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Old 10-16-2004, 04:43 PM
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alternator not charging battery again

i replaced the alternator with ease and all connections hooked up fine. but the battery will not charge up after running the car for 15 minutes.still dead and i know the battery isnt bad its not 6 months old. how long does it take for the battery to charge? ive been told 15 minutes. i have ran the car for 20 more minutes and disconected the neg battery terminal and the car turned off. so the alternator is not charging the battery. what could cause this new phenominon

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Old 10-16-2004, 07:29 PM
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Doc here

It takes 6 to 8 hours on a slow 6 or 8 amp charge to rebuild the battery...anything else is a surface shot...then dead again if your output is low to begin with...and an alternator is not going to bring up a totally dead battery off a jump start and some run time...just ain't happenin' USE A CHARGER made for that purpose.

Even though your battery is less than 6 months old, It can still be shot...especially if you have been draining it as hard as you say...your cells will die off or short out or sulphate like a big dog...and it might be out of water, cooking the battery each time you charge it. Maintenance free or not, CAREFULLY pull the caps and check...

Get a DMM and check your battery, If it reads less than 11 volts get a new's shot! If it reads 11.5 or above it's really dead...charge it with a PROPER battery charger for 8 hours...If it's 12.75 to 14.4 volts it's just fine.

The engine stalling after pulling the cable off, is another problem altogether, UNLESS the battery is so toasted the Field on the alternator is not getting enough power to self excite the field.

As far as The alternator, Be sure you have a Battery ground at the block, and run another wire from that ground to the alternator mount bracket or case. Then Run a Ground back to the body to be sure all is on a hard ground.

Is it internally Regulated or have an external regulator?

If external, check to see that you have 12 volts at the output and the points on the relay coil are closing on charge, you may want to burnish them with fine sand paper as they do build up carbon and won't make contact. Check the gap and make sure they close at charge.

If you have an idiot light, Does it come on with the key, not running? If not replace the bulb, some charging systems won't charge if the light is blown out. some stay on after you shut it off..

Lastly, look on the main cable at the alternator, does it have a fusible link? (you may have to follow it back a ways) Is the link blown? If so replace it.


Last edited by docvette; 10-16-2004 at 07:48 PM.
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Old 10-18-2004, 11:58 PM
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Right on, Doc! 73, first thing to do: FULLY CHARGE THE BATTERY!!!
An alternator is a maintaining device, meant to keep the battery at max charge while various draws are working off of it. If you have a completely dead battery and you try to charge it with the alternator only, you will burn out the new alternator. Now be it internal or externally regulated, at the least this will usually burn out the regulator. Quite often it will melt the varnish coating on the stator wires and short out the stator. If, by luck, you alternator is still good, a quick and dirty test to see if it is charging is to touch a wrench, screwdriver, ect. to the back bearing cover. If the alternator is energized and putting out, there will be a reasonable magnetic field here. The harder the alternator is working, the stronger the field.

Check all elctrical connections.
  • * Dirty battery posts can cause the battery not to charge, but the idiot light will go out.
    * Next check all fusible links, even the ones to the starter.
    * Make sure the stud in the back of the alternator is tight in the housing.
    *Bypass the charge wire by using a booster cable from the alternator stud to the positive battery post.
    *Slide a small screwdriver in the "D" shaped hole in the back of the alternator. If the alternator starts to work, regulator is bad. If, after all this doesnt work, try a new (fully charged) battery, and a new alternator.
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