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Re: Alternator Problems or so I thought help please!! Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 9 Feb 2007 10:31:58
In Reply to: Alternator Problems or so I thought help please!!, Jason H, Fri, 9 Feb 2007 05:01:04 Members do not see ads below this line. - Help Keep This Site Online - Signup |
I echo Gene N.'s questions. After you installed the new alternator, do you still get a battery light when the engine is running? If not, do you get a battery light if the key is turned to ON but the engine not started?
As Gene says, the voltage regulator is built into the back of the alternator. That's the little diamond-shaped device with the bump on the back of the alternator, held on with two screws. Alternators themselves rarely fail - after all, an alternator is just a coil of wire with another coil of wire spinning around. Not a lot to fail. The voltage regulator, on the other hand, can and usually does fail. It also has a set of brushes, and those brushes wear down with time. Replacing the VR gets you a new set of brushes in the deal.
There is one other thing inside the alternator that can fail - one or more of the internal diodes. They don't fail nearly as often as VRs go bad, but I have had a diode fail. It is theoretically replaceable, but for a bad diode, I just put in a new alternator. The typical troubleshooting path is to replace the VR first; if that doesn't do the trick, replace the alternator. With the proper test equipment it is possible to troubleshoot a bad diode. Most folks don't have an oscilloscope lying around. Most electrical shops, and many of the larger autoparts stores can test an alternator in-car.
Of course, that doesn't help you right now. You've replaced the alternator already. A few possiblities come to mind.
First - if the BAT light is OFF when the engine is running, and it is ALSO OFF if the key is turned to ON but the engine isn't running, then there is a specific wire not hooked up. On the back of the alternator there are two wires - a big, fat red wire that goes to the battery, and a thin, usually yellow or green wire. That thin wire goes from the D+ connection on the back of the alternator to the BAT light in the dash. When you turn the key to ON, current flows from the battery, through the ALT light, through the thin wire, and into the D+ connection on the alternator. This powers up the field coils in the alternator. An alternator is a generator that uses an electromagnet instead of a permanent magnet to create the magnetic field. No magnetic field, and the alternator is just a lump of spinning metal that produces nothing but a faint whirring sound. When the key is first turned ON, that current energizes the field coils, so that when the engine starts and spins, the alternator can produce voltage.
So the light should be ON when the key is turned ON, because current is flowing through that wire. Once the alternator starts producing voltage itself, it takes over supplying the field coils. So no current flow through that thin wire, and the BAT light goes out. Or should.
So if the wire didn't get connected, the BAT light won't go on when the key is turned to ON, AND the alternator won't produce voltage.
OK, what if when you turn the key to ON the light goes ON, AND it doesn't go out when you start the car? Two things-
First, you could have that thin green wire tied to ground. This could be because it has worn and shorted to ground. Or it could be that when you hooked it back up, you accidently connected it to a ground screw on the alternator, not the D+ connection. It happens. If this happens, the light will always be on, because the bulb is simply connected between the battery and ground. And the alternator won't work.
Second, you could have a bad alternator. It does happen. Not every new part works.
I'm assuming that the belt went back on correctly, and you can see the pulley of the alternator spinning when the engine is running.
In your case, I'd first answer the light questions. Second, check the wiring on the back of the alternator (a flashlight and a mirror is very helpful here). Make sure the thin wire goes to the D+ connection, and isn't shorted to ground.
If all looks good, put a good charge on the battery. And call up the nearest Pep Boys or Autozone, and ask if they can test an alternator in the car. It would be great if the place you bought the alternator from can test them in-car. Then limp the car down there and check the alternator. Do it in the daylight, keep the headlights off, keep the blower motor off, and use the brakes lightly (brake lights take power!). If you can have a buddy with jumper cables follow you, it would be nice.
posted by 192.249....
, Fri, 9 Feb 2007 10:31:58 <-- Viewing This Message
, Fri, 9 Feb 2007 08:48:23, Fri, 9 Feb 2007 05:16:10
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