Problem with alternator

mngreen

mngreen

Senior Member
I replaced my Delco 10-DN alternator with a remanufactured one recently since the bearing was shot and making a lot of noise. I have an old mechanical Delco voltage regulator on the firewall. 12V system. Battery is good and fully charged.

The "new" alternator charges correctly; goes up to 10 amps then tapers down to zero as it should. However, once the engine goes to idle, it registers a 10 amp discharge and stays there at idle until I hit the throttle again, when it then charges and tapers back to zero, as long as I am throttled up. I do not get a discharge when the engine is off and ignition switch is off, so I surmise that there is no voltage loss other than in the charging circuit.

Perhaps the remanufactured unit has some diodes burned out?? Or might a bad regulator be the culprit? :confused: The old alternator did not do this and I did not change the wiring (2-wire setup, I think, no idiot light).
 
the alternator should hold excite once reved over 1000 rpm. I would blame the regulator or other parts on the back of the alternator. The remanufactured alternators are hit and miss these days. My model A got a good one first try. My farm truck is on its third funky one. Rewired the circut isolated thinking I couldn't get 3 bad ones. The farm trucks one is doing what yours does. take it back, mark it with a sharpie to make sure they are not cycling them on the shelf.
 
Alternator is not turning fast enough to stay excited at idle, just like the old Chrysler systems did in the 60s and 70s. The unit you bought might have a 2 amp rotor which will take more rpm to saturate stator coil to start charging. Installing a smaller pulley might help. Sounds like system is charging fine when rpm increased. A 10si self exciting one wire alt is also an option.
 
If your old alternator works good, other than the noisy bearing, why don't you just replace the bearing(s) in it. Not hard to do.
 
Mike's reference is for a built-n regulator, like the 10SI has. Vince is spot on - check pulley size. katy has the simplest solution, probably.

So long as you don't leave it idling until the battery dies, it won't hurt anything. Like the salesman says, "That's not a problem, that's a FEATURE!"
 
If the other suggestions do not work, As Vince mentions above, try a smaller pulley.


I believe the venders have them, and it is common when converting from generator to alternator to also change the pulley to overcome/partially overcome the excitation min voltage.
 
Well, problem solved, for now....:o

Swapped back to the old alternator. Negligible discharge at idle and charges good and tapers off, so no problem with the regulator. Maybe the squeaking bearing will go away and was just a too tight belt or maybe even the weather! At least it's not squeaking now....:p I think Vince's post is spot on.

Lesson learned...you get what you pay for! $40 for "remanufactured" Chinese crap was just that...CRAP! :mad:
 
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