My car does not charge correctly. I started thinking it was the alternator, but after replacing it several times nad switching to a heavy duty unit, I still have the same problem. When I start my car the altenator belt (replaced and tightened) screams. Then the alt. under charges or charges correctly (its about 50-50). The only none stock electronics I have are a secondary starter solenoid, a sony head unit pushing 50x4 channels, and a 200 watt sub box (two 8's). Everything is waired to factory set ups and the box is wire into my power seat hot wire. What can be wrong?

 

Because you said that the belt driving the alternator "screams" even though it is new and tightened, I would suspect that the belt is not properly tightned. I suppose 0.5" belt deflection at the midpoint of the belt between the two longest points would be considered "proper".

If the belt "screams", as you put it, that would indicate to me that the alternator is in fact working, but the belt is slipping a lot - for whatever reason. A bad pulley, a bad belt (a bad "new" belt???), oil/grease or other impurity on the belt or pulley somehow, etc.). Even when the alternator is at full output, the belt should not slip. EDIT: The belt should not slip enough to cause it to "scream" - of course there'll always be some slippage because the belt relies upon its tightness upon smooth surfaces to make a connection, unlike a gear, chain or cog belt.END EDIT

I could offer more specific suggestions if I were to know the exact voltage of the electrical system (to the tenth of a volt, which you'll be able to easily determine with a digital [DMM] voltmeter) with the car not running, running at idle and running at speed (over 1500 RPM), running at idle and at speed with and without all the accessories operating, and so forth.

Have you confirmed that your battery is good? Has a load test been performed?

Batteries can often be tested free of charge at many places in the U.S.

I suggested a couple ways to test a battery yourself (although probably not as well as with a load tester) in previous posts. Perform a search (use my name or "battery", etc.) if you're interested.

[This message has been edited by Stuart Moss (edited June 21, 2001).]

 

I tightened the belt until I attained the tension you specified. I am still haveing the same problems. My dash gauge just barely clears the red zone when the belt slips at startup. It contiues to charge like this after the belt stops slipping until I restart the car. I get a little over 13 on the gauge when the belt doesn't slip at startup.

 

The reason you see a lower voltage when you first start the car is because the alternator is working harder at this time because it has to charge the battery (every time you start the car it is discharged somewhat).

The reason you see a normal voltage later is because the alternator is not working as hard, thus presenting less of a load to the engine, thus the belt will not slip as much (as when first started) because there is less resistance, thus the alternator will spin faster, and thus produce more voltage.

All this is normal if the belt is slipping. What is not normal is the excessive belt slippage.

1. I know the belt is new. But is it the correct type? Are you sure? Is it in good condition?

2. Try tightning it a little more. Does it still slip? If so, try tightning still a little more. Now, if it no longer slips after you've tightned it several times over normal (the belt flexes less than 1/2" at the midpoint of the two longest points), either it's correctly adjusted (and you had not properly measured/adjusted it before) or it's too tight and if left this way, will cause the alternator bearings (and anything else connected to this belt) to wear prematurely.

I know there are belt dressings to eliminate belt sweaking, although I've just used a bar of soap applied to the belt while it's moving to stop sweaking. But 9 times out of 10 the problem is a loose belt.

Can you try another belt, old or new, and see if the problem goes away?

 

I know what your saying. My problem is well after the engine has started and run a while. Sometimes I can run on the highway at 2200 RPM and the altenator will not charge. That is when my belt slips. But it is super tight