# Voltage regulator on alternator keeps dying



## johnpinetree (Sep 5, 2012)

1.8L, 225 engine

I've had the voltage regulator replaced twice now on the alternator and both times it works fine for about three minutes and then it craps out and dies. Rather frustrating. Any ideas as to how I can be killing these things? Do these alternators have diodes in then as well that could be failing?

Help please


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## sciroccohal (May 4, 2005)

*all have diodes*

So what is a diode?....it's an electronic check valve....often there are three.
Otherwise your ALTERNATOR would be a generator.

Alternators make alternating current...but your battery is DIRECT current...the diodes make pulses of power that are direct current.
so an alternator needs to be making 14.6 volt. 2-2.5 volts is all that going to the battery...just two volts.

Check grounds, terminals, and battery....massive current drain may burn out the 'rectifier' the electronics package that incoroprates the diodes.

NEVER JUMP START OTHER CARS WITH YOUR TT...THIS WILL BE AN INSTANT 'NEW ALTERNATOR'.


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## johnpinetree (Sep 5, 2012)

Got it. So am I correct in thinking that these Bosch alternators have both diodes to get to DC and voltage regulators to make it a clean voltage?


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## 20v master (May 7, 2009)

sciroccohal said:


> NEVER JUMP START OTHER CARS WITH YOUR TT...THIS WILL BE AN INSTANT 'NEW ALTERNATOR'.


Do you just make this stuff up to take pleasure out of fooling people? Absolutely not true.


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## sciroccohal (May 4, 2005)

*I'm an engineer!*

I do not make stuff up...WHEN you've been working on VW/Audi products for 40 years AND you have owned your own VW shop....you learn a few things.

So lets put this civily....If you want to jump start a car from your Audi TT and or another VW/Audi product.....she better have REALLY nice ta-ta's....ok?:laugh:

I have replaced dozens upon dozens of diodes (rectifier sets) *for JUST this reason.*

ps the voltage regulator does not provide 'clean power' it keeps the output between a certain range

12.5 v-16 v remember the alternator itself is dumb..it produces x voltage at 2000 rpm an xxx voltage at 7000 rpm....the only way to 'condition' the voltage output is with the voltage regulator.:wave:


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## johnpinetree (Sep 5, 2012)

So you can service the diodes yourself? I took this thing to an "alternator repair shop", where that's all they work on. Seems like all they want to do is replace the voltage regulator. Real classy.

If I can replace the diodes on this thing it seems like a good way to go. I've looked a bit, but haven't found any auto parts vendors. Do you just get something off of DigiKey?


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## 20v master (May 7, 2009)

That's great, but I'm an engineer too. Ironically, I jumped off a TT with another TT yesterday, and neither needs a new alternator. :screwy: This isn't the first nor will it be the last time, but I don't own a shop so I must be wrong. :banghead:


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## sciroccohal (May 4, 2005)

*the world is not B&W...even your world*



20v master said:


> That's great, but I'm an engineer too. Ironically, I jumped off a TT with another TT yesterday, and neither needs a new alternator. :screwy: This isn't the first nor will it be the last time, but I don't own a shop so I must be wrong. :banghead:


1. you've been lucky
2. completely flat batteries are the main culprit...causes the alternator to run at max output for too long...this is what 'blows up the diodes'
3. You should use a charger whenever possible...not on 50A either.
4. it is your car and you of course can do what you want.
5. She must be good looking! LOL:laugh:
6. I don't own the shop anymore...not fun working on others cars....miserable actually.


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## 20v master (May 7, 2009)

sciroccohal said:


> 1. you've been lucky
> 2. completely flat batteries are the main culprit...causes the alternator to run at max output for too long...this is what 'blows up the diodes'
> 3. You should use a charger whenever possible...not on 50A either.
> 4. it is your car and you of course can do what you want.
> ...


It has nothing to do with luck, and yes, we know you hate working on cars. It's why you have a stock TT and hang out here telling us that all of our cars are unreliable. :screwy:


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## johnpinetree (Sep 5, 2012)

Uh, so... anyone ever changed out the diodes on a Bosch alternator?


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## sciroccohal (May 4, 2005)

*rebuild shop*

Just get the 'rectifier set'....it's all one piece....a little printed circuit board with all the 'stuff on it'.
the replacement is straightforward.


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## Non_Affiliated (Feb 12, 2002)

Wow, just wow. Properly jusmping a car will not kill the alternator. And actually you have to REALLY work hard to drop more than a couple cells. I had so far only seen one car battery that when taken out of a car it was reading around 1.5 Volts, put it on a charger for SAG's and ireally just settled at about 4Volts. I looked at the guy I was helping with his '91 GLI and shook his hand and Said "Congratulations, you have totally killed a automotive battery further than I have ever seen.
I have jumped many, and I mean many vehicles with my Corrado. The only alternator issue I had was the pully nut backing off (Unrelated).

The Diodes I am not sur which you might speak of, there are diode trio (on some style alts) that are part of the feedback loop and source of current for the field windings to the Voltage regulator. Those might be what your talking about, but usually when one talks dioeds they are talking about the diodes in the rectifier. Those often they are mounted on a metal ring. Most of these are relativly large diodes with a axial lead type set up. Because each pair hang off the stators Phase off the Y Configuration of the Stator. IF you lose rectifier diode(s). The current output capacity of the alt goes down, usually taked out the VR not much later. If the VR goes it usually just shuts down the alt function altogether, or the Voltage is so low of an output you only see battery voltage.


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## speed51133! (Aug 5, 2002)

I have jumped cars at least a dozen times with my audi tt...

this guy is full of it.

im sure the full moons made the alternator fail.


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## RKM337NNY (Oct 24, 2011)

*Huh?!*

Come one guys; given the amount of VW/Audi's this lad has seen over the years I would have to say the percentage of blown rectifiers/diodes, Voltage regulators, etc. caused by jump starting "INCORRECTLY" was/is a common thing for him. How many folks no how to actually jump start a vehicle properly??!! With that being said, in the 12 years I've been working on vehicles it is rare that I've actually had to replace a voltage regulators and/or rectifiers because of improper jump starts. These days I am replacing them on a more regular basis, along with batteries because, IMO the over usage of electronics in our vehicles with say short commutes and/or leaving all that high speed gear plugged in all the time is adding stress in those specific areas. Phantom draws, parasitic draws, alternators not designed for all the added electronics, old technology batteries, etc. are also an added contribution. Europeans have been using AGM batteries mainstream for a long time while us Americans are still using the big bulky lead/acid types. I use AGM batteries in all my vehicles, but I also keep them plugged in to a battery minder when they aren't started for a while.


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