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Alternator light,? WHERE?
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tencentlife
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PostPosted: Fri Dec 03, 2010 11:44 am    Post subject: Reply with quote

Except it's spelled embarrassed, with an a, two r's, two s's.

Funny thing to me is that the Spanish for "pregnancy" (but not pregnant) is embarazo, but it also means "embarrassed". What I see in that word is bearing, as in burdened with something, which could be a baby or could be shame, but that's just me. My dictionary tells me that the Latin root means "in a noose" (barassa). Aint words phun?


Coil-wound (as opposed to permanent magnet) alternators consist of two separate sets of copper wire windings, a stator and a rotor. The stator, as its name suggests, is stationary, it makes up the bulk of what you find inside the chassis enclosure if you open one up. The rotor, it doesn't take a genius to figure out, rotates.

In a car alternator the rotor windings are called the "field windings". Electrical current can be caused to move in a conductor by passing it thru a magnetic field, or vice versa the field can move while the conductor is stationary. This process is called induction.

So the field windings rotate within the stator windings. The field windings are connected to power and ground via carbon brushes riding on slip-rings, so there is a circuit thru the field windings while the rotor can spin. The magnetic field induces current to flow thru the stator windings. That current emerging from the stator windings is the electrical supply for the vehicle, it charges the battery back up after the starter motor has used some of the stored energy, and supplies a source of electrical power for all the vehicle functions while the engine is running.

But, in order to intiate the process, the field windings require an input of power, to create the magnetic field that will induce current in the stator. This is called "excitation", some power is used to "excite" the field. The excitation power is delivered to the alternator from the ignition switch, via the charge warning lamp. When you key on, power flows from the battery, thru the igniton switch, thru the lamp, and to the field winding in the alternator, and thru the windings to ground. That sets up a weak magnetic field, and the rotor spinning induces a weak current in the stator. A portion of that weak stator power is diverted to the field windings to keep them excited; the alternator is now "self-exciting". Turn by turn the voltage level builds up so the process of power generation is constant from then on. The portion diverted is controlled by the regulator, it controls current flowing thru the field to whatever intensity is required to sustain a set system voltage.

The stator is actually three separate windings, called "legs". The power coming out of the stator windings is "wild" ac, meaning its cycles per second ("Hertz") varies with the rotor speed. The wild ac is rectified to a DC current by a pack of diodes connected to the output of the three stator legs. This diode pack is called a "full bridge rectifier", as it rectifies the wild ac waveform into a steady DC current.

So, key on, engine not turning yet, current flows from source (battery) to sink (ground at the other end of the field windings). Along that path is the warning lamp, so since current is flowing thru it, it glows. The same small current establishes a weak magnetic field as it flows thru the field windings .

Start the engine, the alternator shaft spins the rotor, the spinning magnetic field induces stator current, and some of that current is diverted to uphold the field, which becomes stronger, so stator voltage climbs, and field voltage climbs with it, and so on until they are both at the predetermined system voltage. The field is now at about the same voltage as the stator voltage, which the regulator is maintaining at a little above battery voltage. Since at one end of the lamp circuit is the battery, and at the other end is the field, and the voltages are nearly the same, there is little to no voltage differential, so little to no current flows, and the lamp stops glowing visibly.

Let the field voltage drop, due to a problem in the regulator, poor contact at either rotor brush, or a problem in the stator or rectifier, and there may once again be a large voltage differential between battery and field, so enough current once again will flow thru the warning lamp to make it glow visibly.

One way to test an alternator that does not appear to be charging while the engine is running is to very briefly jump power from the main alternator + pole to the D+ field input while measuring voltage at the + pole. This will directly excite the field and force the alternator to produce current. If it sustains voltage after doing this, the alternator is basically OK and there is a problem with the lamp/exciter circuit. Since the rotor often retains a weak magnetism even without excitement power being applied, these alternators will often self-excite just by revving the engine higher for a second.
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Tom Powell
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PostPosted: Fri Dec 03, 2010 11:55 am    Post subject: Reply with quote

tencentlife wrote:
Except it's spelled embarrassed, with an a, two r's, two s's. .


