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Tue Jul 19, 2011 10:07 am

Yesterday I noticed my alternator light was staying on. So I plugged in the battery last night to give it a full charge and today I tested the voltage with a multimeter. I got 12.5 volts with the engine off, and over 16 volts with it on.

My understanding is I should see 12.3-14 volts with it on. Correct? And would the voltage being too high cause the alternator light to stay on?

And lastly, is there a fix other than a new alternator.

Thanks for any help.

Tue Jul 19, 2011 1:31 pm

Is this an internally or externally regulated alternator? External you could try getting a different voltage regualtor. Internal, well, depends on the make and model, sometimes you can get a new regulator for those.
-Andy

Tue Jul 19, 2011 2:39 pm

glutamodo wrote: Is this an internally or externally regulated alternator? External you could try getting a different voltage regualtor. Internal, well, depends on the make and model, sometimes you can get a new regulator for those.
-Andy

I believe it is internally regulated. I was under the impression that all alternators were. I thought only generators used external regulators.

Tue Jul 19, 2011 2:53 pm

Stock beetles from late 73 up had externally regulated alternators. Look at the alternator for the number of wires on it. Internal only has 1 positive.
Here is an external:
http://www.thesamba.com/vw/forum/viewtopic.php?t=472544&highlight=alternator+regulator

Tue Jul 19, 2011 3:47 pm

Here's some examples of some styles:

Tue Jul 19, 2011 3:57 pm

If you have an internally regulated alt it will have just a B+ terminal (heavy gauge wire that charges the battery) and the D+ terminal which connects to the Gen light in the speedo. The D+ wire is the feedback from the electrical system which allows the regulator to determine how much to charge.
Disconnect the D+ wire at the alternator and with the ignition ON (engine NOT running) test the end of the wire for voltage. You should read very close to 12v. If this voltage is much lower it will cause the regulator to continuously overcharge the battery.

And to your question of whether an alternator outputting 16v would cause the Gen light to lite up... Definitely Yes!
The 12v coming from the speedo over the blue wire would be over powered by the 16v coming from the D+ terminal. This would result in 4v of current flowing from the D+ terminal towards the Gen light. That should be enough to get the bulb to glow (though, not too brightly).
This is a very interesting situation as the Gen light is connected to two positive sources and no ground. The difference in voltages causes current to flow through the bulb and light it up!

Tue Jul 19, 2011 4:17 pm

SOLVED

Thanks for the help everyone. I figured out the problem, and just in case anyone searches for this topic I wanted to post the fix (er, my fix)

First off I was testing the voltage at the alternator not at the battery terminals with a multimeter. I now realize it should probably be tested at both.

As it turns out the connection/wire from the alternator to the positive battery terminal was broken. So while the alternator was putting out 16v, none of that was reaching the battery. Once I found and repaired the break, it reads 13-14v at both ends.

Thanks again

Sun Nov 11, 2012 4:11 pm

Wanted to bring this back up so i didn't create a new topic.
I have the same problem as mentioned above. I have measured the voltage at the alt output and the battery terminal while its running. 14.9-15.5 is what im getting right now. My dash voltmeter is only showing about 13.5-14 volts, which is correct, but i dont want to blow up my battery or anything. Also my alt light is coming on prior to start up, and goes out and stays out the whole time the car is running. Any ideas besides the internal regulator? The alt is an internally regulated bosch.

Mon Nov 12, 2012 12:10 am

kangaboy wrote: I have measured the voltage at the alt output and the battery terminal while its running. 14.9-15.5 is what im getting right now. My dash voltmeter is only showing about 13.5-14 volts, which is correct, but i dont want to blow up my battery or anything.
Your dash voltmeter and your test multimeter may be calibrated differently. Use the same meter to test the voltage behind the dash to confirm if there is a voltage loss from the battery to the fuse box.
More than 1v loss and it probably means your wiring connections could be cleaned up to improve the voltage transmission.

kangaboy wrote: Also my alt light is coming on prior to start up, and goes out and stays out the whole time the car is running. Any ideas besides the internal regulator? The alt is an internally regulated bosch.
Are you thinking the Alt light shouldn't be acting like this? The light comes on with the ignition switch in the ON position. This shows the alternator is grounding the Alt light and the field circuit its powered. If this light is not ON the alternator will not charge. Once the engine is turning this voltage flow is balanced by the alternator output on the D+ terminal, and the light should turn OFF. If the light turns ON at any other time you have a problem.

Mon Nov 12, 2012 8:12 am

Ashman, i have read a few other posts and they make it sound like the alt light will come on when overcharging is occurring. Right now my light is not coming on after the start up and high voltage readings. Should it light up with 15.5 volts coming from the alt?

