Battery staying on light on after start up

trixyben

Car hasn't been used for a few weeks and was going fine before, just started it up and the battery light is staying on so im guessing it isnt getting charged, checked all the cables and all secure, anyone have any guess whats the problem?

Strange thing is the exact same thing happened before when i went on holidays for 2 weeks before, stuck a 2nd hand alternator in and it was fine then.

Surely it has to be something simple? or am i best to just replace alternator again?

JustRoss23

did you test the alternator with a multimeter? that will tell you if its good or not:D the battery could just fecked it might not be holding the charge.

I worked on plant auto work before and an old schooler told me that the easiest way to find out if the alternator is working properly if you have no multimeter is to start the car, while its running, disconnect the negative battery terminal wire. If the car dies then the alternator isn't charging properly, if the car continues to run, then it is fine.
But saying that i have never tried that method

Joe 90

JustRoss23 wrote: »

did you test the alternator with a multimeter? that will tell you if its good or not:D the battery could just fecked it might not be holding the charge.

I worked on plant auto work before and an old schooler told me that the easiest way to find out if the alternator is working properly if you have no multimeter is to start the car, while its running, disconnect the negative battery terminal wire. If the car dies then the alternator isn't charging properly, if the car continues to run, then it is fine.
But saying that i have never tried that method

That in fact would show if the alternator was charging or not. The question is, would you try it on a modern car with all sorts of electronics? At a guess I would think probably safe enough.
But I wouldn't try it, I did say guess.:)

Have you checked the belt?

antodeco

JustRoss23 wrote: »

disconnect the negative battery terminal wire.

Is it not meant to be the positive connector? Ive done it on mine to check the alternator and Im fairly positive it was the positive!

JustRoss23

tbh i would imagine it would be the positive i no if i was going to try it it would be the positive i would hope off i didn't question the old man as i was a young apprentice at the time and new no better i am not saying to try the method especially on new modern cars with all forms of electronics but that is just what was mentioned to me

Joe 90

antodeco wrote: »

Is it not meant to be the positive connector? Ive done it on mine to check the alternator and Im fairly positive it was the positive!

From the point of view of the test it would not matter. But if you touch any metal part with the disconnected wire you shouldn't do any damage if it is with the negative which is the earth on any car of the last 40 years or so.

joujoujou

Positive or negative - does not matter. Disconnecting ANY of terminals will cut the battery off the installation. :P

Don't know how it may (or not) affect modern car electronics though.

antodeco

joujoujou wrote: »

Positive or negative - does not matter. Disconnecting ANY of terminals will cut the battery off the installation. :P

Don't know how it may (or not) affect modern car electronics though.

I think its something to do with a voltage spike?

dgt

Emmmmmm.... What car????

ABajaninCork

The alternator's probably on it's way out...

corktina

joujoujou wrote: »

Positive or negative - does not matter. Disconnecting ANY of terminals will cut the battery off the installation. :P

Don't know how it may (or not) affect modern car electronics though.

it certainly does matter.... disconnect negative.

jomoloney

JustRoss23 wrote: »

tbh i would imagine it would be the positive i no if i was going to try it it would be the positive i would hope off i didn't question the old man as i was a young apprentice at the time and new no better i am not saying to try the method especially on new modern cars with all forms of electronics but that is just what was mentioned to me

always when disconnecting any battery - first then +

when fitting a battery vica versa, + first, then -

trixyben

Checked battery with multimeter and it read 12v, started up car and it dipped to 11.8 to 11.9v then when put on heater, light etc dipped to 10.9.

I checked all cables and all tight and corrosion free, the belt is tight and spinning away no problem, what i cant understand is how the alternator can just stop working after being left unused for a few weeks bearing in mind this is the second time this has happened!

So is it another alternator im looking at or is there anything else i can do or test for?

Thanks

JustRoss23

yea new alternator mate. or recondition the old one. ya always no the difference in a good one or not when you put it to your ear and spin it the one that's fecked sounds so much different

cletus

You put in a second hand alternator, so it could easily be gone. Try either a new or refurbished one, rather than just lifting one out of a car in a scrappy.

What car, by the way (make, model, year etc)

trixyben

ok lads just noticed that the metal casing of the alternator is cracked and at the back of it there is bits of the metal missing!! im guessing this is maybe causing the problem?

I charged the battery there to 12.5v and tested it again under load, the charge does increase very slowly but when under load from heater light etc it drops easily, the highest it would climb to on its own was 12.9v

So another alternator looks like the way to go, ah well at least fitting it will be handy enough