Alternator fault

rickyroma

I have a drain on my battery. In the diagnostics report it states that the Alternator is charging at 12 amps instead of 14 and I need a new Alternator. 
  But the battery is fine when I'm driving it regularly. The battery loses charge over 2-3 days when the car is stood. I thought the Alternator only charges the battery when the car is running?  The man who did the diagnostics told me the fault can also drain the battery when the car is stood. Is this correct? 

CliveOfIndia

rickyroma said:

I have a drain on my battery. In the diagnostics report it states that the Alternator is charging at 12 amps instead of 14 and I need a new Alternator. 

Presumably you mean volts, not amps.  Alternators should usually put out about 13-14 volts.

rickyroma said:

 I thought the Alternator only charges the battery when the car is running?

Correct.

rickyroma said:

The man who did the diagnostics told me the fault can also drain the battery when the car is stood. Is this correct? 

Unlikely that an alternator fault would drain the battery when it's left standing, but other electronic components (alarms and what-not) can.

What car is it, and how old is the battery?  There are lots of electronics in cars these days that can put a drain on the battery when it's left sitting there, and if the battery is on its last legs then it's not uncommon for it to go flat if left for a few days.

It's generally reckoned that a battery has a lifespan of roughly 5 - 7 years or so, something like that.  Less if it's been completely discharged a few times.

If the battery is pretty old, it's probably worth getting a new one anyway (though most garages will be able to test it for you to check how healthy it is).  Batteries are widely available online for much cheaper than Halfords etc., and are a doddle to fit yourself assuming it hasn't got stop-start technology.

You may find that does the trick - though if the alternator really is kicking out only 12 volts, you may want to look into getting a new (or reconditioned) one.

But if it were me, I'd get the battery checked first, replace if necessary, and see how it goes from there.

rickyroma

CliveOfIndia said:

rickyroma said:

I have a drain on my battery. In the diagnostics report it states that the Alternator is charging at 12 amps instead of 14 and I need a new Alternator. 

Presumably you mean volts, not amps.  Alternators should usually put out about 13-14 volts.

rickyroma said:

 I thought the Alternator only charges the battery when the car is running?

Correct.

rickyroma said:

The man who did the diagnostics told me the fault can also drain the battery when the car is stood. Is this correct? 

Unlikely.

What car is it, and how old is the battery?  There are lots of electronics in cars these days that can put a drain on the battery when it's left sitting there, and if the battery is on its last legs then it's not uncommon for it to go flat if left for a few days.

It's generally reckoned that a battery has a lifespan of roughly 5 - 7 years or so, something like that.  Less if it's been completely discharged a few times.

If the battery is pretty old, it's probably worth getting a new one anyway (though most garages will be able to test it for you to check how healthy it is).  Batteries are widely available online for much cheaper than Halfords etc., and are a doddle to fit yourself assuming it hasn't got stop-start technology.

You may find that does the trick - though if the alternator really is kicking out only 12 volts, you may want to look into getting a new (or reconditioned) one.

But if it were me, I'd get the battery checked first, replace if necessary, and see how it goes from there.

Sorry. I forgot to say I have tried a new battery. I just called the garage again to check the alternator can drain a stood vehicle and he insisted it can. Plus he did put amps

• Garage diagnostic - alternator charging at 12amps and should be at 14amp

TadleyBaggie

It really is Volts, if he's got that basic thing wrong I'm not sure how much you trust him.

CliveOfIndia

rickyroma said:

CliveOfIndia said:

rickyroma said:

I have a drain on my battery. In the diagnostics report it states that the Alternator is charging at 12 amps instead of 14 and I need a new Alternator. 

Presumably you mean volts, not amps.  Alternators should usually put out about 13-14 volts.

rickyroma said:

 I thought the Alternator only charges the battery when the car is running?

Correct.

rickyroma said:

The man who did the diagnostics told me the fault can also drain the battery when the car is stood. Is this correct? 

Unlikely.

What car is it, and how old is the battery?  There are lots of electronics in cars these days that can put a drain on the battery when it's left sitting there, and if the battery is on its last legs then it's not uncommon for it to go flat if left for a few days.

It's generally reckoned that a battery has a lifespan of roughly 5 - 7 years or so, something like that.  Less if it's been completely discharged a few times.