I em bare assed

tp
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irgsmoore4
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PostPosted: Fri Dec 03, 2010 4:38 pm    Post subject: Reply with quote

Cool so now i feel like i have friends! i certainly do have vanaganitis and i still have a problem. I tried the light thing, i got a 12 volt incan light hooked it to the +on the coil and the +on the alt and when i hooked the bat up it came on! is this normal?? the alt was still reading 12.33 on the multimeter. so tencentlife wrote a whole book about the alt, all of which i understood,except at the end he explained how to do a test again i got all of it apart from when he said " Briefly jump power from the main alternator + pole to the D+ field input" , explain the "D+ field input " please. I drove Elsie from San Diego to vermont where my family and i will spend a year befor going home to SD and i hope while we are here i can learn as much as i can about Elsie and her idiosynchrosies. [/quote]
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DAIZEE
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PostPosted: Fri Dec 03, 2010 5:15 pm    Post subject: Reply with quote

Wow, Elsie's already been across the Continent (well almost) Smile
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tencentlife
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PostPosted: Fri Dec 03, 2010 6:33 pm    Post subject: Reply with quote

Quote:
explain the "D+ field input " please.


Where the wire from the warning lamp attaches to the back of the alternator. There is the large connector B+, and to the right a small push-on connector usually clearly marked "D+" embossed in the casting. It should have a small blue wire connected to it.

If you connect your voltmeter between the B+ and ground, you should see battery voltage at any time. Start the engine, and with it idling, very briefly jump from B+ to D+. The measured voltage should rise above its previous value. If the first test doesn't work, try holding the engine revs up a bit and try it again. If the voltage never rises, the alternator is probably not working, it is most probably the regulator or brushes, which come as a single replacement part (it's a two-fer: the regulator also acts as the brush carrier) and are easily replaceable with the alternator in place.
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PostPosted: Fri Dec 03, 2010 6:43 pm    Post subject: Reply with quote

thank you , i understand now(at least i think i do !) . i just checked out some of you work , nice motors. On our way back to cali we may have to stop in ,(so long as mine lasts another 10 months in vermont),i can see one of those nice shiny motors in the back of my Elsie. thank you again for your help, patience and replies. Cool
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PostPosted: Sat Dec 04, 2010 6:21 am    Post subject: Reply with quote

happy saturda to one and all. Are all alternators the same ?? will i be able to get brushes/regulator from any parts store? Cool
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PostPosted: Sat Dec 04, 2010 8:01 am    Post subject: Reply with quote

so i think i fixed the problem ,after starting her up up followed Tencentlies instructions and nothing so i disconected all the alt cables cleaned them put them back then did the A+ jump to D+ thing and the volt meter reads 13.98 so this being higher than the batt does this mean the problem is solved? Cool
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PostPosted: Sat Dec 04, 2010 8:15 am    Post subject: Reply with quote

irgsmoore4 wrote:
so i think i fixed the problem ,after starting her up up followed Tencentlies instructions and nothing so i disconected all the alt cables cleaned them put them back then did the A+ jump to D+ thing and the volt meter reads 13.98 so this being higher than the batt does this mean the problem is solved? Cool


Well Done!
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PostPosted: Sat Dec 04, 2010 8:21 am    Post subject: Reply with quote

Quote:
happy saturda to one and all. Are all alternators the same ?? will i be able to get brushes/regulator from any parts store?


No, not all the same. If the alt you have is the specified one for your year/model, then you should be able to get a new reg on that info.

But you said it's new (rebuilt I imagine). Maybe you should take the whole alt in, a lot of the places can bench-test them, and get an exchange if it doesn't check out.

Did you try artificially grounding the alt chassis to the van body with a jumper wire? I take it you are able to start the engine with the starter motor? If so, that says that at least you have good grounding of the trans/engine assembly and battery, but it has been known to happen that a mounted alt didn't ground well thru the bracket as it should. I always add a nice 10ga. wire direct to the alt chassis and ground it to the engine block.

