ignition requires 6A. Batteries need about 5A
to charge, bringing the total to 25A or 322W. Add this figure to the accessories
you want to install and you get 567W. If this number is greater than your
alternator's output, someone's got to pay. The alternator is rated at only
532W, which leaves a negative 35W. Your lights will be slightly dim and
the ignition system will have less voltage output to the spark plugs, though
enough to keep the engine running, However, your battery will suffer the
most because it will not receive enough power to charge as you ride. This
problem may not show up right away, but sooner or later the battery will
know that it's Sunday and you're 100 miles from nowhere and decide to go
dead. But
all is not lost, Remember that one of your accessories was a horn, Because
the horn is not in constant use, you can subtract its power requirement
from your total accessories. That brings down the total watts to 497W,
The alternator that can produce 532W so everything should be OK, as we
have 35W to Spare. While this is only an example, it's not too far off
what many motorcycle charging Systems are required to do in the real world.
In our example, the charging system is on the edge of being overtaxed.
The electric vest should be turned off in slow traffic and the 100W high
beam should only be used with the engine turning a decent rpm. Also, with
93% of the alternator's 532W being used, it's going to wear out faster
than if it only had to power the stock electrics. Back
to how a circuit operates and how you can apply this knowledge to fix a
problem. Typically, most electrical gremlins on motorcycles are caused
by unwanted high resistance. A slow turning starter or dim headlight is
usually caused by hidden, unwanted resistance in a circuit. The high resistance
will drop the available voltage and not allow enough amperage to flow to
the load device, The opposite is true if a fuse keeps blowing. The blown
fuse is caused by too low resistance in the circuit that the fuse protects.
The low resistance causes high amperage to flow through the circuit. This
raises the temperature of the fuse, melting it in the process. Understanding
the relationship between amperage and resistance will solve most electrical
problems. When resistance goes down, amperage will always go up and, conversely,
if there is low resistance the amperage flowing will be high (Figure 4). Circuit
Types Instead
of memorizing lots of rules about series and parallel circuits, what you
need to know is how to tell them apart and how they are different. There
are three things that are important about a series circuit. MOTORCYCLE
CONSUMER NEWS 29
JANUARY2OOO The
first is that all of the voltage will be used up by the load devices. Look
at Figure 6. Voltage before the bulb will be 12V, Voltage after the bulb
will be OV. This is because the bulb, or load device, uses up all of the
source voltage (Figure 5). The
second point is that when load devices are added to a series circuit, the
resistance of each load will add to the total resistance of the circuit.
As resistance goes up, amperage in the circuit will go down. In Figure
7, the more light bulbs that are added, the dimmer they will all become
because there is less current flowing in the circuit. The voltage will
he divided between the loads based on each load's resistance. The
third item is that amperage will be the same throughout a series circuit
on both the negative and positive side. In Figure 6, three-amp meters are
shown connected to a series circuit. There are two series type amp meters,
meaning that the meters become part of the circuit itself, and one inductive
type of amp meter that clamps around the wire and measures amperage by
the magnetic field present in the wire (Figure 6). There
are very few, if any, series circuits used in a motorcycle. However, when
a circuit has a bad wire or poor connection, the circuit essentially turns
into a series circuit. This is why it is important to understand how a
series circuit works, so you can identify one and repair the condition. Most
circuits found on a motorcycle are parallel circuits. In a parallel circuit,
voltage, amperage and resistance work the same in a part of the circuit
and differently in other parts of the circuit. Voltage will be the same
everywhere on the positive side of the circuit and will not be divided
up between the loads. Each load in a parallel circuit will use all of the
source voltage going to it, just like a series circuit. In Figure 7, notice
that the ground side of each bulb is at OV because all of the voltage is
used up by the bulb. As
loads are added to a parallel circuit, the total resistance of the entire
circuit goes down. This will cause the amperage to increase. Take a look
at Figure 8. If bulbs I, 2 and 3 are on, they will each use 6A. Because
the power for all the lights will flow through the fuse, a 20A rating is
required. When the switch to the motor is closed, the fuse will blow because
the total resistance of the circuit has dropped. At 1 ohm, the motor has
the least amount of resistance and will consume the most power. The total
resistance of this circuit will be smaller than the smallest resistance
in the circuit, or slightly less than one ohm. Each bulb uses 6A (I 8A
total) plus the 12A for the motor, a total of 30A. The highest amperage
will be before the point that the circuit divides, or where the fuse is
located. If
you have a poor connection or bad wire section, a series-parallel circuit
is formed, creating various electrical problems- - . In Figure 9, think
of bulb I as a bad connection. Because bulb I is in series with bulbs 2,
3 and 4, it will affect how much voltage and amperage is available for
each. Bulbs 2, 3 and 4 will be dim because of the -poor connector. Remember,
as resistance goes up, amperage will come down. If you have a series-parallel
circuit, the rules for each type of circuit apply to that pan of the circuit
only. Now
you know why a poor connection or frayed section of wire can cause a slow
turning starter or dim headlight. The trick is how to find the bad connection
or wire without unraveling the wiring harness on your motorcycle. Stay
tuned, next month it will be "hands-on" time, when we explain voltage drop
testing and how to read a volt-meter in our next electrical story.
3rd
Edition by
Tony Tranter Code B93-ME~C, $23.95 Motorcycle
Electrics Without Pain by
Mike Arman Cod~B93-ELEX, $11.95 Both
publications listed are available from Whitehorse Press. 30JANUARY
2000. MOTORCYCLE CONSUMER NEWS
Whiteliorse
Press
P.O.
Box 60
NottI
Conway, NH 03860-0060
(800)531-1133
www.Whitehorsepress
.com
D Where
E is electromotive force in volts, I is current in amps, and R is resistance
in ohms, then: