74 Super Beetle charge light on but its charging

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RSorak 71Westy
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Re: 74 Super Beetle charge light on but its charging

Post by RSorak 71Westy » Tue Mar 12, 2013 8:03 pm

Unfortunately a regulator at Autozone is $30 today and If I buy one I cant return it and the customer is getting tired of the bill going higher. So does your last post mean my alternator man sucks and I still need an alternator? As it seems from reading thru your experience replacing regulators was no help and the alt was what fixed it.
Take care,
Rick
Stock 1600 w/dual Solex 34's and header. mildly ported heads and EMPI elephant's feet. SVDA W/pertronix. 73 Thing has been sold. BTW I am a pro wrench have been fixing cars for living for over 30 yrs.

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Re: 74 Super Beetle charge light on but its charging

Post by RSorak 71Westy » Wed Mar 13, 2013 10:16 am

Ok from this I gather you're saying my alternator man is wrong. and I still need an alternator because thats what fixed yours. Well I just got off the phone with said alternator man and he insists that theres no other diodes in that aLt beside the 6 that rectify the output and they are fine. Its seems to me all the descriptions of how this alt works, is that there are diodes in the exciter circuit. In short Im confused and a $30 Autozone VR has been ordered.
Take care,
Rick
Stock 1600 w/dual Solex 34's and header. mildly ported heads and EMPI elephant's feet. SVDA W/pertronix. 73 Thing has been sold. BTW I am a pro wrench have been fixing cars for living for over 30 yrs.

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Amskeptic
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Re: 74 Super Beetle charge light on but its charging

Post by Amskeptic » Wed Mar 13, 2013 1:41 pm

RSorak 71Westy wrote:Ok from this I gather you're saying my alternator man is wrong. and I still need an alternator because thats what fixed yours. Well I just got off the phone with said alternator man and he insists that theres no other diodes in that aLt beside the 6 that rectify the output and they are fine. Its seems to me all the descriptions of how this alt works, is that there are diodes in the exciter circuit. In short Im confused and a $30 Autozone VR has been ordered.
I really cannot say, I know it is frustrating, but I am sitting at a desk. I do NOT lay claim to any possibility without being there testing it with my own eyes. I have deferred to different designs behaving differently from my own experiences as reiterated here from an article on Pelican Parts:

Bosch is nine diodes 3 output B+ / 3 excitor D+ / 3 common. What can I say?
Image
There are four connections to the alternator itself. D+, DF,D-, and B+. If you look at the Haynes book, what is not readily apparent, but is true nevertheless, is that the set of diodes that connect to the D+ terminal are a duplicate set (except for lower curent rating) to the ones for the B+ terminal, which is the actual high current output of the alternator. The D+ terminal is therefore a duplicate output terminal of the alternator, with less current capability. The lower set of diodes on current track 80 is common to both the D+ and B+ functions, and forms the ground return for both the B+ and D+ outputs. The DF or "Dynamo Field" terminal connects to the ungrounded end of the alternator field winding, and is an input to the alternator. The current supplied to the DF terminal determines the strength of the magnetic field that penetrates the output windings, and thus controls the alternator's output. The D- terminal is connected to the alternator frame, and is the ground return for the voltage regulator. The other end of the field winding is also connected to ground at this point.
The Bosch alternator is incapable of self-excitation, or "boot-strapping" itself to an operating condition. Older DC generators and some U.S. alternators have residual magnetism retained in the core, or some other scheme to get enough field current to get themselves up and running. The Bosch alternator uses a different scheme. The charge warning lamp is connected between the ignition switch and the D+ terminal. When the car is first started, there is no output from the alternator at either the B+ or D+ terminals. The voltage regulator, sensing no output, is attempting to command maximum field current... it effectively shorts the D+ and DF terminals together. This places the D+ terminal close to ground potential, because the resistance of the field winding is not large. This means that there is +12 volts on one side of the charge warning lamp, and the other side of the lamp is grounded through the alternator field winding. Current thus flows through the lamp, lighting it. This same current, however, also flows through the alternator field winding, producing a magnetic field. This magnetic field is what the alternator needs to start up, and if everything is working correctly, that's exactly what happens. The alternator now begins to develop identical voltages at the D+ and B+ terminals. The D+ terminal is connected to one end of the charge warning lamp, while the other end of the lamp is connected to the battery via the ignition switch. Since the B+ terminal is hard-wired to the battery, and since both the D+ and B+ diodes are fed from the same set of windings in the alternator, no voltage difference can exist between these two points. The warning lamp goes out.

