Low Voltage On 07 Nbs

illMATTic · January 30, 2009

I just purchased an 07 NBS Silverado with a 4.8. It only has 8K miles. I picked it up on saturday. Monday we got alot of snow so I havent really got to drive at a normal speed/rpm. Traffic here is pretty heavy. in the morning when I start it, the voltage is at 14+ volts. after about a half hour of bumper to bumper traffic at an idle, the voltage drops to what looks like 12 volts on the gauge. Today i was only running the heater.

I am pretty sure the alternator should keep up with this load at an idle.

what is the output at 1000 rpm?

Its still under Warr. but I would like to know what the deal is before I take it in to the dealer.

thanks, matt

VMax2007 · January 30, 2009

It's fine.

The new alternators fluctuate output based on demand. Thank CAFE.

MarkD · January 30, 2009

Yeah, but your voltage should stay around 14.

illMATTic · January 30, 2009

I charged the battery last night and it seemed to be fine today. maybe the battery was low from sitting on the lot for a while and with the low rpms I have been running, it never got fully charged.

does anyone know what the max amp output is on these?

matt

Draenor · January 30, 2009

I charged the battery last night and it seemed to be fine today. maybe the battery was low from sitting on the lot for a while and with the low rpms I have been running, it never got fully charged.

does anyone know what the max amp output is on these?

matt

Depending on which one you have its 140A or 160A(snow plow pkg). As for output a 1000rpm, it depends on your load. Also you need to put a DMM and get a true reading. The guage is not totally accurate.

Zembonez · January 30, 2009

These gages are not exactly scientific (really just meant to determine if the system is functioning normally) Don't believe the exact voltage they say they are delivering. I'd bet on a low battery from the truck sitting on a lot.

Hope all is well.

illMATTic · February 1, 2009

thanks guys,

I have some new results. Upon starting the engine the voltage goes up to 14.56V (checked with a DMM) and then drops slowly down to 12V. this happens after about 5 seconds. If I re-start the engine, it will do the same thing. The voltage will not rise back to 14 even after driving it.

I have also charged the battery and still get the same results.

Any ideas?

Matt

BuckFeverZ · February 1, 2009

Sounds fine to me. As Jeff said, the voltage will fluctuate depending on the load. My gauge does the same thing.

illMATTic · February 1, 2009

Sounds fine to me. As Jeff said, the voltage will fluctuate depending on the load. My gauge does the same thing.

So what you guys are saying is the alternator turns off when the battery is full?

VMax2007 · February 1, 2009

Sounds fine to me. As Jeff said, the voltage will fluctuate depending on the load. My gauge does the same thing.

So what you guys are saying is the alternator turns off when the battery is full?

No, it just alters the output based on demand. That way it never works harder than it has to and thus, saves 13 drops of fuel per tank of gas.

norsemanberg · February 1, 2009

Tell you what, you go and do the same test but with all your accessories on and then give us the reading

Spurshot · February 1, 2009

Tell you what, you go and do the same test but with all your accessories on and then give us the reading

+1 and add to that your headlights/highbeams, etc., turn the heater blower on full as well. Motors are big consumers of power.

illMATTic · February 2, 2009

I did this. I even let all the accessories run for a while without the engine running. after I started it, the volts stayed up above 14V. OK, so I am with you guys on the variable voltage thing.

are the new systems that efficient that it can run a half hour before having to charge? OR does the alternator just give just enough voltage to keep everything within spec?