what voltage should the alternator be pushing out?

[Garethsd1]

After leaving the car unused for a week or so, I've had to jump start it twice in the morning this week already.

Fired up fine on Monday but only did a local run to fuel up, unused Tuesday, had to jump it Wednesday, started ok yesterday, needed a jump again this morning.

With the lights, heater, rear demist and radio on, I'm getting 13.5 ish volts from the battery terminals. When the cooling fan kicked in, it dropped to 12.8 ish. With every thing off, I'm getting 14.5 volts.

Am I wasting my time putting the battery on charge for the weekend? I'd expect 14 volts all day long off the alternator regardless of load. I've done a similar comparison test on a Rover 25 diesel tonight and the voltage changes from 14.8 nothing on to 14.7 everything on...

The battery is only a year old with 3 years warranty left on it but I'm suspecting the alternator may be on its way out?

[chillyphil]

You are getting 14.5 volts from the alternator, that's there or thereabouts.

I would suspect the battery, try to find a garage who can load test it.

[350zwelgje]

Agree with you, alternator is suspect and it sounds like the regulator to me that is on the way out. The regulator can be replaced and if you do a search hints and tips will come up.
It should be able to maintain way over 13.5 Volts all the time. Think the battery is fine, but not getting the amps to keep it topped up and if continuing like this, it will kill the battery.

Rob

[Polly]

That's quite a load you are putting on the alternator, since we know your battery is low, all of the load is being supplied by the alternator. It's not the regulator, because 14.5v is correct. Possibly the brushes might be worn, thereby reducing the output a little, but I suspect if you simply charge the battery properly all will be well.

[Mdan]

I think battery the voltage is a bit weird but it's the amps you need to test for which you can't do with a multimeter ever go to Aylesbury u can pop into the garage where I work and I can do fully charing system and battery test for a pint :}

[casperdog21]

with those readings your alt is ok its the battery that is the problem, it will be a bad cell

[COLVERT]

If your battery was flat you will need to charge it for at LEAST 30 hours on a charger.

You don't say when you checked the voltage with a lot of things running if you revved the engine or not.

At 2,000 rpm or over you should get around 14 volts. If you do the alternator is OK.

PS. Have a read of my posts in the ---'Really really useful' thread at the top of the main page.( Posts 73 and 80. )



Colvert. :D

[COLVERT]

With each bad cell the battery voltage reading will drop by about 2 volts.

ie One dud cell-----10 volts.

This is a battery check with everything switched off.

[Mdan]

I disagree bad cells vary not set at 2v. 2v is the max a bad cell could be 1v down it's all to do with resistance of the plates caused by different levels of sulphation

[chillyphil]

6x2.2 volts = 13.2 v = 12 volt battery.

However, regardless of the theories, the answer is to this problem is to remove the battery from the car, charge it for 20-30 hours using a decent charger, take it to a garage and get it drop tested.

Simples really :}

[SD1too]

Am I wasting my time putting the battery on charge for the weekend?
Of course not Gareth. :D That's exactly what you need to do, and for 30 hours as Colvert recommends. The longer you leave your battery in a discharged state, the shorter it's life will be, so don't delay!

Simon

[Garethsd1]

Thank you everyone for your advice! :}:}:}

The battery is on the bench and charging now. Off the car and just before being wired up, I checked the voltage again - it was reading 12.56 volts.

I will report back Monday ando again on Friday with results. :}

[COLVERT]

Hi there.

12.56 volts is not very good. Be prepared for bad news from your battery in the near future and be ready to wave it Goodbye.--:eek::eek::eek:

You'll have a very good idea how it's fairing in less than two weeks.




Colvert.---;)

[COLVERT]

I disagree bad cells vary not set at 2v. 2v is the max a bad cell could be 1v down it's all to do with resistance of the plates caused by different levels of sulphation

Please go read the posts in the thread I referred to in another post.

Sulphation reduces the capacity of a battery not its voltage.

Failure of a cell and the obvious fact that the engine won't even turn over is because the plate pack inside the battery has become detached and this shows as a sudden voltage drop.

Sulphation in a battery that has passed the stage of chrystaline sulphation to that of compacted sulphation will not take a charge. A battery goes through various stages of sulphation as it charges or discharges.

Just before a battery dies from compacted sulphation it can show a high voltage charge but have NO capacity. ( ie. it contains insufficient electricity to do work. ) It will also appear to fully charge in a very short time as there is very little usable plate that can take a charge.

As I say please have a look in the thread------'really really useful info' at the top of the main page and learn a bit more about batteries and how to be kind to them. Lol


Colvert. :bowdown::D

[Garethsd1]

After a 30 hour charge, the car fired up fine on Sunday afternoon and read 14 volts at the battery terminals with everything on and engine running.

Fired up no problem at an indicated minus 1 yesterday morning and today too but it's been too dark to check voltage presented to the battery by the alternator.

I will try to get a voltage reading tonight when I get home but it does look like a slow long charge has restored service.

[freddie]

After a 30 hour charge, the car fired up fine on Sunday afternoon and read 14 volts at the battery terminals with everything on and engine running.

Fired up no problem at an indicated minus 1 yesterday morning and today too but it's been too dark to check voltage presented to the battery by the alternator.

I will try to get a voltage reading tonight when I get home but it does look like a slow long charge has restored service.


You can check the alternator voltage in the dark without even lifting the bonnet.
Use the obd .Same way as checking your true temprature reading.


If not sure read here
http://www.the75andztclub.co.uk/forum/showthread.php?t=55585

Go to nineteen then go to nine9 (Instead of the 7 for the temprature)
You can then sit in the comfort of you car and switch things on and off and watch the results.

[Garethsd1]

Thanks Freddie, love this forum!

[Jakg]

You can check the alternator voltage in the dark without even lifting the bonnet.
Use the obd .Same way as checking your true temprature reading.


If not sure read here
http://www.the75andztclub.co.uk/forum/showthread.php?t=55585

Go to nineteen then go to nine9 (Instead of the 7 for the temprature)
You can then sit in the comfort of you car and switch things on and off and watch the results.

I've used this in the past but not found it very accurate.

[Garethsd1]

I'll do both then, so my feedback is accurate.
:}

[Borg Warner]

Perhaps not so inaccurate as to where the take-off is connected I would suspect? Just checked mine and there is a difference of approximately 0.3v between the display on the dash and a Fluke multi-meter.

[Vossy]

Just checked mine after reading this, my alternator is new, only a 6 week old Valeo, battery is about a year. Across the terminals was 14.3 and the IPK showed 14.1 so there isn't much in it on mine.

[DMGRS]

It's worth bearing in mind that charge voltage at idle may be a tiny bit lower than at 1000RPM+. Both of mine used to read about 13.8-14.0 at idle, and 14.2 when RPM held above 1000.

[COLVERT]

I'll do both then, so my feedback is accurate.
:}

Now don't forget to pop back in three or four weeks to let us know what's been happening.


:driving::driving::driving: