possible bad alternator?

[randomriot]

About a two weeks ago all the idiot lights on the dash started flickering on and off, then the radio started losing power. Finally last weekend it was having a hard time starting. It would start with no problems if it was sitting for several hours but if i were run it for awhile, stop and then try to start it up again, it would take a while to catch like the battery was dead. I assumed it was the alternator thinking that the battery was being drained after useage not leaving enough juice to start back up.
I bought a battery/alternator tester from Radio Shack which told me my battery was low and my altenator was fine. Replaced the battery and it ran fine for about 3-4 days. Now I am having the same problem again. After usage it is having trouble starting back up. I replaced the alternator 7 months ago, it was done by a auto shop and they used a 'rebuilt alternator', which probably means that it came from a junk yard.
Does this sound like the alternator is dying again or could it be something else?
Thanks

[darkaccord]

Possibly a bad ground on the battery?
Or wires?
Probably not though.

[BeEfCaKe]

Rebuilt alternator isn't from a junk yard.. what you do, you give them YOUR alternator, pay a price, and they give you back another one.. They take your old alternator and replace certain parts inside, (such as the pulley and others), spray it with this metallic substance, and then they can sell that again.. A friend works at one of those places, and I watched him do it.

Its almost certainly the alternator that's the problem here.

[INF3RN0666]

Most likely that your alternator is losing its ability to produce power when the car heats up, thus draining the battery when that happens. Therefore, you should check your alternator at several instances while you're driving and you should check how to properly do it for your specific car. It's probably all the same on all cars, but with the "new" and "old" designs that are comming out, you never really know how your car is wired. Practically, all cars these days are a ticking time bomb. When one thing fails, everything is gonna go down with them. It might not be true for all car makes but it sure is for the fucking civic my dad has. Ever since then, he's never bought a civic in his life.

[Dr Sparks]

Check that alt belt isn't glazed, which means it just heats up and slips against the pulley instead of turning it. What to look for: Normal volts and amps at idle, but low or no charge at RPM increase; Belt squeal with raised RPM; belt that looks shrunken as far as how it sits in pulley; a burned looking alt pulley i.e. pully will be discolored, heat checked, blistered if painted. Remember, when a belt screams, go see what it wants.

[bisho1p]

I would concur that is is an electrical system failure, specifically the alternator. The reason that the tester said you battery is low is because the alternator is failing to recharge the batttery after is is used initially to give power to the starter and alternator. You need a new alternator, and a good recharge to the NEW battery couldnt hurt (for all the hell it's been through). Go over to the local Advance Auto Parts and stick em in.

[V-8Fan]

As long as the alternator is applying about 13.8 to 14 volts to the battery (engine running, of course) then the alternator is fine. Flickering lights spell a bad connection. A bad connection can often become an even worse connection when things are really hot because metallic conductors become more resistant to current flow as they heat up. I would be checking out the fusible link and other connection points. The radio losing power, as you stated, is a dead giveaway to a poor connection somewhere unless your talking about some 500 or 1000 (or more watt) monster stereo system. Be sure to take a good look at your battery cables too.

[TorinoGT69]

Actually the voltage is not all that important. That is the problem with most at home testers, thats all they check. Tha amps are whats important if there is not enough current flow from the alternator then over time it will drain power from the battery. Not to mention the diodes in the alternator could be bad and will put out normal voltage and drain the battery with the vehicle turned off.

[ivymike1031]

Actually the voltage is not all that important. That is the problem with most at home testers, thats all they check. Tha amps are whats important if there is not enough current flow from the alternator then over time it will drain power from the battery.

But you can't drain the battery at 14V. As long as the alternator is keeping the system voltage above the battery voltage, the battery is being charged, not discharged. If the alternator wasn't supplying enough current, then the battery would have to make up the difference, which would necessarily result in the measured voltage being less than the battery "resting" voltage.

[jeffescortlx]

Originally Posted by ivymike1031

Actually the voltage is not all that important. That is the problem with most at home testers, thats all they check. Tha amps are whats important if there is not enough current flow from the alternator then over time it will drain power from the battery.

But you can't drain the battery at 14V. As long as the alternator is keeping the system voltage above the battery voltage, the battery is being charged, not discharged. If the alternator wasn't supplying enough current, then the battery would have to make up the difference, which would necessarily result in the measured voltage being less than the battery "resting" voltage.

ivymike1031 is correct, as long as the voltage from the altinator is higher than the voltage of the battery the current is flowing the the direction to charge the battery.
If the motor is running and the vehicals voltage is below 12 than the current is comming from the battery and not the altinator, the battery will be dead in a certain amount of time.
If the voltage of the car is around 13 or 14 than the current is comming from the altinator and charging the battery.

[V-8Fan]

Voltage cannot be present without current flow, so if the correct voltage is present, then the alternator is supplying current to recharge the battery. HOWEVER, two observations:

1. It IS possible for a component in the charging system to be bad and to discharge the battery with the ignition turned off. It would be wise to check the battery's current flow with the ignition turned off. I would expect to see less than 100 milliAmps, and if there was more, I would start disconnecting circuits until I found the one that's loading the battery down.

2. When you use a voltmeter to measure DC voltage, it tells you little to nothing about any alternating current present in a circuit. If a regulating diode is bad, it is possible for there to be an alternating current present in the charging system, but if this was the case, I would not expect the DC measurement to be "on the money".

So, everyone has made a valid point regarding this problem.