Alternator charging question?

[muleman51]

The Densco alternator on my 7635NH quit charging. Let me back up, the light on the dash doesn't come on when I turn on the key like it used
to, I normally just increased the rpm's a little and the light would go out and charge at any rpm. Checked voltage at battery and alternator
both the same. The battery drains done from starting and lights etc. but doesn't start charging. There is an external little box is this the
voltage regulator, could this be the issue and how do you test it. Thanks for the help. Jim

 

[Harry in Ky]

I don't know that series very well, but have only seen Bosch or Marelli alternators. Both were internally regulated. Sometimes there was a small box attached.
Looked like something similar to a relay, but was actually a diode. Had little or nothing to do with charging or not charging.

Since the battery light doesn't come on, the first thing I'd check is the bulb. If the bulb is out, the alternator won't get an exciter signal and therefore won't charge.

 

[used red MN]

Depending how hard it is to get to the actual bulb in the dash it may be worth your effort to pull it to see if it has lost continuity as in the filament has burned out. In many systems the charging excite circuit relies on the dash bulb filament to complete a circuit, or I should say earlier ones did mostly pre 1990. A wiring diagram could very well tell you if the above applies to your machine. Yes, it is a good chance the box you are talking about is the voltage regulator. I am going to say the only way to get that tested would be to find someone in the alternator rebuilding or repair business that has a regulator tester.

 

[Fritz Maurer]

Check for broken and/or corroded wires before you replace any components.

 

[guido]

mu;eman51,

How about doing some voltage readings? Battery voltage with engine off, then with the engine running to start?


Guido.

 

[rustred]

i would check the bulb first, if its burnt out it can be that simple. i am presuming your checking voltage with the engine running. kinda pointless checking it not running. should show over 14 volts max about 14.8 running.

 

[sotxbill]

Some alternators will not charge with the bulb out,,, BUT.. will charge after they have been revved up one time, to self excite the field coil. As others said. read the bat voltage non running... should be around 12.6 volts. Read it after started.. it should be climbing up from the start and eventually settle between 13.8 and 14.8 volts. if not rev up the engine one time, and check voltage again. make sure all wires on back of alternator are plugged in and none have fallen off. Two of them are on spade lugs and can slip off if gently pulled on.

Lots of times the wiring harness will go flakey and some of the gauges and lights on the dash quite working although the alternator still charges.

 

[muleman51]

When I checked it it was 11.6 running or stopped. Thats why I knew it wasn't charging. I'm going to bypass the diode and see if that makes a difference as advised by a dealer this afternoon. As a new diode is $97 and once the box is open it's yours. They weren't sure if the light had anything to do with it, but they thought not.

 

[guido]

Ameman51,

The light is just a charge indicator.
It goes off when it is charging

Guido.

 

[JMOR]

There are very, very few "universal" truths.