voltage question? does anybody know?

kipw31

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01 jetta
I have a 01 jetta, Does the altenator charge all the time? I check the voltage when the car is running and sometimes it shows only 12 volts, i can turn the car off and re start it and the voltage will go to 13.5 volts. When it reads (whatever volts is in battery) 12 volts and car is running, i put load tester on it and flip switch and the altenator kicks right in and will pull the engine down from being under such load. I took altenator to shop and mechanic says it is okay. I guess my question is this normal, or does it supposed to charge all the the time, or does it just charge when voltage gets low (maybe to conserve horsepower for economy) any info will be helpful.
 

Airliner

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kipw31 said:
I have a 01 jetta, Does the altenator charge all the time? I check the voltage when the car is running and sometimes it shows only 12 volts, i can turn the car off and re start it and the voltage will go to 13.5 volts. When it reads (whatever volts is in battery) 12 volts and car is running, i put load tester on it and flip switch and the altenator kicks right in and will pull the engine down from being under such load. I took altenator to shop and mechanic says it is okay. I guess my question is this normal, or does it supposed to charge all the the time, or does it just charge when voltage gets low (maybe to conserve horsepower for economy) any info will be helpful.
It should be "charging", or at least deliver power to the car's electrical equipment as long as the engine is running. And you should have above 13v on the battery with the engine running.

To me this sounds like a bad voltage regulator, but if the mechanic checked the alternator (and if he knows what he is talking about) this should not be the problem.

Have jo checked the "alternator load" or something with VAG-COM ?
 

Powder Hound

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Everytime I have checked the voltage with the engine running it came up as 14.5.

The voltage regulator's function is to turn the alternator on and off by controlling the voltage in the armature coils which then excite the field coils that generate the electricity. There is a diode pack on those output coils that rectifies the generated alternating current to direct current.

Whether this is a digital type on off function or an analog function that will change the actual voltage level in the armature coils is not something I know, but the description above is generally accurate.

If all you are getting out of the alternator is 13 volts, then you have some problems. Now, whether it is in the alternator itself, or in the battery or the cables in between is something you'd have to examine the car to determine.
 

Drivbiwire

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Forget voltage, what is the amperage output from the alternator?

You know the old saying, if it aint' broke don't fix it!

IF the battery is at 12 volts after shutdown THAT is what matters.

DB
 

Airliner

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Drivbiwire said:
Forget voltage, what is the amperage output from the alternator?

You know the old saying, if it aint' broke don't fix it!

IF the battery is at 12 volts after shutdown THAT is what matters.

DB
Okay, so what your saying is that voltage should be at 12V with the engine running ? BULL****

When the voltage is at 12V with the engine running something IS broken.
 

Andrewh

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Allen, TX
Have you considered your volt meter isn't right?
That is to say if your car is running fine, and the guy that checked the alt(if he knew what he was doing,) says it is good, then perhapes your voltage meter is off by a volt or volt and a half.

I agree, when the engine is running it should read at least 13 volts. I do know sometimes if falls bellow that, but that is normally under a load. So it could also be bad in that sense. Did they load test?

For instance, my 65 dodge has that problem. Normal output is 34 amps from the alt. If I turn on headlights, the a/c, and kick on an electric fan, voltage drops from the normal 13 to around 11 at idle. At 3000rpm, it comes back up to about 12, but that is not enough. So I swapped out to a 74 amp alt. At idle, it hits 13 volts with all that running, and at speed it hits around 14.
 

chromeBuddha

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If your alternator had 150-200K miles on it, it could be your pickup brushes. If you are in this mileage range, consider replacing the voltage regulator. I believe the brushes are integrated into the regulator.
 

alanp

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Set up the voltmeter so you can see it from the drivers seat. Get the engine running, watch the meter, when it drops to 12.0 volts turn on your rear defroster or heated seats or high beams. The volt meter should respond immediately by showing 14 volts, if not look for corroided wires or replace the regulator module (if replaceable). My experience with alternator guys goes from fair to poor.
 

n1das

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Drivbiwire said:
Forget voltage, what is the amperage output from the alternator?

You know the old saying, if it aint' broke don't fix it!

IF the battery is at 12 volts after shutdown THAT is what matters.

DB
...12V after shutdown AND with a load on it matters too. The battery may show 12V with no load on it but may die when any kind of load is placed on it.

Here's an easy test which tests the battery and the car's charging system while under load:
  1. Turn the key to the ON position but do not start the engine and also have the headlights ON.
  2. Measure the battery voltage with the engine OFF (key in ON position but engine not started yet) and with the battery loaded by the headlights. If the engine is totally cold and cold enough for glowplugs, they'll operate too but don't worry about that for now. Measure the battery voltage after the glowplugs turn off.
  3. Start the engine and measure battery voltage again with the engine running and headlights still ON. The voltage should be somewhere between 13.5 and 14.5 Volts.
:cool:
 

kipw31

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nc
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01 jetta
altenator question

when the car starts up the alt. is either charging ok (14 VOLTS). OR it is not charging at all. The meter will only show what is in the batt. I have not seen the alt. stop charging once the car is started and the alt. is charging like it should. I have put load tester on it when it was NOT charging and flip the switch to put it under a load and the alt. kicked in and started charging like should (even pulled engined down from such a load). I have looked at volt meter with car runnig and turned on lights an AC and when alt. charging it resonds like it should.
the car ahs 80k miles on it
i have two batteryies since oct. 06, just put 2nd batt in on 1/27/07
 
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n1das

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kipw31 said:
when the car starts up the alt. is either charging ok (14 VOLTS). OR it is not charging at all. The meter will only show what is in the batt. I have not seen the alt. stop charging once the car is started and the alt. is charging like it should. I have put load tester on it when it was NOT charging and flip the switch to put it under a load and the alt. kicked in and started charging like should (even pulled engined down from such a load). I have looked at volt meter with car runnig and turned on lights an AC and when alt. charging it resonds like it should.
That says the alternator is working fine. As DBW said, don't fix it if it ain't broke.

