Download Charging System Tests and Voltage Information

Charging System Tests
& Voltage information
Checking the charging system with just a volt meter
First Step
Always check the battery first. A bad battery can affect the
charging test.
Battery Voltage should be 12.6 volts when car is off. If not we
need to find out Why? If over it is probably because the car
has been running and was just shut off. If under it is bad or not
being charged. Battery state of Charge if below 12.45 charge
before testing.
Charging system must supply enough energy to run the
demands of the car and charge the battery.
Turn off everything run at 2000-2500 for
2 minutes and check charging system
voltage. The results should be some
where around the following specs.
Sealed Maintenance free battery
above 15.5V overcharging
14.5V -15.4V normal
13.2V - 14.4V may be to low
12.6V - 13.1V too low
12.6V or less not charging
Low Maintenance battery
above 14.8V overcharging
13.2V - 14.7V normal
12.6V - 13.1V too low
12.6V or less not charging
New cars at 80 degrees
Ford 14.4V- 14.8V
Gm 14.5V - 15.1V
Chrysler 13.3V - 13.9V
Generic Quick Specs
• Battery Voltage should be 12.6 volts when car is
off.
• Voltage should be with car running at 2000 RPM
about 13.8-14.8 Volts
• Voltage should never fall below 13.2 Volts
Things to Remember
• Temperature changes charging voltage
• Higher in cold weather
• Age of battery changes charging voltage
• Older batteries have less charge acceptance,
will elevate voltage faster
Things to Remember
• State of charge, changes charging voltage
• Low battery voltage, charging voltage will
be lower
• Impurities, If you have added tap water
charging voltage will be lower
Check for overcharge
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1. Engine off - Write down voltage of Battery
2. Turn all accessories off
3. Run at idle - Write down voltage
4. Run up to 2000 RPM - Write down voltage
Voltage should not go up 2.5 volts over battery
voltage from step # 1
Check for undercharge
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•
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1. Engine off - Write down voltage of Battery
2. Run for 2 minutes at 2000 RPM
3. Turn on all accessories
4. Take voltage reading, Should go up at least .5
volts Minimum voltage is 13.2 But if charging
system is working right I like to see it in-between
13.8-14.8 Volts (CDX says 13.7-14.4)
Tech Tips
If voltage does not go up full field the Charging system.
Put battery voltage into the coil windings to check the
Alternator. (Cannot be done on some cars with internal
voltage Regulators or cars that the regulation is
controlled by the computer.)
If diode trio burns out on GM products idiot light will
be on but it will still charge. (might be dim)
Some Things You don’t want to do
Never Ground the field coil wire.
Never Arc across the Output Post.
Never Disconnect the battery cable to see if the car still runs.
Never try to charge a dead battery by using the alternator, you
could burn up the alternator.
Never allow the voltage to go over 16 volts
Never work on electrical components without disconnecting the
Battery (will the radio screen go blank if you take away the
power and do you have the codes to fix it.)
Voltage drop
• You always want to perform a voltage drop test
when checking out a charging problem. Also
can be called a circuit resistance test.
• You need to check the ground side and the
insulated side vehicle must be running and a
load must be applied. You can add a load by
just turning on the lights, heater and other
accessories.
Voltage drop Insulated
• Hook up Positive lead
to the output of the
alternator
• Hook up Negative lead
to the Positive terminal
of the battery
Voltage drop Insulated
• The reading should be less then .5 Volts This one is
at .154 volts.
Meter should
be in the DC
volt scale
Voltage drop ground side
• Hook up Positive
lead to the Negative
side of the battery.
• Hook up the negative
lead to the frame of
the alternator.
Voltage drop ground side
• The reading should be less then .2 Volts This one
is at .036 volts.
Lead hook up
• Some times students look at lead hook up
on charging systems and think that we
have the wrong one on the wrong side.
• Think about it what charges the battery so
what is the most positive connection.
• You can on a digital voltmeter hook up
either way but what you will have is a
negative sign on the reading.
Checking Ripple Voltage
(AC voltage)
Thanks for Picture from Fluke
Checking Ripple Voltage
(AC voltage)
• Checking Ripple Voltage Ripple voltage
or (AC voltage) can be measured by
switching your DMM to AC and connecting
the black lead to a good ground and the
red lead to the "BAT" terminal on the back
of the alternator, (not at the battery). A
good alternator should measure less than
.5 VAC with the engine running. A higher
reading indicates damaged alternator
diodes.
Thanks for Info from Fluke
The End for Now
Get into the habit of checking the charging
voltage on every car that comes into the shop.
Not just when you have a problem. Then
when a car comes into your shop you should
know what the voltage is or should be before
you even hook up a meter.