If the battery is pretty old, it's probably worth getting a new one anyway (though most garages will be able to test it for you to check how healthy it is).  Batteries are widely available online for much cheaper than Halfords etc., and are a doddle to fit yourself assuming it hasn't got stop-start technology.

You may find that does the trick - though if the alternator really is kicking out only 12 volts, you may want to look into getting a new (or reconditioned) one.

But if it were me, I'd get the battery checked first, replace if necessary, and see how it goes from there.

Sorry. I forgot to say I have tried a new battery. I just called the garage again to check the alternator can drain a stood vehicle and he insisted it can. Plus he did put amps

• Garage diagnostic - alternator charging at 12amps and should be at 14amp

OK.  Well, an alternator can drain the battery (faulty diodes are the usual culprit), though it's not very common, which is why I suggested the battery first.  But if that's the case then you probably will have to replace it.  Check the price difference between a new and reconditioned unit - depending on the age and model of the car, a reconditioned one may be perfectly acceptable.

ratrace

Check the battery terminals for corrosion they need a good clean (these get overlooked)

also check the condition of the fan belt a slipping belt may also cause the the alternator to not put out the volts it needs

also the alternator need to be tested under load ie: turn on the blowers lights etc... and see what the reading is as it could be a weak alternator when its loaded but once the loads are off its ok as the draw is less

hope that helps mate

rickyroma

ratrace said:

Check the battery terminals for corrosion they need a good clean (these get overlooked)

also check the condition of the fan belt a slipping belt may also cause the the alternator to not put out the volts it needs

also the alternator need to be tested under load ie: turn on the blowers lights etc... and see what the reading is as it could be a weak alternator when its loaded but once the loads are off its ok as the draw is less

hope that helps mate

Whatever the Alternator is doing while I'm driving every day or two it seems to be enough to keep the battery topped up OK. My problem is the drain on the battery over none driving days. I could replace the Alternator but be wasting my money if it doesn't solve the drain issue.

What I'm asking.. is.. Could the reduced charge from the Alternator give the impression all is well but somehow cause the battery to lose charge when the car is stood? 

ratrace

rickyroma said:

ratrace said:

Check the battery terminals for corrosion they need a good clean (these get overlooked)

also check the condition of the fan belt a slipping belt may also cause the the alternator to not put out the volts it needs

also the alternator need to be tested under load ie: turn on the blowers lights etc... and see what the reading is as it could be a weak alternator when its loaded but once the loads are off its ok as the draw is less

hope that helps mate

Whatever the Alternator is doing while I'm driving every day or two it seems to be enough to keep the battery topped up OK. My problem is the drain on the battery over none driving days. I could replace the Alternator but be wasting my money if it doesn't solve the drain issue.

What I'm asking.. is.. Could the reduced charge from the Alternator give the impression all is well but somehow cause the battery to lose charge when the car is stood? 

If the battery is going flat over a few days then you car could have what we call in the trade a parasitic draw which could explain the drain issue, but they a somtimes hard to find we had a car in that had a drain everything was fine for about 5 hours then suddenly a module would just wake up and drain the battery i found it under the dashboard with  my thermal camera the module was faulty once replaced all was well but it took us a while to find it

im not saying you have a drain but you have to rule the battery and alternator out ruling the battery out is easy with a battery tester machine and the alternator may need to go get checked for any issues once that have been done and confirmed as ok then you can chase the drain you may have to take it to a auto electrician as they have better tools dignostic tools than a normal garage

rickyroma

Well it turns out my warranty covered the alternator so that's been swapped so new alternator and newish battery in place now.  The garage who swapped the alternator assured me that was causing the drain and all is fine now.  But is it? 36 hours after driving home (car hasn't moved since) and the voltage across the terminals has dropped to 12.4v.  
Reading online I get different opinions on what is a normal voltage drop overnight. Some would say dropping to 12.4v in 36 hours is OK while some reckon it should still be up there at 12.6v.
Is this normal or is there still a drain?

400ixl

12.4v is normal for a battery which is not currently being charged by the alternator. That is the level it should sit at. 14.4v will be whilst it is running.

Ganga

400ixl said:

12.4v is normal for a battery which is not currently being charged by the alternator. That is the level it should sit at. 14.4v will be whilst it is running.

I agree with this and after all it will have a 12volt battery so 12.4 volts is ok.