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Technician’s Version
“How To Test”
The Vehicle
Base System
of
Shared Current Paths
for
Voltage Drop
Demo
Left click the mouse to advance.
The full version of this CD contains the following:
63 slides on "Understanding Voltage Drop and Shared Current Paths“
How Connections Affect Voltage Drop. 3 page word doc.
27 slides on "Meters", Set Up and Probe Placement When Testing for Voltage
and Voltage Drop.
General Rules for Allowable Voltage Drop in Vehicle Circuits. 5 page
word doc.
53 slides on "How to Do Voltage Drop Testing".
52 slides on "How to Test Vehicle Shared Current Paths for Voltage Drop"
All slide programs are in Power Point Show.
You must have power point to view them.
This demo reviews:
"How to Test Vehicle Shared Current Paths for Voltage Drop"
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About the material on this CD
The power point and word documents contained on this CD are
provided without expressed or implied warranty. The entire risk as to the
quality and use of this information is totally the responsibility of the end
user. Should any information contained in this CD prove to be defective,
the end user assumes the entire cost of any and all incidental and
consequential damages.
Vested LLC does not warrant that the test setup and techniques
shown will meet the end uses requirements. Vested LLC does not
warrant that the test procedures are error free. All tests presented have
been performed by a Vested LLC representative with vehicle responding
results.
Vested LLC, its officers, agents, or representatives will in no way be
liable for any damages, including loss of profits, loss of savings, or other
consequential or incidental damages arising out of the use of the test
procedures contained in this CD.
The tests procedures presented on the CD have been performed
with the results shown. Vested LLC does not intend or imply that the
test procedures replace vehicle manufacturer's authorized or
recommended test procedures. Always check the information given
against that recommended by the manufacturer of the vehicle you are
working on. Use Left Mouse Button to Advance
How to use this
Vehicle Testing Guide
1. When you see “notes” at the bottom right of a slide, right click your
mouse then left click on “speaker notes” for additional information.
Try this now. Right click on the mouse.
Now left click on “speaker notes”.
2. Never use the “Enter” key on your computer. If you inadvertently hit the
enter key or left mouse button, just right click the mouse button, and
left click on “previous” to take you back.
3. Only use the left mouse button to push only the “action buttons”.
4. Use the “back” button to return to an index.
5. To begin viewing the testing guide, push this action button
How To Test the Vehicle Base System of Shared Current Paths
X Always Begin at the Battery.
X Starter Motor Voltage Feed Side Tests.
X Starter Motor Ground Side Tests.
X Battery Positive (+) Cable Pigtail Wire Tests.
X Battery Negative (-) Cable Pigtail Wire Tests.
X Ground Straps Not Attached to Negative Battery cable - Tests.
X Generator Voltage Feed Wire Tests
X Generator Ground Tests.
X Other Generator Tests.
Battery Tests
How? X First, Do an open circuit voltage (OCV) test.
How?
If OCV is too low, Charge the battery.
How?
Do a load test with a VAT 40 or 45 if needed.
or if you don’t have a load tester:
How?
Do a load test without a load tester if needed.
How?
Do a 3 - minute charge test if you suspect the
battery is sulfated.
How?
Do a parasitic drain test if needed.
With all necessary battery tests finished, go to:
X Tests for Voltage Drop in the Starter Motor
Voltage Feed Side. ©
Back to
Index
How to Test the Open Circuit Voltage of the Battery
1. Key is OFF.
2. Meter set to read volts DC.
3. Positive (+) probe to battery (+)
4. Negative (-) probe to battery (-)
Battery voltage with the engine OFF is called
“open circuit” voltage. There is no significant
load (only parasitic) on the battery. This test
is a sign of the battery’s “health”. The chart
to the right shows what “state of charge” a
battery is in based on the open circuit voltage
tested. The minimum voltage you should
accept as a base line for doing further testing
is 12.5V. This value tells you that the battery
is over 75% charged. If you find less than
12.5V, even 12.49V, trickle charge the battery
overnight, if possible. If you don’t have time,
fast charge for at least 4 hours at 5 to 10
amps. Only after being assured that the
battery open circuit voltage is 12.5 or above
can you test with accuracy to see if the
battery is good or bad.
Notes
© Back
Open Circuit
Voltage Test
tells Battery
state of charge
12.6V = 100%
12.5V = 75%
12.3V = 50%
12.1V = 25%
How to Test for Voltage Drop in the Starter Motor
Voltage Feed Side Current Path
How? X Do the “all-inclusive” voltage drop test.
or,
How? Test the cranking voltage , the “available voltage” to
the starter motor.
If excessive:
How? Test solenoid contacts if needed.
How?
Test connectors and connections if needed.
How?
Don’t overlook excessive amperage draw as the
cause of higher than normal voltage drops in the
starter motor circuit.
When all necessary starter motor voltage feed side
tests are complete, go to:
X How to Test the Starter Motor Ground.©
Back to
Index
How to Test for the Actual Voltage Drop Between
the Battery (+) Terminal and the Starter Motor Armature Lead
(-) Meter Probe
negative (-)
probe to starter
motor armature
lead.
