Alternator questions

[mcandmar]

My alternator has started doing very strange things. When i start the car the volt gauge starts from 12volts and then climbs all the way to the top of the gauge before dropping back to 14volts. Then it flickers constantly between 14-15volts, headlights and interior lights flicker too which can’t be good for the more sensitive electronics!

I'm assuming the voltage regulator is on its way out because this isn’t the first time. In the last six years i have had the unit reconditioned three times. Each time it died completely and had new regulator/brushes fitted. Has anybody ever seen anything like this where they pack up every two years as its getting a little irritating

My other option is a 90amp Valeo alternator from an S2 Avant, does anybody know if they are a direct replacement or do they have different plugs? The thought of a French part in the Audi kills me but i've had it with this Bosch unit

Thanks,

Mark.

[S-Express]

when you've had the alternator reconned, did they replace the bridge rectifier also?

[Nuvo]

Have the slip rings ever been replaced at any time in its life? More likely to be the diode pack to be on its way out as suggested.

If you have a scope you can check too see if you have rectified dc or half wave peaks which would point to diode failure.

[macspring]

Mark,

Whose re-"conning" it for you every two years.

There may be a better company in the city to do it if you can't get a secondhand one?

Does anyone know does the alternator come on any other non Audi cars, as they is a distinct lack of S2's in the breakers over here?

Kind regards.

[S2central.net]

As David says - whoever yuo are taking it to for rebuilds is having a laugh... That Bosch alternator is perfectly good. When its time for reburb then they should really get proper treatment. Go only to a certified Bosch rebuild place and get the guys to specify everything they do for the money. A good shop will put your Alternator on a bench test rig and should be able to tell you exactly whats wrong pretty quickly. I also suspect the voltage regulation circuit is knacked, but that should really have been renewed during a refurb.

[Nuvo]

But why is the voltage regulator failing time and again? I would suspect one of the phases not being full-wave rectified, with one or more rectifier diodes short circuit , the excessive ripple will eventually kill the regulator.

[S2central.net]

I agree with Nuvo - if the diode bridge is bad and never replaced (lazy rebuilder) then it would explain a stressful life for a voltage regulator.

[mcandmar]

Interesting, i'm not aware of the diode bridge being replaced. Backing plate, bearings, and slip rings have been replaced as the unit was in bad shape the first time it was rebuilt. Its been though a few different specialists who all gave it a clean bill of health after their rebuild. I would have assumed they would have picked up any problems in that area.

I'll pull it out again this weekend and see can i fit the Valeo unit. Anybody know where i can source the diode bridge and regulator as i may as well do it myself this time.

Thanks,

Mark.

[S2central.net]

Doubt the diode bridge is available as an Audi part - you'd need a Bosch man I think for that.

[Nuvo]

Mark, you can order these parts from Bosch. They'll probably have the regulators on the shelf, the bridge will doubtless cost a packet and be on back order. You should be able to source the diodes from a decent electrical components supplier and just replace these instead.

This should help you on your way.

[macspring]

Mark,

Could you post a few photos of the troublesome one and maybe we can spot a decent one in the breakers for a couple of quid?, might be less hassle than to find all the bits to refurbished yours?

What is the amp output 90 amp or 120 amp?

Thanks.

[mcandmar]

Thanks Nuvo thats invaluable info to have. I'm sure i can source some diodes from Radionics if needed.

David its a 90amp Bosch unit, i will snap a pic when i have it out

Thanks,

Mark.

[S2central.net]

Nice doc Mr Nuvo...

[Flat on my back]

.

You can get the regs from Woods Auto, only a couple of £. I bought a spare just in case...fitted one to my 7A alternator just recently.

[mcandmar]

Fantastic, you guys are a gold mine of information

http://www.woodauto.com/Component.aspx?Ref=EXA211127902 Can you remember off hand which part number yours was?