Boy I'm tired. It took me from nine this morning until three thirty to put that regulator on. Before I put it on the battery light would come on after I shut her down and took the key out of the ignition, and no charge to the battery. Now with the new voltage regulator all the lights come on before I crank her, but the battery light stays on while running. The light gets dimmer at low rpm's and brighter as the rpm's increase. I drove out by the parts store to see if the battery was charging, and it is. What could make the battery light stay on while running. Appreciate your thoughts.

Hugh Sr

1984 190d (W201) 123,538

I am not as familiar with the particulars of the wiring in a 190D but the principal is this ... the battery light on the dash is supplied positive current at all times with the key in the run position
lamp not illuminated:
- the bulb in the lamp carries the positive current across its filament and passes it to the alternator which uses the current to initiate the alternators charging.
Lamp illuminated:
- the bulb in the lamp is grounded by the alternator to display a no charge state prior to starting or in the event the alternator is not in fact charging

now that is the theory ... as I have come to understand it
my knowledge of the exact mechanisms/components within the alternator that are brought to bear are not as complete as others here I am sure.

I hope this was at least some help

Sounds like there may be a significant AC voltage getting through. This would be a sign of a rectifier diode breaking down. The only sure way to determine the problem is with some voltage readings. A multimeter will tell you more about where to start.

With a meter connected across the battery, check voltages in both VDC and VAC. VDC should read ~13VDC with initial charging after the start. VAC should be less than 100mVAC and should not increase with an increase in rpm.

If the VDC is very low then the regulator is usually at fault. If the VDC is high, check VAC and it will probably be high as well, pointing to failing rectifier diodes.

An alternator is really very simple electronics. It initially produces AC voltage, which is easier and requires lighter hardware. The rectifier diodes change the AC to DC voltage and then the regulator smooths out the result to maintain constant voltage with variations of rpm.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

Possible

#1. Defective new regulator.

#2. Failing alternator.

#3. Seriously bad wire harness or connection at the alternator?


.

__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

Hugh, with your comment: Before I put it on the battery light would come on after I shut her down and took the key out of the ignition, this is a classic sign of a bad diode/rectifier bridge as SD Blue has noted, too.

Unless you have a rebuilder in your area, you are probably going to have trouble finding the parts to do this. I'd buy a replacement alternator, pull your (slightly used) regulator out before you return it for the core, and then you can sell it to recover a few dollars.

That said, if you do have a rebuilder in your area, give them a call, they can probably fix yours for a reasonable fee or sell you the parts if you want to spend another day. If you're going that route I'd definitely buy the bearings and replace them at the same time, but then you have to pull the pulley and clutch off the thing...

Good luck.

Where is the rectifier diode located?

Hugh Sr

The rectifier diodes are located internally in the alternator.

Before going to the headache of pulling parts, a multimeter will help considerably to define the problem. Lowe's, Home Depot, Radio Shack and most auto part stores have multimeters for about $30 that will do the job.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

The about $5 Harbor Freight Digital Meter will work and it cost even less when on sale.

If not, set your meter to Volts AC and you should have a reading of ~100mVAC.
If the VAC is too high, then look for a rectifying diode failure.

I think the easiest way to see if it is the Alternator is while the Key is out and the Charging Light is still on simply disconnect the Electrical Connector from the Alternator. If the light goes out it is a good chance it is the Alternator.
If the Light stays on with the Connector pulled you likely have a Wiring issue and/or possibly an Ignition Switch issue.

__________________
84 300D, 82 Volvo 244Gl Diesel

The McParts stores can also test for bad diodes. Perhaps do both tests as confirmation.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Simplest way I see is this. Pull the alternator, get it tested at local auto parts store. If it tests bad, pull new voltage regulator off and put old one back on (if you still have it). Then buy a new alternator and turn old one in as a core!

__________________
2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Assuming you can SAFELY get to the connector without shorting anything, this is probably the easiest and quickest way to isolate the issue to the alternator (or to rule it out as the culprit).

Otherwise, I'd be with the others, pull the alternator, take it in and have it tested.

Good luck. I know how much this must suck after spending most of a day on what you thought would be the fix. But stay after it, you'll get there.