How can I tell if my alternator is dying? The truck's gauge drops all the way then suddenly springs back. It's not consistent anymore, and the lights are getting dim when the voltage drops. Don't alternator's usually just die??? Do they give you some time before they die usually?

 

alternators can get weak before they die but it sounds like you might have a voltage regulator going out or a short somewhere if it is not consistant. Autozone or most other parts stores will check your alternator for free. You just have to take it out of your truck.

 

Check your battery ground connection at the block and the condition of the ground cable itself.

Billy

 

easiest way to tell is to put a multimeter on the battery while it is running. Voltage when running should be in the ball park of between 13.7 and 14.3. Those are good starting points for a check. Check that and post your results and i can probably help your from there.

 

Easiest way to check a dying alternator is to start the truck and while its running, disconnect the positive battery cable. If the truck still runs, the alternator is working, if not, well. The problem you described sounds like either a dead voltage regulator (internal to the alternator) and/or a dead diode (again internal to the alternator).

 

Actually, removing the battery cable with the engine running is a GREAT way to RUIN an alternator.



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Understanding how an "ALT"ernator works would make one realize that it will NOT kill it. All the alternator is responsible for doing is running the engine electronics! The fact that it also happens to send some current back to the battery is irrelevant! Hence the term ALTernator! Once the engine is running, a working alternator can handle the electrical requirements of the ignition system just fine without damage. Now I wouldn't recommend running the stereo, headlights, and Warn 9000 like that but the ignition system uses alternator power to keep the engine running. If this was NOT the case, we would all be replacing our batteries every few days or at most weeks! Once the battery has started the engine, its the alternator that keeps the engine running. When it doesn't, you end up running the engine off the battery and killing the BATTERY...NOT the alternator! Ask you A.S.E. mechanic if you think I'm wrong.

 

Hi You didn't say which year yours is. If it is a mid 80's to early 90's check the alternator connectors. This is important because one may be shorting out. You should also check the alternator harness for rubbing shorts.
Last Sunday, my alternator connector did short and caused a fire. Right now I am fighting my insurance compainy to prevent them from totalling my Bronco.
Bruce (Big Red (flame red) Bronco)

 

 

Disconnecting the battery may be harmful to the alternator. The word alternator is derived from Alternating Current, a sinusoidal function of voltage/current...not because its an ALTernate source of current.

Now, the alternator provides a float charge for the battery after it has been used to START the engine. The alternator, battery make up a sort of HOT UPS system. Once a battery is used and its voltage drops, the alternator will provide the equalization voltage and current to float the battery back to its 13.8 volts.

The alternator is a current source, providing the current to run all the electronics and electrics on the vehicle, the battery's primary function is to provide heavy current for the starter motor, (or electrics when the engine is not running)...otherwise it sits there doing very little. However, the current is drawn from the battery and replenished via the alternator/rectifier source.

Now, on many alternators, the fields must be energized by the battery, if not, the alternator will not function or function poorly, depending on the alternator design - some external regulator designs provide the winding voltage - other internal or integrated designs - the charge is provided by the 12V battery.

So, the battery and alternator system are dependent on each other, and disconnecting the battery during engine run will reveal very little and may cause more problems than enlighten.

I hope this helps of makes some sort of sense.

Mark Bohaichuk CET - Certified Electronics Engineering Technologist

 

Oops, I guess theory is nice, but an answer would be nicer to the problem at hand-

To check the charging system - here is a simple test:

1 - check battery voltage with engine off - s.b 12V approx.
2 - start engine - check battery voltage - should be about 13.8-15V
3 - Have someone turn on the headlights or other current draw - while monitoring battery voltage - it should drop and then quickly come back up to the 14/15Volt level.

If the voltage is not within this range, you could have a bad regulator, alternator internal components (i.e. diodic) or a general alternator fault.

If the voltage jumps up and down - this is more than likely in the charging system as indicated - if your alternator has an integrated VR, you probably would be best to change the alternator.

MB

 

I talked to two different licensed master mechanics on this issue for you - one here at work that manages a fleet, and my Father - private practice -

They both conclude that you probably will not damage the alternator, but both agree that disconnecting the battery makes no real sense and would not do it. They subsribe to the test I mentioned above.

There is however a lot to be considered in regards to type of alternator, regulator etc and where the field charge is supplied from etc.

This concludes my 2 cents on the topic....hope it helps

 

>I talked to two different licensed master mechanics on this
>issue for you - one here at work that manages a fleet, and
>my Father - private practice -
>
>They both conclude that you probably will not damage the
>alternator, but both agree that disconnecting the battery
>makes no real sense and would not do it. They subsribe to
>the test I mentioned above.
>
>There is however a lot to be considered in regards to type
>of alternator, regulator etc and where the field charge is
>supplied from etc.
>
>This concludes my 2 cents on the topic....hope it helps
>
>


Thank you all for your input. It was infact the alternator standing on its last leg. When presented with a draw (i.e. Headlights, A/C Compressor, etc), it simply wasn't giving a charge. I changed is out - all is well again.

Thanks!