Roger and I have an exciter wire question
11-19-2007, 04:06 PM
#47
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New alternator on the way to Tim just in case it is a faulty new alternator.
While we are waiting for Tim to find the time to make the next tests as suggested lets backtrack a little.
With both the old (Valero/Paris Rhone) and the new (Bosch) alternators, the lack of charge does not manifest itself until the alternator is HOT. Both systems worked fine until after about 40 mins of running.
Tim is going to check the alternator duct to ensure smooth flow of clean ambient air from under the fender.
Question for the Boffins
What is the overheat (No or not enough cooling air flow) effect on the alternator?
Does it shut down with some overiding circuitery?
Does it just burn and die?
The Bosch alternator (928 603 114 AX) is the correct unit for 77 to 84 cars with the caveat that on the 77 to 82 cars you must add/modify the cooling shroud and change the resistor in the pod. This accordinging to the information available is not applicable to the 83 to 84 models.
In Tims case he also replaced the old shroud with the new one along with a new gasket.
While we are waiting for Tim to find the time to make the next tests as suggested lets backtrack a little.
With both the old (Valero/Paris Rhone) and the new (Bosch) alternators, the lack of charge does not manifest itself until the alternator is HOT. Both systems worked fine until after about 40 mins of running.
Tim is going to check the alternator duct to ensure smooth flow of clean ambient air from under the fender.
Question for the Boffins
What is the overheat (No or not enough cooling air flow) effect on the alternator?
Does it shut down with some overiding circuitery?
Does it just burn and die?
The Bosch alternator (928 603 114 AX) is the correct unit for 77 to 84 cars with the caveat that on the 77 to 82 cars you must add/modify the cooling shroud and change the resistor in the pod. This accordinging to the information available is not applicable to the 83 to 84 models.
In Tims case he also replaced the old shroud with the new one along with a new gasket.
__________________
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
11-19-2007, 04:32 PM
#48
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Forgive the content of my recent posts - they seem to indicate that I glossed over your input. In fact it was you who awakened me to the need to ground the alternator as it exists unscrewed to the body of the car. Voltage to the casing had nowhere to go!
I have clamped a jumper cable to the casing and grounded it to the car, so the electrons now have a full circuit along which to travel.
Big thanks for your help and for the wealth of posted research you've done for us.
11-19-2007, 07:42 PM
#49
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Tim,
This may have been said before, but I have an experiment for you.
Re-connect your dash and alternator including grounding the alternator chassis. Leave the exciter wire disconnected. Measure the exciter terminal to ground with the key on and off.
With key off, exciter terminal to ground should be 0 volts.
With key on exciter terminal to ground should be 0-0.5 volts approx.
Ground the exciter wire and check the generator light with key on and key off. Light should come on with key on only.
Variations from these numbers suggest to me an internal problem with alternator/voltage regulator.
Dave
This may have been said before, but I have an experiment for you.
Re-connect your dash and alternator including grounding the alternator chassis. Leave the exciter wire disconnected. Measure the exciter terminal to ground with the key on and off.
With key off, exciter terminal to ground should be 0 volts.
With key on exciter terminal to ground should be 0-0.5 volts approx.
Ground the exciter wire and check the generator light with key on and key off. Light should come on with key on only.
Variations from these numbers suggest to me an internal problem with alternator/voltage regulator.
Dave
11-19-2007, 08:14 PM
#51
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Roger--
I'm not familiar enough with the way the voltage regulator limits output on overheat condition. In general, alternators have very simple regulators built in, just a few diodes, a zener for a voltage reference, and resistors to make a divider network for the reference. The regulator will feed excitation to the armature until the components melt. The good news is that the hot windings produce less current, so there's a tiny bit of protection there, but it's not dependable enough to be considered a safety feature.
The 'runs OK for the first 40mins' is a head-scratcher. The alternator is self-exciting as soon as it starts to charge, and that excitation doesn't go away until the alternator stops spinning. If it gives up charging after 40 mins of continuous running but the engine isn't shut down someplace in the middle of the process, it points to the alternator itself. If it fails to charge on restart, shortly after 40+ mins of running and then a shutdown, you would be looking more at the external excitation through the bulb abd resistor network in the dash.
