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[Terbs]

Hi fellas,
Neighbours car would not start....flat battery. She had the AA in, who started it and told her to leave it running.
So I put my multi meter on it. Question is.....do all cars have the same battery readings as the ones in our Omega test.
The readings I am getting...maximum under load is 13.89. Off load its about 13.86. Pointing me towards the Alternator, on the basis that all cars are the same. Car is a VW Golf 2011 reg.

[Nick W]

That's about the minimum you ever want to see at idle. More would be better, especially if it's a recent car with lots of gadgets. Does the voltage increase when you rev it?

[Terbs]

Maximum at 2000 rpm is 13.89, so its just about putting in a bit of charge imo

[Bigron]

Do you have a clip=on ammeter so that you can check the actual current feed to the battery?

Ron.

[TD]

Could be the battery is still pretty flat pulling the voltage down.....would be best to stick it on a battery charger overnight and try your tests again...at 2k revs with a charged battery you would expect to see a shade over 14V.
Also check the battery connections are clean and tight.

[Terbs]

No Ron. unfortunately. To be honest, I am not going to get too involved, as a look under the bonnet put me off trying to put a regulator on for her. Whilst the alternator looks you in the face, the auxillary belt is a different game.
I said, 'Didn't the AA bloke do the check I have just done'. She said he didn't, just started it and said the battery was ok. I'll check the battery in the morning to see what it is holding.
How he came to the conclusion the battery was ok, I haven't got a clue.
Now I have told her that it seems an alternator problem, she will probably take it to a friend of theirs who is a mechanic. I did stress, that if he comes to the same conclusion, not to just splash out on an alternator, try the regulator.

TD...yes, all connections tight and very clean. Just a smear of grease on the terminals

[TD]

TBH, I'm amazed the AA blokey didn't try to sell her a battery 

[minifreek]

I have a quick test to check whether its battery or alternator.. might be a bit unconventional, but it works everytime...

Get the engine running, then remove the earth cable from the batttery.... if it keeps running, the alternator is fine, if it stops the alternator needs replaceing....

It can however, cause a bit of damage to the alternator, so do this at idle....

[Bigron]

Ouch! 

Ron.

[Kevin Wood]

I have a quick test to check whether its battery or alternator.. might be a bit unconventional, but it works everytime...

Get the engine running, then remove the earth cable from the batttery.... if it keeps running, the alternator is fine, if it stops the alternator needs replaceing....

It can however, cause a bit of damage to the alternator, so do this at idle....

A very irresponsible thing to suggest on a modern car.

[Doctor Gollum]

I have a quick test to check whether its battery or alternator.. might be a bit unconventional, but it works everytime...

Get the engine running, then remove the earth cable from the batttery.... if it keeps running, the alternator is fine, if it stops the alternator needs replaceing....

It can however, cause a bit of damage to the alternator, so do this at idle....

Is that Wiganese for " Don't try this at home kids..."

[TheBoy]

Is her normal usage not getting sufficient charge in?

From what I've read (trying to diagnose if I have a battery problem) is that start/stop batteries might be slightly lower voltage...  ...though struggling to find this via a reliable source, rather than crap that people randomly write on t'interweb.

Also, if its Euro 5 or later, the alternator might be playing silly beggers, adjusting voltage to suit charge.

[Bigron]

You could well be right, TB. Back in the days when you could take the caps off the individual cells and see the electrolyte, you KNEW when the battery was fully charged because it started to produce hydrogen and oxygen bubbles. This would be a good time to drop the charging voltage back to trickle/maintaining level!
I supposae with sealed and/or gel batteries, temperature oof the battery would be just as informative? 

Ron.

[Terbs]

I think TB is on the right track.......They took it to Reading at the weekend, and I see she has gone to work in it this morning. All of half a mile !!!!!!!!
So must have charged up.

[ronnyd]

I think TB is on the right track.......They took it to Reading at the weekend, and I see she has gone to work in it this morning. All of half a mile !!!!!!!! ::)
So must have charged up.

Blimy, must be quicker to walk. (hope she hasn,t got mobility issues)