Car troubles: electrical

delroland

So, my battery was dead this morning. I get it jumped, drive it to work, and find that the battery died again when I try to drive to lunch. I get it jumped again, drive to Kragen, and the guy tells me that the battery is a little low but seems to be holding a charge. He then tells me that it is probably the alternator.

Personally, I think he is full of shit as far as the alternator goes, as I am not having any problems while driving the car; I don't lose power, the lights, AC, and radio work fine, etc. However, I am not a car guy, so I was wondering if the alternator could drain the battery when the car was turned off.

I also noticed that my interior lights sometimes would not turn off, and I think that might have been the drain. I think I fixed that problem, so I shall see if the car starts in the morning, but if it is dead in the morning, do you guys really think it could be the alternator?

TexiKen

How old is the battery? Even if it says 5 or 6 year battery, I've always had usually one less year than what it says on the case. Also check the water level in the battery.

The alternator would be the problem if you saw the battery indicator drop while driving. It happened to me once, it's similar to having the car run out of gas.

I think the battery may have just run out. What make/model is it, by the way? You might want to check to see if your vehicle has noted electrical problems.

fuelish

Sounds like a bad battery or something is drawing power when the car is off(Like the interior lights you noticed)

Thanatoid

If you have a mechanically inclined friend, borrow his services. He will have a multimeter.

With this device, you can tell whether your charging system is working or not. The battery at idle should measure 12.20-12.50 volts. When you rev the engine, it should read 13.50+.

If these readings are good, you have an effective charging system, but might need a new battery (much cheaper than the new alternator that dishonest mechanics like to sell).

Might not be your cup of tea, but it is a way to figure out whether the mechanic is lying or not.

Dalboz

What you're describing sounds like a dead battery. If it was dead and you had to jump it in the morning, you would probably need to jump it again when you needed to start the car, like you said you needed to at lunch. The battery is mostly used for powering the electrical stuff when the engine is off and for starting the engine. When the engine is running, the alternator should kick in. If the battery is new, it's possible that the alternator could be bad, causing the battery to take over and drain it quickly. It happened to my cousin's car. If that's the case, you would need to get the battery replaced anyway.

Daenris

delroland wrote: »

So, my battery was dead this morning. I get it jumped, drive it to work, and find that the battery died again when I try to drive to lunch. I get it jumped again, drive to Kragen, and the guy tells me that the battery is a little low but seems to be holding a charge. He then tells me that it is probably the alternator.

How far is your drive to work? After jumping a dead battery you need to have the car running for some time to recharge it (assuming it is just a dead battery and not some other electrical problem). If you only drove for a few minutes and then turned your car off again it's no surprise you needed to get it jumped again at lunch.

Sir Carcass

It's been a while since I had battery problems, but I seem to remember a mechanic telling me an easy way to check the alternator is to start the car and unhook the battery. If the car dies, the alternator is bad. The voltmeter method is probably the most reliable, though, and is very easy. Just touch the posts of the battery with it and read the voltage it's reporting (though I was thinking 14 was what the alternator output while idling).

If it is just the battery going bad, then you can charge it all day long but it won't hold much and will die pretty quickly. I had a battery slowly die that way. Supposedly every time the battery is drained, it removes a certain percentage of it's total charge.

Usagi

Sir Carcass wrote: »

It's been a while since I had battery problems, but I seem to remember a mechanic telling me an easy way to check the alternator is to start the car and unhook the battery. If the car dies, the alternator is bad.

This is a very simple method of testing your alternator. Or you can drive it to an AutoZone or a Sears and have them test your battery for free.

fuelish

Sir Carcass wrote: »

It's been a while since I had battery problems, but I seem to remember a mechanic telling me an easy way to check the alternator is to start the car and unhook the battery. .

This is a bad idea. It can damage the diodes in the alternator it can also cook the regulator. It would throw a code in a computer controlled car and might do other damage due to a possible volatage spike. Much cheaper to buy a multimeter from RadioShack(or nearly anywhere) you can get one for $10 and a really good one for less than $100. They can even be used for other things(My Fluke has an adaptor for temp testing)

Iceman.USAF

fuelish wrote: »

Sir Carcass wrote: »

It's been a while since I had battery problems, but I seem to remember a mechanic telling me an easy way to check the alternator is to start the car and unhook the battery. .

This is a bad idea. It can damage the diodes in the alternator it can also cook the regulator. It would throw a code in a computer controlled car and might do other damage due to a possible volatage spike. Much cheaper to buy a multimeter from RadioShack(or nearly anywhere) you can get one for $10 and a really good one for less than $100. They can even be used for other things(My Fluke has an adaptor for temp testing)

Indeed. As a rule, if you're going to fuck with your vehicle WHILE IT'S RUNNING you need to be EXTREMELY FUCKING CAREFUL