-----
The alternator works by making the armature in to an electro-magnet, and spinning it inside the stator coils to move the electrons. The regulator decides how much magnetism is needed, and adjusts excitation current according to the voltage it sees at the output post. The armature and stator windings are copper with an enamel finish on them similar to varnish. The varnish serves two purposes-- it provides electrical insulation between the coils, and also adds mechanical stability to the coils so they don't get physically distorted. Remember that all of the mechanical torque applied to the pulley is transferred through the armature windings to the stator windings. At 90 amp output for instance, there's about two horsepower of drag working to twist the two sets of windings. Higher current equals more heat, and eventually the varnish will melt or burn if the heat is too high. Once that happens, the windings will start to shift, may short together electrically, requireing more excitation current and therefore making even more heat in the un-shorted areas. Death spiral from there. This kind of points to the need to maintain the battery and connections well, replace thge battery when it deteriorates to the point where it takes a lot of current just to keep it floated, and avoid running the 1000 watt amps at full volume without adequate cooling air flow through the alternator.
Dirty primary connections between alternator and battery are also killers of alternators, where voltage fluctuates not just with load but also with the varying resistance in the wiring connections.
Dave McK--
The open-circuit voltage measured on the exciter lead is likely to be very close to battery voltage, especialyy measured with a DMM. The meter just doesn't put enough load on the circuit there to make the voltage drop much. The bulb and the resistor, in parallel, have a much lower impedance than the meter in series with them.
I'm not familiar enough with the way the voltage regulator limits output on overheat condition. In general, alternators have very simple regulators built in, just a few diodes, a zener for a voltage reference, and resistors to make a divider network for the reference. The regulator will feed excitation to the armature until the components melt. The good news is that the hot windings produce less current, so there's a tiny bit of protection there, but it's not dependable enough to be considered a safety feature.
The 'runs OK for the first 40mins' is a head-scratcher. The alternator is self-exciting as soon as it starts to charge, and that excitation doesn't go away until the alternator stops spinning. If it gives up charging after 40 mins of continuous running but the engine isn't shut down someplace in the middle of the process, it points to the alternator itself. If it fails to charge on restart, shortly after 40+ mins of running and then a shutdown, you would be looking more at the external excitation through the bulb abd resistor network in the dash.
-----
The alternator works by making the armature in to an electro-magnet, and spinning it inside the stator coils to move the electrons. The regulator decides how much magnetism is needed, and adjusts excitation current according to the voltage it sees at the output post. The armature and stator windings are copper with an enamel finish on them similar to varnish. The varnish serves two purposes-- it provides electrical insulation between the coils, and also adds mechanical stability to the coils so they don't get physically distorted. Remember that all of the mechanical torque applied to the pulley is transferred through the armature windings to the stator windings. At 90 amp output for instance, there's about two horsepower of drag working to twist the two sets of windings. Higher current equals more heat, and eventually the varnish will melt or burn if the heat is too high. Once that happens, the windings will start to shift, may short together electrically, requireing more excitation current and therefore making even more heat in the un-shorted areas. Death spiral from there. This kind of points to the need to maintain the battery and connections well, replace thge battery when it deteriorates to the point where it takes a lot of current just to keep it floated, and avoid running the 1000 watt amps at full volume without adequate cooling air flow through the alternator.
Dirty primary connections between alternator and battery are also killers of alternators, where voltage fluctuates not just with load but also with the varying resistance in the wiring connections.
Dave McK--
The open-circuit voltage measured on the exciter lead is likely to be very close to battery voltage, especialyy measured with a DMM. The meter just doesn't put enough load on the circuit there to make the voltage drop much. The bulb and the resistor, in parallel, have a much lower impedance than the meter in series with them.
