Electrical/Electronic Systems with solutions
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1. 50 of the cold cranking amperage should be pulled for 15 seconds On a battery with a rating of 700 cold cranking amps how many amps should be drawn from the battery for the test Solution 700 50 700 0 50 350 amps Electrical Electronic Systems Work Example 4 WorkKey Level 3 NATEF Automotive Tasks VLA Look at the voltmeter below The spec sheet says that the voltage drop must be less than 0 3 volt Which of the following readings is are acceptable 400mv 300mv 200mv 100mv None are acceptable electricalsystem solutions doc p 3 Solution Since the voltage drop must be lt 0 3 volts there are two acceptable readings 200mv and 100mv Electrical Electronic Systems Work Example 5 WorkKey Level 3 NATEF Automotive Tasks VIA Which of the following readings is are acceptable if the spec sheet states that the voltage drop must be less than 0 5 volts 0 500v 0 050v 0 005v 5 000mv none Solution Since the voltage drop must be lt 0 5 volts there are three acceptable readings 0 050v 0 005v and 5 000mv Electrical Electronic Systems Work Example 6 WorkKey Level 4 NATEF Automotive Tasks VIA You are checking voltage at a switch There are 12 2 volts at Terminal A and 11 4 volts at Terminal B What is the voltage drop Solution The voltage drop is 12 2 11 4 0 8 volts electricalsystem solutions doc p 4 Electrical Electronic Systems Work Example 7 WorkKey Level 6 NATEF2. Automotive Tasks VI A 12 VI A 14 VI H 7 The customer wants to know if he can attach his power booster to his radio circuit His power booster uses 200 watts can he attach it to the radio circuit Use Ohm s law to show him if he can or cannot do this Use the drawing and chart to show the customer where he can hook up his power booster The battery voltage is 12 6 V x R Ohm s law Component Amp Cig lighter 12v Fuse box Solution First you must decide how many amps the power booster needs 200 12x x 200 12 16 6 The booster alone will need 16 2 3 amps Next we need to determine how many open amps each component has Radio 10 6 4 open Cigarette lighter 20 10 10 open Windows 20 15 5 open Auxiliary 20 open The only place the customer can attach his power booster is to put it in auxiliary Electrical Electronic Systems Work Example 8 WorkKey Level 4 NATEF Automotive Tasks VI A 10 VI A 12 What is the reading on the ohmmeter shown below Where would the needle point if the switch was moved to x1000 electricalsystem solutions doc p 5 Solution By looking at the odometer the reading is approximately 26 Since the switch is pointed to the x100 you must multiply the reading by 100 26 100 2600 ohms If the switch was pointed to x1000 then the reading would be 2600 1000 2 6 ohms Electrical Electronic Systems Work Example 9 WorkKey Level 4 NATEF Automotiv
3. e Tasks VI B 1 You must determine whether a battery should be replaced You take a specific gravity reading of each cell The readings are as follows Cell Reading 1 1 145 2 1 182 3 1 131 4 1 131 5 1 158 6 1 173 Your service manual states that a battery must be replaced if there is a range of 0 050 50 points in the specific gravity readings of the cell a What is the lowest specific gravity reading of the cells b What is the highest specific gravity reading of the cells c What is the range of the specific gravity readings of the cells d Should you replace the battery electricalsystem solutions doc p 6 e Howcan you explain the need for a new battery to a customer Solution a Reading from the chart cells 3 and 4 have the lowest reading of 1 131 b Reading from the chart cell 2 has the highest reading of 1 182 c The range of specific gravity readings is 0 051 highest lowest 1 182 1 131 0 051 d Yes e Answers will vary Electrical Electronic Systems Work Example 10 WorkKey Level 4 NATEF Automotive Tasks VI B 1 Open circuit voltage test sealed batteries Your service manual states that the battery must pass the state of charge or open circuit voltage test before a capacity test which provides a realistic determination for battery replacement If the battery shows less than 12 2 volts it should be recharged before the capacity test If t
4. electricalsystem solutions doc p 1 Name Date Electrical Electronic Systems Work Example 1 WorkKey Level 4 NATEF Automotive Task VI D 1 The specs for this alternator reads puts out 90 of output The alternator reads 112 amps and has a rated output of 135 amps a Is this within specs b What would the acceptable performance limit have to be in order for this to be an acceptable reading c What would the alternator have to produce to be within 90 of the rated output Solution a No b The acceptable performance limit would have to be approximately 82 9 112 amps 135 amps 0 8296296296 c The alternator would have to produce 121 5 amps 135 amps 90 135 amps 0 90 121 5 amps Electrical Electronic Systems Work Example 2 WorkKey Level 3 NATEF Automotive Tasks VI B 1 While testing a battery under no load the battery has 12 1 4 volts What is the approximate state of charge percentage according to the chart below Percentage of charge Open circuit volts OR State of charge 11 7 volts or less 0 12 0 volts 25 12 2 volts 50 12 4 volts 75 12 6 volts or more 100 electricalsystem solutions doc p 2 Solution 12 1 4 12 25 which is approximately 12 2 Reading from the chart the percentage of charge is approximately 50 Electrical Electronic Systems Work Example 3 WorkKey Level 4 NATEF Automotive Tasks VI B 2 During a battery capacity test