Mon Nov 12, 2012 8:24 am

Well i just went out and checked the battery this morning. Its about 50* F out, and the batt still reads 14.5 volts, which makes me think my volt meter has taken a shit on me after only 2 years. I checked a few others and they were 13+. A fully charged battery is 12.5ish correct? Im pretty sure it wouldnt be able to hold a 14+ volt charge. THis also means that my dash gauge is likely correct.
Ill get a new volt meter before i start cruising in it again just so i dont blow anything up.

Mon Nov 12, 2012 10:01 am

An overcharging alternator does NOT cause the warning lite to come
on. The fellow who posted originally had that happening because his
alt was not actually connected to the batt (broken wire). The warning
lite is connected to the alt output (thru some diodes at D+ terminal) on one side, and
on the other is connected (thru the ign. switch) to the same output at B+ terminal,
so there is normally NO voltage across the warn. lite bulb when the alt is charging.

Mon Nov 12, 2012 10:19 am

ashman40 wrote:
Your dash voltmeter and your test multimeter may be calibrated differently.

The understatement of the century! The average voltmeter in a car's dash is good for knowing there they may be a slight possibility that voltage is present. I have never seen one approach anything near accurate. Always within 3 volts or more. For me, that's just too much to be trusted. But I used to work with test equipment, with tolerances within one one thousandth of one volt, so..

Mon Nov 12, 2012 11:13 am

kreemoweet wrote: An overcharging alternator does NOT cause the warning lite to come on.
This is not actually true.

There are three cases when you Alt/Gen light will come ON:
1) When the ignition is ON and the engine is not spinning [this is normal]. The alt/gen end of the #61/D+ wire will be grounded when the alt/gen is not spinning and voltage will flow from the fuse box, through the Alt/Gen light and ground at the VR(?).

2) When the engine is running and the voltage from the fuse box (battery voltage) is more than a few volts higher than the output from the #61/D+ at the alt/gen end. This indicates the alt/gen is not putting out enough voltage (or the battery is putting out too much voltage?). The difference in voltage causes current to flow towards the alt/gen. Current always flows from higher voltage (potential) to lower voltage.

3) When the engine is running and the voltage from the fuse box (battery voltage) is less than a few volts lower than the output from the #61/D+ at the alt/gen end. This indicates the battery is not putting out enough voltage. The difference in voltage causes current to flow towards the fuse box.

When the positive voltage from the fuse box and the positive voltage from the #61/D+ post (engine spinning) are nearly equal, there will be 12v in the circuit (relative to ground) but no current flow because neither end of the wire has a lower voltage, nor a path to ground. The alt/gen light will be OFF.

Small voltage differences will not be enough to allow current flow to light up the filament in the 2W bulb. Some voltage difference may make the bulb "glow" at night when the headlights are drawing most of the current from the fuse box.

Check for dirty connections which increase the resistance in the circuit between the battery and the fuse box.

A 12v car battery is normally made of six 2.1v cells. That works out to 12.6v for a fully charged one. Some may hold a higher surface charge right after being charged, but overnight or after a load should settle voltage down to normal state of charge.

Not clear which meter you used and saw 14.5v first thing on a cold morning? What you are interested in is the difference in voltage between the battery posts and the fuse box, using the same meter. This will show you how much voltage is lost as the current flows from the battery to the front. If it is more than 1v, consider going through and cleaning each connection with a wire brush.

Weird voltage readings are usually caused by bad grounds. Check all grounds and make sure there are good/clean connections.

Mon Dec 24, 2018 1:56 am

Hi All,

I hope you dont mind me rehashing and old thread, but it seemed logical to keep going with the same issue (mine now).

My 1916cc has an externally regulated alternator. Its the third from the top above (2nd of the external regulators), with 3x wires running to a Bosch RE57 regulator.

All was running OK when I first got the buggy (a week ago, bought sight unseen).

A few days back I decided to try and tackle the birdsnest that is the engine wiring. Lots of weak connections, some crimps fell apart just while unwrapping the elect tape, some no connection at all, etc (though still seeming to work).

Some how I stuffed up and swapped the D+ and DF wires at the reg. The engine fired for a second, but then blew the 15amp fuse. Not realising I had made the error, I chucked another fuse in, cranked and the fuse went again.

Upon spotting the amber dash lamp on, i traced back to the reg and spotted the swapped wires. I swapped them back, fired the motor, all ran fine, light was out, accept... now the volts were off the chart (increased with RPM, redlined the volt gauge at 18V at 2500rmp).

I gave it another test today, volts still the same and amber light back on.

So obviously, Something is still not right somewhere.

1. Could I have 'blown' the reg?
2. The alternator (again 3rd from top above) has a small bolt that appears to be an earth for other devices. Its that small hole in the photo and on my buggy (being fibreglass) seems to take the earth off a range of things such as the tail lights. The very short thread seems damaged, so I dot have it firmly screwed down. Could that be an issue and what size thread is it meant to be?