11-19-2007, 08:40 PM
#52
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Roger--
I'm not familiar enough with the way the voltage regulator limits output on overheat condition. In general, alternators have very simple regulators built in, just a few diodes, a zener for a voltage reference, and resistors to make a divider network for the reference. The regulator will feed excitation to the armature until the components melt. The good news is that the hot windings produce less current, so there's a tiny bit of protection there, but it's not dependable enough to be considered a safety feature.
The 'runs OK for the first 40mins' is a head-scratcher. The alternator is self-exciting as soon as it starts to charge, and that excitation doesn't go away until the alternator stops spinning. If it gives up charging after 40 mins of continuous running but the engine isn't shut down someplace in the middle of the process, it points to the alternator itself. If it fails to charge on restart, shortly after 40+ mins of running and then a shutdown, you would be looking more at the external excitation through the bulb abd resistor network in the dash.
-----
The alternator works by making the armature in to an electro-magnet, and spinning it inside the stator coils to move the electrons. The regulator decides how much magnetism is needed, and adjusts excitation current according to the voltage it sees at the output post. The armature and stator windings are copper with an enamel finish on them similar to varnish. The varnish serves two purposes-- it provides electrical insulation between the coils, and also adds mechanical stability to the coils so they don't get physically distorted. Remember that all of the mechanical torque applied to the pulley is transferred through the armature windings to the stator windings. At 90 amp output for instance, there's about two horsepower of drag working to twist the two sets of windings. Higher current equals more heat, and eventually the varnish will melt or burn if the heat is too high. Once that happens, the windings will start to shift, may short together electrically, requireing more excitation current and therefore making even more heat in the un-shorted areas. Death spiral from there. This kind of points to the need to maintain the battery and connections well, replace thge battery when it deteriorates to the point where it takes a lot of current just to keep it floated, and avoid running the 1000 watt amps at full volume without adequate cooling air flow through the alternator.
Dirty primary connections between alternator and battery are also killers of alternators, where voltage fluctuates not just with load but also with the varying resistance in the wiring connections.
Dave McK--
The open-circuit voltage measured on the exciter lead is likely to be very close to battery voltage, especialyy measured with a DMM. The meter just doesn't put enough load on the circuit there to make the voltage drop much. The bulb and the resistor, in parallel, have a much lower impedance than the meter in series with them.
I'm not familiar enough with the way the voltage regulator limits output on overheat condition. In general, alternators have very simple regulators built in, just a few diodes, a zener for a voltage reference, and resistors to make a divider network for the reference. The regulator will feed excitation to the armature until the components melt. The good news is that the hot windings produce less current, so there's a tiny bit of protection there, but it's not dependable enough to be considered a safety feature.
The 'runs OK for the first 40mins' is a head-scratcher. The alternator is self-exciting as soon as it starts to charge, and that excitation doesn't go away until the alternator stops spinning. If it gives up charging after 40 mins of continuous running but the engine isn't shut down someplace in the middle of the process, it points to the alternator itself. If it fails to charge on restart, shortly after 40+ mins of running and then a shutdown, you would be looking more at the external excitation through the bulb abd resistor network in the dash.
-----
The alternator works by making the armature in to an electro-magnet, and spinning it inside the stator coils to move the electrons. The regulator decides how much magnetism is needed, and adjusts excitation current according to the voltage it sees at the output post. The armature and stator windings are copper with an enamel finish on them similar to varnish. The varnish serves two purposes-- it provides electrical insulation between the coils, and also adds mechanical stability to the coils so they don't get physically distorted. Remember that all of the mechanical torque applied to the pulley is transferred through the armature windings to the stator windings. At 90 amp output for instance, there's about two horsepower of drag working to twist the two sets of windings. Higher current equals more heat, and eventually the varnish will melt or burn if the heat is too high. Once that happens, the windings will start to shift, may short together electrically, requireing more excitation current and therefore making even more heat in the un-shorted areas. Death spiral from there. This kind of points to the need to maintain the battery and connections well, replace thge battery when it deteriorates to the point where it takes a lot of current just to keep it floated, and avoid running the 1000 watt amps at full volume without adequate cooling air flow through the alternator.