I don't see where you have tested the warning light circuit. You should key on, and touch the D+ wire at the alt to ground. The warning light should glow brightly (if you have an OXS indicator below it, it wil glow too, that is normal). Try grounding it directly to the alt chassis, if it glows then you at least know there is a ground circuit thru the chassis; if it doesn't glow there, try grounding it to the van chassis itself. If the light never glows, then there is a break in that circuit, but if that is the case, the alt should still excite and make voltage by the little test I described yesterday. If the light does glow when you ground it, then the problem is likely in the alt itself.

Thanks for the props on my engines. But don't expect to buy one on short notice, should you ever want one, you have to order in advance, I'm normally booked 4 or 5 months out.

<edit> Oops, I see you made some progress while I was typing. Good for you!>
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PostPosted: Sat Dec 04, 2010 3:34 pm    Post subject: Reply with quote

so after testing it a socound time im not so sure the prob is fixed , i started her up the revs ran high ,put the multimeter on the A+ ,12.33, put on D+ still 12.30 .The fist time i did this the Alt climbed to 14.26, so do i put on new brushes? a $50 part may be the answer? then i guess its find out why the light on the dash does not work, i cant find LED's anywhere.
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PostPosted: Sat Dec 04, 2010 3:48 pm    Post subject: Reply with quote

irgsmoore4 wrote:
i cant find LED's anywhere.


Radio Shack!
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PostPosted: Sun Dec 05, 2010 6:10 pm    Post subject: Reply with quote

so i pretty sure that the alt is fine every time iv tested it the alt has read higher than the battery (bat 13.35, alt 13.99/14.25) is this good? this week i plan on putting in a new LED in the cluster,if i can ever find one that is! and i dont plan on using her until im 100% sure shes good, Cool (being stuck in VT in the snow/cold is not on my list of things to do!)
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PostPosted: Sun Dec 05, 2010 10:04 pm    Post subject: Reply with quote

irgsmoore4 wrote:
so i pretty sure that the alt is fine every time iv tested it the alt has read higher than the battery (bat 13.35, alt 13.99/14.25) is this good? this week i plan on putting in a new LED in the cluster,if i can ever find one that is! and i dont plan on using her until im 100% sure shes good, Cool (being stuck in VT in the snow/cold is not on my list of things to do!)


Cedge wrote:

The darned alternator light would not go out, no matter how many times I "blipped" the engine. A trip to the local alternator shop showed that the alternator was fine, but the light, being an LED, wasn't creating enough load to trigger the system.

Steve


The voltages sounds good, but I don't think you want a LED in the cluster. It won't create a sufficient load to excite the alternator. Most likely it is an incandescent bulb in the cluster. I don't know the size or a part number, but that might be available from the Bentley or a knowledgeable Samba member. At this point you can remove the bulb and replace it or probably continue for awhile with the temporary wiring that you used to excite the alternator. I don't exactly what you did to get it excited. You said, "did the A+ jump to D+ thing" I don't know the consequences of leaving that connected with the engine not running, but a new bulb should make that unnecessary. It looks like your problem was a burned out bulb or poor ground. The ground cleaning is part of Vanagon maintenance and the "did the A+ jump to D+ thing" synthesized the bulb to alternator excitement circuit. Hopefully Tencentlife will read this and correct me if I've made any misstatements or spelling errors.

