If the battery is bad or has a bad cell will it not charge? And will that show on the guage? I purchased a new 200 amp alternator and when I put it in it showed about 13 - amps. Then a little later it drifted down to between 9 - 10. I took it off and sent it back to the company and the did a comlete search and said they bench tested it for more than 20 minutes and it was OK. I installed it again today when I went to start the car the battery was completely dead. I have an optima red-top but it is about 3 - 4 years old. I did a jump on it and immediately it started charging but only lasted about 5 minutes and drifted down to the 9 - 10 range. If the optima is bad could it cause this???

 

Your description sounds like a typical alternator failure, but if the company tested it thoroughly then maybe it's not.

Any battery that has gone out on me has only caused the car not to start. Once it is jumped the car stays running.

May want to check that the alt. is connected properly and all the cables are in good condition and not corroded.

 

I just had the battery tested and it tested out OK. Now I'm stumped! Could it be a short of some kind?? The alternator is brand new and has been tested twice. The cables are all brand new and are the large red cables.

 

You mentioned 13 AMPs (???), however, the LT1 cars come equipped with a voltmeter in the instrument panel. An alternator should provide a “float voltage” of 13.5 to 14.5 volts to charge the battery. A typical lead acid battery (alone) has an output voltage of 12.6 volts, not sure what the Optima is (around 12+ volts).

To check your charge system and battery, get a test voltmeter (DMM). First check the battery voltage (without the car running), it should be 12+ volts. Start the engine and check the float voltage, it should be 13.5 or greater.

You could also have a short that is loading down the system.

WD

 

As batteries go through charge/discharge cycles, they form sulfates and lose capacity. Deep discharge cycles are especially hard on them. A highly sulfated battery will charge normally at first, but fill up the remaining charge area relatively quickly. It sounds to me like you could have used up your optima. I have a severely abused yellowtop in an electric minibike that is about 4 years old, but I use a desulfater when I charge it and the capacity is still OK.

 

When I check the battery - now that they charged it for me at the place where they tested it - it reads about 12.4. When I start the car and check with the alternator "producing" it floats between 9.5 and 10.5. Although I have large wires and good grounds I moved the ground and check it again and it is still the same reading. I am thinking about taking the alternator off again and taking it to a local alternator shop and have them bench test it. Just to get the opinion of a disinterested third party. I know what the supplier said but something is wrong. I didn't have this problem until I installed the new 200 amp alternator. Quick question: This alternator is all chrome. Would that make it more difficult to get a good ground???

 

To provide any charge to the battery, the float voltage from the alternator must be "greater than" the 12 volts of the battery (typically 13.5 volts or more). If your alternator voltage is "less than" 12 volts, then you're not charging.

Chrome should be a good electrical connection, providing it isn't plastic chrome.

WD

 

So, am I looking for a short somewhere?? If so, where do I begin? I just can't seem to shake the fact that none of this started until I installed this new alternator. Coincedences just bother me and this is one! Assuming it is a short how do I go about tracing it down???

 

The GM type alternators have three rectifier diodes. One or more of those diodes can short and that can cause several problems. 1. It can cause a discharge path for the battery while the engine is off and 2. The alternator won't have the correct output voltage 13.5 volts (it will be too low).

To check the alternator for shorted diodes, you need to remove the charge wire from the alternator (with the engine off). Then use an amp-meter connected between the charge wire and alternator terminal to see if the battery is discharging back through the alternator.

Also, have you added some big stereo amps to your car? They are often the source of unexplained current drains. If so, disconnect them to see if the problem goes away.

WD