battery or alternator?

[mynameisjonas]

ok well it's starting to get cold up around where i live (above philly). on one of the first cooler mornings my car was dead. so i initially just thought it was battery. i just jumped it tonight because i needed to drive it and as i was idling at a stop sign the lights started dimming and the radio cut off so i had to keep the engine revving and it was fine. i made it the rest of the way home (about 10 minutes) fine. so is this definately the alternator?

[quiksilvia]

alternator sounds possible, take it to a midas or something and have it tested

[GroundZero]

had the same problem with my rx7, it's your altenator, to be more specific it's the power redulator in the altenator, and it sounds like when the alternator went it took the battery with it( they tend to do that)

[Chingon]

have you checked the liquid level in your batterY?

[lbrowne]

Had the *exact* problem and it was the battery.

The car's system is not an ideal way to recharge a battery. On newer batteries you're fine but on ones with a bit of age it usually doesn't go well. Technically you are suppose to hook a battery up to a battery recharger....but not many do that

My money is on the battery, hands down.

[Toahk]

I had a similar problem recently, but I would have my battery/brake light come on below 2k rpm's, turned out the alternator was bad as was the battery.

[180fan]

If your car is running and your power starts to cut in and out (most noticiable in my car via my stereo) then it's your alternator (check the belt first though). If your car has a hard time starting, its your battery. Though, if your alternator's not functioning properly, it's not going to charge your battery. If you're running a SOHC, what happened to me was my water pump was leaking and dripping coolant on the belts, causing my alternator to slip. But at the same time, I had just bought a new redtop optima, so I thought it was that. After a new alternator, I discovered it was the water pump via a drop of coolant hitting my face when I was under my car installing the new alternator. Just some things to check out.

[randybunctious]

why dont you just jump the car off to start it and put a voltmeter to the battery post and see if the alternator is charging 14 volts , if its charging 14 its the battery, if not alternator or both, id sayprobably the alternator but guessing doesnt make a damn

[f8sjester]

i kinda agree it's the battery. . . it sounds like the alternator is still putting out voltage but the alternator will not put out it's maximum voltage at idle. (should put out 14.7 somewhere around 2k rpm) at idle, the battery is used as a kind of "reserve" to handle excess load . . . especially when you're at a stop light and you have your headlights on and whatever accesories going. . .

blah blah blah. . get em both tested and be safe about it

[mynameisjonas]

thanks you guys for your suggestions. yeah i gotta get a voltmeter, i'll try to pick one up tomorrow. but i'm thinking it's the alternator. i charged the battery yesterday for like 10 minutes and i took it for a drive(with all accesories on), everything was fine. came home, turned it off, started right back up. i did this about 5 times and evertytime it started, so i'm guessing it's the alternator not giving a charge. i'm gonna try to start it again after sitting a day. if it starts, it's gotta be the alternator, but i'll test it with the voltmeter nevertheless.

[Nathan]

I think it's just the battery...I've had something similar happen in my girlfriends car, drove me nuts and I swore it was the alternator until her dad (a mechanic) got there and just got her a new battery, no problem ever since.

[mynameisjonas]

i checked it and it is only putting out 11.6 volts at idle. i revved it with the throttle valve and it only went up to 12.8 or something like that. so it is the alternator. is there a way to test just the battery with the meter to see if that is bad too?

[Scott McLellan]

Does it have a green "eye" on the battery? Our Saturn seems to be having the same problem actually but I know it's not the battery cause I replaced it like 2 weeks ago. I think maybe when the alternator is going out it kinda acts up, works sometimes, sometimes not. I could be wrong though.

[mynameisjonas]

no it doesn't have the eye thing, that would be too easy

[randybunctious]

you can get your battery tested for free at any autozone or advanced, on or off the car.

[CanadianCoch]

i checked it and it is only putting out 11.6 volts at idle. i revved it with the throttle valve and it only went up to 12.8 or something like that. so it is the alternator. is there a way to test just the battery with the meter to see if that is bad too?

Car battery should read 12.6 when off, when it's on it should read mid/high 13's. If it's not getting that high when it's on, it's your alternator.

