Charging issues---exciter diode? Longish...
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From: Foxboro,Ontario,Canada
engine running, you should see very close to battery voltage there when charging. With engine running, the momemntary connection to battery voltage should bypass the supply that's normally through the lamp and the pod resistor, and cause the alternator to self-excite if it wasn't doing so already.
Cheers,
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Happy to report that Dr Bob's suggestion proved succesful.
The second i touched momentarily the "patch wire" from the field connection to the jump post voltage went from 12.2 to 14.2-14.3. and stayed there as expected.
So if the exciter circuit works as its supposed to with the "old" alternator and with the NEW resistor(which i have verified is the correct one for the Bosch alternator , and it does so--
-and- the only difference between the working "old" alternator and not working "new" alternator is the alternator itself-can one reasonably suspect the new alternator?
-OR have i solved nothing at this point and still have a problem in the exciter circuit somewhere between the light and the CE Panel that is ONLY present with the new alternator.If this is so...then i shall carry on with the diagnosing as both Wally and Alan have instructed.
Thanks as always
The second i touched momentarily the "patch wire" from the field connection to the jump post voltage went from 12.2 to 14.2-14.3. and stayed there as expected.
So if the exciter circuit works as its supposed to with the "old" alternator and with the NEW resistor(which i have verified is the correct one for the Bosch alternator , and it does so--
-and- the only difference between the working "old" alternator and not working "new" alternator is the alternator itself-can one reasonably suspect the new alternator?
-OR have i solved nothing at this point and still have a problem in the exciter circuit somewhere between the light and the CE Panel that is ONLY present with the new alternator.If this is so...then i shall carry on with the diagnosing as both Wally and Alan have instructed.
Thanks as always
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With Apologies to all---i think i have worked it out.
There was on my old alternator the unit pictured below, and i have always transferred it to whichever alternator was being installed.I did this because in a previous thread of mine from 2 years ago Alan identified this unit as a capacitor saying "it won't do any harm".
In any event, i apologize for not including this in this thread as i thought it to be irrelevant.
I just removed it from the "new" alternator(on a hunch) and i appear to have intermittent normal function.I do not think it has anything to do with the capacitor, just coincidence perhaps, because now i have been able to wiggle the exciter wire at the terminal with engine running and have the alternator begin charging...have replicated this several times.
Tested the wire for resistance from the 14pin to the end where it connects at the terminal and it shows no resistance (0.00) -wire is part of a complete new wiring harness.
It would seem that the terminal itself is not making a good connection within the alternator, i do not know if this is correct, or if it is correct whether it would be best to replace the alternator or try and fashion a repair.
Surely appreciate the help, i know my posts can be arduous for you guys because i have so much to learn, but as i said i very much am grateful.
cheers,
There was on my old alternator the unit pictured below, and i have always transferred it to whichever alternator was being installed.I did this because in a previous thread of mine from 2 years ago Alan identified this unit as a capacitor saying "it won't do any harm".
In any event, i apologize for not including this in this thread as i thought it to be irrelevant.
I just removed it from the "new" alternator(on a hunch) and i appear to have intermittent normal function.I do not think it has anything to do with the capacitor, just coincidence perhaps, because now i have been able to wiggle the exciter wire at the terminal with engine running and have the alternator begin charging...have replicated this several times.
Tested the wire for resistance from the 14pin to the end where it connects at the terminal and it shows no resistance (0.00) -wire is part of a complete new wiring harness.
It would seem that the terminal itself is not making a good connection within the alternator, i do not know if this is correct, or if it is correct whether it would be best to replace the alternator or try and fashion a repair.
Surely appreciate the help, i know my posts can be arduous for you guys because i have so much to learn, but as i said i very much am grateful.
cheers,
Last edited by Five-8; Jun 10, 2015 at 05:30 PM. Reason: Forgot picture
Chronic Tool Dropper
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Are you sure you have the exciter lead connected properly on the new alternator? I don't have hands-on knowledge of the Valeo alternator you are using, but you did take it to be tested and they did connect excitation to the alternator somehow to get it to test OK. Is where they connected the same place you are connecting?
Chronic Tool Dropper
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Sorry--
We were typing at the same time on the previous exchange. I didn't realize you had dinked with the add-on capacitor as I was typing.
Glad you were able to identify the problem. If the alternator is under warranty, I wouldn't start 'fixing' things before consulting with the seller. Some "rebuilders" are better than others, to the point that some will leave original parts like regulators and brushes if the look OK and seem to work. Meanwhile, intermittent problems wth those parst don't always show up during the extensive testing regimen the rebuilds are subjected to. For them it's easier to replace the occasional 'defect' than to replace all the pieces in all the rebuilds.
I've had good luck getting Genuine Bosch remanufactured alternators. They look and perform like new, with new slip rings, brushes, regulators and bearings. There's no hint anywhere that they are less than brand new alternators in a 'remaunfactured'-label box. Our vendors carry them already clocked correctly for the 928, with the shroud gasket too.
Others have reported good results with Delco and Motorcraft alternator conversions. No cooling duct fitment available though.
We were typing at the same time on the previous exchange. I didn't realize you had dinked with the add-on capacitor as I was typing.
Glad you were able to identify the problem. If the alternator is under warranty, I wouldn't start 'fixing' things before consulting with the seller. Some "rebuilders" are better than others, to the point that some will leave original parts like regulators and brushes if the look OK and seem to work. Meanwhile, intermittent problems wth those parst don't always show up during the extensive testing regimen the rebuilds are subjected to. For them it's easier to replace the occasional 'defect' than to replace all the pieces in all the rebuilds.
