Color Figures Multiplier Tolerance Failure Rate*
Black 0 1 ±20 _
Brown 1 10 ±1 1.0
Red 2 100 ±2 0.1
Orange 3 1,000 ±3 0.01
Yellow 4 10,000 ±4 0.001
Green 5 100,000 _ _
Blue 6 1,000,000 _ _
Violet 7 10,000,000 _ _
Gray 8 100,000,000 _ _
White 9 _ Solderable*
Gold _ 0.1 ±5 _
Silver _ 0.01 ±10 _
No Color _ ±20 _
■ Figure 15. Color Band System (Two Significant Figures).
POTENTIOMETERS
A potentiometer is an adjustable or variable resistor.
■ It has connection points at each end of the resistive material and has a movable center contact known as a “wiper” that can be manually positioned anywhere along the body of the resistive material between the two contacts.
A potentiometer is sometimes called a “pot” for short.
Potentiometers have broad applications in this field:
■ In audio: to control volume, tone, and balance levels.
■ In security: to control sensor sensitivity.
As the wiper is adjusted, the ratio of resistance between the center contact and each end contact is changed.
■ An audio signal applied to one end point and measured at the wiper will change in level as the wiper is repositioned.
■ This is how volume and tone controls accomplish their missions, and why they are sometimes called variable voltage dividers.
■ Troubleshooting Potentiometers - Troubleshooting or checking a potentiome-ter to see if it is good takes a few steps. Because a potentiomepotentiome-ter has a mechan-ical feature we can not rule out its failure and must check its operation.
■ Since a potentiometer has three leads, and two leads are tied to the full resistance, it can troubleshoot just like a typical resistor. The third lead is tied to the wiper arm and traverses the length of the resistor element. The wiper arm can be bent or broken and cause the resistance between it and either other lead to be intermittent, infinite, or stationary when you try to adjust the potentiometer.
✍
A potentiometer is an adjustable or variable resistor.■ Figure 16. Common Potentiometers.
INDUCTORS
An inductor is an example of an electronic component that possesses the proper-ty of inductance.
■ Inductance is the property that a component possesses that opposes any change in current flow.
■ While resistance limits the flow of current in a circuit (regardless of the frequency), inductance opposes any change in the current.
Think of an inductor as being like a flywheel. The flywheel has inertia, and once it’s spinning at a certain RPM, it will resist any changes in RPM and continue to spin at a fixed rate.
Coils have this property of inductance. Therefore, inductors are coils of wire that resist changes in the flow of current through them.
■ High frequency signals represent rapidly changing currents.
Therefore, inductors can be used to limit the strength of higher fre-quency signals, while still allowing lower frequencies to pass.
An inductor wired in series with a subwoofer allows the low frequency audio signal to power the speaker but blocks the higher frequency signals, creating a low-pass passive crossover.
■ In this case, AC is the audio output from an amplifier.
■ Different values of inductors establish different crossover frequency values.
■ Inductor values are measured in Henries.
■ 1,000 Millihenries = 1 Henry.
■ Millihenries are written simply as “mH”.
Margin Notes
✍
Inductance is the property that a component possesses that opposes any change in current flow.✍
Inductor values are expressed in Henries.■ Figure 19. Inductors (coils).
■ Figure 17. Inductor Symbols.
Top: Air-core.
Middle: Ferrite-core.
■ Figure 18. Ferrite-core Inductor Construction.
Applying the series connection formulas we discussed in Section 1, when induc-tors are connected in series, the total inductance is the sum of the inductance of each component:
Lt = L1 + L2 + L3... + Ln
When inductors are connected in parallel, the formula looks like this:
Lt = L1 x L2 L1 + L2
CAPACITORS
A capacitor is an electronic component that possesses the property of capacitance.
■ Capacitance is the property of an electronic component that opposes change in voltage across the component.
■ Capacitors are constructed by separating two or more conductors - called plates - with an insulator, called a dielectric.
■ A typical construction is two long strips of aluminum foil with plastic sheeting between the foil sheets, which is wound up to minimize its size.
■ If an AC signal is applied to its plates, the current will flow through the capacitor. What actually happens is that if an AC signal is applied to the plates, the capacitor will charge one way (hence current flows), then when the AC signal reverses direction the capacitor discharges and then charges in that direction (again current flows), this action makes it appear that AC current is flowing through the capacitor.
■ A DC voltage connected to the plates will not pass through the dielectric, and no direct current will flow. This will appear to look like an open circuit.