The voltage regulator "watches" the voltage at the D+ point, which should be the same as that applied to the battery. It now changes the short between the D+ and DF terminals into a variable resistance. This effectively controls the field current (whose source is now the output from the D+ terminal, and not the charge warning lamp) and thus regulates the output voltage of the alternator.

Fault conditions: When something happens to the charging system that causes it's output to be insufficient, the result is almost always a net voltage difference across the charge warning lamp, causing it to light. For example: Suppose an output (B+) diode opens. The efficiency of the main output is now considerably reduced. The voltage regulator does not know this, however, because it is looking at the D+ point. So, the B+ output is now lower than the D+ point and the warning lamp lights. Let's say that one of the D+ diodes failed: The D+ output is now reduced considerably. This means that the voltage regulator will have difficulty in maintaining sufficient field current for normal output. The field regulating resistance is low or short (between D+ and DF terminals) and the resulting load on the crippled D+ system drops it's voltage well below the battery voltage. Therefore, there is a net voltage difference across the charge warning lamp and it lights.

The bottom line is that in order for your light to light, you must have a net imbalance in the outputs of the D+ and B+ sections of the alternator (or between the D+ output and the battery voltage, which amounts to the same thing).

To trouble-shoot the problem, you need to check the various sections independently. Thus the first check: Connect +12 volts from the battery to the DF terminal on the relay board. This is the maximum field current situation, and should result in maximum output of the alternator. Note that this checks the B+ diodes, the alternator windings, and the common diodes. It does NOT check the D+ diodes.

To check the D+ portion of the system, it is necessary to find out if the D+ output can produce enough current to drive the alternator to full output. To do this, short the D+ and DF terminals on the relay board. This will provide the maximum field current to the alternator that the alternator ITSELF can supply (not the battery, as in the earlier check) and so checks the remainder of the circuitry. If this test puts the light out, then the alternator is good, and the trouble is elsewhere. If it doesn't, then the alternator is almost certainly bad, with one other possibility:

In the Bosch system, the size of the charge warning lamp bulb is critical. Too low a wattage bulb will not supply enough field current for "bootstrap" operation to be reliable. The Bosch book that I have states that the lamps must be at least 2 watts for 12 volt systems. If you have replaced your charge warning lamp recently, then too small a lamp may be your culprit.

I hope this is of some help.... Good Luck, Jim T.
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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RSorak 71Westy
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Re: 74 Super Beetle charge light on but its charging

Post by RSorak 71Westy » Wed Mar 13, 2013 5:49 pm

All this info about a Bosch Alt is of no help, I have a Motorola
Take care,
Rick
Stock 1600 w/dual Solex 34's and header. mildly ported heads and EMPI elephant's feet. SVDA W/pertronix. 73 Thing has been sold. BTW I am a pro wrench have been fixing cars for living for over 30 yrs.

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dingo
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Re: 74 Super Beetle charge light on but its charging

Post by dingo » Wed Mar 13, 2013 10:12 pm

Bosch,Moto = same system ...in fact majority of alts use that system (few exceptions like Denso)

anyways...how to do your own test for bad diodes

Ripple voltage or (AC voltage) can be measured using a digital multimeter. Make sure your meter is on an AC scale. Connect the black lead to a good ground (bolt on the engine or bare metal) and the red lead to the “battery" terminal (sometimes labeled “BAT” or simply “B” – usually a red wire) on the back of the alternator, (not at the battery). A good alternator should measure less than .5 Volts AC (that’s point five i.e., one-half a volt) with the engine running. A higher reading indicates damaged alternator diodes – typically open.

To check alternator diode leakage, connect the multimeter in series with the alternator output terminal when the car is not running. This is accomplished by disconnecting the battery lead wire and connecting the digital muitimeter’s red lead to the battery terminal on the alternator and the black lead to battery lead. Leakage current should be a couple of milliamps at most; more often, it will be on the order of 0.5 milliamps on a current scale of your multimeter – more that a few milliamps indicates a shorted diode and this will definitely zap your battery in a day or so.
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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Amskeptic
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Re: 74 Super Beetle charge light on but its charging

Post by Amskeptic » Thu Mar 14, 2013 8:03 am

dingo wrote:Bosch,Moto = same system ...in fact majority of alts use that system (few exceptions like Denso)

anyways...how to do your own test for bad diodes

Ripple voltage or (AC voltage) can be measured using a digital multimeter. Make sure your meter is on an AC scale. Connect the black lead to a good ground (bolt on the engine or bare metal) and the red lead to the “battery" terminal (sometimes labeled “BAT” or simply “B” – usually a red wire) on the back of the alternator, (not at the battery). A good alternator should measure less than .5 Volts AC (that’s point five i.e., one-half a volt) with the engine running. A higher reading indicates damaged alternator diodes – typically open.

