I have been having some weird problems with charging on my car. I was driving one night everything was working fine, all the lights were bright. I shut the car off for one minute to run in a store quick and when I come back out the car wont start and the battery is completely dead. So I figured I needed a new battery, changed the battery and the car was good for 2 months till now the other day it went dead again. I hooked up a voltage meter to the car while it was running a it was reading 13.9 with nothing on. With the headlights and heat, rear defroster and radio on it was reading like 12.5. Is this normal or is my alternator shot. I have heard about these cars having charging problems caused by other things besides the alternator like a bad connection or something but I cleaned the connection at the battery so now I dont know what to do. Also is there a no charge light that would come on if the alternator was not working? Thanks for any info!!

 

Sounds to me like you have a short somewhere that is trickling current out. Did you install a stero recently? Your voltage numbers sound about right. Try hooking up an ampmeter and measure the current draw with the car off and all accessories off. There should be minimal draw. You can calculate the total amount of Power drawn my multiplying the current you measure times the voltage accross the battery with the car off.

P = E*I

units are in watts

This way you can compare it to some values you know, say a 60watt light bulb. You shouldn't be pulling more then a few watts with the car off. So if it seems high, then you have something sucking your juice.

 

With your car running your alterator should be able to maintain 14V + with anything or everything running. Three problems come to mind. 1) Alterator 2) Loose belt 3) Bad connection between alternator and battery.
If you rev engine while turning everything on, does this increase the voltage? If it does that would lead me to believe it's not a connection problem but more likely alt. or belt.

 

Yeah check the belt first. But alternator failure is pretty much destiny for most third gens, there's a flaw in its design where the brushes burn into the pickup rotor. Either the brushes are too hard or the rotor is too soft, the brushes end up making deep channels in the rotor.

 

Your no load idling volts seem ok, could be better.
Your load idling volts are way too low, at that voltage you're running off the battery with no alternator input at all. Yes there is a battery light for when your alternator goes south, but yours seem half a.s.s (not completely dead) that's why it's not triggering the light.

Adamis, no need for ohms law in this case. Save you neg/pos voltage drop test for when it's really need.

 

heh, heh, just thought I'd throw it in since it's the only thing I have learned in that class so far. Sure engineers might not be cool, but electrical engineers are just plain crazy! I'm glad it's the only class I have to take for that stuff.

 

Thanks for all the info guys! I haven't got a chance to try out that equation yet adamis. The voltage goes up when I rev the car. Since that day that the battery went dead I haven't touched anything and it has been fine. I think this thing is half shot like CandiMan said. The car was sitting for almost a year and half till just 2 months ago so a lot of crap probably built up in the alternator. Needless to say I picked up an alternator the other day but I haven't put it in yet cause it's been raining all week. Luckily the car has been fine, but well see how long that lasts. Thanks again!!!!

 

With you breaking out the volt meter and checking voltage I assumed you had checked the basic as Max4me suggested because using a volt meter is more than what most will do.