Electrical troubleshooting

[slowmobile]

When my car is sitting off the battery is only indicating 9.8 volts. When I pull the alternator wire off the battery it jumps to about 10.3 volts.

When I start it, I only get about 12.75 max even when I rev it up. When the car sits for a while it drains the battery completely and even while running it can't seem to keep up with the electrical accessories. Shouldn't I be in the 13.5-14 neighborhood when running? Do I have a bad battery? I believe that the alternator is only a 50 amp.

Thanks for any help.

[Warpspeed]

Sounds to me as though the alternator is faulty and drawing power from the battery with the engine stopped. That could be caused by one of the diodes being faulty, especially one of the small ones that energizes the field winding.

Try fitting a replacement alternator.

The battery is probably o/k, and just needs charging up properly.

[af2]

Sounds to me as though the alternator is faulty and drawing power from the battery with the engine stopped. That could be caused by one of the diodes being faulty, especially one of the small ones that energizes the field winding.

Try fitting a replacement alternator.

The battery is probably o/k, and just needs charging up properly.

Tony, that was my first thought. If a diode goes it could and will go to earth and drain the battery.

[BLACK BART]

You will have a dead battery very soon if you do not fix that. I agree with Warpspeed that the alternator could be bad, but you should also check to see if there are any items that get power from the alternator that could be drawing power only with it hooked up.

The difference in voltage with the engine running vs not running is normal, but you have low voltage in both cases and can see a draw on the system.

Remember that amps and voltage are two different things and one does not take the place of the other. Think of it like pressure and volume. You have pressure in an air tank, but no volume is flowing if it is just sitting there. When you use an air tool and the tool causes air to flow, you now see volume. Your voltage is like pressure and your amperage is like volume. CJ

[slowmobile]

So it doesn't sound battery related then?

Thanks.

[MDT]

If the 9.8 10.3 voltages are after the battery has been charged the battey is bad as well- may be sulfated. If it is not after it has been charged ,I would think it may be ok.

[Warpspeed]

First try a different alternator. The battery voltage should rise to about 14.0 to 14.2 with the engine running.

The battery may fully recover, or it may not. But at least give it a chance before replacing it.

[BCjohnny]

Short cirucited positive main power diode in the rectifier, more than likely. Allowing the battery a bleed path to earth (3-4amps) and suppressing the charging output.

Normally accompanied by a "wahhhhhing" electrical moise and elevated alternator temperature.

As advised, give the battery a chance, but if deep cycled enough times it'll probably need replacing.

John.

[bulitpruf]

Considering you may not be able to hear the alt, let the car run at hi idle about 5 min. The alt will be hot. You should be able to touch it but not hold it. If it too hot to put your hand on it its bad. An alt with a bad diode or rectifier will over heat very fast and very hot. I know hot is relative.
Try some other known good alt /car to get a feel.

[Warpspeed]

This suggested violent overheating, and all these noises will only occur if the problem is with the main rectifier diodes and main windings.

I believe the problem is more likely to be with the smaller field diodes, in which case there will be no obvious overheating or noise associated with it.

Just change the alternator !

[slowmobile]

Just change the alternator !

Where can I find a decent output mini denso for an even more decent price?

[MileHighMan]

I use a company called Starters and Alternators of New Mexico. Hermans company does excellent work. Very High Quality, Very Good Prices. 1-505-344-5025. Tell him Pro-line sent you. Good Luck. Dan.