Question: Need advice on Electrical

[82ColEd]

Bill: Cant wait..


As an example, what would the experts here say to this:

As per my ALDL data, my Battery Voltage says 17.6 at startup then goes to 5.6 and stays around the 6's (5.9, 6.3 etc) while i drive and back up to 18.6 before i turn it off..

Battery or Alternator ? CAN that affect Idle performance (car running in general) or not? Lights are usually on, no radio on, no AC or fan. No additional accessories aside from what GM put in the car.

 

[John Robinson]

Bill: Cant wait..


As an example, what would the experts here say to this:

As per my ALDL data, my Battery Voltage says 17.6 at startup then goes to 5.6 and stays around the 6's (5.9, 6.3 etc) while i drive and back up to 18.6 before i turn it off..

Battery or Alternator ? CAN that affect Idle performance (car running in general) or not? Lights are usually on, no radio on, no AC or fan. No additional accessories aside from what GM put in the car.

Ok you woke me up

In my experience what you describe sounds like a bad diode in the alternator. I had a similar problem with a motorcycle that would have a bright headlight and then it would dim etc. The problem there was one of the three phase diodes went bad intermittently and the alternator was spiking voltage and then it would quit and the bike ran on the battery. If I were you I would charge the battery overnight and then do a load test on it to verify that it is good. If the battery is good then put a volt meter on the battery and measure the voltage at the battery with the engine running. This will give you a look at what the alternator is doing and also let you know if the meters in the car are anywhere near right.

One of the tricks I use is to plug in a cigarette lighter (I got mine at Radio Shack) adaptor with a fuse and on off switch and hook up the voltmeter to it inside the car then I can observe it side by side with the meters on the dash.

 

[82ColEd]

Ok you woke me up

snip

Sorry John (also, for kinda sidetracking your thread, but i figured i ride your coattails as your issue is done), didnt mean to wake you. :L

It's not the AMP reading gauge but the ALDL being read. The AMP reading shows loading good at 13/14, whereever the needle be. Guess, i should get my battery checked in any case. It has been a while since i had a new one. Where do i get a side terminal battery here? Oh the fun living back home. :eyerole

And this one is being hooked up to a Charger/Maintainer every night. I need it to run daily. I dont see any issues with dimming headlights or somesuch, so i was guessing the alt is fine, hence my whole question regarding battery and idle speed/performance of the car.


-Stefan

 

[John Robinson]

Sorry John (also, for kinda sidetracking your thread, but i figured i ride your coattails as your issue is done), didnt mean to wake you. :L

It's not the AMP reading gauge but the ALDL being read. The AMP reading shows loading good at 13/14, whereever the needle be. Guess, i should get my battery checked in any case. It has been a while since i had a new one. Where do i get a side terminal battery here? Oh the fun living back home. :eyerole

And this one is being hooked up to a Charger/Maintainer every night. I need it to run daily. I dont see any issues with dimming headlights or somesuch, so i was guessing the alt is fine, hence my whole question regarding battery and idle speed/performance of the car.


-Stefan

No problem and you did not hijack my thread.

Actually I am very pleased that it has stirred up so much friendly banter and am waiting impatiently for the upcoming promised article.

With people on this forum willing to share their training and knowledge this becomes a place to go back to school as it were and learn from those who have been there and done that. Any time you come away from a response from someone that makes you say I didn't know that you gained new insight.

So keep the information flowing and wake me backup when the article is published.

 

[TedC]

Alternators depend on battery resistance to manage voltage output. Can you run your car without a battery attached? Sure, just understand the possible risk of damage caused by voltage spikes that can exceed 20 volts. Even a dead or near dead battery can appear to the voltage regulator as an open circuit and cause similar issues. Some voltage regulators include disable protection if battery voltage drops below a set level. Enough on that topic. If the ALDL (serial data) is showing out of range voltages, but lights remain steady, could this be a computer issue? Poor connection to computer or defective computer?

 

[geekinavette]

Stefan... something is very wrong there. I would put a REAL voltmeter (digital multi-meter) on it and see if it follows that ALDL reading. If it does...you have major charging problems! I doubt it does...you may just have a flaky A/D converter in the ECM...but verify that!

