Alternator Voltage Regulator D+ volts

[wayneesch]

My old alternator started making a noise so I purchased remanufactured Bosch AL64X. I installed and after 20 seconds the not charging alternator light went out and all was good.  Within 100 miles, the alternator light would occasionally flicker on at 60-70 MPH. After 300 miles at startup, it might take 30 seconds for the light to go off. At 500 miles, the light came on and stayed on for several minutes. Eventually did not go out during that 50 mile trip and continued to stay on.

I purchased a new replacement Generatorregler voltage regulator with plastic case from Pelican Parts (Pelican part#901.603.206.02). Still did not charge the battery - no difference from the original voltage regulator.

Ordered replacement alternator under warranty and installed.  Alternator charging light remains on.

Checked the three wires from voltage regulator to alternator with brake light bulb to verify connectivity and no high resistance. Also check B+ wire to battery, and the alternator housing to battery ground. Wires all checked good.

Local auto parts stores can not test this alternator because their test machines are not programmed for this alternator.

Battery has 12.4 volts and after starting, very slowly rose to 13 volts and stayed there (not the expected 14.7 volts) until engine shut off.

Turned on ignition (without starting) and D+ was a 2.2 volts. Started engine and D+ very slowly rose to 8 volts and stopped there.

Can someone verify if 2.2 volts is correct with ignition on and what should the value for D+ be when running? Could not find this information in our forum or manuals.

Do I have two bad alternators in a row;  or a bad, or wrong, new voltage regulator;  or something else?

[BobH]

Have a read of this, it's not specific to our cars, but same principle applies.  Seems strange that you have had 2 new alternators and a new regulator, so could be the wiring, seems you should get approximate battery voltage at terminal D+

https://bmwr65.org/htdocs/yabbfiles/Attachments/Charging_Tests.pdf

[awolff280sl]

could the belt be slipping?

[wayneesch]

Installed a new belt with the first replacement alternator. Was a no name belt and did not last long, tensioned it twice. Installed a new Continental belt which works good - and also checked the tension now which is still good. Thanks for the suggestion.

[wayneesch]

Can someone please test the D+ voltage at the voltage regulator with the key on and then when the engine is running?  The voltage regular is located above the passenger wheel well and has three connections, D+ is the connection with 2 wires.

An alternator repair shop checked my new alternator and said it was working, however, it was making a noise and may work intermittently. Repair shop does not have parts supplier for ALX64 so did not disassemble the alternator. The auto parts supplier does not have another alternator in stock. Anyone recommend supplier for Bosch ALX64?

[Charles 230SL]

hello Wayne, on my regulator I'm seeing .5 VDC at the D+ terminal with the key on and without the engine running. With the engine running I'm seeing 14 VDC at the D+ terminal. I'd take a look at the wiring between the alternator and the regulator and the wire between the alternator and the starter (schematic below).  I just find it hard to believe you've gotten 2 bad alternators. I personally have seen some squirrelly things with 55+ year old wiring.   

[lpeterssen]

Dear friends

You should always read at the “D+” terminal the same voltage as in the battery.  If not clean very well terminals inside the connector to external voltage regulator.

If that persists it is time to call the doktor

Best regards
LP

[wayneesch]

I checked all the wiring connections associated with charging, cleaned all the connections. Tried the alternator again, no charging.

Thank you Charles for taking your time to measuring the D+ voltage, it was the clue I needed to finally point at the new alternators. 

I ordered a third remanufactured BoschAL64X from a different supplier, installed and it works great. What a relief...