how do you tell if your alternator is going? [Archive] - GrandAmGT.com Forum

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cardude007617
11-04-2007, 08:28 PM
the past 2 days my voltage has been dropping more than it used to. like i could normally bump at 42-44 on my deck without too many probs. but not the last 2 days, at 35 or so, my cap read 12.6 meaning my alt isnt keeping up. the thing i dont get is, if i have the stereo down lower, it reads 14.6 or so which is pretty good. so, any ideas; is it going or could weather be doing it

drumking1721
11-04-2007, 08:49 PM
Autozone does free tests

ryanbgb22
11-04-2007, 09:17 PM
usually makes a weezing noise too. w/e their cheap and easy to install.

cardude007617
11-04-2007, 09:41 PM
nah, a high output (like i need) go for 190+. but wouldnt voltage be lower under no load though too? cuz all im seeing is 14.5 or more

OneFstGt
11-05-2007, 06:56 AM
Mine is making noise :-(

ZOMGVTEK
11-06-2007, 09:26 AM
.

notsoaveragej0e
11-06-2007, 10:43 AM
Isn't there a trick where you can hold a metal screwdriver to the back of it, and if it has a strong magnetic pull then its good, if not, then its done...?

nate2023
11-07-2007, 07:38 PM
with the car running pull the negative terminal off of the battery if the car stalls its shot. Or use an voltage meter, should read about 13.80 or above with loads off.

ryanbgb22
11-07-2007, 07:45 PM
with the car running pull the negative terminal off of the battery if the car stalls its shot. Or use an voltage meter, should read about 13.80 or above with loads off.

i thought that was a bad idea....?

cardude007617
11-07-2007, 07:54 PM
yeah, i thought that can fock ur electronics.....

When it sounds like a supercharger?
meaning u just gained 50HP!!!!!!!! WEEEEEEEEEEEEE!!

Mike Jung
11-07-2007, 08:41 PM
with the car running pull the negative terminal off of the battery if the car stalls its shot. Or use an voltage meter, should read about 13.80 or above with loads off.
:nono:

Your battery acts as a voltage regulator.
If you disconect your battery, your voltage can spike up & down.
& then you can say fried electronics !

nate2023
11-07-2007, 08:53 PM
NEVER had a problem on my car or any other car when i tested it like that. If the alternator was good it would run like normal with loads off, obviously you can't have Amps or large voltage eaters on.

Mike Jung
11-07-2007, 09:05 PM
from: http://www.pacificpowerbatteries.com/aboutbatts/Car%20Battery%20FAQ/carfaq14.html
14.6. Test the alternator by disconnecting the battery with the engine running.

A battery as like a voltage stabilizer or filter to the pulsating DC produced by the alternator. Disconnecting a battery while the engine is running can destroy the sensitive electronic components connected to the entire electrical system such as the emission computer, audio system, cell phone, alarm system, etc., or the charging system itself because the peak voltage can rise to 40 volts or more. In the 1970s, removing a battery terminal was an accepted practice to test charging systems of that era. That is not the case today. Just say NO if anyone suggests this.
+ we had this discussion with Di (an engineer from GM) along time ago.

& came to the conclusion that it was not something that you want to do.

Shadowfaxgt1
11-07-2007, 09:15 PM
Isn't there a trick where you can hold a metal screwdriver to the back of it, and if it has a strong magnetic pull then its good, if not, then its done...?


This is was a feature on the old Delco alternators. You could put a screwdriver in the back of the alternator and provide full field output. Todays SI alternators don't have the same feature. Best thing to do is go to someone that can load test the charging system and alternator (Autozone was mentioned). It is the only true way to test the system without guessing.

nate2023
11-07-2007, 09:22 PM
from: http://www.pacificpowerbatteries.com/aboutbatts/Car%20Battery%20FAQ/carfaq14.html

+ we had this discussion with Di (an engineer from GM) along time ago.

& came to the conclusion that it was not something that you want to do.

I'm not saying it couldn't happen and/or maybe i'm just lucky that somthing hasn't happened yet :angel . But at least i can check with a voltage meter when handy ;)

Yea autozone could check it, I know some walmart TLE's have the device to do the charging system check.

rocketfast123
11-07-2007, 09:25 PM
:nono:

Your battery acts as a voltage regulator.
If you disconect your battery, your voltage can spike up & down.
& then you can say fried electronics !

It's kind of hard to convence old school mechanics of this.

nate2023
11-07-2007, 10:32 PM
Gotta love the good 'ol days :)