When your car is on, the alternator give it all the juice it needs, and also rejuices the battery.

Dr.

[deftdrummer]

its definetely your alternator i would have to say. Reason being, is that the SAME EXACT THING happened to my 1992 300zx (lights dimming, car turning off at stop lights).

The reason this happened in the first place i found out later was because i hooked up jumper cables to the battery incorrectly with the positive on the negative and vice/versa and it fried the alternator. (i was an idiot at the time i know) so i then had the alternator fixed under warranty and all was well. Then i totalled it a month later :-(

[Silvia2b]

Right lots of good suggestions here on this post, but think about it here are the functions of the electrical systems components. The battery is a storage cell for electrical energy used when the engine is turned off and used to power up the starter motor to life when you ignition is energized. It also powers accessories for limited periods when key is off.The alternator converts mechanical energy from the power plant and generates enough current to supply the cars accessories while also adding extra voltage to charge the battery for it’s consumption before starting. The voltage regulator can be built into the alternator or separate. This device is responsible for managing demand and output deciding when to react or change the operation of the system to accommodate the needs of your car. These components are all interdependent, to keep your cars electrical stuff in good health, if one fails the others will likely try to compensate for the weak link, and eventually this will cause the others to failure. Then you’ll have the problem you described at the stop light. Good chance you battery isn’t being charged for a long enough but may still have some life, you need to have your system load checked for proper operation. Good luck, post back if you get it fixed. Success stories are always fun.

[Dr. Evil]

Take your car to a shop.

Have them test the battery and alternator. If the guy comes out with a voltmeter, he doesn't know what he's doing.

Read the battery. Find the 4 character code on the front/top/side. There are usually 4 characters. The last two are the important ones. One should be a letter, the other a number. The number is the year the battery was made, the letter is the month, meaning.

XXA6 january 1996XXB6 February 1996XXG9 July 1999 etc (the XX are usually manufacturer specific codes). Sometimes it is reversed, the number and letter are first. ACDELCO, INTERSTATE and anything sold at sears all conform to this code, as do most other domestic batteries made after 1970.

If your battery is more than 60 months old, replace it. It is no longer dependable. Holding a charge? maybe. Starting up the car? maybe. Dependable ? NO. You don't want to gamble that when there is an emergency and your car will not start.

If the mechanic has a battery/alternator tester, make sure he knows what he is doing. If he doesn't read your battery and search for the cold-crank amp rating of the battery, he doesn't know what he is doing. Basically, the battery is tested by supplying it with current while applying load (simulating the current drawn for the car's electrical system). The load applied should be aprox 1/2 the cold crank amp rating. If he just twists the knob all the way and holds it, he doesn't know what he's doing, take the car somewhere else.

If the battery test comes up good, he should test the alternator. This test should take at least 10-15 minutes. The car should be running (obviously), and left to idle. If the voltage remains a consistant number, not fluctuating more than 0.1 to 0.3 (max), you are in the clear. Different cars with different alternators have different volt ratings, but the generally accepted "minimum" volt reading for a properly functioning alternator at idle is above 12.9, volts. Different mechanical vocational disciplines state otherwise, but nothing but the best for my customers. Brand NEW Alternator only charging at 12.8? Forget it.

I don't believe I left anything out. A good alternator is ACDelco. They are remag cores, the best thing about it is the warantee, not necesarily the product. Same thing said about their batteries. They offer a great adjustment on a faulty battery. Interstate is the same grade. You wouldn't go wrong with either.

I recommend NIPPON DENSO for all your Japanese OEM needs. Not remags, brand new. I've had cases where we tried 2 different alternators, both nissan OEM from the dealership, and they did not charge properly. Used a NIPPON DENSO, worked like a charm.

Best of luck

[Scott McLellan]

Or you can take your alternator off and have it tested in 30 sec. for free at a parts store. 10-15 minutes for a check at a mechanics shop and you'll be set back some serious dough. There is no reason to check it that long either. The idle speed will change enough in that time period that it will probly fluctuate more than .1 to .3 anyway. By the way, the way you test volts is with a voltmeter.