High Voltage??

schmittygm · February 15, 2007

Hey guys- quick question.

My '99 silverado has what seems to have high voltage output from the alternator. The gauge reads way past 14V which is what caused me to be concerned. When I put a voltmeter on it, it reads just over 15V (while running of course). The Batt says 12.45V when eng is off. Is 15 volts too much??? Do you guys think I have to worry about eventually frying my alternator?? The battery always seems to hold charge and it never starts hard. The battery is a few years old but I doubt it is a problem. What do you guys run normally?? Anyone have over 15V??

lerbud · February 15, 2007

13.5 to 14.5 is normal for the alternator. the alternator may be bad and overcharging. i would get the whole system checked. if your battery is going bad the alt. could be overcharging trying to get the battery to charge up. if this is happening the battery could blow up. be careful & wear safety glasses if you do any more testing yourself.

schmittygm · February 16, 2007

Yeah, I'd kind of hate to fry the alt over a dumb deal like this. Any one else ever heard of this?

MrLM7 · February 16, 2007

Mine usually runs at 15, too. Perfect time to get some pulleys!

Nice rig · February 16, 2007

Sounds normal to me, mine usually reads around 15ish. But if your that concerned about it your local automotive store should be able to check out the entire charging system for free.

dreman · February 16, 2007

I had a job driving a 3/4 ton Chevy to deliver truck parts years ago. One day the truck started showing somewhere around 16-18 volts on the gauge. A day or two later it wouldn't start. The high voltage boiled the battery, leaving it about 1/3 full. With the old Delco sealed batteries, that meant get a new battery. The problem was in the voltage regulator.

RobD · February 18, 2007

I have only had my 2001 Suburban for 2 weeks, but I noticed my VOLTS gauge was doing this same thing. I replaced the battery the day after I bought it, so now I'm worried I might be cooking my new DuraLast. The volts needle is usually pegged at the 75% mark (~16.5V). Yesterday on the family drive, it did dip down to what I would say was about 15.5V during some of the trip.

I should assume that this isn't normal and should have the charging system looked at? I know on real cold mornings (it sits outside) the alternator does make a bit of a groan at times. A co-worker said it sounded like a bushing going bad in the alternator.

redvett · February 18, 2007

Take a digital volt meter and do some checking with engine running at the pos at the alternator and at the battery. 14.5v should be about max at the alternator and the battery about 13.7 if fully charged but will drop back to about 12.7v after a while when sitting with no charging or discharging.

Remember an alternator cannot fully charge a battery only a generator or a battery charger.

activ · July 24, 2007

Mine was about 14 or so volts but dropped down around idle (600 give or take) and the volts seemed to jump around from time to time so I replaced the alt. Now it runs 15V or slightly higyher on the gauge (need to drop a VOM on the batt) idle or not.

BUT I created a new problem. The battery symbol on the message center just flashes red on and off. The new alt is charging fine - I can tell from the Vgauge. There was a "tech tip 660" in the alt box that gave a specific order in which to unhook and rehook the wires and warned if one doesn't then one gets what I got. The pisser is that I did precisely what it said...

I tried hooking up a code scanner but there is no code. I've run the truck about 20 times and it hasn't cleared the code. Any idea what could be wrong? Is there a way to reset the computer if that's all it is? (I am going away for a week so could disconnect the batt for the entire time)

2002 Sierra Denali (6.0L)

Thanx for any insight