In the mobile electronics environment, capacitors have many uses:
■ They allow passage of high frequency energy (tweeter capacitors).
■ They store an electrical charge for use later.
■ They block the passage of DC (accessory noise suppression).
■ They attenuate low frequency energy (midrange capacitors).
There are many types of capacitors. The three most popular are:
1 Polypropylene.
2 Mylar.
3 Electrolytic.
Margin Notes
✍
There are many types of capacitors. The three most popular are polypropylene, Mylar, and electrolytic.✍
Capacitance is the property of an electronic component that opposes a change in voltage across the component.Polypropylene and Mylar are known for their excellent sound quality and are used for the higher crossover frequencies.
■ Most installers agree that the difference in sound quality between polypropylene, Mylar, and electrolytic is minor in the lower frequencies.
A capacitor wired in series with a tweeter and connected to an amplifier will allow the amplifier’s high frequency signal to power the tweeter, while limiting the lower frequency signals, thus creating a high-pass passive crossover.
Capacitor values are expressed in Farads.
Capacitance for mobile electronics applications is usually measured in Microfarads (µF). 1 million Microfarads (µF) = 1 Farad.
Margin Notes
✍
Capacitance for mobile electronics applications is usually measured in Microfarads (µF).■ Figure 20
■ Figure 21.
■ Figure 22
■ Figure 23
■ Figure 24
■ Figure 25
■ Figure 26
Regardless of type, all capacitors have a tolerance rating, which is stated as a plus or minus percentage.
■ The smaller the percentage, the more accurate the crossover frequency.
Capacitors are also rated by voltage (maximum voltage applied).
■ This rating is very important to observe when constructing passive crossovers, since the amplifier output (AC voltage) may be far higher 12 volts. Many capacitors used in passive crossover networks use 50v and 100v ratings.
■ Other capacitors used for power applications might use 16v, 18v, 20v, or 24v ratings such as the input storage and filter capacitors in amplifier power supplies and “stiffening capacitors” for example.
Some capacitors are “polar” electrolytic capacitors that have a negative and a pos-itive terminal and must be installed in the proper electrical orientation.
■ These types of capacitors are not used in crossover work, but are used in power supply circuits (such as a “stiffening capacitor”) or in noise suppres-sion and filtering circuits on an automotive distributor, coil, or alternator.
Remember! For series and parallel combinations, the formula used to find total capacitance is the opposite to that of a resistor or inductor.
In series, the formula looks like this:
When capacitors are connected in parallel, the total capacitance (Ct) is the sum of each component:
Ct = C1 + C2 + C3... + Cn
Margin Notes
CTOTAL
CTOTAL =
C1 C2 C3 Cn
1 C1
1 C2
1 C3
1 Cn
1
+ +
………
■ Figure 27. Capacitor Formula.
FUSES AND CIRCUIT BREAKERS
If installed properly, a fuse can save you a lot of time and headaches. Think of a fuse as cheap insurance.
■ A fuse is simply a device that contains a wire or strip of metal which is installed in series with a power line.
■ This strip of metal is designed to melt if it receives an excessive amount of current.
Fuses are used as a safeguard against circuit or system damage. For example, if you have a customer who is a bit aggressive with the volume control of his stereo system, you can protect his tweeters from “blowing” by installing a fuse in series -with the tweeter.
To determine the proper amperage of the fuse, you’ll need to know the ohm load of the tweeter as well as its continuous or nominal power rating.
■ The formula to find the amperage of the proper fuse is equal to the square root of the continuous power handling, divided by the ohm load of the tweeter.
Amperage = Square root of Continuous Power/Ohm load.
Sometimes you’ll run across a situation where the recommended fuse value is higher than the largest available fuse.
■ You could install fuses in a parallel combination, but that can get bulky.
■ A circuit breaker works better in these situations, because like fuses, they are designed to blow (or open) when the current becomes excessive.
■ A circuit breaker is different from a fuse in that it usually can be reset. Circuit breakers that can be reset come as 2 types - Manual Resetting or Auto Resetting.
A circuit breaker is a device placed in series with a power line which, when an excess amount of current is sensed, will open the power connection, thus pro-tecting a circuit or system.
For protection at the battery, use either a fuse or a circuit breaker. The idea behind these devices is simply to open the circuit before any wires burn.