Voltmeter positive (+) probe to clean
post top or side mount positive (+)
nut – NOT on cable or clamp.
Voltmeter negative (-) probe to the
starter motor armature lead – NOT
on nut, washer, or solenoid stud.
The voltmeter is set up to read volts DC.
This voltmeter lead setup tells you exactly how much voltage is dropping
between the battery positive (+) terminal and the starter motor armature while
CRANKING. This “all-inclusive” test checks the following for voltage drop:
connection between the positive (+) battery terminal and the clamp,
connection between the copper in the cable and the clamp, any connections
in the current path to the starter armature; this could include
a solenoid. Maximum allowable is 2 1/2 Volts.
©
Back
(Notes)
How to Test for Voltage Drop in the Starter Motor Ground Side Current Path
How? X Do the “all-inclusive” voltage drop test.
If excessive:
How?
Test between the starter motor housing and the
block if needed.
How?
Test between the battery negative terminal and
the frame or block where the negative cable is
attached if needed.
How?
Test between the negative cable and the battery
post if needed.
How?
Test between the negative cable and its
connector if needed.
Once all starter ground testing is complete, go to:
How to Test for Voltage Drop in a
X
Battery Positive Cable Pigtail Wire. ©
Back to
Index
How To Test the Voltage Drop Between:
Battery Negative (-) Terminal and the Starter Motor Housing
An “All-inclusive” Test of the Starter Motor’s Ground
Set Voltmeter to
read millivolts or
on the lowest volt
setting.
.800V Max
800mV Max
Engine must be
CRANKING
while meter is read.
Disable engine from
starting – this is a
test of the starter
ground while
cranking.
Voltmeter (-) probe or clip to a clean
post or side mount bolt,
NOT on cable or clamp
(Notes)
Back
Voltmeter (+) probe to
a clean spot on the
starter housing,
NOT on block, exhaust
manifold, etc. ©
How To Test the Voltage Drop In A Battery Positive (+) Cable Pigtail Wire
Attached To a BEC (Bussed Electrical Connector), or a Fuse Block
How? X Do the "all-inclusive" voltage drop test.
Test between the battery + and the fuses.
How?
Test connectors and connections if needed.
When all positive pigtail testing is complete, go to:
X How to Test for Voltage Drop in a
Battery Negative Pigtail Wire.
©
Back to
Index
How To Test the Voltage Drop Between
Battery Positive (+) Terminal and Fuses
DVOM + Clipped to
Battery Positive +
DVOM (-) on top
of any active fuse
DVOM (-) on top of any
different active fuse
Meter set to millivolts
Engine Running
In Park
At Idle
This Result
This Result
143mV
138mV
300mV Maximum
This all-inclusive test checks for any serious voltage drops between the battery
positive terminal and the connections to fuses in the fuse box or BEC – bussed
electrical connector. Select two or more fuses that are active with engine
running. You should see close similarity between the voltage drops of all fuses
active. The more current the fuse tested sees, the higher the voltage drop. If
your meter shows charging voltage, that fuse is connected to ground, and is
not active until whatever it protects is activated. Consult the fuse box or BEC
cover for fuse description.
Back to Testing
©
(Notes)
Battery + Pigtail
How to Test for Voltage Drop in a
Battery Negative (-) Cable Pigtail Wire.
How? X Do the "all-inclusive" voltage drop test.
How?
If excessive:
Test of connectors and connections if needed.
With all voltage drop testing complete on the Battery
Negative (-) Pigtail wire go to:
X How to Test for Voltage Drop in Ground Straps
that are Not Directly Attached to the Battery
Negative Cable.
Back to
Index ©
How to Test the Voltage Drop Between the Battery Negative (-) Terminal
and a Battery Negative (-) Pigtail Attached to Sheet or Frame Metal
Set Voltmeter to
read millivolts or
on the lowest volt
setting.
Voltmeter (-) probe
on clean battery (-)
post or side mount,
NOT on cable clamp
100mV Maximum
.100V Maximum
Battery negative
pigtail ground wire
(Notes)
Engine OFF
turn on all
accessories.
Maximum
allowable
voltage drop
100mV
.100V
Voltmeter (+) on
clean sheet metal
NEAR pigtail
connection,
NOT on bolt
or pigtail eyelet
Back
Follow same procedure if the negative pigtail is attached to frame metal ©
How to Test the Voltage Drop in Ground Straps that are Not
Directly Attached to the Battery Negative Cable.
How? X Do an "all-inclusive" voltage drop test between the bulkhead
How?
ground strap and the battery negative terminal.
If excessive:
Test between the bulkhead and the block if needed.
How?
Test between battery negative terminal and where the negative
cable is attached to the frame or block if needed.
How?
Test between the battery negative cable and terminal if needed.
How?
Test between the cable and the cable eyelet material.
How?
Test between sheet metal cab to bed if needed.
With all grounds checked, go to:
X How to test the generator voltage feed side.
