Without getting it to a shop, how can I tell if my Alternator is bad?

Question

I'm trying to rule out things like relays. The battery was bought about 3 months ago. When you try to crank the car, there is nothing. You plug it up to another vehicle and it doesn't give enough power to start the engine. I don't want to have to spend the time and the money to replace the alternator if that's not the problem. I'm almost 5 months pregnant and can't get underneath vehicles like I once did. So... give me some sound advice any mechanics out there.

I would test the alternator while the car is running... but I can't get the car to running without power. :)

Answer 1

Do not disconnect the battery with the engine running ! This could cause a voltage surge and severely damage expensive electronic units such as your ECU.
If it does not start even with a jump then your problem is either the starter motor or bad connections such as earths or battery leads.
Try getting a jump from another car, but this time connect the leads up and start the second (working) car. Do not try to start your car instaed rev the second car to about 2500 rpm and hold this for about 5 minutes. This will allow the second car to charge up your cars battery. After about 5 minutes keep the second car running and now try to start your car.
This should have given your battery some power and your car could start from its own battery assisted buy the jump leads, rather than just through jump leads.
If you can get your car started get a voltmeter and take the reading accross the battery ( make sure the second car is not connected at this time). It should read at about 13.5 volts with the engine reving at about 2500 revs. If it is less than about 12.5 volts then your alternator is at fault or your fan drive belt is loose.

Answer 2

If the alternator is bad, the car should still start if you hook another car up to it. Especially if you let the other car run for a while to partially charge your battery. So I question if the problem is the alternator. However, If you can get it started, hold a wrench beside the alternator a good alternator makes an elctromagnet and will pull the wrench. a bad alternator will just spin and ignor the wrench.

Answer 3

if you cant jump start it that's not the alternator, it can be bad ,but that would be either a battery gone bad or the starter has went out on it,an alternator wont stop it from starting,so you might be able to rule this out for now,you,ll have to get it started to check it though,you don't need to be trying to work on this ,get someone to help you,remember your going to have a baby,don't take any chances ,good luck.,,PS pulling the battery cable of isn't a good idea on some of the newer cars it can actually cause damage to the alternator,good luck.

Answer 4

So jumping it dosent work and with a new battery..... it might be the starter.... but get the car started, then with it running remove the positive terminal, if the car stays running the alternator is good, if the car dies the alternator is bad.

Answer 5

Start you car. Take a volt meter, put the setting on 20v, and touch the red and black probes to the battery. You should read anywhere from the high 13s to around the 15s. Your battery will read about 12.8 volts when car is off, so if the meter reads around what I said when running then your alternator is working.

Answer 6

You're going to have some one go under the car to check the wires and solenoid at the starter because it sounds like that might be why it won't start, at least turnover for now. Alt. after it starts.

Answer 7

start your car and then disconnect the positive cable from the battery if the vehicle shuts off your alternator is no good.

Answer 8

michael r is right