shogun
10-15-2012, 10:51 PM
by Fluke, excerpt:
Testing Electrical Systems with a Digital Multimeter
Alternator AC Leakage
An alternator generates current and voltage by the principles of electromagnetic induction. Accessories connected to the vehicles charging system require a steady supply of direct current at a relatively steady voltage level. You can't charge a battery with alternating current, so it must be rectified to direct current.
Fig 4 - 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.
Fig 5 - Alternator Leakage Current To check alternator diode leakage, connect the multimeter in series with the alternator output terminal when the car is not running. Leakage current should be a couple of milliamps at most; more often, it will be on the order of 0.5 milliamps. Use care when disconnecting the alternator output wire; make sure the battery is disconnected first.
Alternators
A DMM's accuracy and digital display make regulator/alternator diagnosing and adjusting easy. First determine if the system has an integral (internal) regulator, then whether it's type A or B. Type-A has one brush connected to battery + and the other brush grounded through the regulator. Type-B has one brush directly groundedand the other connected to the regulator.
Next, isolate the problem to alternator or regulator by bypassing the regulator (full-fielding). Ground Type-A field terminal. Connect Type-B field terminal to Battery +. Ifthe system now charges, the regulator is faulty. Use a rheostat if possible. Otherwise, just idle the engine (lights on) so the voltage doesn't exceed 15V.
Fig 2 - Verifying a Good Alternator The battery must be fully charged (see fig. 1). Run the engine and verify that no-load voltage is 13.8 - 15.3V (check as in fig. 1). Next, load the alternator to rated output current with a carbon pile across the battery. Run the engine @ 2000 RPM. Check the current with an 80i-410 or 80i-1010 current clamp. The unit must maintain at least 12.6V @ rated output.
Fig 3 - Checking Field Current Worn brushes limit field current, causing low alternator output. To test: load unit as in Figure 2 and measure field current with current clamp or use 10A jack on DMM. Readings range from 3 to 7 amps. On integral GM units: with alternator not turning, jump terminals #1 & #2 (fig. 4) together and connect both to Batt + with DMM in series set to measure 10 amps. Field current should be between 2 & 5 amps, higher current with lower battery voltage. Control battery voltage by loading it with a carbon pile.
http://assets.fluke.com/appnotes/automotive/beatbook.pdf
and for the alternator do not forget the idiot light
Idiot Light - keeps the promise of "what's in a name!" (http://misterfixit.com/idotlite.htm)
Testing Electrical Systems with a Digital Multimeter
Alternator AC Leakage
An alternator generates current and voltage by the principles of electromagnetic induction. Accessories connected to the vehicles charging system require a steady supply of direct current at a relatively steady voltage level. You can't charge a battery with alternating current, so it must be rectified to direct current.
Fig 4 - 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.
Fig 5 - Alternator Leakage Current To check alternator diode leakage, connect the multimeter in series with the alternator output terminal when the car is not running. Leakage current should be a couple of milliamps at most; more often, it will be on the order of 0.5 milliamps. Use care when disconnecting the alternator output wire; make sure the battery is disconnected first.
Alternators
A DMM's accuracy and digital display make regulator/alternator diagnosing and adjusting easy. First determine if the system has an integral (internal) regulator, then whether it's type A or B. Type-A has one brush connected to battery + and the other brush grounded through the regulator. Type-B has one brush directly groundedand the other connected to the regulator.
Next, isolate the problem to alternator or regulator by bypassing the regulator (full-fielding). Ground Type-A field terminal. Connect Type-B field terminal to Battery +. Ifthe system now charges, the regulator is faulty. Use a rheostat if possible. Otherwise, just idle the engine (lights on) so the voltage doesn't exceed 15V.
Fig 2 - Verifying a Good Alternator The battery must be fully charged (see fig. 1). Run the engine and verify that no-load voltage is 13.8 - 15.3V (check as in fig. 1). Next, load the alternator to rated output current with a carbon pile across the battery. Run the engine @ 2000 RPM. Check the current with an 80i-410 or 80i-1010 current clamp. The unit must maintain at least 12.6V @ rated output.
Fig 3 - Checking Field Current Worn brushes limit field current, causing low alternator output. To test: load unit as in Figure 2 and measure field current with current clamp or use 10A jack on DMM. Readings range from 3 to 7 amps. On integral GM units: with alternator not turning, jump terminals #1 & #2 (fig. 4) together and connect both to Batt + with DMM in series set to measure 10 amps. Field current should be between 2 & 5 amps, higher current with lower battery voltage. Control battery voltage by loading it with a carbon pile.
http://assets.fluke.com/appnotes/automotive/beatbook.pdf
and for the alternator do not forget the idiot light
Idiot Light - keeps the promise of "what's in a name!" (http://misterfixit.com/idotlite.htm)