Do I need a new alternator?

[sneakyalien]

Hi everyone,
My VW T25 1.9 petrol (Hight top) has had the battery light come on and my battery became flat and the engine would not turn over.
I called out roadside assistance and the mechanic put one of those jumper pack things on and the van started right away. He checked the voltage coming from the alternator (whilst van was running) and it read 12.5 volts. He said the alternator is probably shot and should be replaced and he also recommended putting a brand new battery on.

Is the Alternator definitely shot? I don't mind putting a new one on, but would just like it confirmed before I spend the money on it.
Thanks for nay help.
Cheers

[davidoft1]

sounds like its toast, does the dashlight stay on ?

[sneakyalien]

sounds like its toast, does the dashlight stay on ?

Not sure, the van got me home, but battery is now flat as a fluke again and van will not even attempt to start, so I can't see what the light is doing. When driving home the light went off(flickered every now and then), but if I stopped at lights it came on again and started flashing, so it seemed to be at low revs the light came on and flashed.
Cheers

[937carrera]

You might just need a voltage regulator for the alternator - much cheaper, check what is suitable first

https://www.brickwerks.co.uk/voltage-re ... 14-5v.html

[Mocki]

Alternator or wiring?

Easy to establish
Take a voltage reading at the Battery with the engine off , another at alternator ( using the casing as neg ) with engine off
Then again with engine running

If you have a difference if more than 0.5v between those readings and the readings at the battery it’s connections or wire fault
If it’s no different ( ie less than 14v at alternator it’s brush pack or alternator)

On the petrol engined T25s it’s common for the main cable from the alternator to the starter motor fails, not always visable as internally it goes high resistance

Changing the brush pack is a ten min job and £10 gamble
https://www.brickwerks.co.uk/voltage-re ... 14-5v.html" onclick="window.open(this.href);return false;

[sneakyalien]

Thanks guys, I have ordered a brush pack - hopefully that will fix the alternator.

I think I may need a new battery because this battery has been layed up for quite some time. Will the battery most likley be kaput?
Any recommendations for a good battery?
Thanks.

[asterix_the_gaul]

Battery may be toast, but I have revived many with a smart charger, this is the one I have, https://rover.ebay.com/rover/0/0/0?mpre ... 3917269491 it's a 10amp output so will take most of a day to fill a battery completely but only a few hours if it's needs topping up. A full revive might take well over 24hrs. I have plugged them in and left them it will sit in a float charge when it's done.
If it is dead, I think a 096/100 size battery will fit, plenty more cranking power and reserve than the standard about 50-60 quid delivered off eBay, but get the alternator running first or it will just kill it again.

[sneakyalien]

Battery may be toast, but I have revived many with a smart charger, this is the one I have, https://rover.ebay.com/rover/0/0/0?mpre ... 3917269491 it's a 10amp output so will take most of a day to fill a battery completely but only a few hours if it's needs topping up. A full revive might take well over 24hrs. I have plugged them in and left them it will sit in a float charge when it's done.
If it is dead, I think a 096/100 size battery will fit, plenty more cranking power and reserve than the standard about 50-60 quid delivered off eBay, but get the alternator running first or it will just kill it again.

Thanks, I'll buy one of those chargers and hopefully my battery is not Kaput.
Cheers

[sneakyalien]

https://www.ebay.co.uk/itm/12V-Volkswag ... 1438.l2649" onclick="window.open(this.href);return false;
Would this be a good replacement battery?
Thanks

[937carrera]

I would charge the battery up and see how it goes before buying a new one.

Running a battery flat is not good for its long term health, but equally it does not kill it straight away.

[asterix_the_gaul]

https://www.ebay.co.uk/itm/12V-Volkswag ... 1438.l2649
Would this be a good replacement battery?
Thanks

No, that's a leisure battery, you don't need that

This is all you would need if battery won't come back to life with smart charger and you get alternator working
https://rover.ebay.com/rover/0/0/0?mpre ... 1232380774

[sneakyalien]

Thanks guys,
I'll charge he battery and hopefully my brush pack will cure the alternator.
Cheers

[sneakyalien]

Quick update, this might help those who may be having similar problems with battery light flashing:
I removed the alternator (what a job as it had a rounded nut) and I removed the brush pack and it was indeed worn and the spring loaded contacts were quite short, I also noticed the copper contacts on the rotor appeared to have grooves in them, so maybe I do need a new alternator.
Anyway I replaced the brush pack, put my old battery back on after a 6 hour charge and the van started and the red flashing battery light no longer flashes. I need to put a volt meter on the Alternator to get reading.

Weird thing is the little red light in the temp gauge light is flashing even with a cold engine. I let the engine warm up and the needle just sat under 3 /14 way on the gauge.

Cheers

[937carrera]

Red flashing light is probably because you are low on water. Top up the tank at the rear through the flap. The sender units also fail giving these symptops.

[asterix_the_gaul]

How did you get on with testing your alternator? I only ask as I had very similar problem, diagnosed as dead alternator by rac man with laptop and dc clamp etc so duely replaced alternator only to find problem remains, 12.55v at battery when engine running, same as before so must be wiring I assume, wish I had read this thread before buying new alternator!