Voltage regulator symptoms

[Boobouna]

Hi all,

Can a faulty voltage regulator cause running problems in a CS running factory zeniths? I’ve had hot running issues where after driving for 15min when I come to a stop at traffic lights my idle starts to hiccup ie drop then bounce back to normal. Constant hiccups only when stopped. No issues once driving. I just had the carbys restored and the same problem exists. My mechanic now says he is seeing strange voltage ranges from 12 at idle to 17 in some instances at load. He reckons voltage regulator is at fault (I’ve had the alternator rebuilt also). He said it also explains why I’m having headlights flickering and also indicators flicking slow at idle but ok whilst driving. Any thoughts?


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[Wes]

YES...
This is what happened to me two weeks ago after driving 200km with lights, heater and wipers on full on account of a storm
Had my regulator checked and it was struggling at 12v with motor under load. I think what happens is that you drain the battery over time until the battery cant keep up.
This wasn't a problem for me until I came off the highway and the motor came down to idle. The car coughed a couple of times and stopped. My sparky told me it was because
with in effect a dead battery the ignition system was wholly reliant on the alternator current for load, which wasn't working on account of faulty regulator. My caveat here is I'm not an electrical guy but the theory makes sense to me. We switched out the regulator and no more issues.

 

[Boobouna]

YES...
This is what happened to me two weeks ago after driving 200km with lights, heater and wipers on full on account of a storm
Had my regulator checked and it was struggling at 12v with motor under load. I think what happens is that you drain the battery over time until the battery cant keep up.
This wasn't a problem for me until I came off the highway and the motor came down to idle. The car coughed a couple of times and stopped. My sparky told me it was because
with in effect a dead battery the ignition system was wholly reliant on the alternator current for load, which wasn't working on account of faulty regulator. My caveat here is I'm not an electrical guy but the theory makes sense to me. We switched out the regulator and no more issues.

Oh wow I hope this is it cause I have replaced everything and haven’t been able to solve it. Makes sense.


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[Simufly]

I have NOS BMW voltage reg for sale!

 

[Marco 54]

I have NOS BMW voltage reg for sale!

pm sent.

 

[jmackro]

My mechanic now says he is seeing strange voltage ranges from 12 at idle to 17 in some instances at load.

You do NOT want voltages as high as 17v in the e9 electrical system. The electronic tach and quartz clock can fail at those levels (ask me how I know). Instead of just replacing the regulator, you might want to swap in a later, internally-regulated alternator. These are more reliable and provide more precise voltage regulation. You can keep your old regulator in place (disconnected of course) if you want the underhood area to still look original.

 

[Boobouna]

I have NOS BMW voltage reg for sale!

My mechanic has already replaced with a Bosch unit.


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[Boobouna]

You do NOT want voltages as high as 17v in the e9 electrical system. The electronic tach and quartz clock can fail at those levels (ask me how I know). Instead of just replacing the regulator, you might want to swap in a later, internally-regulated alternator. These are more reliable and provide more precise voltage regulation. You can keep your old regulator in place (disconnected of course) if you want the underhood area to still look original.

I’ve had my alternator rebuilt so money already spent. I will consider it if it fails.


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[Ohmess]

I had voltage in excess of 19 volts in my car at one point. Problem was not the voltage regulator (at least not until the problem fried the voltage regulator). The little blue wire that goes from the alternator to the dash light had a splice in it that was deteriorating.

Normally, when the voltage draw from the battery exceeds the output from the alternator, this little blue wire first tells the alternator to put out more voltage. If it does so quickly, the voltage from the alternator cancels out the voltage from the battery and the dash light does not illuminate. If it does not, and the voltage from the battery output exceeds the alternator output, the blue wire acts as a ground for the voltage from the battery to the dash light and the light illuminates. This is why the light comes on brightly when the car is starting because all the voltage comes from the battery before the alternator is operating. It is also why when alternators are gradually failing, the light is dim at first and then gradually gets brighter as the alternator output decreases.

The splice in my wire increased the resistance in the circuit, decreasing the voltage to the voltage regulator, causing the voltage regulator to tell the alternator to put out more and more voltage until the regulator failed. My dash light did not illuminate because the voltage from the alternator was greater than the voltage seen from the battery (even though this voltage was incorrect).

