Ronnie

What's your battery voltage after charging or driving for a while?

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Sorry I took so long to respond to the question about rethinking the rate of the charging system I got myself locked out of the fourm. 13.8 is the minimum, lower then that is discharging ( on average it takes 9 volts to keep the engine running) and when you add in lights, heat, radio etc. the alt. has to work harder. On the other hand 14.5 is the maximum, you can get voltage spikes (cold starting) because the starter motor generally pulls 250 amps from the battery on start up higher if the oil is cold (synthetic oil would reduce that exponentially ) any constant charging above 14.5 will shorten the life of the battery.  KDirk is right that the more things you add to the car the higher the alt. amps should be, but you can overkill.  I built my own hydrogen system and installed it on my S-10 it draws 30 amps to run ( I control the amps. and frequency by using a pulse-with modulator ) but had to replace the alt. with a 120 amp to handle the extra load.  If on your GM product you are seeing a voltage of 13.8 or less you can determine the cause ( week alt. or bad voltage regulator) by looking at the back of the alt. Most GM alternators have a half round hole in the back and it is in line with a tab on the regulator. With the engine running and a volt meter on the battery insert a small screwdriver blade into the hole and ground out the tap to the case of the alt. this is called full fielding the alt. By doing this you bi-pass the regulator. A good alt. should read 16 to 18 volts, if it does then the regulator is bad if not the alt. is bad   

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Ronnie a way to load test a battery without a load tester ( load tester is best) . Unplug the feed to the coil or coil pack install a volt meter to the battery and (cold conditions)  have someone crank the engine for 30 sec. and watch the volt meter. wait 30 sec. and do the test again.Not as good as a load tester but effective enough to give you a good indication of the state of the battery.. One other thing, there is a tool you can get for testing amp loads on the car. It's a hand held gage that you hold on a wire (battery cable) and it will read the load when cranking. This is good for checking the starter motor anything over 250 amps and the starter is weak. Note..This gage is also good for tracing down electrical shorts. Hold it against a harness and slide the gage down the harness the needle will start to move the closer you get to the short.  Just thought I would throw this in, When looking for a short remove the poss bat. cable and install a volt meter between the cable and the battery wait for the timeout modules to time out. Turn the volt meter to the 10 amp scale make sure you do this before you connect it to the battery. ( The meter should have a 10 amp fuse inside it) once the system times out you should read 0.2 mill. amps (normal) anything higher is a short. While watching the meter pull one fuse at a time until the meter drops to zero. The system that fuse controls has the short (glove box light, cig. lighter etc. etc.) Now you will know where to look.

Edited by retiredmechanic74 (see edit history)

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2seater ...It is my belief that the BCM is more of a monitor then a regulator. It "knows" what the alt. should do when accessories are used and if all the accessories are used and the alt. is weak and can't keep up with the supply of energy needed the BCM will sense that a will put out a message. ( An electrical problem has been detected) it doesn't tell what caused the problem, it just tells you there "is" a problem. The regulator is what regulates the flow and when the battery reaches full charge will stop the flow until the battery has discharged some of its energy and the cycle starts over again. I believe the engineers incorporated the BCM ( They ran ALL the accessories into the BCM) just to complicate things. An analog volt meter on the dash is more reliable.     

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7 hours ago, retiredmechanic74 said:

2seater ...It is my belief that the BCM is more of a monitor then a regulator. It "knows" what the alt. should do when accessories are used and if all the accessories are used and the alt. is weak and can't keep up with the supply of energy needed the BCM will sense that a will put out a message. ( An electrical problem has been detected) it doesn't tell what caused the problem, it just tells you there "is" a problem. The regulator is what regulates the flow and when the battery reaches full charge will stop the flow until the battery has discharged some of its energy and the cycle starts over again. I believe the engineers incorporated the BCM ( They ran ALL the accessories into the BCM) just to complicate things. An analog volt meter on the dash is more reliable.     

Yes, you are correct. It only works as the nanny and a sort of fancy charge indicator light. I agree an analog voltmeter has its uses as well as an analog oil pressure gauge. I stand corrected.:rolleyes:

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