Margin Notes
✍
A fuse is simply a device that contains a wire or strip of metal which is installed in series with a power line.✍
A circuit breaker is a device placed in series with a power line which, when an excess amount of current is sensed, will open the power connection, thus protecting a circuit or system.Section 3
Basic Electrical Troubleshooting
Now that you’re familiar with many of the electrical components used in mobile installations, it’s time to discuss common problems that occur when some of these components fail or are improperly installed.
VOLTAGE DROPS
In Section 1, you learned about resistance and how it opposes the flow of current.
■ When a device in a circuit has resistance, it will convert an amount of energy into heat, which results in a certain amount of power loss.
■ This loss is commonly referred to as a voltage drop.
■ A bad connection or any point of resistance in the power circuit will cause a voltage drop.
A drop in voltage can manifest itself in a variety of ways:
■ Voltage drops result in poor performance, which a customer could attribute to a particular product.
■ Often, it has nothing to do with the product, but with the misappli-cation during an installation.
Here’s an example of the multiple possibilities for voltage drops to occur:
■ When a power window is activated, a circuit is completed.
■ This circuit starts from the positive “+” battery terminal and runs through the key switch accessory terminal, the fuse block, and then through the pressed window switch and one window motor lead.
■ It then runs out the other motor lead, through the un-pressed win-dow switch, through the chassis ground and the metal of the vehicle, and finally, through the battery ground strap to the negative terminal of the battery.
In an ideal world, the load on the battery would be determined by the motor’s elec-trical characteristics.
In the real world, the motor determines most of the load unless there is a circuit problem.
■ If a switch contact wears, or a connector corrodes, the motor may not receive the power it requires.
■ The circuit problem prevents full power from reaching the motor;
some of the voltage that would normally go to the motor is lost across a weak circuit connection or contact.
Margin Notes
✍
A bad connection or any point of resistance in the power circuit will cause a voltage drop.■ A loss can also occur if you install a window roll-up system and make wiring connections with smaller gauge wire than that of the stock wiring (See the figure below).
Margin Notes
TO OTHER WINDOW
M
VEHICLE CHASSIS BATTERY
motor
motor
IGNITION KEY
■ Figure 28.
■ Figure 29. ■ Figure 30. ■ Figure 31.
■ Figures 28 - 31 Power Window Circuits.
VOLTAGE DROPS - SERIES CIRCUITS
In our discussion on series circuits, we mentioned that resistance in a series cir-cuit is additive.
Adding up the resistances will give you the total resistance of the circuit.
If the current flowing in a series circuit needs to be known (amperage), go back to Ohm’s Law, I = E/R.
■ Current remains the same anywhere it’s measured in a series circuit.
■ Add the total series resistances together and divide by the voltage.
■ To find the voltage, or voltage drop, across each resistance in the cir-cuit, use another Ohm’s Law, E = I x R.
■ Multiply the total circuit amperage times each individual device’s resistance to obtain the voltage drop across that device.
Voltage in a series circuit is distributed among the devices in that circuit, accord-ing to their resistance. The sum of the individual voltage drops in a series circuit must be equal to the applied voltage.
For example, in the following diagram, with an input voltage of 6 Volts, the volt-age drop across each of the lamps is 2 Volts.
In a parallel circuit, as the next diagram illustrates, the voltmeter reading has absolutely nothing to do with the value of the resistor, as the probes of the meter are theoretically connected directly across the power supply.
Margin Notes
✍
Adding up the resistances will give you the total resis-tance of the circuit.✍
The sum of the individual voltage drops in a series circuit must be equal to the applied voltage.■ Figure 32. Electrical Diagram.
R1
■ Figure 33. Electrical Diagram.
GROUND LOOPS
A ground loop is probably the greatest cause of noise problems in car audio.
■ A ground loop is more than one ground path where the differences in cur-rent potential of each path create a voltage diffecur-rential.
■ This can allow alternator whine to enter the system, as well as other problems.
A ground loop is created by any non-zero resistances between the wiring paths used to ground or interconnect each piece of equipment. Even the frame of the vehicle itself, which is the battery ground of the car, can have varying voltage dif-ferentials caused by current flowing through different circuit paths in the frame.
In today’s high powered audio systems, the supply current can easily be over 50 amps. Even a .01 Ohm resistance caused by a faulty crimp connection or corrosion can develop up to a .5 volt drop, which could create a source for system noise.