Dirty primary connections between alternator and battery are also killers of alternators, where voltage fluctuates not just with load but also with the varying resistance in the wiring connections.
Dave McK--
The open-circuit voltage measured on the exciter lead is likely to be very close to battery voltage, especialyy measured with a DMM. The meter just doesn't put enough load on the circuit there to make the voltage drop much. The bulb and the resistor, in parallel, have a much lower impedance than the meter in series with them.
I wasn't clear enough. I think the exciter terminal on the alternator body with the exciter lead disconnected, should be at ground unless the alternator is running. Once connected and the exciter goes to 12V with the alternator running, the alt. light goes out since there is no voltage difference. If the alternator belt snaps and the alt. stops turning the exciter terminal goes back to ground voltage and allows current through the alt. light (and resistor).
If the terminal on the alternator is at 12V all the time, there will be no exciter current, no charging, etc. This could occur if there is an internal short to hot in the alternator or voltage regulator.
I could be wrong, definitely, but I'd like to learn if I am.
Thanks, Bob
11-20-2007, 12:20 AM
#53
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Tim,
This may have been said before, but I have an experiment for you.
Re-connect your dash and alternator including grounding the alternator chassis. Leave the exciter wire disconnected. Measure the exciter terminal to ground with the key on and off.
With key off, exciter terminal to ground should be 0 volts.
With key on exciter terminal to ground should be 0-0.5 volts approx.
Ground the exciter wire and check the generator light with key on and key off. Light should come on with key on only.
Variations from these numbers suggest to me an internal problem with alternator/voltage regulator.
Dave
This may have been said before, but I have an experiment for you.
Re-connect your dash and alternator including grounding the alternator chassis. Leave the exciter wire disconnected. Measure the exciter terminal to ground with the key on and off.
With key off, exciter terminal to ground should be 0 volts.
With key on exciter terminal to ground should be 0-0.5 volts approx.
Ground the exciter wire and check the generator light with key on and key off. Light should come on with key on only.
Variations from these numbers suggest to me an internal problem with alternator/voltage regulator.
Dave
Did these...
With key off, exciter terminal to ground should be 0 volts. 0.25V
With key on exciter terminal to ground should be 0-0.5 volts approx.0.25V
Ground the exciter wire and check the generator light with key on and key off. Light should come on with key on only. Indeed it did, with key turned to second position.
11-20-2007, 12:20 AM
#54
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Thanks Dr Bob for the input.
As both the original and the new alternator suffered the same problem my gut is telling me that its not an alternator problem. We will find out shortly when Tim fits another new alternator. If it is a bad alternator and another new one solves it I will be very happy.
On the other hand - thinking ahead - three alternators (two being Premium Bosch remanufactured units) with the same problem seems very unusual as well.
If cooling air is not getting to the alternator for some reason and the unit is overheating (after 40 mins use) I would expect - I am an eternal opptomist 8>) - that the electrics would shut down in some way.
We will see.
As both the original and the new alternator suffered the same problem my gut is telling me that its not an alternator problem. We will find out shortly when Tim fits another new alternator. If it is a bad alternator and another new one solves it I will be very happy.
On the other hand - thinking ahead - three alternators (two being Premium Bosch remanufactured units) with the same problem seems very unusual as well.
If cooling air is not getting to the alternator for some reason and the unit is overheating (after 40 mins use) I would expect - I am an eternal opptomist 8>) - that the electrics would shut down in some way.
We will see.
11-20-2007, 12:31 AM
#55
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Meanwhile, following a conversation with Roger, I looked into the "other side" of the alternator. I opened up the front left wheel well and examined the intake tubing that connects to the shroud. I noted that there was a possible short to the sensor that is located at the junction point between the two portions of tubing.
As for the tubing itself, it appears intact. The alternator end is somewhat frayed and has absorbed some power steering fluid from leaky connections above. Nothing that a zip strip can't remedy, methinks.
What a great thread! Thanks everyone.
As for the tubing itself, it appears intact. The alternator end is somewhat frayed and has absorbed some power steering fluid from leaky connections above. Nothing that a zip strip can't remedy, methinks.
