Battery or alternator? Gauges going crazy
Battery or alternator? Gauges going crazy On my way home today the car was running fine but then all the lights in the cluster started to go on and off. The radio faded in and out along with the headlights.
When i got home i could not start the car again, it just clicked.
is the battery dead, or the alternator?
the connections on the battery look good
When i got home i could not start the car again, it just clicked.
is the battery dead, or the alternator?
the connections on the battery look good
jump the car.
If it dies right away its probably the alt.
If it stays running Its probably the battery.
You can check the output of the alt with a volt meter. If its putting out 13-14.5v it may be ok. That does not mean the diodes in the bridge are good though.
Also it wouldnt be bad to have the battery checked.
How old is that battery? I dont think LA gets cold enough to make a difference?
Does all the other stuff turn on in the car?
Turn the headlights on. Note how bright they are, then jump a good known battery too it. Do they get brighter?
If it dies right away its probably the alt.
If it stays running Its probably the battery.
You can check the output of the alt with a volt meter. If its putting out 13-14.5v it may be ok. That does not mean the diodes in the bridge are good though.
Also it wouldnt be bad to have the battery checked.
How old is that battery? I dont think LA gets cold enough to make a difference?
Does all the other stuff turn on in the car?
Turn the headlights on. Note how bright they are, then jump a good known battery too it. Do they get brighter?
i know how to check the battery, but how would i go about checking the alt.
btw i have no idea how old the battery is, it was in the car since i got it 2.5 yrs ago from NJ
thanks for the input
btw i have no idea how old the battery is, it was in the car since i got it 2.5 yrs ago from NJ
thanks for the input
One thing I do is with a voltmeter and car at idle measure how much charge (in terms of voltage) battery is receiving. Increase RPMs and again see if the volts increase accordingly. It should climb up to 14V or 14.5V...at idle it can go from 11.5 to 12.5...thats aprox. GM states that a idle voltage of 11.1 (in F-bodies) is acceptable although I feel a bit uncomfortable with it.
Launching!
Joined: Jun 2009
Posts: 268
Likes: 1
The simplest way to see if the alternator is charging is to get the car started then unhook the positive cable while the car is running. If it dies then the alternator is not doing its job. It should be able to stay running disconnected from the battery because it is producing enough juice to keeps itself alive. Thats how I would go about it for sure.
NEVER NEVER NEVER NEVER NEVER NEVER NEVER NEVER EVER DO THIS. The battery controls voltage spikes and if you do this it will be your worst nightmare. Check the voltage at 1100 RPM'S it should be between 13.5-14.7 depending on battery state of charge. At idle with a meadium load it should never drop below 13.1V. Have the battery load tested at the parts store. You can also have the alt tested as well. Once again NEVER DISCONNECT A BATTERY WHEN A CAR IS RUNNING.
Trending Topics
The simplest way to see if the alternator is charging is to get the car started then unhook the positive cable while the car is running. If it dies then the alternator is not doing its job. It should be able to stay running disconnected from the battery because it is producing enough juice to keeps itself alive. Thats how I would go about it for sure.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo NEVER NEVER NEVER NEVER NEVER NEVER NEVER NEVER EVER DO THIS. The battery controls voltage spikes and if you do this it will be your worst nightmare. Check the voltage at 1100 RPM'S it should be between 13.5-14.7 depending on battery state of charge. At idle with a meadium load it should never drop below 13.1V. Have the battery load tested at the parts store. You can also have the alt tested as well. Once again NEVER DISCONNECT A BATTERY WHEN A CAR IS RUNNING.
NEVER NEVER NEVER NEVER NEVER NEVER NEVER NEVER EVER DO THIS. The battery controls voltage spikes and if you do this it will be your worst nightmare. Check the voltage at 1100 RPM'S it should be between 13.5-14.7 depending on battery state of charge. At idle with a meadium load it should never drop below 13.1V. Have the battery load tested at the parts store. You can also have the alt tested as well. Once again NEVER DISCONNECT A BATTERY WHEN A CAR IS RUNNING.
Alright guys my bad... I knew better than that I just had a brain fart. I've played with old small blocks that you could do that with WAY too long. A voltage spike would fry some stuff in a hurry if you unhooked the battery on that thing running. Words of wisdom: DON'T POST STUFF WHEN YOU'RE HAMMERED!!!! Once again my bad guys... Im really not an idiot... Just used to the old school stuff.
Alright guys my bad... I knew better than that I just had a brain fart. I've played with old small blocks that you could do that with WAY too long. A voltage spike would fry some stuff in a hurry if you unhooked the battery on that thing running. Words of wisdom: DON'T POST STUFF WHEN YOU'RE HAMMERED!!!! Once again my bad guys... Im really not an idiot... Just used to the old school stuff.
we don't disconnect the positive cable from a battery why exactly? it'll fry the newer computer systems? is that right?
i just did this to my friends (1999?) dodge to see if his battery was dead or the alt. but i learned that trick from autoshop. my teacher was an "old timer"
i just did this to my friends (1999?) dodge to see if his battery was dead or the alt. but i learned that trick from autoshop. my teacher was an "old timer"
Launching!
Joined: Jun 2009
Posts: 268
Likes: 1
That spes is the maximum output of the designed alt capacity. For some reason GM gives that number and it is useless. AT that voltage you are running on battery power and discharging the system. All in car voltage readings must be higher than 12.9V. Example police cruisers and ambulances would conk out when the voltage goes below 10.9. If left to idle at 11-12V you are discharging the battery. I have a contract with the local town and we service all the municipal vehicles. If a police car is at an accident or with the light bar on and all the other accessories it would eventually kill the battery. If left that way for an extended period of time with a low voltage output It will conk OUT. It will also set a code in the ECM . (LOW ALT OUTPUT). The old theory of disconnecting the battery to test a ( GENERATOR ) is a holdover from the old days. Alternators are EXTERNALLY EXCITED and will go nuts without a voltage reference from the battery. Remember an alternator has a VOLTAGE REGULATOR not a current regulator. Generators have both voltage and current regulation. Remember you need .2 volts for each cell over voltage to keep the battery charged and healthy . 12 volt batterys have 6 cells so the charge rate should never be under 13.2 V. Modern batterys have memory. If they are always undercharged they will never be able to be at there full capacity. Never undercharge a a battery. Especially GEL CELLS. (OPTIMA ETC) Hope this explains this. Nice discussion guys thats what its all about. Peace TOM
Last edited by tom falco; Jan 13, 2010 at 04:46 AM.