5. he state of charge is 75 or more the battery is considered charged Using a digital multimeter DMM set on DC volts you perform an Open circuit voltage test by checking the voltage across the positive and negative battery terminals The results of this test can indicate a battery s state of charge You measure 11 8 volts at 80 F on the open circuit voltage test Open circuit voltage State of charge at 80 F 12 6 or greater 100 12 4 to 12 6 volts 70 100 12 2 to 12 4 volts 50 75 11 7 to 12 0 volts 0 25 11 7 or less 0 a What voltage reading indicates a 100 charge b What does your reading indicate c What reading indicates a 75 charge d Should you recharge or replace the battery e Howcan you explain the need for a new battery to a customer electricalsystem solutions doc p 7 Solution a 12 6 volts or greater Read from the chart b Our reading of 11 8 volts indicates a 0 to 25 charge c 12 4 volts Read from the chart d Recharge the battery first e Answers will vary Electrical Electronic Systems Work Example 11 WorkKey Level 5 NATEF Automotive Tasks When you apply your brake all three brake lights are dim The two brake lights each have a resistance of 2 ohms The center brake light has a resistance of 4 ohms Your meter reads 4 ohms at the base of the parallel circuit Is the reading within the circuit s parameter Solut
6. ion Ry Ry x Ro x R3 Ri R2 R3 Re 2 2 42 2 4 16 8 2 Since R 2 and the meter reads 4 ohms it is not within parameters Ry 2 R xkR 22 4 Ket hy 2 2 4 Rox R EQ Ta EA RO Regt R 1 4 5 Electrical Electronic Systems Work Example 12 WorkKey Level 5 NATEF Automotive Tasks On a parallel circuit R is 2 ohms and Rz is 4 ohms Find the total resistance and total current draw on a 12 V battery electricalsystem solutions doc p 8 Solution Rr total resistance in a parallel circuit R 2 ohms R 4 ohms Rr 2 e 4 2 4 8 6 4 3 1 3 ohms 1 Ry 3 4 3 4 12 1 9 amps Electrical Electronic Systems Work Example 13 WorkKey Level 4 NATEF Automotive Tasks The lights are not working in a car and you are testing several electrical components When you test the wiring for your headlight the amp meter gives a reading of 2 5 amps The headlight has a resistance of 5 Q Is there a problem in the wiring Solution 12 6 v 5 ohms 2 52 amps No Electrical Electronic Systems Work Example 14 WorkKey Level 4 NATEF Automotive Tasks Ohm s law states that E I R where E voltage I amperage and R resistance Find the resistance if the voltage is 12 and the amperage is 2 Solution E I R 12 2 R 12 2 R 6 R The resistance is 6 ohms electricalsystem solutions doc p 9 Electrical Electronic Systems Work Example 15 WorkKey Level 4 NATEF Automotive Task
7. n automotive starter relay switch is 0 4 volt There are 12 7 volts at terminal D What is the voltage at terminal E Solution 12 7 volts 0 4 volt 12 3 volts electricalsystem solutions doc p 11 Electrical Electronic Systems Work Example 19 WorkKey Level 6 NATEF Automotive Tasks A given V8 will have an ideal current draw of 200 amps The specs allow for a tolerance of 10 Starter circuit resistance is 0 03 and battery voltage is 12 6 V Will the circuit fall within specifications Solution Ohm s law Volts Amps x Ohms A car has 12 6 volts and the resistance is 0 03 ohm Amps 12 6 0 03 420 amps Since 220 amps is the maximum range the starter circuit is not within range
8. s The reading on the ohmmeter is 0 342 and the switch is on 2k ohms a What is the reading in ohms b What is the reading in milliohms Solution a 0 342 ohms x 1000 342 Q b 342 ohms x 1000 342 000 mQ or 0 34 KQ Electrical Electronic Systems Work Example 16 WorkKey Level 3 NATEF Automotive Tasks In a series circuit the sum of the resistors equals the total resistance of the circuit In a circuit resistor 1 3 ohms and resistor 2 8 ohms What is the total resistance of the series circuit Solution 3 ohms 8 ohms 11 ohms total resistance Electrical Electronic Systems Work Example 17 WorkKey Level 5 NATEF Automotive Tasks You are helping a buddy install a light bar on his four wheel drive truck which has a 12 volt battery It uses four huge spotlights so he can 4 wheel at night They are hooked up in parallel and use 1 ohm resistance bulbs He is continually blowing 30 amp fuses Does he have a short or is the fuse too small Oh yeah Well prove it electricalsystem solutions doc p 10 circuit R fa resistance tos t 5 t R4 Y aa RRQ O Ohm s law E IxR 1 Calculate total circuit resistance using the attached diagram 2 Use Ohm s law to figure the current 3 Determine the problem Solution 1 R 0 250 2 48A 3 The fuse is too small Electrical Electronic Systems Work Example 18 WorkKey Level 4 NATEF Automotive Tasks VI A 8 The voltage drop in a
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