transmission/electrical problem on diesel
Went out to my motorhome this morning to take it to get new tires. its a 2001 allegro bus with a Cat engine. started it up and backed out and shifted to drive. it would move fine then all the ligh...
Forum Discussion
My guess and opinion of where to start testing, after I check grounds...
(from Fluke)
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.
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.
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 grounded and the other connected to the regulator. Next, isolate the problem to alternator or regulator by bypassing the regulator (fullfielding).
Ground Type-A field terminal. Connect Type-B field terminal to Battery +. If the 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.
Verifying a Good Alternator The battery must be fully charged. Run the engine and verify that no-load voltage is 13.8 - 15.3V. Next, load the alternator to rated output current with a carbon pile across the battery. Run the engine @ higher RPM. Then check the current with. The unit must maintain at least 12.6V @ rated output.
Checking Field Current Worn brushes limit field current, causing low alternator output. To test: load unit as in and measure field current with current clamp or use 10A jack on DMM. Readings range from 3 to 7 amps.
(from Fluke)
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.
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.
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 grounded and the other connected to the regulator. Next, isolate the problem to alternator or regulator by bypassing the regulator (fullfielding).
Ground Type-A field terminal. Connect Type-B field terminal to Battery +. If the 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.
Verifying a Good Alternator The battery must be fully charged. Run the engine and verify that no-load voltage is 13.8 - 15.3V. Next, load the alternator to rated output current with a carbon pile across the battery. Run the engine @ higher RPM. Then check the current with. The unit must maintain at least 12.6V @ rated output.
Checking Field Current Worn brushes limit field current, causing low alternator output. To test: load unit as in and measure field current with current clamp or use 10A jack on DMM. Readings range from 3 to 7 amps.
