voltage drop question
12-05-2001, 01:33 AM
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voltage drop question
Hello people
I have a question concerning voltage drops.
If anyone so happens to have the same ref. material then look here(NAPA Trainning manual,Diagnosis 911 page 51).Im having a brain fart bigtime. Here go's.
Starter voltage drop on positve side, connect a digital voltmeter with positive lead to the positve battery terminal, and connect the negative lead to the positve cable at the starter. Why would this show a voltage drop or voltage reading itself? Would it be that the positive bat. connection at the stater is now a negative or more negative point, the starter itself being a resistor in the circuit (obvioulsy.
Also if you please(may be the same answer) page 47 checking engine ground, negative lead of DVOM to negative post of bat and positive lead of DVOM to engine block/chassis ground. how and why would it show a voltage?
People I thank you in advance, and if no one answers well thanks anyway.
I have a question concerning voltage drops.
If anyone so happens to have the same ref. material then look here(NAPA Trainning manual,Diagnosis 911 page 51).Im having a brain fart bigtime. Here go's.
Starter voltage drop on positve side, connect a digital voltmeter with positive lead to the positve battery terminal, and connect the negative lead to the positve cable at the starter. Why would this show a voltage drop or voltage reading itself? Would it be that the positive bat. connection at the stater is now a negative or more negative point, the starter itself being a resistor in the circuit (obvioulsy.
Also if you please(may be the same answer) page 47 checking engine ground, negative lead of DVOM to negative post of bat and positive lead of DVOM to engine block/chassis ground. how and why would it show a voltage?
People I thank you in advance, and if no one answers well thanks anyway.
12-05-2001, 02:18 AM
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Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
I don't have the book, I'll try theory.
Let's see, V=IR (voltage = current times resistance).
Measuring voltage across the starter cable: Would be zero without the starter engaged (no current, resistance could be infinate, voltage would still be zero). So, you turn the key to start, say 20 amps flows through the starter, the DVM reads 2 volts, so the cable has .1 ohms resistance at that amperage.
You're measuring resistance of the cable by measuring the voltage drop across it. You're testing for a bad cable.
Similar story with the ground measurement. If you read a voltage, you've got a poor ground from the engine to chassis.
Make any sense? You have to have a substantial current flowing for this to work.
------------------
82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4, 2300 stall TC. Ported World 305 heads, Crane PowerMax 2050 cam. ZZ3/4 intake, oil pump, pan & baffle. Accel HEI SuperCoil & module. Hooker 2055 headers, 3" Catco cat & 3" catback w/dual-opposite Flowmaster 80. 2.93 limited slip. Spohn SFCs waiting to be installed. AMSOIL syn lubes bumper-to-bumper. Daily year-round driver. Best ET, speed TBD...
57 Bel Air, my 1st car. '66 396, 9.7:1 forged TRWs, Weiand Action+, Holley 750VS w/4150 conversion, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 700 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).
Let's see, V=IR (voltage = current times resistance).
Measuring voltage across the starter cable: Would be zero without the starter engaged (no current, resistance could be infinate, voltage would still be zero). So, you turn the key to start, say 20 amps flows through the starter, the DVM reads 2 volts, so the cable has .1 ohms resistance at that amperage.
You're measuring resistance of the cable by measuring the voltage drop across it. You're testing for a bad cable.
Similar story with the ground measurement. If you read a voltage, you've got a poor ground from the engine to chassis.
Make any sense? You have to have a substantial current flowing for this to work.
------------------
82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4, 2300 stall TC. Ported World 305 heads, Crane PowerMax 2050 cam. ZZ3/4 intake, oil pump, pan & baffle. Accel HEI SuperCoil & module. Hooker 2055 headers, 3" Catco cat & 3" catback w/dual-opposite Flowmaster 80. 2.93 limited slip. Spohn SFCs waiting to be installed. AMSOIL syn lubes bumper-to-bumper. Daily year-round driver. Best ET, speed TBD...
57 Bel Air, my 1st car. '66 396, 9.7:1 forged TRWs, Weiand Action+, Holley 750VS w/4150 conversion, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 700 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).
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