: Low voltage while car is running BUT bench test...



Marlin
04-17-11, 11:55 AM
I am working on a 2005 STS with the 3.6L V6.
The voltage at the Alt is between 13.1 and 13.5 while running, mostly staying at 13.3.

I bench tested the Alt and it comes back good. All the wiring looks ok and the battery holds a charge after trickle charging.

Anybody had this happen on their car? I have seen this before and it was still a bad alt but want to make sure I am not missing a charging switch, fuselink, etc...

Thanks

SlickCityStan
04-17-11, 12:06 PM
what is the problem? If I remember correctly when checking voltage while running thru the DIC that's sounds normal.

ddalder
04-17-11, 12:37 PM
Agreed. The system will adjust the charge rate based on demand and its estimated battery state of health (computed using a few different criteria). This doesn't seem unusual at all, unless you're experiencing other problems.

Marlin
04-17-11, 01:51 PM
what is the problem? If I remember correctly when checking voltage while running thru the DIC that's sounds normal.

I am checking at the Alt/Batt and with a load (AC, Radio, and High beams on) it still stays at 13.3. Even when the batter was weak or after charging.


The problem is the battery was drained. Battery was charged and started car a couple times and let sit over night and still held its charge.
But the Alt, warm or cold, will still stay at 13.3v. My CTS with the same motor/alt stays in the correct 14ish range warm or cold and with a load or not.

SlickCityStan
04-17-11, 02:20 PM
A common problem with the STS is when battery problems start such as you mentioned the culprit is usually the battery. May be hard to believe but true. Also you will find that the normal operating parameters for the STS- V6 or V8- can't be compared to any other GM make or model even with the same engine. The STS is IMHO a singular entity of its own in the automotive universe. Anyway have your battery checked.

onlyuscars
04-17-11, 10:15 PM
The car starts and everything works? I have had vehicles with whacked voltmeters before. I wouldn't lose any sleep over 13's instead of 14's.

kschwed
04-18-11, 02:14 AM
13.3-14.4 is completely normal

Check the voltage coming out of your walls. It will fluctuate anywhere between 115 and 122. Sometimes a little lower or higher. A volt doesn't make a very big difference even in a 12v system.

However, if your battery is dying, it is probably the battery. How old is it? If it is >4 or 5 years, it is not uncommon at all for it to die depending on the brand. AC Delco (The OEM battery is a pretty good one). Buy an optima red or yellow and you won't have any issues for >5 years guaranteed.

ddalder
04-18-11, 02:31 AM
We have started a switch to Odyssey batteries in our fleet. Our vehicles present significant electrical demands and from tests done to date, these have proven better than Optima. They are quite expensive though.

Marlin
04-18-11, 07:37 AM
13.3-14.4 is completely normal

Check the voltage coming out of your walls. It will fluctuate anywhere between 115 and 122. Sometimes a little lower or higher. A volt doesn't make a very big difference even in a 12v system.

However, if your battery is dying, it is probably the battery. How old is it? If it is >4 or 5 years, it is not uncommon at all for it to die depending on the brand. AC Delco (The OEM battery is a pretty good one). Buy an optima red or yellow and you won't have any issues for >5 years guaranteed.

The battery is not dieing its just not getting charged. The car was turning over but got slowwer and slowwer till it would not start.
Battery was trickle charged over night and starts the car fine now. Let the battery sit over night again and still works fine.

SlickCityStan
04-18-11, 08:41 AM
For the sake of being clear How often does this cycle repeat itself or has this only happened once? If it is happening repeatedly I would say you have a dead cell in your battery. If it only happened once then it's just the nature of the beast. But your charging system is working.

Marlin
04-19-11, 06:16 PM
Happened once but was not charging on weak battery and some items got dimmer when all were turned on and still did not go over 13.3v

Fully charged the battery and going to have it tested tonight. If it test bad will replace first if not then alt.

Will update.

Subsailor613
04-19-11, 06:36 PM
Start with AT Rest Voltage, usually around 12.6
Start the engine, anything above this "At Rest" voltage is
"Charging Voltage", the fact that you have everything ON,
is more of a deterrent that you will NEVER see 14+ volts on any meter.
This is what determines whether to charge, and how much, is the lower
voltage, determined by the "LOAD", the Load pulls the voltage down,
and the alternator senses this, and charges the system to "TRY" to:hmm:
Keep up with the load, and maybe a little more to charge the battery.
We have a 150 Amp alternator, it will do it's job faster than most other
cars, which have a 30 amp alternator, a older police car may have a 60
Amp alternator.:hmm:
Ask yourself, Does the car start the next morning OK ? :shocked::shocked::shocked:
Or get on of those 3 LED plug it into your cigar lighter, Red=Not charging
Amber= low charge, and Green= Normal Charging this way you can monitor
it as often as you like , under operating conditions. :cheers::cheers:

Good Luck, and Have Fun.

ddalder
04-20-11, 01:36 AM
Your most likely problem is the battery. If your battery tests good, which I suspect it won't, I would not recommend replacing the generator without first understanding the way the charging system works. The system in this car is fairly complex and charge levels/generator output is determined by many factors. Ambient temperature is a factor, both when the vehicle was last shut off, most recently turned on and throughout engine operation. Current draw is factored in using a current sensor on the negative battery cable. This is monitored by the Instrument Panel Module (IPM). The IPM communicates with the ECM which is actually the device that controls the generator. Output of the generator is duty cycled based on what the IPM/ECM decides is necessary, it is not simply charging or not charging based on battery/system voltage. There is also a load management system built into these cars which controls devices based on the health of the battery and charging system.

The problem with those "charge indicator" devices you plug into the cigarette outlet is they are relatively meaningless in these cars. Frequently what would register as not charging, or low charge is exactly what the system computes and would be considered normal at that moment in time. Personally, I wouldn't waste any money on one of these. Probably fine in your '84 Chevy, but not in modern vehicles.

If you're planning on doing any degree of work on this car, a service manual is a really good idea. Most of these systems are not simple and a lot of what goes wrong can't be properly diagnosed without some level of knowledge and understanding along with appropriate test equipment.

Marlin
05-08-11, 07:19 PM
Well I took both the Alt and Battery to another parts store. Battery tested good so they went to test the alt. Well the alt needs special brackets so they keep working on it and working on it. Another person just walked up and asked if I needed help. I told him I was getting the Battery and Alt tested. I guess he thought I said I wanted them tested not I am getting them tested so he test the Battery again. This time it failed. Seems one of the cells was flaky and would test good then bad.

So new battery and voltage popped back up to 14ish range.
So 3 battery test with 2 good and 1 bad.