How old is the battery and how well does it crank the engine during a cold start?
 
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Dimitri16V

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kipw31 said:
when the car starts up the alt. is either charging ok (14 VOLTS). OR it is not charging at all. The meter will only show what is in the batt. I have not seen the alt. stop charging once the car is started and the alt. is charging like it should. I have put load tester on it when it was NOT charging and flip the switch to put it under a load and the alt. kicked in and started charging like should (even pulled engined down from such a load). I have looked at volt meter with car runnig and turned on lights an AC and when alt. charging it resonds like it should.
the car ahs 80k miles on it
i have two batteryies since oct. 06, just put 2nd batt in on 1/27/07
Go get another regulator, yours is about to fail. measure voltage with engine running right at the alt using the engine block as ground. if it is 14V there and 12+ on the battery, check the grounds. the brushes are probably worn out, if at idle the voltage is only 12V and at 3K it raises to 13-14V.
Voltage does matter, and definitely fix it before it breaks. FYI, you don't have to drop the alt to replace the regulator, you can do it from the top using short 10mm sockets, 1/4 rachet, and short phillips screwdriver.
 
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Dimitri16V

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Airliner said:
Okay, so what your saying is that voltage should be at 12V with the engine running ? BULL****

When the voltage is at 12V with the engine running something IS broken.
Is DBW for real ?
 

rdkern

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Drivbiwire said:
IF the battery is at 12 volts after shutdown THAT is what matters.

DB
After shutdown. With engine off. That's what I read.
 

unitacx

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What you should see..

It's the regulator/brush assembly. Read on.

With the car running, the voltage should be between 13.8 and 14.4 (not sure about the high number), unless you have "everything" on and the car is idling.

If you're getting 12 volts with the car running something is wrong. It's possible that it's a major electrical load, but that's easy enough to determine: lights, fan, rear defroster, seat heaters.

That out of the way, probably the alternator is "weak", the most likely cause being worn brushes. On some Bosch alternators, the regulator and brushes are a single assembly, and easy to change. I'm wasn't sure if VW used these, even about my car (an '00) but according to the Russian parts site http://www.vagcat.com/epc/cat/vw/GOLF/2000/203/57/2461102/ the car definitely has one.

These alternators will start to fail by running as you described, i.e., by intermittantly not charging. This indicates the brushes are worn out.

The voltage regulator is available at any of the usual outlets, as well as NAPA. Unplug the alternator at the connector. According to Bentley, the A4 has a protective cover. Remove the 2 or 3 screws to remove the cover. Then remove the two screws that hold the voltage regulator on (look at the new one). Remove the old regulator/brush assembly. You may have to rotate it to get the brushes to clear, but Bentley doesn't mention this so it may not be necessary on current model alternators.

Install the new one. Most have a slot which accepts a thin plastic tube, such as a WD-40 tube, for the purpose of holding the brushes retracted until the assembly is installed.

I've been through several of these on my MBZ since '81. They're easy to change out.

NOTE: Somewhere around '02 or '03, the replacable brush/regulator assembly was discontinued. Apparently these are identified by no protective cover. And a $200 pricetag on a replacement alternator.

- stan
'00 Golf (Rocketchip II, 520, TT 17 wheels, Valeo E-codes, and probably a Bosch alternator.)
 
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tdi techee

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What everyone has forgotten is the field wire. The alt. requires a field wire in order for it to know when to charge. The way you describe the volts jumping up intermittently tells me the alt doesn't know to turn on. Everyone is correct in saying that the voltage should be 13-14volt when activated. But if it can't tell when there is a load it won't turn on. Note there is always a load on a running vehicle. Is there a battery lite on in the instrument cluster.(the field wire is grounded via the cluster) But check this for me, I've seen this several times. There is a connector 3 wires I believe,on top of or near the starter. One of the wires is the field wire from the alt.(blue I believe)Make sure it isn't broken at that point.

good luck
 

dld

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The blue wire

Exactly what happened on our 97 Passat. The blue wire in the bundle by the reverse light switch broke and the alternater would only charge above 1700 rpm. You can live with it, or repair the wire.

Doug
 

kipw31

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nc
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01 jetta
tdi techee said:
What everyone has forgotten is the field wire. The alt. requires a field wire in order for it to know when to charge. The way you describe the volts jumping up intermittently tells me the alt doesn't know to turn on. Everyone is correct in saying that the voltage should be 13-14volt when activated. But if it can't tell when there is a load it won't turn on. Note there is always a load on a running vehicle. Is there a battery lite on in the instrument cluster.(the field wire is grounded via the cluster) But check this for me, I've seen this several times. There is a connector 3 wires I believe,on top of or near the starter. One of the wires is the field wire from the alt.(blue I believe)Make sure it isn't broken at that point.

good luck
this is the answer im looking for. Thanks
 

Dimitri16V

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kipw31 said:
this is the answer im looking for. Thanks
if the startup voltage is not there , you will get a battery warning in your cluster. the blue wire "jumpstarts " the alt.
 
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