my battery light is coming on, dim.

 

when i rev the car over 3000rmp or so, the light goes off.

 

ive charged the battery, and it still comes on.

 

 

is this the alternator? if i remove the battery when the cars started and it still comes on will that confirm the alternator?

 

 

or mite i be lucjy to just tighten the fan/alternator belt?

From the description it would point to the diode pack within the alternator, oh and disconecting the battery with the engine running can potentially cause damage to the alternator anyway so best not, the diode pack can be replaced but by then you may as well go for a recon, or a tested used item.

 

Jeff TT

thanks mate,

 

so you dont think its a slack belt then.

An Alternator ain't the cheapest option so for the sake of 10mins tightening a belt up, it's worth a try and it's free eh.

smithy

will check on the weekend.

 

 

so when the engine revs over 3000rpm, the light goes out.

 

i take it that will be charging the battery then yea?

 

 

just wont charge it while driving slow?

You should try to put a voltmeter on the battery terminals to see what the charge voltage is.

 

As JeffTT points out there is probably a duff diode in the rectifier or the soldering has melted away on one of the joints. Sometimes you can still be getting 50% or enough charge to keep things going but I remember an alternator fault on a previous car that meant the battery was given full charge current the whole time it was running. Needless to say as well as a new regulator for the alternator I ended up needing a new battery as it got cooked!

 

Worth checking the connections to the alternator for any corrosion etc. ...and look for a 2nd hand one meantime

sorry to bump this,

 

 

what should happen if i put my multimeter on the terminals, when car off, then started?

 

will the fact that the car has been off the road nearly a year ruin the battery? iv had to charge it 3 or 4 times to start the engine every so often.

 

 

i have a battery from my escort gona put in there to do some tests on,

 

how can i check if the battery is crap, use multimeter on a known good 1 in what way?

you should get a good 12 to 13 volts from the terminals on a fully charged battery.

 

you should get around 14 to 14.5 volts when the engine is running and the alterntor is charging.

 

If the battery isn´t holding the charge then some cells are probably dead.

you should get a good 12 to 13 volts from the terminals on a fully charged battery.

 

you should get around 14 to 14.5 volts when the engine is running and the alterntor is charging.

 

If the battery isn´t holding the charge then some cells are probably dead.

 

 

when i charge the battery, i think its at 11-12volts.

 

when the car is started, iv put a multimeter on there, it reads 14.3volts.

 

as its 14.3volts when running, this means the alternator is working/charging?

 

but the battery is just shit/cant hold charge isit?

 

battery light is on still tho

Why don't you get the local garage to check the battery, save all the guess work.

 

Paul

Why don't you get the local garage to check the battery, save all the guess work.

 

Paul

 

yea will do,

 

 

but thaught thats all they would do is what ive done now...

well when the cars running, the battery shows 14.3v

 

so asumed alternator was fine.

 

 

ive swapped the battery to a new one today, but the light is still on.

(the battery is slightly smaller, as its from my escort) but still its new.

 

 

does this confirm its the alt? is my battery just going to die after a week or so?

 

ive swapped the battery to a new one today, but the light is still on.

(the battery is slightly smaller, as its from my escort) but still its new.

 

 

Does an escort battery have the same Amp rating as a battery for a Z ?

Alternator exciter circuit is FAULTY

 

Jeff TT

ok thanks.

 

so this means my battery is just going to get drained everytime i drive?

 

or will it still charge, but not to full potential?

ok thanks.

 

so this means my battery is just going to get drained everytime i drive?

 

or will it still charge, but not to full potential?

 

Bit of both really, the alternator has a built in function where the required charge is regulated accordingly, so after a cold start when the battery drain has been high turning over a cold engine the alternator will go onto high output mode, as the battery recovers from the discharge the alternator output regulator will slowly reduce the amount of output current.

 

Now assuming no high power accessories are used the alternator current will become a float charge, the voltage however will stay around the 13.1v mark.

 

The voltage output you have measured suggests the alternator is charging at a moderate float charge but will not extinguish the dash charge light until 3000 revs, this shows the current charge is only high at the higher revs.

 

It is important to distinguish between Current output and float charge voltage as if not it can lead to mis-diagnosis

 

Going back to the original answers to the thread, a diode pack within the alternator is is responsible for converting the alternator output from AC (Alternating current) to DC (Direct current) this also is what makes the charge light go out, so hence the with a faulty diode pack you get an inconsistant and low current output and the dimly glowing light.

 

Going back to the charge rate been a float charge, if you now switch on high power accessories the useage will be more than the current supplied by the alternator so the battery then will start to discharge, running like this will eventually lead to a flat battery, usually the next new start when the engine is cold.

 

 

 

Hope that helps

 

 

Jeff TT

ok thanks.

 

so new alternator required then.

 

 

shame i threw one out without knowing :(

some interesting points above, I have similar but not exactly the same problem.

 

Battery charges well, 14+ volts after start up, dropping down to mid 13's after 5-10mins. However, when applying full throttle, my battery light comes on dimly and also my 'lights' light.

 

Those warning lamps also come on after prolonged driving in rain accompanied by a nice electrical buzzing noise from the dash :eek: All physical lights still work at this point and all is well for the next drive.

some interesting points above, I have similar but not exactly the same problem.

 

Battery charges well, 14+ volts after start up, dropping down to mid 13's after 5-10mins. However, when applying full throttle, my battery light comes on dimly and also my 'lights' light.

 

Those warning lamps also come on after prolonged driving in rain accompanied by a nice electrical buzzing noise from the dash :eek: All physical lights still work at this point and all is well for the next drive.

 

Any issues with the charge light glowing at high, medium or even low revs almost always points to the alternator.

However the charge light circuit terminals at the back of the alternator can some times corrode and cause a high resistance circuit which will cause similar issues, unfortunately due to the lack of access to check this out the alternator needs removing.

 

An auto electrician should be able to perform tests including a full load current check which should help decide on the best course of action, one final thought, check the battery connections, both for tightness of the battery terminals and for corrossion between the terminal and the cables both earth and positive.

 

Jeff TT