To check alternator diode leakage, connect the multimeter in series with the alternator output terminal when the car is not running. This is accomplished by disconnecting the battery lead wire and connecting the digital muitimeter’s red lead to the battery terminal on the alternator and the black lead to battery lead. Leakage current should be a couple of milliamps at most; more often, it will be on the order of 0.5 milliamps on a current scale of your multimeter – more that a few milliamps indicates a shorted diode and this will definitely zap your battery in a day or so.
Thanks, dingo.

Have you read this thread through? Can you critique the diagnostic path I laid out for errors and omissions? I would like to edit it down so that a searcher could get through it . . . actually enlightened.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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dingo
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Re: 74 Super Beetle charge light on but its charging

Post by dingo » Thu Mar 14, 2013 10:45 pm

It looks OK to me...but i think it would be cool to have a nice colored flow chart that encourages someone to grab a voltmeter and make some simple, methodical readings...and thus make some simple eliminations and unravel the confusion of the moment....or at least simplify the confusion a bit. This alt issue comes up so frequently and i see people meandering thru very haphazaed tests and half-tests
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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RSorak 71Westy
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Re: 74 Super Beetle charge light on but its charging

Post by RSorak 71Westy » Fri Mar 15, 2013 11:32 am

There is an easy to test for a bad alt....Put a light bulb between D+ and B+ if it glows the problem is in the alt......I also have 2-3 volt of AC on D+ Back to the alt shop and try to teach the rebuilder.....Wish me luck.
Take care,
Rick
Stock 1600 w/dual Solex 34's and header. mildly ported heads and EMPI elephant's feet. SVDA W/pertronix. 73 Thing has been sold. BTW I am a pro wrench have been fixing cars for living for over 30 yrs.

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dingo
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Re: 74 Super Beetle charge light on but its charging

Post by dingo » Fri Mar 15, 2013 11:41 pm

If he pulls it apart and you can access all the diodes, measure each one at at time. Should be a few hundred Ohms with meter leads in one direction, and with leads reversed 'Nothing'. Good luck !
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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dingo
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Re: 74 Super Beetle charge light on but its charging

Post by dingo » Sat Mar 16, 2013 12:28 pm

something like this for 'charging system troubleshooting' would be cool in colin's trademark watercolors

http://www.ifitjams.com/index.htm
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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Amskeptic
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Re: 74 Super Beetle charge light on but its charging

Post by Amskeptic » Mon Mar 18, 2013 6:56 am

dingo wrote:something like this for 'charging system troubleshooting' would be cool in colin's trademark watercolors

http://www.ifitjams.com/index.htm
Yes it would be interesting. At my current rate of output, we'll have it spooled up in 2032.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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RSorak 71Westy
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Re: 74 Super Beetle charge light on but its charging

Post by RSorak 71Westy » Tue Mar 19, 2013 4:10 pm

Ok today the rebuilder called and said to come get it, no charge !! When I got there he said dont ask any questions.....I wanted to. He did put it on the tester and showed me that D+ was putting out. So tomm when I get it back on the car it should be fixed.
Take care,
Rick
Stock 1600 w/dual Solex 34's and header. mildly ported heads and EMPI elephant's feet. SVDA W/pertronix. 73 Thing has been sold. BTW I am a pro wrench have been fixing cars for living for over 30 yrs.

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Amskeptic
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Re: 74 Super Beetle charge light on but its charging

Post by Amskeptic » Wed Mar 20, 2013 10:52 am

RSorak 71Westy wrote:Ok today the rebuilder called and said to come get it, no charge !! When I got there he said dont ask any questions.....I wanted to. He did put it on the tester and showed me that D+ was putting out. So tomm when I get it back on the car it should be fixed.
We'll be waiting . . .
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

User avatar
RSorak 71Westy
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Location: Memphis, TN
Contact:
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Re: 74 Super Beetle charge light on but its charging

Post by RSorak 71Westy » Wed Mar 20, 2013 2:42 pm

It is fixed. The charge light goes out instantly with the start of the engine, no need to rev it to get it to start charging.
Take care,
Rick
Stock 1600 w/dual Solex 34's and header. mildly ported heads and EMPI elephant's feet. SVDA W/pertronix. 73 Thing has been sold. BTW I am a pro wrench have been fixing cars for living for over 30 yrs.

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