CHAPTER 5 RESISTORS

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 RESISTORS HAVE ONLY 1 OHMIC VALUE WHICH CANNOT BE CHANGED TYPES INCLUDE COMPOSITION CARBON, METAL FILM, CARBON FILM, METAL GLAZE, AND WIRE 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 RESISTORS A RESISTOR WHOSE VALUE CAN CHANGED OR VARIED OVER A RANGE AVAILABLE IN DIFFERENT CASE STYLES AND POWER RATINGS TYPES INCLUDE RHEOSTATS, POTENTIOMETERS, THERMISTORS, PHOTO-RESISTORS

RHEOSTATS TWO WIRE VARIABLE RESISTOR HAS MOVEABLE LEVER THAT VARIES RESISTANCE EXAMPLES: DASH LIGHTS DIMMER, FUEL SENDING UNITS, WIPER DELAY SWITCHES

POTENTIOMETERS THREE WIRE VARIABLE RESISTOR USED AS A POSITION INDICATOR (INPUT TO A LOGIC DEVICE) EXAMPLES: THROTTLE POSITION SENSOR (TPS), EGR POSITION SENSOR, HVAC DOOR POSITION SENSOR

THERMISTORS TWO WIRE SENSORS RESISTANCE VARIES WITH TEMP CAN BE “PTC” OR “NTC” USED AS INPUT TO A LOGIC DEVICE EXAMPLES: COOLANT TEMP SENSOR, INTAKE AIR TEMP SENSOR, BATTERY TEMP SENSOR, IN CAR TEMP SENSOR

PHOTO RESISTORS TWO WIRE VARIABLE RESISTORS RESISTANCE CHANGES WITH DIFFERENT LEVELS OF LIGHT INPUT EXAMPLES: AUTOMATIC HEADLIGHTS, SUNLOAD SENSORS ON HVAC SYSTEMS, ASSEMLY LINE SWITCH INPUT

REVIEW 1. NAME TWO FUNCTION OF RESISTORS? 2. WHAT IS FIXED RESISTOR? 3. NAME THREE TYPES OF FIXED RESISTORS? 4. WHAT EFFECTS POWER RATING? 5. NAME AN ADVANTAGE OF WIRE WOUND RESISTOR. 6. WHAT ARE THE COLORS FOR? 7. WHAT IS A VARIABLE RESISTOR? 8. NAME THREE TYPES OF VAR. RESISTORS.

THAT’S ALL FOLKS!!!