Aloha
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PostPosted: Mon Dec 06, 2010 7:15 pm    Post subject: Reply with quote

Tom....
I left the LED indicator installed, parallel to the incandescent bulb, simply for cosmetic reasons. The LED definitely won't do the job on it's own, but works fine when piggybacked to the heavier load of the older style light. Things are now good in my world...(grin)

Steve
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PostPosted: Tue Dec 07, 2010 2:42 pm    Post subject: Reply with quote

today i added a ground directly to the alt and it runs like a champ, so whatb is the bulb in the cluster if it isnt an LED? Cool
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PostPosted: Tue Dec 07, 2010 2:44 pm    Post subject: Reply with quote

irgsmoore4 wrote:
today i added a ground directly to the alt and it runs like a champ, so whatb is the bulb in the cluster if it isnt an LED? Cool


it's an incandescent
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PostPosted: Tue Dec 07, 2010 2:55 pm    Post subject: Reply with quote

The Vanagon alternator light is an LED. This works fine since VW provided a resistor path around the LED to provide the excitation current initially to the alternator. If you look at the Bentley diagrams for ANY year you can see the resistor there in parallel with the LED. If you look at Bentley page 90.8, lower right, there is a resistor listed as R3, explained as "series resistor for alternator pre-exciter circuit (150 ohm)".

Mark


Tom Powell wrote:
irgsmoore4 wrote:
today i added a ground directly to the alt and it runs like a champ, so whatb is the bulb in the cluster if it isnt an LED? Cool


it's an incandescent
tp
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PostPosted: Tue Dec 07, 2010 4:15 pm    Post subject: Reply with quote

crazyvwvanman wrote:
The Vanagon alternator light is an LED. This works fine since VW provided a resistor path around the LED to provide the excitation current initially to the alternator. If you look at the Bentley diagrams for ANY year you can see the resistor there in parallel with the LED. If you look at Bentley page 90.8, lower right, there is a resistor listed as R3, explained as "series resistor for alternator pre-exciter circuit (150 ohm)".

Mark


Tom Powell wrote:
irgsmoore4 wrote:
today i added a ground directly to the alt and it runs like a champ, so whatb is the bulb in the cluster if it isnt an LED? Cool


it's an incandescent
tp


Please correct me if my thinking is wrong or my knowledge insufficient.
I am assuming that an inoperative LED does not not pass current the same as a burned out incandescent bulb.

I didn't look at the diagram or the bulb and assumed it was an incandescent and it's resistance caused the alternator to be excited if working and not excited if the bulb was burned out.

I am assuming that an inoperative LED does not pass current like a burned out incandescent bulb does not pass current.

If the resistor is in parallel then an inoperative LED wouldn't affect the excitation to the alternator unless the resistor was a size that the excitation circuit required both.

If the resistor is in series then either a burned out bulb or a burned out resistor (open) wouldn't excite the alternator

It appears that the statement, "series resistor for alternator pre-exciter circuit (150 ohm)" and the Bentley diagram showing a resistor in parallel are contradictory. I don't have the Vanagon Bentley in front of me so I'm at a loss for confirmation.

Isn't the inoperative or burned out light and lack of alternator excitation a Vanagon idiosyncrasy that most owners don't recognize? Haven't many owners replaced alternators when the problem was the light or wiring in the excitation circuit? In another post regarding alternator problems here's a quote that I found on the search, "The light circuit does double-duty: feeding a little current into the field winding to get it charging, at which point it self-excites, and letting you know when the field voltage is lower than the battery's, which means no charging." I also found this in the search, "... an LED requires a series resistor to keep it from burning out instantly"

If the bulb is a LED and is so important to the alternator exciting circuit, why don't any of the Vanagon parts vendors or the classifieds have it as an available part?

I don't mean to be argumentative. I'm only trying to increase my Vanagon knowledge and the information available on TheSamba.

Thanks for your reply and correction.


Aloha
tp
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PostPosted: Thu Dec 09, 2010 3:49 pm    Post subject: Reply with quote

so if the "series resistor for the alternator pre-exciter circuit" is burned out where o where do i get a new one? i just called van cafe and veeparts both in CA and they dont have one and cant get one. is this a common problem? i thought that the problem was fixed but the alt is still not putting out, i rode elsie to work today and when i got there i put the multimeter on the alt and it was 12.30 the same as the battery, should i change the voltage reg/brushes? I have yet to test the resistor ,thats going to wait till the weekend its 2 degrees here! Cool
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