Trace your blue wire and make sure it has clean connections, no breaks and no splices. I ended up completely replacing mine.

 

[Boobouna]

I had voltage in excess of 19 volts in my car at one point. Problem was not the voltage regulator (at least not until the problem fried the voltage regulator). The little blue wire that goes from the alternator to the dash light had a splice in it that was deteriorating.

Normally, when the voltage draw from the battery exceeds the output from the alternator, this little blue wire first tells the alternator to put out more voltage. If it does so quickly, the voltage from the alternator cancels out the voltage from the battery and the dash light does not illuminate. If it does not, and the voltage from the battery output exceeds the alternator output, the blue wire acts as a ground for the voltage from the battery to the dash light and the light illuminates. This is why the light comes on brightly when the car is starting because all the voltage comes from the battery before the alternator is operating. It is also why when alternators are gradually failing, the light is dim at first and then gradually gets brighter as the alternator output decreases.

The splice in my wire increased the resistance in the circuit, decreasing the voltage to the voltage regulator, causing the voltage regulator to tell the alternator to put out more and more voltage until the regulator failed. My dash light did not illuminate because the voltage from the alternator was greater than the voltage seen from the battery (even though this voltage was incorrect).

Trace your blue wire and make sure it has clean connections, no breaks and no splices. I ended up completely replacing mine.

I just read your message after already speaking with the mechanic who confirmed he has replaced the voltage regulator and the car voltage is nice and steady now with correct outputs at idle and under load. He will do long test runs today to see if it solves my drive ability issues. I will mention to him the above though too for completion.

Will update you on if this solves my problems.


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[Ohmess]

I just read your message after already speaking with the mechanic who confirmed he has replaced the voltage regulator and the car voltage is nice and steady now with correct outputs at idle and under load. He will do long test runs today to see if it solves my drive ability issues. I will mention to him the above though too for completion.

Will update you on if this solves my problems.


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The test is simple. Disconnect the wire from the alternator and from the dash light (some contortion is required) and measure the resistance.

 

[Luis A.]

I had voltage in excess of 19 volts in my car at one point. Problem was not the voltage regulator (at least not until the problem fried the voltage regulator). The little blue wire that goes from the alternator to the dash light had a splice in it that was deteriorating.

Normally, when the voltage draw from the battery exceeds the output from the alternator, this little blue wire first tells the alternator to put out more voltage. If it does so quickly, the voltage from the alternator cancels out the voltage from the battery and the dash light does not illuminate. If it does not, and the voltage from the battery output exceeds the alternator output, the blue wire acts as a ground for the voltage from the battery to the dash light and the light illuminates. This is why the light comes on brightly when the car is starting because all the voltage comes from the battery before the alternator is operating. It is also why when alternators are gradually failing, the light is dim at first and then gradually gets brighter as the alternator output decreases.

The splice in my wire increased the resistance in the circuit, decreasing the voltage to the voltage regulator, causing the voltage regulator to tell the alternator to put out more and more voltage until the regulator failed. My dash light did not illuminate because the voltage from the alternator was greater than the voltage seen from the battery (even though this voltage was incorrect).

Trace your blue wire and make sure it has clean connections, no breaks and no splices. I ended up completely replacing mine.

Hey Chris, You have some correct statements in here, however, the blue wire going from the external regulator plug to the dash light does not control in any way what the regulator or alternator does. You can cut that wire clean and all that will happen is that the alternator dash light will never come on. The blue wire which is between the external regulator and the alternator is what controls the alternator voltage output level.

If the alternator is internally regulated then the connection between regulator and alternator that controls voltage output is direct and internal and the blue wire, if retrofitted to the spade on the back of the alternator, only connects to the dash light.

 

[Stevehose]

I thought the dash light was needed inorder to excite the circuit into charge mode?

 

[Luis A.]

I thought the dash light was needed inorder to excite the circuit into charge mode?

it does but it serves no function in regulating the voltage output. It being cut wouldn’t be the cause of the alternator putting out high voltage. Definitely not with an internal regulator and with an external only if the wire was being grounded somewhere, which would make the alternator see lower voltages and crank up the rotor field voltage to counter that.