I reckon its around M5/5mm which is similar to 3/16 or 13/64. I cant get any of those to work and don't want to put a tap down to clean the thread until I know.

Any help is greatly appreciated.

Mon Dec 24, 2018 8:43 am

AaronJ1970 wrote: My 1916cc has an externally regulated alternator... with 3x wires running to a Bosch RE57 regulator.
<...>
Some how I stuffed up and swapped the D+ and DF wires at the reg.
<...>
now the volts were off the chart (increased with RPM, redlined the volt gauge at 18V at 2500rmp).
<...>
1. Could I have 'blown' the reg?
"Yes".

I found a pic of a Bosch RE57 regulator:

I've not heard of anyone using this VR on the external regulated Beetle alternators. Where did you see a reference to use this part in place of the stock part? Please describe in detail how you have this VR wired to your alternator? Specifically which wire goes to which terminal and where is the blue #61 wire running? This VR may be okay to use but it is this is the first time I'm hearing of someone using it with a Beetle. It seems to be commonly used with T2s?

Test your external VR. Follow the steps described here:
https://www.pelicanparts.com/techarticles/914_alte...eshoot.htm
The external VR basically takes voltage coming in on the D+ wire and regulates it out on the DF wire to control the (B+) output of the alternator.
From what you describe, the VR seems to be outputting max voltage (12v) on the DF wire all the time.
Try disconnecting the DF and see if the alternator continues to output high voltage. If it does, then the alternator is bad.

This diagram from Speedy Jim's site may help you with the wiring.

AaronJ1970 wrote: 2. The alternator (again 3rd from top above) has a small bolt that appears to be an earth for other devices. Its that small hole in the photo and on my buggy (being fibreglass) seems to take the earth off a range of things such as the tail lights. The very short thread seems damaged, so I dot have it firmly screwed down. Could that be an issue and what size thread is it meant to be?
The externally regulated alternators are primarily grounded thru the body of the alternator being in contact w/ the alternator stand/engine/transmission/trans ground strap. So unless you are missing you ground strap you shouldn't worry about the alternator being grounded.

The external VR has a dedicated ground wire that runs between the VR and the alternator. This is the D- wire (brown). This wire makes sure the VR and alternator share the same ground potential. This way when the VR measures a voltage it is the SAME voltage reading the alternator has. It is possible (due to different resistances) that different ground points around the car measure the same voltage differently.

All generators and many alternator will have a ground point (screw hole). The generators used this for the D- wire described above. On later alternator this may have been discontinued as the regulator was internalized.
This ground screw is definitely a good spot for grounding anything in the engine compartment. Especially if you have a fiberglass body you have a lack of ground points in general. Just be careful not to create a spider web of wires that get in the way. The last thing you need is one of these wires getting caught in the fan belt.

Mon Dec 24, 2018 3:32 pm

Hi Ash,

Firstly, about to run off on holiday, so will go over your post in detail once we're settled But thank you for the effort.

Its an Australian made Bosh regulator, commonly used for VW's here (loads of references on all of our local forums). I cant give any further background, reason, etc.

Secondly, it is wired D+ to D+, DF to DF and D- to D- and the blue wire (not blue in my case) goes to the amber light on the dash.

As for spider web of wires... my problem exactly. I think I counted 6 wires running to the ground!

Thanks again, I'll get back to you ASAP.

Oh.. that one Q I had about the screw/thread size on the alt. Any idea what size it is???

Sat Jan 12, 2019 8:59 pm

Hi Ash
With the DF wire disconnected the volt meter reads around 12v.
Plug it back in and voltage through the roof at +18v.
Does that point to the reg being bad?

Sun Jan 13, 2019 8:17 am

AaronJ1970 wrote: Hi Ash
With the DF wire disconnected the volt meter reads around 12v.
Plug it back in and voltage through the roof at +18v.
Does that point to the reg being bad?

I'd say so.

Sun Jan 13, 2019 11:11 am

Review the Pelican Parts link above and run the troubleshooting steps.

With everything connected properly, test the voltage reading on the D+ wire. This voltage should be in the range 13.8-14.0v. While it is a different circuit than the B+ it functions the same. It is possible for one to fail while the other works normally. They are both linked to the DF as the control of the field circuit which controls charging. Compare this D+ voltage with the B+ voltage measured at the alternator. They should be the same. If the B+ is higher than the D+ then your alternator internals are bad.

Also test the voltage on the DF wire. The VR should be regulating this voltage so it is LOWER than the voltage on the D+. If the voltage on the DF is always the same as the D+ then your VR on not regulating at all and should be replaced.