What a great thread! Thanks everyone.
11-20-2007, 12:33 AM
#56
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Dave:
Did these...
With key off, exciter terminal to ground should be 0 volts. 0.25V
With key on exciter terminal to ground should be 0-0.5 volts approx.0.25V
Ground the exciter wire and check the generator light with key on and key off. Light should come on with key on only. Indeed it did, with key turned to second position.
Did these...
With key off, exciter terminal to ground should be 0 volts. 0.25V
With key on exciter terminal to ground should be 0-0.5 volts approx.0.25V
Ground the exciter wire and check the generator light with key on and key off. Light should come on with key on only. Indeed it did, with key turned to second position.
11-20-2007, 12:45 AM
#57
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Now why didn't it before?
Might I have "fixed" something in the instrument cluster in taking it out and cleaning it up (before smoking it)?
This thread has brought together some pretty heavy hitters. Bob, Alan, Dave, Roger, Dave A. I have been in great hands and minds.
Peace,
Tim
11-20-2007, 12:55 AM
#58
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Yep, it does.
Now why didn't it before?
Might I have "fixed" something in the instrument cluster in taking it out and cleaning it up (before smoking it)?
This thread has brought together some pretty heavy hitters. Bob, Alan, Dave, Roger, Dave A. I have been in great hands and minds.
Peace,
Tim
Now why didn't it before?
Might I have "fixed" something in the instrument cluster in taking it out and cleaning it up (before smoking it)?
This thread has brought together some pretty heavy hitters. Bob, Alan, Dave, Roger, Dave A. I have been in great hands and minds.
Peace,
Tim
Another problem is what Roger is referring to, and that is a heat relating failure after 30 minutes. Did you fix that? Well maybe. On the other hand, I wonder if your cooling duct to alternator is kinked or blocked? (edit) Noticed you said it was OK, sorry.
BTW those other guys are "heavy hitters", I wait to see what they write.
11-20-2007, 01:52 AM
#59
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Does anyone have a the back film layout of the cluster?
If I can get a copy, I can do the art work in PCB cad (I co-authored part of the package) and see if there is a company in Silly Valley who will do a few pieces.
If I can get a copy, I can do the art work in PCB cad (I co-authored part of the package) and see if there is a company in Silly Valley who will do a few pieces.
11-20-2007, 10:11 AM
#60
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The heat related failure is in my mind a common wearout mechanism of these regulators... usually manifested in just poorer generation at low rpm when hot - but presumably goes all the way to basically no generation (<Batt voltage).
That this should happen on a reconditioned unit is odd - but maybe the regulator tested OK and was not changed...?
I see some heat related degradation on my car (original alternator)... obviously Phoenix is a good test for this.
It is clearly worse in summer - but also gets worse in winter after extended use. My shroud & duct works fine - it takes a lot more than 30 mins to heat up in winter.. but slow traffic in summer might engourage this in 30 mins.
I'm considering options to swap out - but most special alternator shops employ "black magic marketing". e.g. to my questions of "what current can it sustain at >13.5v at idle rpm" (with alternate pulleys if desired) - they just tell me it will be "better than stock - trust us..." I'd just like a simple factual answer - preferrably from a bench test of the actual alternator they will sell me... Nobody bites - even for good money
Alan
That this should happen on a reconditioned unit is odd - but maybe the regulator tested OK and was not changed...?
I see some heat related degradation on my car (original alternator)... obviously Phoenix is a good test for this.
It is clearly worse in summer - but also gets worse in winter after extended use. My shroud & duct works fine - it takes a lot more than 30 mins to heat up in winter.. but slow traffic in summer might engourage this in 30 mins.
I'm considering options to swap out - but most special alternator shops employ "black magic marketing". e.g. to my questions of "what current can it sustain at >13.5v at idle rpm" (with alternate pulleys if desired) - they just tell me it will be "better than stock - trust us..." I'd just like a simple factual answer - preferrably from a bench test of the actual alternator they will sell me... Nobody bites - even for good money
Alan