charging/alternator thread*more confused than ever*

[dieselweasel]

I have a feeling the other end of the blue wire circuit is not grounding correctly/easily. . Perhaps I need to add an independant ground going from the cluster to the battery.

Maybe I confused you with my previous post...the blue wire grounds through the alternator, not at the cluster.  If the light is on when key is on, chances are the cluster is not the problem.  There may be a problem with the alternator or the blue wire.  The terminal for the blue wire is usually marked D+.  How many terminals are on this alternator and how are they marked?  

Turn the key on (engine off) and remove the blue wire.  Connect your volt meter between end of blue wire and batt-.  What do you get?  What does the light do?  What do you get if you connect your meter between b+ and that terminal?  Then start the engine and take the above readings again. 

As ORCoaster has alluded to, and I have experienced myself (with a fresh rebuild), sometimes an alternator will not begin to charge until the engine is revved a bit.  I have been told Bosch alternators are notorious for this.  This is because the output of the alternator stator also supplies the regulator with current.  There is residual magnetism in the rotor which will induce more current into the stator the faster it spins.  Just for fun, try revving the engine to 3-4 k RPM and see if the alt starts charging.

[Smokey Eddy]

I'm aware of the reving issue and I've been doing that to no avail. I will take those readings and post them.
This alternator has identical posts and inputs as the old 65 amp one did.
I'll also make sure the nuts on the post are not grounding to the body of the alternator.

[Smokey Eddy]

Okay so when i took the blue wire off the alternator and grounded it through my multimeter i only got 6.5V with the key in the ON position and when the engine was running it was 6.9V...
But it doesn't end there...
If i start the car without the blue wire on it at all and i check the D+ post i get 0.65V.
If I connect the blue wire to it (or any wire supplying voltage like from the B+ post) I get the battery voltage. I take these wires off with the car still running and check the D+ post I still see the battery voltage. This sounds totally wrong to me... Either that or i don't understand anything. I was planning on temporarily fixing this by jumping the B+ to the D+ but clearly this is already happening and doesn't do anything.

One thing i did notice was i could turn the head lights on and off by grounding the blue wire (turns them off) and then touching the D post turned them back on again.
I'm completely lost now. No idea what is wrong or what to do next...

[Smokey Eddy]

Here is a question, what if I'm not getting voltage from my blue "charge now" wire? What do I do then? I've replaced the connections on all the wires but its still the original wire.
Prior to my old 65 amp (i just bought a 90) breaking the battery diode would very dimly glow and sometimes come on periodically.
I'm going to go re-clean all the contacts I think. Paying special attention to the grounds...

Then you need to trace the source of the problem back to the dash/cluster/ignition. Is anything else not working?

Alternatively, you can just run a new wire to it. It needs switched 12 volt power (it will drain the battery if directly connected).  

The very faint alternator light glow that you can see on a dark night is caused by the alternator path to ground not being a perfect conductor compared to  the the rest of your electrical system. I don't believe it's a problem but perhaps you could directly ground the alternator anyway.

I don't understand how running a switched 12V wire to the D+ post does anything at all if the D+ post puts out the battery voltage ANYWAYS? To me, it's like running a power wire into another power wire and expecting something to change or be different.

[dieselweasel]

Read this Eddy to help you undestand how the system should work:  http://www.pelicanparts.com/techarticles/914_alternator_troubleshoot/914_alternator_troubleshoot.htm

Look at the wiring diagram.  He talks about 4 terminals but note that 2 of those (DF and D-) are internal between the alt and regulator.

D+ acts like a ground for the dash light until the alternator starts charging, at which point D+ should have the same voltage as B+, causing the light to go out due to the same potential present on both sides of the light. 

When you took your voltage readings, are you sure you had a good ground for your meter?  I like to go to batt-.  There's something not right if you can control your headlights through the blue wire.  I would look at a schematic to see what these circuits have in common...

So when you jump from b+ to d+ the alternator doesn't begin to charge, ie. voltage from the b+ terminal doesn't start to rise?  Even if you rev the engine a bit?  If not I suspect something wrong with the alternator...let us know.

[Smokey Eddy]

I just did a few trials and here's what I have.

With the blue wire disconnected the entire time.

With the key in the ON possition:
Battery: 12.06v
D+ to (-): 0.50v
D+ to B+: 11.56v

With the engine running:
Battery: 11.5v
D+ to (-): 0.50v
D+ to B+: 11.0v

So then I started to try some things.
Key in the ON possition:
Blue wire hanging free: 7.0v Batt. Light is ON
Blue wire to D+ Batt. Light is ON
Blue wire to (-) Batt. Light is ON
Blue wire to (+) Batt light is dim

Engine Running:
Blue wire hanging free: 7.0v Batt. Light is ON
Blue wire to D+ Batt. Light is Dim
Blue wire to (-) Batt. Light is ON
Blue wire to (+) Batt light is Off <-- Doing this turned on my headlights and they remained on. Blue wire to (-) turned them off again. Pretty sure I should have day time running lights... any ideas with this one?