Back to
Index
How to Test the Voltage Drop Between the Battery Negative Terminal and
the Bulkhead (firewall) Ground Strap
Voltmeter negative (-) probe on a
clean spot on the post top or side
mount nut, NOT on cable or clamp
Voltmeter positive (+) probe on a clean
spot NEAR the bulkhead ground strap
attaching point, NOT on cable, eyelet, or
nut.
Voltmeter set to read millivolts or on the lowest volt setting.
Engine OFF, all accessories on.
.300V Maximum
300mV Maximum
©
(Notes)
Back
How to Test the Voltage Drop Between the Generator
Output and the Battery Positive (+) Terminal
How? X Do the "all-inclusive" voltage drop test.
If excessive:
How?
Test connectors and connections if needed.
When the voltage feed side of the generator testing is
complete, go to:
X How To Test For Voltage Drop In The Generator
Ground.
Back to
Index ©
How to Test the Voltage Drop Between:
the Generator Output and the Battery Positive (+) Terminal
Set voltmeter to read
mV DC
Run engine at
1800 RPM
for 30 seconds,
now, read meter.
Voltmeter (-) to
Battery (+) Side
Mount Nut or
Top of Post, NOT
on cable or clamp.
Voltmeter (+) probe to generator side of
B+ wire connection, NOT on outside
nut, cable connector, or stud.
200mV (.200V)
Maximum
This in an “all-inclusive” test.
This test checks for voltage drop between the following conductors and
connections: the connection between the B+ terminal of the generator and
the wire eyelet, the connection between the wire itself and the eyelet metal, the
connection or connections that may exist anywhere between the B+ terminal
of the generator and the battery positive (+) terminal.
©
(Notes)
Back
How To Test the Voltage Drop of Connectors
and Connections Of Battery Positive Pigtail Wires.
Voltmeter set to millivolts
Meter Positive Probe to
Generator Side of B+ Stud
Connection.
Engine running, all accessories on.
Should be zero voltage drop. Less than
50mV would be of no concern.
Voltmeter negative probe on
a T-pin in correct pigtail wire
that goes to battery positive.
It is one of these three on this
vehicle. Check wiring diagram.
T-pin here, or closer to
generator if available.
(Notes)
Back
How To Test the Voltage Drop In The Generator Ground
How? X Do the “all-inclusive” voltage drop test.
If excessive:
Test between the generator housing and the
How?
block if needed.
How?
Test between the block and the battery negative
terminal if needed.
How?
Test between the negative cable and its
connector if needed.
Test between the negative cable clamp and the
battery terminal if needed.
When the generator ground testing is complete, go to:
How?
X Other generator tests. ©
Back to
Index
How to Test the Voltage Drop of the Generator Ground
Set Voltmeter to read
millivolts or on the
lowest volt setting
100mV Maximum
Run engine at
1800RPM
for 30 seconds.
Keep at 1800RPM.
Now, turn on all
accessories
for 30 seconds.
Keep them on,
and read the voltmeter.
Voltmeter (-) probe to a clean
post top or side mount bolt,
NOT on cable or clamp
Voltmeter (+) to
aVoltmeter
clean spot(+)
on
probe
to
a
clean
the generator
spot
on the
housing
generator case
The generator grounds through its block mounting. This in an “all-inclusive”
test. If excessive, do “parts and pieces” testing to find the
problem. Don’t overlook the battery negative cable-to-block
(Notes)
Back
connection.
©
Other Generator Tests
How? X Test for generator charging voltage.
How?
Test for shorted diodes with a DVOM
"diode test mode“.
How?
Test for shorted diodes with a micro-amp
draw test.
How?
Test for “AC riding on DC”.
How?
Verify a good generator.
©
Next
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To go back to the beginning,
push this button:
or, to end the program,
right click the mouse,
then left click on “End Show”.
How to Test the Generator Charging Voltage
Set voltmeter to read volts DC.
Put voltmeter positive (+) probe
on battery (+) terminal.
Put voltmeter negative (-) probe
on battery (-) terminal.
Run the engine at 1500 RPM,
and turn on every load that can
be turned on – AC compressor,
blower motor, rear window
defogger, head lights, etc.
Let engine run for more than
1 minute after all loads are on.
Source voltage will be between
13.5 and 14.9 on most vehicles.
If above 15volts, this could be
caused by a faulty generator
regulator.
©
(Notes)
Back
How to Verify a Good Generator
The battery must be good, and fully charged.
Run the engine 1200 rpm.
No accessories on.
Set up DVOM to accept an inductive pick up to indicate current.
Hook inductive pick up around wire that goes from the B+ terminal of the
generator to the battery.
Engine running, no load battery voltage should be between 13.8 and 15.3 volts.
Load the battery with a carbon pile load tester across the battery terminals.
Check the current output of the generator with the inductive current clamp.
Loaded, a good generator will charge to within 10% of its stamped rating.
If the generator is a rebuild, you cannot always trust the stamped rating.
Keep in mind, that the majority of the vehicles on the road today operate
efficiently with 65 amps generators. Use this figure as a guide.
© Back