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Generator light on and voltmeter maxed out
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dagimp
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PostPosted: Thu Aug 27, 2015 6:08 am    Post subject: Generator light on and voltmeter maxed out Reply with quote

Was driving around Monday and I noticed that my voltmeter in the dash was pegged all the way past the 16v mark. After a half hour or so of driving, the generator light started glowing dimly and after a while, went fully on. Now this morning I started it up and the generator light is on immediately (didn't notice where the volt meter gauge was at). I haven't had the time to get to measuring all the contact points with the volt meter, but has anybody seen something like this before? Thanks a lot.
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Bashr52
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PostPosted: Thu Aug 27, 2015 6:29 am    Post subject: Reply with quote

Overvoltage indicates bad regulator. If light is on solid now, I'm betting regulator is fried.
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dagimp
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PostPosted: Thu Aug 27, 2015 7:47 am    Post subject: Reply with quote

Bashr52 wrote:
Overvoltage indicates bad regulator. If light is on solid now, I'm betting regulator is fried.


OK. If I get over voltage on the outgoing tab (can't remember which one it is off the top of my head) on the regulator, it sounds like it's time to replace. Hmmm, too bad. Relatively low use solid state Bosch regulator without too many miles.
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tallman206
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PostPosted: Thu Aug 27, 2015 8:35 am    Post subject: Reply with quote

Make sure your Field wiring (DF) on the regulator end or the generator end is not shorted to ground. If the field wiring shorts to ground, the generator will put out full voltage and current, regardless of what the voltage regulator tells it to do. This is very stressful to the generator (max voltage and current).

Unfortunately, if you now have red light on syndrome, the generator might now be damaged, but you will not know until you go through some basic troubleshooting steps with the regulator disconnected.
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tjsectek
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PostPosted: Fri Aug 28, 2015 5:26 am    Post subject: Reply with quote

Check battery connections too. My positive cable popped off, pegging voltmeter at 16v... no warning, though. I have swapped to an internally-regulated alternator, which makes mine a little different if you're stock...
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vwwestyman
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PostPosted: Fri Aug 28, 2015 11:54 am    Post subject: Reply with quote

Since the light works by having 12v going through it, and goes out when the generator starts making 12v (therefore balancing the voltage on either side of the bulb) if the generator is making 16v, then there would again be an imbalance in the bulb, causing it to glow.

So the fact that the bulb is glowing doesn't necessarily mean the whole generator is fried.

Right?
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tallman206
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PostPosted: Fri Aug 28, 2015 2:26 pm    Post subject: Reply with quote

Not necessarily true. Once the generator is producing output, and if it indeed goes to a high voltage of 16V, the cutoff relay in the regulator directly connects the generator D+ output directly to the B+ output, so there would be no imbalance to make the light glow. This can be confirmed, because it was observed with the dashboard voltmeter that was reading 16V, and the voltmeter is connected to the battery (via the ignition switch).
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dagimp
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PostPosted: Sat Aug 29, 2015 12:47 pm    Post subject: Reply with quote

Hmmmmm. OK, I had the chance to do some more checking. Voltage across battery is still 12.5v. I disconnected both wires from the generator, jumped the DF to the generator frame (ground). Checked the D+ voltage from D+ to ground and got between 2 and 5v depending on rpm. Not good. For kicks, I turned the voltmeter to circuit test and touched the leads to DF and D+ and it indicated a circuit. I'm assuming this is a BAD THING. I then tested from both DF and D+ on the regulator (wires still plugged in at regulator) and also got a circuit. ???? This reminded me of Tallman's comment about a ground at DF. Could this have happened within the generator or in the regulator and then fried my generator? Or am I just missing something about the circuit testing?
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tallman206
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PostPosted: Sat Aug 29, 2015 2:11 pm    Post subject: Reply with quote

Circuit testers are not really going to tell you the whole picture. The field windings inside the generator on one end are connected to the DF terminal. The other end of the field wiring is connected internally to the D+ terminal. So what your continuity tester is probably showing you is that there is a connection between the two. You are probably measuring the field coil resistance, which is probably in the 8 to 15 ohms range. A continuity tester simply thinks that is a short circuit or 'connection'.

If you measure the voltage regulator DF terminal on an old electromechanical voltage regulator, it should look like it is shorted to ground. This is because when you first start the engine, the regulator should connect the DF directly to ground so that the generator puts out full power. When the generator gets up to speed, the voltage regulator will stop grounding the DF lead, actually hundreds of times a second (off and on), as it performs voltage regulation. I dont know how the Bosch solid state VR measures at rest though.

What is telling to me, if you disconnected the generator wiring, then grounded the DF terminal, you should get 15-20 volts on the D+ terminal. If not, first check your brushes to make sure they are not worn out, and also check to see if the commutator looks burned. It should smooth and normally be a nice clean light brown color, indicating that the brushes have created a nice film on the commutator. If the commutator looks scored, or has a bright copper color, or if you see molten solder splashed around in there, bad news. Your 16v episode (likely caused by a failed voltage regulator), probably stressed out your generator (brush or commutator failures), and that is when the red light came on dim and then bright, as the generator finally stopped producing output voltage. You may be able to ressurect the generator with new brushes and a commutator cleaning, if there is no other physical damage.
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dagimp
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PostPosted: Sun Aug 30, 2015 7:15 am    Post subject: Reply with quote

tallman206 wrote:

What is telling to me, if you disconnected the generator wiring, then grounded the DF terminal, you should get 15-20 volts on the D+ terminal. If not, first check your brushes to make sure they are not worn out, and also check to see if the commutator looks burned. It should smooth and normally be a nice clean light brown color, indicating that the brushes have created a nice film on the commutator. If the commutator looks scored, or has a bright copper color, or if you see molten solder splashed around in there, bad news. Your 16v episode (likely caused by a failed voltage regulator), probably stressed out your generator (brush or commutator failures), and that is when the red light came on dim and then bright, as the generator finally stopped producing output voltage. You may be able to ressurect the generator with new brushes and a commutator cleaning, if there is no other physical damage.


OK, looks like my generator got fried. The commutator looks bright copper color. Guess it's time for an overhaul. Depending on price, I may just have an alternator installed. Damn, things were going well with Otto recently and I was just starting to drive it this summer. Probably not a job I'm going to tackle myself. Back to the shop for you!
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tallman206
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PostPosted: Sun Aug 30, 2015 9:41 am    Post subject: Reply with quote

Before you panic, try replacing the brushes, and cleaning the commutator.
Use something like a scotchbrite pad held against the commutator while its turning to freshen it up. Rinse out with contact cleaner or Brakleen. Examine to see if the gaps between the copper commutator segments are slightly below the surface of the copper (undercut). If good, fire it up and test the generator again (as you did before) for output. There is no need to polarize it if the generator has not been taken apart. If you get output, replace the regulator, and you should be good to go, and you can save the extra bucks for something else.
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