Dead alternator

[spinna]

Think my alternator has packed up. Went to start the trol up to go to work other day and nothing, looked at volt meter and read 0. Cus i was in a rush i jumped it off our astra and went to work but noticed volts only crept up to about 4. Dont think my batteries are at fault as it was fine day bfore and we never had cold weather to pull them down.
This may seem a silly question but is there anything i should know before removing alternator for refurb/replace? Thanks

 

[rayf3262]

I had a similar experience with a 6 month old car, left work drove 3/4 mile stopped came back 40 mins later barely able to illuminate the dash lights never mind start!
Called RAC, confirmed battery dead, replaced battery, all fine for the next 2 1/2 years.

Batteries can just "die", just be sure it is the alternator.

 

[Fez_uk]

check what voltage the alternator is giving when running.

Should be about 13.5-14v.

 

[96terrano]

check what voltage the alternator is giving when running.

Should be about 13.5-14v.

Mine puts out 15v, 16 when revved :doh

 

[solarman216]

Mine puts out 15v, 16 when revved :doh

for a car alternator that is far too high, 14.8 max is the norm, that is why car bats are not fully charged as 15.2 is fully charged (depending on battery type)but cars are limited generally to 14.8 to stop them cooking in an engine bay that is hot, bearing in mind that the battery has done its job on starting the engine, it is not use after unless the load is greater than the alternator output, Rick

 

[96terrano]

for a car alternator that is far too high, 14.8 max is the norm, that is why car bats are not fully charged as 15.2 is fully charged (depending on battery type)but cars are limited generally to 14.8 to stop them cooking in an engine bay that is hot, bearing in mind that the battery has done its job on starting the engine, it is not use after unless the load is greater than the alternator output, Rick

Yeah, the alternator is fried, well....the regulator is anyway as when it's revved the lights and things brighten, it almost working as I dynamo.

 

[spinna]

Just ordered new belts, pick em up 2mos so going to fit them and test output first. The batteries are atleast 3 years old to be fair. Cant to anything till weekend but atleast i can get hold of test meter then.

 

[spinna]

It is alternater thats shot. been told it could be a diode inside. Going to take it off 2mos and take it for refurb.

 

[glanrichbex]

The PD across my battery is 16volts when the engine is running, no problems here because I know my battery is on the way out.

If you place a Digital voltmeter across a battery on charge, the reading will reflect the current drawn by the battery so if there is no demand i.e battery is full or near open circuit, the PD will read 15-16 volts. If the battery is charging ( drawing current ) the PD will drop to around 13 - 14volts.

Its like a seasaw - The lower the voltage across the battery the higher the current


You need at least 15volts PD across the battery to get any decent current flow through the battery to charge it but the battery will pull the voltage down whilst it is drawing current so this is not an accurate method of checking an alternators output.

If the voltage regulator were to go short - the output voltage would be > 20volts with a little revs. The large current drawn by a saturated battery would take out the fuse.

I would say your alternator was working O.k and your battery / connections may be the problem. The battery will normally pull the alternator voltage down to 14.7 - 15volt at full state of charge and the fact this happens causes small heat build up internally which is concidered normal losses.

If you were able to run the engine without the battery ( totally open circuit )you would find the PD to be in excess of 16volts.

 

[spinna]

removed alternater today and had it tested, it is faulty/not charging. Should be repaired monday (fingers crossed)