1979-1993 & 94 Conv [Subscribe to Daily Digest] |
Alt appears to be a pretty simple device - rotor, stator, diode unit and voltage regulator.
Current flows thru the rotor and when one is rotating it makes stator to generate the voltage across it's terminals. Since the voltage is of AC nature then it goes to diode unit that rectifies it making sorta quasi-DC. Voltage regulator senses the output and when it's above certain value (say 14.4V for most 12V car applications) it brakes rotor circuit. If the voltage is below certain value (14.2V) it engages the rotor.
Given specs for voltage are for EU cars. US can be tuned to a bit lower values (around 13.6V or so).
If you have performed basic mechanical troubleshooting (that includes not only bearings and belt inspections and whether rotor hits the stator but electrical ground cables and well as terminals checks) then you'd go deeper in. An oscilloscope is of very much help here but you can try some "organoleptical study" with your hand, VA-meter and good common sense:
- rotor is shorten. Check resistance across rotor terminals. 0.7-3 Ohms should be good although note that each alt has it's model-specific specs. Less - new rotor is required; more - rotor can be fixed (in most cases) but used alt seems to be a good way to go.
- VR faulty. Pick up some AAA (AA or whatever you have) cells and check if it turns its brushes on when 12V applied to the sense input and if they're disengaged when 15V are applied. New VR's can be found in most parts stores.
- stator faulty. Oscilloscope picture will determine it fast but you can try your luck and measure the resistance between stator terminals and between each of them and ground. But you'll only be able to determine fully dead stator and won't be able to see if there're any interturn short circuits or not. Resistance between every terminal and ground should be infinite while the resistance between each terminal and two others should be equal for all measurements. You won't rebuild the stator (even Ari or CMyles will not do that) so used alt... See sect #1 above
Most alts get VERY hot when stator goes down. Also you may hear saw-stiled noise in your stereo (but may not).
- the rectifier (aka diode unit). There should be no signs of high temperature or fire and every diode should be operable (finite resistance on one way and infinite in reverse)
Good luck,
Zig
posted by 85.140.10...
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