1. CHAPTER 5
RESISTORS

4. USES OF RESISTORS
1. LIMIT CURRENT FLOW
2. ACT AS A VOLTAGE DIVIDER

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

6. 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)

7. FIXED RESISTORS HAVE ONLY 1 OHMIC VALUE WHICH CANNOT BE CHANGED
TYPES INCLUDE COMPOSITION CARBON, METAL FILM, CARBON FILM, METAL GLAZE, AND WIRE WOUND

8. RESISTOR POWER RATINGS
IF POWER RATING IS EXCEEDED= LET THE SMOKE OUT IT

9. 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%

10. 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

11. STEPPED WIRE WOUND USED ON BLOWER MOTORS TO CONTROL SPEED

12. 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

14. 1500 ohms with 10% tolerance

16. 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

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

26. 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

27. 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

28. 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

29. 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.

30. THAT’S ALL FOLKS!!!