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lep lep is offline
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Generator warning (red light)

I have a relatively new (1year) Bosch voltage regulator and generator brushes with plenty of "meat", which were also replace about a year ago.

That pattern has been that sometimes the red warning light comes on dimly and then goes off after speeding up (longer duration of time) and then goes out. This is only intermittent, however, and it happens only once and a while. Most of the time the red light is not on at all after start-up and drive.

Before I start looking at the fuses, is there anything else that an intermittent red warning light would be characteristic of?

Old 08-11-2013, 07:36 AM
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It doesn't hurt anything, this is just the characteristic of the 912, especially with the smaller generators. With lights and radio on the red light will show up at very low rpms or stopped at a light. Don't drive at night, in the rain, and leave the radio off, you will never see it again.

There was a Bosch alternator kit that would take care of that visual problem. At last-- it is no longer available.

However, if it is coming on after 2000 rpms. Your fan belt could be loose and you will need to remove a shim or two. Or you could have a regulator starting to go bad. Sometimes they do this, even newer ones.
Old 08-11-2013, 09:14 AM
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lep lep is offline
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I unhooked the leads going to DF+ and D terminals on the generator, and then hooked up a grounded voltmeter to DF+ and then grounded the DF terminal. Nothing, nada!

So with new brushes and reasonably belt and visible turning over of the generator shaft with revs --> I believe the generator is dead.

It has never been replaced since I purchased the car in '81 -- so no worries, I'll replace it.
Old 08-11-2013, 12:22 PM
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Otto H. Wegkamp
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Iep,

Detach the wires from the generator. Measure the voltage between D+ and the ground terminal. The voltage should rise to a maximum of 14.5 volts when reving the engine.

If there is no voltage at all, (one of) the brushesor or internal connecting wires could be broken. A short in between windings of the coils would not definitely result in zero volts at the output. Please report more details regarding the measurements, like rpm, testing points, positive/negative voltage.

Otto
Old 08-11-2013, 01:09 PM
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lep lep is offline
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With the D+ and DF leads unhooked from the generator, there's no voltage measured between the two terminals at run-time using a DC voltmeter. Revving it up to a several k didn't change results either. For confirmation, the voltmeter reads 12V between the battery terminals.
Old 08-11-2013, 01:40 PM
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lep lep is offline
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I also inspected the brushes and dusted them off with a can of computer dust blaster (air), but no luck. Wiring to both brushes was intact and the fastening screw for the leads were tight. Didn't notice any loose wires inside the generator. I did notice that the copper leads under the brushes to each segment of the armature have very little "tread" and are quite worn down, to the extent that it may have a few months left.
Old 08-11-2013, 01:46 PM
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Otto H. Wegkamp
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If the generator is relatively new, as you said in your first posting, I don't think the commutator - the copper segments - is worn within that year. I forgot to say that you have to connect D-/DF during the test.

Another way to test the generator is - again with D-/DF shorted and the fan belt removed - to put 12 V from the battery on the generator, plus to D+ and minus to D-. The generator should run gently as an electromotor.

The regulator could be the cause of your problem. Which is likely regarding the reaction of the control lights in your dash.

Please perform the tests again and report the results.

Otto
Old 08-12-2013, 01:45 AM
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lep lep is offline
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The original msg said the volt regards and brushes were new. Checked voltage 2 ways. (DF is -, D+ is positive):

Removed leads going to D+ and DF, and left the heavy brown ground wire attached.

1. Grounded DF. Grounded the negative on voltmeter. Ran positive on voltmeter to D+. Zero volts at run-time and revving up.

2. Connected pos and neg from voltmeter to D+ and DF, respectively. Zero volts at run-time and revving.

Confirmed voltmeter gave 12v at battery-yes.

Generator is more than 30 years old.
Old 08-12-2013, 07:38 AM
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Otto H. Wegkamp
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Iep,

Could you put the 12 V from the battery to D+ and minus to to D- - as I described before - in order to check if the generator will run as an electromotor. Just for a few seconds is enough. Longer could cause damage to the generator. The generator is then polarized and should function propperly again.

Does the generator not spin at all, it is indeed dead. I would take it apart and check the internal wiring. There must be a short or open circuit. Dirt or worn commutator would result in some output voltage. Use your Ohm-meter or continuity tester to check the internals.

Otto
Old 08-12-2013, 03:55 PM
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lep lep is offline
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The generator turned over when the battery leads were connected (several seconds). Replaced the pulley halves, belt, fastener nut, and then connected the regular generator leads, and after startup and revving up to 2k the warning light is still very solid red.

Probably the voltage regulator.

What does the revolution of the generator when battery leads were connected suggest about robustness (dependency) of the generator?
Old 08-13-2013, 05:41 PM
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Otto H. Wegkamp
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Iep,

That's hard to say what the quality of the generator is, only that it works. Did you measure the generator's voltage after you did the "Žlectromotor-test"? However, it seems that the regulator indeed does not function properly. Replace it by a new one. You could take the original Bosch or an electronic replacement from Bosch in more or less the same housing.

If the generator supplies the right voltage now, I think you will be near the solution of your problem.

Otto
Old 08-14-2013, 12:12 AM
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lep lep is offline
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Otto,

Are you suggesting replacing the voltage regulator instead of the generator?
Old 08-14-2013, 06:07 PM
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Otto H. Wegkamp
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Iep,

If the generator is running like an electromotor, that indicates that it basically should be OK. Perhaps it needs a cleaning and new brushes to optimize functionality, but you already did that.

If the generator functions correctly, the battery is fine - you checked, it is - and the wiring is OK, then the only part left is the regulator. The strange intermittent signal light in your dash already points at a possible failing distributor.

I think it is better not to run the engine with a connected regulator for now. A short in the regulator could damage the generator as well as the battery.

Did you check the generator's voltage (D+/D- and DF grounded) after you did the tric using it as an electromotor? Again, disconnect the regulator. If there is no voltage this time, repeat the "electromotor tric" and repeat the voltage check again. If the generator supplies 15-20 volts or more with no load and depending on the rpm, it should be OK. A new regulator will most likely solve the problem then.

Otto
Old 08-15-2013, 12:07 AM
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lep lep is offline
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Regulators

Otto, if you look at the catalog at Zim's AutoTechnik in Texas, you will see two regulators.

Products > 911 & 912 Parts > Porsche 912 65-69 > Engine Electrical > Charging System > Voltage Regulator

I have the solid state version, but am thinking of going back to the original stock OEM. It may possibly be true that the solid state has been nothing but trouble due to intermittent red lights. However, when I was using the original OEM, the generator had fewer hours of use on it.

I believe I need to purchase both a generator and regulator.

Thanks for all of your help. Leif
Old 08-15-2013, 05:34 AM
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Otto H. Wegkamp
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Leif,

You're welcome. That is where the board is for, try to help each other.

I would first try the regulator and if the battery still doesn't charge (rapidly enough) buy or rebuild the generator. But I can understand that you just want the charging circuit to be reliable. Then the invesment makes sense.

BTW Did you hook up the solid state regulator correctly? If I'm right, the control light should be connected to a different reminal.

I never heard of problems with the solid state version, but that doesn't mean that there are no problems. OEM Bosch is always a good replacement!

I hope you will be able to drive your 912 soon.

Otto

Old 08-15-2013, 08:08 AM
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