Then with the Blue wire free I connected the D+ to the (+) of the battery and the engine bogged down as if the alternator was putting on some load and the voltage rose instantly from 11.4v or 11.8v (it's dark out) to 12.8v and then started to fall. I dropped my piece of wire and saw that the D+ post now showed the battery voltage but it was clear the alternator stopped doing what it had so briefly began to do. touching my wire to the (+) post and to D+ didn't seem to do anything at this point.

Remembering when I had my battery charger hooked up to the battery, after some time the alternator did kick in and start charging and then charge on it's own, perhaps the 7.0V from the blue wire is not enough or correct and im losing the rest of the voltage through a short in the line (i derive this via the batt. light being on at all times even if the blue wire is not grounded).

My question now is why does it not start charging again once 12v is applied to D+ a second time...

The fact that the battery light is on when the blue wire is hanging free tells me that circuit is grounding somewhere it shouldn't be and I have a fantastic time ahead of me figuring out where it's shorting. I'm also confident that the problem lies not within the alternator but with the blue wire as I originally had this problem with my other alternator - in retrospect i now regret buying a new one as there was likely nothing wrong with it. This one, once operational, should output 50% more current though which will be nice.

On a side note; from the site dieselweasel linked at the bottom the author says,
"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. "
Our battery warning light is an LED that probably outputs 1/4 of a watt... Does the mk2 system compensate for that?

[bajacalal]

I don't understand how running a switched 12V wire to the D+ post does anything at all if the D+ post puts out the battery voltage ANYWAYS? To me, it's like running a power wire into another power wire and expecting something to change or be different.

I don't quite understand what you are asking, sorry, but if you want to know why it has to be switched, the D+ exciter wire needs to be switched so that it is not energized when the engine is off... since it is basically grounding through the alternator when the alternator is not producing electricity, it will drain the battery if connected to a constant 12v source.

If you're asking how alternator excitation works, I dunno, lol. But yes, a 12V input is required for it to start making 12V, at which point, the exciter circuit is a electrical source and not an electrical draw... does that make sense. I think it has to do with the fact that an alternator makes power by spinning an magnetic field, but that magnetic field has to come from somewhere, so it is produced by the exciter circuit through the alternator coils until the alternator makes power on its own.

Most alternators have the exciter circuit, but VW just had the clever idea to use an LED through the instrument cluster as part of the circuit. Since electricity only flows one way through a diode (LED) the light only comes on when the alternator is not producing voltage (or in your case, is shorted to ground).

[Smokey Eddy]

So how can I temporarily fix this? Switch a wire to the d+ post and ignore the battery light until I figure out this grounding problem?
Or is it that once the alternator starts charging it will continue to do so since B+ and D+ essentially become the same?
Any ideas about the head light bit?


And yes what you said made sense. I read how it all works last night from that link dieselweasel posted. I dare not try to understand the math but I do understand what and why now. I think the main issue now is the electrical demons in the car with the exciter wire and the head lights.

[dieselweasel]

The fact that the battery light is on when the blue wire is hanging free tells me that circuit is grounding somewhere it shouldn't be

I agree something is wrong in the exciter (blue wire) circuit.

Would be nice to prove that the alternator is working correctly though, and get it charging so you can at least drive the car while figuring out the other problem.  Did you rev up the engine at all when you had b+ to d+ jumped?  I would try that... 

[Smokey Eddy]

Just did exactly that. Nothing. Also checked fuses. all look okay. Is there a relay that may not be working properly? Like the load relay or something.
Jumping d+ to + doesn't make it charge on its own but connecting the battery to a charger does. This I know. Reved it to all hell too partially as a test and also in frustration.

[dieselweasel]

What brand of rebuild was the alt?  Some rebuilds can be pretty sketchy.  If you can, find an auto electric shop and bring your alt to them to test it.  I know you are thinking it is good but I really think it should charge if you put 12v to the d+ terminal.  Wouldn't be the first time I was diagnosing a problem and wound up finding two separate issues.

[Smokey Eddy]

It's a Bosch 90 amp I bought through bestpricecarparts.ca
Advertised as a new alternator. I paid around $300 for it before an $80 core return.

[Smokey Eddy]

I guess ill have to take it somewhere to be tested. perhaps it requires an abnormally high voltage to induce the field. I ask this because as far as I can tell, putting a charger to it will trigger the alternator to start charging and continue to charge once the charger is removed.

[dieselweasel]

perhaps it requires an abnormally high voltage to induce the field. I ask this because as far as I can tell, putting a charger to it will trigger the alternator to start charging and continue to charge once the charger is removed.

Could be.  Like I said, try to take it to an auto electric shop as I would have more confidence in their testing than Cdn. Tire for example.  They should be able to give you a definite answer as to what voltage is required at the d+ terminal. 

[Smokey Eddy]

So I'm pretty confident its a belt problem. Taking the load off the alternator with a battery charger allows the belt to grab the pulley and start spinning. Upon closer inspection the belt is cracking and glazed on the sides. This will be the first time ever the belt has been slipping without any ear piercing screeching sounds. The pulley is also smooth as glass. I'm going to build a better bracket for tensioning, get a new belt and see if I can't sand blast the pulley somewhere or perhaps flap wheel with my dremel.