 

[Ohmess]

Luis -- We have much different views on how that circuit functions. Maybe it will help if I state my understanding differently, leaving out how and when the light illuminates:

The blue wire runs from the alternator (or the voltage regulator portion of the alternator circuit for an external voltage regulator) through the dash light and to the junction at the back of the fuse block that powers circuits 6 and 7, which is the primary power distribution point for switched power in our cars. Through the connection at this junction, the circuit performs a remote voltage sensing function for the alternator, sending back a reading that is then used to tell the alternator when more output is required.

 

[Luis A.]

Luis -- We have much different views on how that circuit functions. Maybe it will help if I state my understanding differently, leaving out how and when the light illuminates:

The blue wire runs from the alternator (or the voltage regulator portion of the alternator circuit for an external voltage regulator) through the dash light and to the junction at the back of the fuse block that powers circuits 6 and 7, which is the primary power distribution point for switched power in our cars. Through the connection at this junction, the circuit performs a remote voltage sensing function for the alternator, sending back a reading that is then used to tell the alternator when more output is required.

The voltage sensing function of the regulator occurs not at the junction past the bulb but rather at the alternator itself where there are 3 small diodes, separate from the high current power rectifier diodes, dedicated to this purpose.

Here is a diagram of the external regulator setup. The blue wire between the alternator and the regulator is what the regulator senses to determine whether to raise the current going to the rotor (DF) to in turn increase the voltage output of the alternator. This blue wire continues on to the dashboard bulb where the bulb responds (i.e., it lights up or not) to the difference in voltage between the blue wire (alternator output) voltage and the battery voltage at the fuse/power junction. But it performs no sensing function to alter the alternator voltage output.

Here you can see the same function on the alternator with an internal regulator. On the diode plate photo you can see the U shaped springy metal contact, coming off the small diodes, and on the regulator photo, on the left, you can see the contact where the regulator rests against that metal contact to directly sense the alternator output voltage. There is still a blue wire feeding the dash warning bulb and you can see the spade coming off the diode plate's small diodes.

Hope this makes sense...

 

[Willem Tell]

Gents, this is a really helpful discussion as I'm "currently" having similar problems on my Tii.
History: at the end of a project, after I had re-connected the battery, I reached in one last time and accidentally touched the output post with a wrench and cooked the harness from the alternator to external V regulator. It was the wrong alternator body for my Tii, so while my motor was being rebuilt I changed it for the correct body with internally regulated 85 amp output. The electrician who installed it rebuilt the harness and reconnected the external V reg. Everything worked, so I left it as is.

For the past several months I have had charging problems. First low voltage out and no charging (~12V @ 1500 rpm). I observed a higher than normal 300mV drop between the alternator body and the negative post of the battery. I charged the battery and everything appeared better (13.6V @ 1500 rpm).

After a day-long drive my voltage was down to 11.9V, the lamp came on and I could hear the alternator laboring (only headlights used during drive; no add'l lamps or blower). I pulled the external V reg, cleaned it up to improve the case grounding, cleaned contacts, etc. Everything worked OK briefly, but now I'm experiencing over-voltage (as high as 16V @ 1500 rpm). The external V reg is getting fairly hot.

Should I cut to the chase, replace the internal V reg and disconnect the external V reg (retaining the blue wire to the lamp? Can the internal regulator be removed without pulling the alternator? (There is clearance at the back on a Tii.)
Any other tests I should try?

 

[HB Chris]

I’m confused, you have an internally regulated alternator but still hooked up to the external regulator? I hope it is only the blue wire that is still hooked up, you can’t use both.

The brushes on the internal regulator includes the diode, it comes out easily and worn brushes can cause low charging. There is no way to bypass this feature.

 

[wilies13]

Hallo,
sorry; in German: Wenn Du nun eine Lichtmaschine mit internem Spannungsregler hast, dann würde ich den externen einfach entfernen.
Und dann müsste sich diese 13..14V einstellen.

 

[Willem Tell]

you have an internally regulated alternator but still hooked up to the external regulator? I hope it is only the blue wire that is still hooked up, you can’t use both.

'fraid so. That's how the electrician re-wired it. I'll be unplugging that before the next drive! The blue wire to the lamp is tied to the external regulator plug, so I just need to disconnect and dress it out of the way.

Dank Wilies13 werde ich den externen Spannungsregler trennen!