I've had good luck getting Genuine Bosch remanufactured alternators. They look and perform like new, with new slip rings, brushes, regulators and bearings. There's no hint anywhere that they are less than brand new alternators in a 'remaunfactured'-label box. Our vendors carry them already clocked correctly for the 928, with the shroud gasket too.
Others have reported good results with Delco and Motorcraft alternator conversions. No cooling duct fitment available though.
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Do you have details of the new resistor you fitted? Was it the stock resistor for a '82 from PET or a resistor for a later car? It seems it may not be correct for the later car's alternator. Not sure when exactly these changed over. What you need is a 68 ohm resistor. You could use an off the shelf part from say Fry's electronics or online - but you will need a 2 watt version and would then need to adapt it to the pod mount. Better to just get the stock late model version say from an '86.
I'd do this first because it seems your new alternator can work - but doesn't with the car in the current configuration. That may be true of other similar alternators too...
With the new alternator - I would not mess with the regulator (if needed ultimately just take the alternator back for a swap). The old regulator behaviour was the reason for the change here so I wouldn't use that whatever else you do...
Alan
I'd do this first because it seems your new alternator can work - but doesn't with the car in the current configuration. That may be true of other similar alternators too...
With the new alternator - I would not mess with the regulator (if needed ultimately just take the alternator back for a swap). The old regulator behaviour was the reason for the change here so I wouldn't use that whatever else you do...
Alan
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Alan i have verified with Roger that i have the correct resistor for the later Bosch Alternator, and it is installed in the car.
Roger is sending a replacement alternator, the new alternator is now charging, but if i mess with the connection (exciter) on the alternator i can replicate a "working then not working" situation.I seem currently to have the exciter post in a "sweet spot" at the minute.---if i go and disconnect/reconnect it, it sometimes will work and sometimes won't .The exciter wire is part of a brand new complete wiring harness, even so, i have checked under the shrink tube at the eyelet and see no trouble and the wire tests fine for resistance from 14 pin to this eyelet.
I know i could be dead wrong, but it sure seems like a poor connection on the alternator itself.Do you think this is plausible?
Thanks as always,
Cheers,
Roger is sending a replacement alternator, the new alternator is now charging, but if i mess with the connection (exciter) on the alternator i can replicate a "working then not working" situation.I seem currently to have the exciter post in a "sweet spot" at the minute.---if i go and disconnect/reconnect it, it sometimes will work and sometimes won't .The exciter wire is part of a brand new complete wiring harness, even so, i have checked under the shrink tube at the eyelet and see no trouble and the wire tests fine for resistance from 14 pin to this eyelet.
I know i could be dead wrong, but it sure seems like a poor connection on the alternator itself.Do you think this is plausible?
Thanks as always,
Cheers,
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Electron Wrangler
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Alan i have verified with Roger that i have the correct resistor for the later Bosch Alternator, and it is installed in the car.
Roger is sending a replacement alternator, the new alternator is now charging, but if i mess with the connection (exciter) on the alternator i can replicate a "working then not working" situation.I seem currently to have the exciter post in a "sweet spot" at the minute.---if i go and disconnect/reconnect it, it sometimes will work and sometimes won't .The exciter wire is part of a brand new complete wiring harness, even so, i have checked under the shrink tube at the eyelet and see no trouble and the wire tests fine for resistance from 14 pin to this eyelet.
I know i could be dead wrong, but it sure seems like a poor connection on the alternator itself.Do you think this is plausible?
Thanks as always,
Cheers,
Roger is sending a replacement alternator, the new alternator is now charging, but if i mess with the connection (exciter) on the alternator i can replicate a "working then not working" situation.I seem currently to have the exciter post in a "sweet spot" at the minute.---if i go and disconnect/reconnect it, it sometimes will work and sometimes won't .The exciter wire is part of a brand new complete wiring harness, even so, i have checked under the shrink tube at the eyelet and see no trouble and the wire tests fine for resistance from 14 pin to this eyelet.
I know i could be dead wrong, but it sure seems like a poor connection on the alternator itself.Do you think this is plausible?
Thanks as always,
Cheers,
Alan
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Replacement Bosch alternator on its way today - I hope it fixes your issue.
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
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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."
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But the proof will be in the pudding, once the replacement alternator gets here.
Cheers,
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Adrian have you checked the old harness to the new one?
IE from the 14 pin connector to the termination points.
Is it possible that the 14 pin connector has been mis wired on your new connector?
Also have you inspected the wire insulation on the car side of the harness
IE from the 14 pin connector to the termination points.
Is it possible that the 14 pin connector has been mis wired on your new connector?
Also have you inspected the wire insulation on the car side of the harness
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I will take a look at the wire insulation on the car side though.
Thanks for this,
Cheers,
Burning Brakes
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After chasing and fighting this problem with a few cars of my own... I finally got mad and just wired in a diode at the fuse panel jumping the input power going to the pod, directly to the input power supply going to the alternator.... Problem solved doesn't matter if the charge light is burnt out or there is a break in the printed circuit or a loose plug, it always works even the guage still works. If the alt isn't charging, you see it in the guage right away...
Chronic Tool Dropper
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After chasing and fighting this problem with a few cars of my own... I finally got mad and just wired in a diode at the fuse panel jumping the input power going to the pod, directly to the input power supply going to the alternator.... Problem solved doesn't matter if the charge light is burnt out or there is a break in the printed circuit or a loose plug, it always works even the guage still works. If the alt isn't charging, you see it in the guage right away...
