Alternator voltage question

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sciphi

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Question about voltage on my Buick's alternator. The PCM will report a voltage of 13.9 volts, yet measured at both the battery and the alternator, I get 14.3 volts. While driving with the engine fully warmed up, the PCM will report 14.4-14.5 volts. The PCM-reported voltage never used to be this high, always right around 13.5-14 volts.

Also, I've replaced every single exterior lamp in the past 2 months due to burnouts.

Could this be a coincidence, or could something be the matter with the alternator?
 
check your voltage regulator.. Thats where I'd start, I don't think you replacing the bulbs was a fluke. It appears your system is over charging by what you describe, thus why lights burn out in short order.
Dusty
 
Someone in this forum reported the cause of a similar problem to be a weak battery. The weak battery was making the alternator work more and causing its output voltage to rise.
 
It's normal. My 3800 reads 13.7-13.9 at the pcm. When its starts reading at 13.2 volts at the pcm and 13.8 at the battery be concerned. Mine was reading at this and the alternator was bad even though I had no starting problems maybe a slightly longer start some times (bad fuel regulator). But my volt gauge was reading right on 13 volts and I knew it should have been slightly past that. My volt light is on permanently from when the original alternator went bad.

I think one of the rectifiers went bad. 2nd hottest summer on record in my area. It was cooking under the hood.

It's colder outside so the alternator has to use a higher voltage(push electrons) to move current to overcome resistance.

I think it's ok. But you want know unless you get it tested.
 
Nothing wrong with 14-14.5V. I would love it. So, not a problem.
But yes, higher than normal voltage will burn out bulbs.

See if you can use another quality voltage measuring device to double check things.

You may have voltage spikes that are not there when you actually check things. The regulator is #1 on the problem list, then. this could blow out your bulbs.
 
Thanks!

I'll take it to the local Advance to use their tester, and see what that machine says.
 
On a car that old slight corrosion at the connections, through out the car, can cause minute voltage drops thus you get different voltage readings. Try reading tail light and plate light voltages and front light and fuse panel voltages.
If you can measure voltage across the fuses you can also detect droppage in M/volts which can account for what you are seeing.
 
Originally Posted By: DC44
I
It's colder outside so the alternator has to use a higher voltage(push electrons) to move current to overcome resistance.


+1, specifically, to charge a chemically comatose battery. This, plus dreary dark winter weather, is why you see so many bulbs out this time of year.
 
Originally Posted By: mechtech2
Nothing wrong with 14-14.5V. I would love it. So, not a problem.
But yes, higher than normal voltage will burn out bulbs.

See if you can use another quality voltage measuring device to double check things.

You may have voltage spikes that are not there when you actually check things. The regulator is #1 on the problem list, then. this could blow out your bulbs.



Right on. I would not be comfortably with 13.x volt charge rate. The RVC will determine the voltage needed and adjust, but you should see readings of 14.x atleast most of the time.
 
Typically, I've seen 14-14.5 volts but about a month ago I was getting over 15 volts (15.1-15.3) from my alternator towards the end life of my OEM AC Delco battery in my truck. It was one of the reasons I knew I was going to need a new battery soon, the other reason was age (5.5 years old). About 2 weeks later, after not starting the truck for a week, the battery was dead.

Luckily for me, I was able to drop in a Penn Deka maintenance free from NAPA (Legend 84 month Grp78) and it's all back to 14-14.5. With my AAA discount, I was out the door just under $100.
 
Took it to Advance after work today. They hooked up their tester, and everything passed with flying colors. I guess the whole bulb thing was a coincidence.

Over the summer, I cleaned every ground I could get at in the engine and the body. So those should be good still.

The only other thing I could think of is the battery cables, which are a known problem area on Buicks of its generation. Those can wait for a warmer day to check for corrosion.

So, looks like a false alarm. Thankfully!
 
Alternator voltage regulators do indeed put out more voltage cold than hot. Some are designed this way, and some do this as a nice circumstance of internal resistance.
Either way, some increased voltage when cold is normal.
 
btw - dont trust a pcm reading with a voltmeter of varying types...the pcm will have a diode in front which will give a .4-.7 voltage drop over what is at the battery
 
btw - dont trust a pcm reading with a voltmeter of varying types...the pcm will have a diode in front which will give a .4-.7 voltage drop over what is at the battery
 
I use a scan gauge and read the live data.I have the analog cluster. I wish I had the DIC display to read mpg,voltage and etc.
 
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