Vetal

iTrader: (3)

Today while driving I saw that voltage is dropping constantly, and in a few minutes it dropped below 8 volts (on the dash) and the car stalled - right when I managed to park it.
Seems like I was running on battery.
What to check first?
Car is 98' TA

sdimess84

iTrader: (4)

I would just take the alternator out and go have it tested

Vetal

iTrader: (3)

Can it be done on a street?

Jon5212

iTrader: (2)

I'd just say your alternator is shot, if you dropped down to 8 volts with engine running its toast. And yeah you should be able to change it on the street.

torlak_t

i just replaced the alternator in my 98 ss cos of the same problem time to get a new one i think..

Vetal

iTrader: (3)

So, the simplest thing I can do is take it off?

Jon5212

iTrader: (2)

Yeah just take it off, you need it for the core charge anyways, just get a new one

stevez2885

iTrader: (9)

im pretty sur eits shot but if you have a multimeter check to make sure when its running that u should have like 14+ volts coming out of the alternator...if not replace it

Vetal

iTrader: (3)

I have multimeter and will try to check what's going in and what's going out of it
Damn, it's money and at least 2 weeks off the road if it's shot

angel71rs

Check all connections 1st. Fully charge the battery b4 you fire it up with the new alternator or you risk frying that one too.

Dex

iTrader: (5)

Thats just a myth i've never seen an alternator fail from a battery that wasnt fully charged.

stevez2885

iTrader: (9)

Yes a weak battery can eventually kill an alternator because when the alternator has to work so hard to keep the battery supplied it shortens the longevity of the alternator

Jon5212

iTrader: (2)

Yes it is true, an alternator is not meant to "charge" the battery, mainly to supplement it and "keep" it charged but yes you can fry the voltage regulator pretty quick doing that.

87gnx

iTrader: (3)

If the car still runs, you can take off the Negative battery cable(while its still running) and if it stops after a min. or so the voltage regulator(inside the alt.) is shot.$.02

angel71rs

As stated in a previous post, alternator is designed to maintain a charge, not recharge a dead battery.

I would advise against this. You can cause voltage spikes connecting/disconnecting, especially dangerous with all the electronics in modern vehicles.

Good info in this link:

http://www.aa1car.com/library/2004/ic120434.htm

Dex

iTrader: (5)

Now your implying he has a bad battery and not that he has a good battery that needs a charge. A bad battery wouldnt start the car or will have a really hard time.
Is anyone an ASE mechanic in here or are you just reading stuff off the internet. Not trying to be a dick just curious

angel71rs

I'm not an ASE, just someone who has worked on cars for ~ 30 years. I'm an electronics technician by trade, military, industrial, and now with the USPS. I have rebuilt alternators (back in the day when it was cheaper or easier to rebuild than to replace), so they aren't mystery boxes to me. An alternator generates AC, 3 phase on every one I've worked on. The 3 sine phases are fed to diode rectifiers. In older alternators, these are discrete devices in metal cans pressed into the back of the alternator case. Newer ones use a diode bridge, looks kind of like a big heavy duty chip.

All diodes have max current ratings, and while power rectifiers can supply large amperages, they too can literally fuse into a silicon lump if overloaded, or just open to infinite resistance. If they fuse, they can instantly become a straight short. So instead of rectifying the AC coming off the alternator windings, they shoot it straight into the vehicles DC supply, obviously not good.

Diodes can fail on their own, but if someone were to replace an alternator, then crank up the engine with a jump start, a run down battery is going to want to draw a lot of current. Unhook the jump and the alternator is going to try to supply all the current alone and this is where the danger lies. It can also present a bit of a risk to a car that might be providing the jump as it's alternator load will increase too, not to mention spikes from hooking and unhooking cables. Batteries in cars where the alternator failed are typically run down to completely dead trying to keep driving... worst case scenario.

I've replaced a lot of alternators and noticed a few years ago that they started to put a note on the output stud of many of them. Says something like "WARNING! Fully charge the battery before installing the alternator. Failure to do so many result in the new alternator failing!" I guess they had a lot of returns due to this and started including the notes. It's best to just play it safe and fully charge the battery. JMO

Swaie

iTrader: (6)

Bottom line...just take off the altermator and have it checked. It's nothing special. take off belt couple of bolts, your done.