car runs 14.5V when it starts???

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MNDuster

MNDuster

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when I start the car, the ALT gauge pegs then slowly comes down after about a minute. Checked voltage at the battery upon starting and it is at 14.53V. I changed the ignition module, voltage reg., starter relay, and ballast. Has not changed. Help!!! Any ideas???
I started the car at night, turned headlights on and tried to pull onto the car trailer. blew out the new headlights and am worried about blowing out anything else if this is not normal.
 
MNDuster said:
when I start the car, the ALT gauge pegs then slowly comes down after about a minute. Checked voltage at the battery upon starting and it is at 14.53V. I changed the ignition module, voltage reg., starter relay, and ballast. Has not changed. Help!!! Any ideas???
I started the car at night, turned headlights on and tried to pull onto the car trailer. blew out the new headlights and am worried about blowing out anything else if this is not normal.
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sounds normal to me...
 
ir3333 said:
check that your voltage regulator is grounded.
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I had a overcharging problem with mine that boiled the battery in a short time and burned bulbs out. It was a poorly grounded regulator.
 
The headlights have the most robust filaments of all the bulbs on the car, and theoretically should be the last to blow from an overcharge condition.The smallest filaments are in; the fender mounted Tsigs,dash, and radio.
I have seen many modern cars running up to 15.5 volts CONTINUOUS charge. Most GMs I have tested are running more than 14.5 volts.
Put your tester on ACvolts,across the battery.If there is AC there, replace the alt. and clean the reg. ground, and its probably a good idea to clean the other grounds as well.The headlights dont care about AC, but Ill bet AC goes right through the reg.And the AC can spike pretty high. Ive seen spikes over 60VAC, which(spikes) wont hurt the battery but no 12vDC bulb will survive that,for long.
 
Your car charging system be putting out between 13.8 to 14.3 volts at FAST IDLE when warmed up. It will put out a couple of tenths more voltage when cold but should not be as high as you have measured at low idle. Try speeding up the idle by hand and watching the voltage at the battery, and see if it rises; if so, that could be one possible explanation for the blown headlights. The ammeter pegging is another good sign of overcharging.

The most likely problem is that the regulator is not seeing the system voltage. When it sees low voltage, it will cause the alternator to increase output to try to compensate.

Check the voltage on the blue wire going the back of the alternator (which also connects to the alternator) while running; it should be only a few tenths lower than the voltage at the battery. If the voltage on the blue wire to the alternator and especially where it connects to the regulator is low, then you have some bad connections or corrosion in the wiring from the ignition switch to the regulator. That is a common casue of this issue.

Then check the voltage on the green wire to the back of the alternator while running; it should be a few volts below the voltage at the battery. If this green wire voltage is low or near 0, then the regulator is likely broken or there is a short on that wire or in the regulator.

Let us know what you measure at the 2 points above. And check the regulator ground as above.
 
AJ/FormS said:
I have seen many modern cars running up to 15.5 volts CONTINUOUS charge. Most GMs I have tested are running more than 14.5 volts.
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But let's keep in mind that this is the design voltage set point for these newer systems. 14.5 to 15.5 volts is not the designed setpoint for the older system; it is around 14.0 v. Being off from that number by as much as it is AT LOW IDLE is a problem indicator.

At this point, we don't know what the fast idle/cruise RPM voltage is on this car. And it is hard to know what (quality of) headlights were in the car. So we need some fast idle voltage readings; that will tell the story.

How much AC voltage is OK and how much is not? That should be posted if you are going to do such a test. (Testing for a shorted diode?) There will always some low level of AC in the system. (And I don't know the answer.....)
 
I lost a fusible link on my 69 Chevelle once...had a ground/short problem on headlight harness where it went through radiator support area to headlights. Amazing how many bulbs it blew when that occurred. Even the dash lights!

Just for fun, check your battery voltage at rest in the morning before starting to see what state the battery is in..
 
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