Thread: Alternator voltage?

13-15 volts on those style alternators.

They really only charge the battery when they need too and that's why you see volts down into the 13's because the demand for more power isn't needed.

The voltage does vary but it's shouldn't be ranging all over the place. If you are getting a Service Charging System something is wrong. You may have a battery that is going dead or a bad connection somewhere or the current sensor. A normal voltage swing will look like this:

The only thing that worries me is that you said it said charging system failure. This can be a bad battery (had that happen and 2 days later dead battery, tested 650CCA one day and 37CCA the day it died). The alternator some of the places can't test them properly so they will say that the alternator is no good, when it's actually their equipment. Did you get a Battery Saver Mode Active on the DIC as well? These 2 together have told me a couple of days in advance that the battery was going dead, even though I didn't know what it meant at the time.

Jeff

That's normal, when there is low demand the PCM will cause alternator will only put out what it needs to maintain the battery at safe level. GM dropped the voltage down so that the battery will last longer instead of pumping it full of electrons all the time. Basically it's like a hose and a bucket with a hole in it. When the demand is low the flow from the hose is low as it is needed or when the PCM determines that there is a need (Reconditioning takes it to 15.1V) it will put out more to maintain the level. If you look at the above graph you can see that it starts at about 12.6 then increases to about 14.1 then it holds there for a little while then it drops back and the battery voltage drops down as time goes by and gets to about 12.6 then it jumps up again. This was on a steady state cruise at about 65 mph and is about 30 minutes of driving. I probably had a bad connection and that's why it's so jagged, usually it's a little more smooth. I had to replace the positive Terminal this weekend since it was broken and finally didn't want to start the car.

Years ago I was in a Impala rental car and had a long drive ahead of me and I had the display set to Volts and after a while I watched as the voltage dropped and dropped until it was at 12.5V it held that for about 20 minutes. As I was about to call the rental car company to see about switching out cars and the closest location and all that the voltage started to climb again and held about 14 for about 10 minutes then dropped down again. After that I noticed that most all of the GM cars I have checked do that since the mid 2000's.

Jeff

12.5 volts still sounds sketchy, from what I dealt with in the past the alts lowest charging voltage should be around 13.6-13.8 for a low charge and 14.8 on the high side. I would be worried about a battery or alt if I seen it that low.

Man this has been going on since the early mid 2000's you guys never noticed because you weren't looking. This is something I see every day.

Someone has a piece of equipment and has it for 20 years and it doesn't give them a problem and it's just over there running and doing its job. Then one day something happens just like every other piece of machinery it breaks. Then everyone is in a panic and people notice things that they never noticed before. For example:

Customer: My controller isn't running, and the light on the CPU is flashing.

Me: That's normal it should flash, think of it as a heartbeat, if it's on or off all the time there is a problem. So what is the scale doing?

Customer: It's not working and that light has Never! done that before.

Me: Yes, it is supposed to flash, so what is the problem? Is it not weighing correctly or is the screen blank or what's going on?

Customer: I have been here for 10 years and I KNOW that light has never done that before there must be a problem!

Me: Look, this is normal operation for the CPU card, what problem are you having, is it not weighing right? What's going on.

Customer: I don't know why this light keeps blinking and it's never done this before.

Me: Sir/Madam I have worked here for going on 20 years and actually had the design on the silkscreen changed from Reset Indicator to Heartbeat to avoid this question I have been asked a million times. Could you please tell me what the problem is....


You really get tunnel vision when you are working on something that hasn't given you a problem before, you focus on things that have no significance and you end up chasing your tail. Lord knows I do it I have been round and round with things that I thought were causing me issues. when you don't know how a system works or don't know the nuances it's kinda hard to trouble shoot it.

Jeff