The alternator produces pulsating DC voltage, and the battery filters out most -but not all - of the ripple. Ripple is the residual AC left on the line after it has been rectified into DC. The ripple is generally variable in frequency and determined by engine speed (alternator spin).
■ Some ripple current will always be present on the supply line and the chassis ground of the vehicle if the engine is running. The bigger the alter-nator output capability, generally the more ripple it will produce.
■ This can create noise in an audio system.
■ That’s why it’s extremely important to measure your ground points back to battery ground and with each other.
Margin Notes
✍
A ground loop is more than one ground path where the differences in current potential of each path create a voltage differential.✍
A ground loop is created by any non-zero resistances between the wiring paths used to ground or intercon-nect each piece of equipment.Amplifier
-■ Figure 34. Typical ground loops.
■ Most good audio products have sufficient filtering on their +12 Volt lines, but not on the ground side.
■ Multiple ground points to the frame can allow small voltage drops to be created. Even the smallest voltage drop can carry alternator noise on it because the frequency of the AC output of an alternator is with-in the audible range of your sound system.
Single point - or single area - grounding is always preferable whenever possible.
■ Though it may not be practical to have a single ground point - unless the radio, equalizer, and amplifier are in close proximity to each other - you want to avoid long high current ground wire runs.
■ This can result in enough resistance to cause a ground loop.
■ A good ground point for the current drawing equipment - radio, equaliz-er, crossovequaliz-er, etc. - is at the firewall, and one good ground point for the high current drawing amplifiers at the trunk will work. Make sure you have ref-erenced the two ground points back to the battery and to each other, and have no significant voltage drops (two-tenths of a volt or less).
Audio system wiring normally has higher resistance than the power system wiring.
■ The higher the resistance, the easier it is for the noise to enter.
■ Low quality, poorly shielded interconnect cables can easily allow noise to enter the system.
■ This is also why high voltage, low source impedance headunits units work well for noise rejection in addition to the other signal transmis-sion advantages.
Margin Notes
Volts
Time 12
0
Volts
Time 12
0 Volts
Time 12
0
■ Figure 35. Ripple on +12VDC.
SHORT CIRCUIT
Since Kirchoff’s Voltage Law states that the voltages dropped in a series circuit must add up to the supply voltage, if a piece of equipment is short circuited, or the wiring becomes shorted out, the voltage dropped across it is reduced to 0 Volts.
■ Since the total of all voltage drops in a circuit must equal the supply volt-age, more voltage must be dropped across the circuit’s wiring and connections.
■ The current in the circuit is equal to the supply voltage divided by the total resistance.
■ As the resistance approaches 0 Ohms, the current in the circuit increases dramatically and often dangerously.
■ In automotive circuits, currents can easily be in excess of 200-300 Amps, resulting in melted wiring looms and electrical fires.
Educated installers wire fuses at the battery to protect their cir-cuits from the expensive, catastrophic failures short circir-cuits can produce.
■ A short circuit will bypass any resistance (speaker, lamp) in a circuit and cause it not to operate.
The following diagram shows a short circuit in operation. The voltage needed to turn on the light bypasses it:
Equate this with a power wire coming from a battery to trunk-mounted amplifiers and the wire has no fusing at the battery.
■ The fuse at the battery is NOT to protect the amplifier, but to protect the wire.
■ This power wire could either be punctured by a screw when the sill molding is put back on the vehicle, or pinched under the back seat.
Margin Notes
✍
The current in the circuit is equal to the supply voltage divided by the totalresistance.
SHORT CIRCUIT = 0Ω
LAMP
= 8 R
Ω
■ Figure 36. Short Circuit Diagram.
✍
The fuse at the battery is NOT to protect the amplifier, but to protect the wire.Using what you have learned so far, you can see that the equipment connected to the wiring will be bypassed and will not operate.
■ To avoid a short circuit and severe damage to the car, ALWAYS FUSE A POWER CABLE AT THE BATTERY AS CLOSE TO THE BATTERY AS POSSIBLE, BUT AT A MINIUM OF 10 INCHES FROM THE BATTERY TERMINAL.
■ IASCA rules require no more than 18 inches from the battery, but for the purpose of this study we will use the MECP standard.
The same thing can happen to speaker leads.
■ When one is shorted to ground, the amplifiers may not work, or may give the appearance of motorboating at about half volume.
■ Most modern amplifiers have “short stopping” ability, and the amp can protect itself.
OPEN/CLOSED CIRCUITS
OPEN/CLOSED CIRCUITS