Alternators depend on battery resistance to manage voltage output.

I REALLY don't mean to or offend anyone...and maybe that was simply mis-worded, but that statement is incorrect. The only thing varying battery resistance will change is alternator CURRENT output...from Ohm's Law: current = voltage/resistance (assuming the resistance does not drop to a point where the alternator's maximum current capability is exceeded...for example a dead battery). The same thing will happen when other loads are applied, like turning lights on...etc. More load = lower total resistance = higher alternator current output.

The regulator generates its own internal fixed reference voltage via a zener diode (approx 1/2 of rated output if memory serves...that may be incorrect I don't recall at the moment), and compares that to the output voltage divided by two (or whatever that ratio is...be it 1/2 or whatever). It uses this difference to determine if the output voltage is in range or not, and compensates accordingly (the method of doing that is a little complex to go into here...but will be explained in the upcoming article).

Can you run your car without a battery attached? Sure, just understand the possible risk of damage caused by voltage spikes that can exceed 20 volts.

Agreed...and previously mentioned! The mention of running an engine without the battery connected was just to make a theoretical point.

DO NOT GO DISCONNECTING YOUR BATTERY FOLKS!

 

[TedC]

Geekinavette, Try this simple experiment. While you have a DVOM attached to a running car, jumper the battery to a second battery that is fully charged. Post the results.

 

[geekinavette]

Before even bothering...I would ask why?

The second battery is another load connected in parallel with the running car, thereby reducing the total resistance load of the running alternator. (Rtotal = 1/[1/R1 + 1/R2 + 1/Rn])

The running alternator will output slightly more current to the extra load (if the second battery is fully charged, since internal resistance is logarithmically proportional to battery voltage...approximately).

In addition the voltage measured will probably change slightly since the extra battery is not only a load but another voltage source (just one that is not sourcing any current)...might go up a little, might go down a little...means nothing.

Not trying to be argumentative...just trying to understand the point of this "experiment"? (which in itself is meaningless unless enough samples are taken and analyzed statistically)



Bill

 

[82ColEd]

Stefan... something is very wrong there. I would put a REAL voltmeter (digital multi-meter) on it and see if it follows that ALDL reading. If it does...you have major charging problems! I doubt it does...you may just have a flaky A/D converter in the ECM...but verify that!

snip

Ok, finally had some time to take some measurements..
I have a cable attached to the battery (which is 4-5 years old, so might be a suspect) for the maintainer, where i took measurements.. Here they go:
Unplug the car from Battery Maintainer, reading: 12.6V
Started the car, reading: 14.7V
After taking a 5 minute drive: 14.6V
Shutdown the engine, then a reading: 13.6V
After 1 hr, it reads: 12.7V
After 4hrs, it reads: 12.4V
After 28Hrs (next day plus): 12.3V
When turning on the light, engine not running: 11.7V
Engine running, lights on: 14.7V
and last, engine off again: 12.7V

Now, It appears to me that the battery holds a charge, yes?
Also, i believe the Alternator charges the system ok, yes?
(How can i measure output from the ALT? I'm hesitant to put my little Voltmeter on the black and red output cables of the ALT hnoes).

Also, does that above indicate a flaky A/D converter? How would i test that, and what can be replaced (Please dont say the whole ECM, did that a few years back, like 10 years ago, and it was $700 odd :ugh)..


Awaiting news before i go further..

Thanks a ton so far..


-Stefan

 

[roger longman]

bump

 

[John Robinson]

New Ideas

Roger you might want to scroll down the technical site to Jan. 20 and read the thread buy ltmark titled voltage/ohm reading. I am including a little sketch that show how to connect the vom as discussed in this thread. I hope this will be helpful.

http://farm3.static.flickr.com/2719/4310729376_641462385e.jpg

 

[roger longman]

Roger you might want to scroll down the technical site to Jan. 20 and read the thread buy ltmark titled voltage/ohm reading. I am including a little sketch that show how to connect the vom as discussed in this thread. I hope this will be helpful.

http://farm3.static.flickr.com/2719/4310729376_641462385e.jpg

Hi John, Thanks but it's not for me. I bumped it for Stefan, who's awaiting some advice. Roger.