CHAPTER 5CHAPTER 5

RESISTORSRESISTORS

USES OF RESISTORS

1. LIMIT CURRENT FLOW

2. ACT AS A VOLTAGE DIVIDER

I= E/R = 15V / 30 OHMS= .5 AMPS

I= E/R = 15V / .0001 OHMS = 150000 AMPS

I=E/R=17.5/300= .05AMPS

A TO B (E=I x R=.05Ax30 OHMS= 1.5V)

B TO C (E=I x R=.05A x 120 OHMS = 6V)

C TO D (E=I x R= .05 x 200 OHMS = 10 V)

FIXED RESISTORSFIXED RESISTORS

HAVE ONLY 1 OHMIC VALUE HAVE ONLY 1 OHMIC VALUE WHICH CANNOT BE CHANGEDWHICH CANNOT BE CHANGED

TYPES INCLUDE COMPOSITION TYPES INCLUDE COMPOSITION CARBON, METAL FILM, CARBON CARBON, METAL FILM, CARBON FILM, METAL GLAZE, AND WIRE FILM, METAL GLAZE, AND WIRE WOUND WOUND

RESISTOR POWER RATINGS

IF POWER RATING IS EXCEEDED= LET THE SMOKE OUT IT

MOST COMMON TYPE: MADE OF CARBON GRAPHITE AND A RESIN BONDING MATERIAL

INEXPENSIVE: HAVE RANGE OF 1 TO 22 MEGOHMS POWER RATINGS OF 1/8,1/4,1/2,1,AND 2 WATT

TOLERANCE RANGES OF 20%, 10%, 5%

WIRE WOUND RESISTORS

*MADE BY WINDING A PIECE OF

RESISTIVE WIRE AROUND A CERAMIC CORE

*USED WHEN A HIGH POWER

RATING IS NEEDED

*ALLOWS AIR TO COOL BY FLOWING THROUGH IT

*SHOULD BE MOUNTED VERTICALLY: CHIMNEY EFFECT

STEPPED WIRE WOUND USED ON BLOWER MOTORS TO CONTROL SPEED

1st Band: 1st Number

2nd Band: 2nd Number

3rd Band: Multiplier

4th Band: Tolerance

If it has 5th Band: 1% Tolerance

If a resistor is replaced, use same tolerance& equal value

1500 ohms with 10% tolerance

VARIABLE RESISTORSVARIABLE RESISTORS

A RESISTOR WHOSE VALUE CAN A RESISTOR WHOSE VALUE CAN CHANGED OR VARIED OVER A CHANGED OR VARIED OVER A RANGERANGE

AVAILABLE IN DIFFERENT CASE AVAILABLE IN DIFFERENT CASE STYLES AND POWER RATINGSSTYLES AND POWER RATINGS

TYPES INCLUDE RHEOSTATS, TYPES INCLUDE RHEOSTATS, POTENTIOMETERS, THERMISTORS, POTENTIOMETERS, THERMISTORS, PHOTO-RESISTORSPHOTO-RESISTORS

RHEOSTATSRHEOSTATS

TWO WIRE VARIABLE RESISTORTWO WIRE VARIABLE RESISTOR HAS MOVEABLE LEVER THAT HAS MOVEABLE LEVER THAT

VARIES RESISTANCEVARIES RESISTANCE EXAMPLES: DASH LIGHTS DIMMER, EXAMPLES: DASH LIGHTS DIMMER,

FUEL SENDING UNITS, WIPER FUEL SENDING UNITS, WIPER DELAY SWITCHES DELAY SWITCHES

POTENTIOMETERSPOTENTIOMETERS

THREE WIRE VARIABLE RESISTORTHREE WIRE VARIABLE RESISTOR USED AS A POSITION INDICATOR USED AS A POSITION INDICATOR

(INPUT TO A LOGIC DEVICE)(INPUT TO A LOGIC DEVICE) EXAMPLES: THROTTLE POSITION EXAMPLES: THROTTLE POSITION

SENSOR (TPS), EGR POSITION SENSOR (TPS), EGR POSITION SENSOR, HVAC DOOR POSITION SENSOR, HVAC DOOR POSITION SENSORSENSOR

THERMISTORSTHERMISTORS

TWO WIRE SENSORSTWO WIRE SENSORS RESISTANCE VARIES WITH TEMPRESISTANCE VARIES WITH TEMP CAN BE “PTC” OR “NTC”CAN BE “PTC” OR “NTC” USED AS INPUT TO A LOGIC DEVICEUSED AS INPUT TO A LOGIC DEVICE EXAMPLES: COOLANT TEMP EXAMPLES: COOLANT TEMP

SENSOR, INTAKE AIR TEMP SENSOR, SENSOR, INTAKE AIR TEMP SENSOR, BATTERY TEMP SENSOR, IN CAR BATTERY TEMP SENSOR, IN CAR TEMP SENSORTEMP SENSOR

PHOTO RESISTORSPHOTO RESISTORS

TWO WIRE VARIABLE RESISTORSTWO WIRE VARIABLE RESISTORS RESISTANCE CHANGES WITH RESISTANCE CHANGES WITH

DIFFERENT LEVELS OF LIGHT DIFFERENT LEVELS OF LIGHT INPUTINPUT

EXAMPLES: AUTOMATIC EXAMPLES: AUTOMATIC HEADLIGHTS, SUNLOAD SENSORS HEADLIGHTS, SUNLOAD SENSORS ON HVAC SYSTEMS, ASSEMLY LINE ON HVAC SYSTEMS, ASSEMLY LINE SWITCH INPUTSWITCH INPUT

REVIEWREVIEW 1. NAME TWO 1. NAME TWO

FUNCTION OF FUNCTION OF RESISTORS?RESISTORS?

2. WHAT IS FIXED 2. WHAT IS FIXED RESISTOR?RESISTOR?

3. NAME THREE 3. NAME THREE TYPES OF FIXED TYPES OF FIXED RESISTORS?RESISTORS?

4. WHAT EFFECTS 4. WHAT EFFECTS POWER RATING?POWER RATING?

5. 5. NAME AN NAME AN ADVANTAGE OF ADVANTAGE OF WIRE WOUND WIRE WOUND RESISTOR.RESISTOR.

6. WHAT ARE THE 6. WHAT ARE THE COLORS FOR?COLORS FOR?

7. WHAT IS A 7. WHAT IS A VARIABLE VARIABLE RESISTOR?RESISTOR?

8. NAME THREE 8. NAME THREE TYPES OF VAR. TYPES OF VAR. RESISTORSRESISTORS..

THAT’S ALL FOLKS!!!THAT’S ALL FOLKS!!!