Alternator regulator overvoltage

[Upnorth]

I have a problem with an alternator which is putting too high a volatge into the start battery. I assume the regulator is faulty. I need to run the engine for a short time before removing the alternator for repair, without frying the battery. So I need to disable the alternator somehow.
Will removing the ignition switch/indicator lamp wires stop the alternator working, or do I need to remove the battery connection as well. The alternator is Hitachi, connections are Bat+, Bat-, L and R.

 

[Graham376]

If the regulator is knackered anyway, I would remove all wires and run the engine.

 

[Refueler]

The Ignition / warning lamp wires are usually using the exciter lead.

Depending on the alternator - some will self excite or even have residual enough to start charging regardless of that connection ...

So answer is no. You need to disconnect the main output of the alternator ... BEFORE starting engine. This is usually pretty easy - just remove the big red lead of the alternator and safely peg it back somewhere out of the way.

Question before you rush off with alternator in hand to repair shop :

1. Do you have split diode charging to batterys with a charge controller ? The system itself may be faulty and alternator is compensating.
2. Is your alternator battery sensed ?

It may be that alternator is OK - but your setup is falsely indicating to alternator regulator which then bumps up the voltage / rate accordingly. Repair shop in that case will test and say alternator is working correct.

 

[LittleSister]

You may well not need to remove the alternator. I had the same problem (though different make of alternator). I just read the exact model number off of the alternator, ordered a new regulator online, and when it arrived fitted it to the in-situ alternator.

Replacing the regulator was probably no more work than disconnecting and reconnecting the alternator, and certainly less than taking the alternator off and then refitting it. (Of course, depending on access and design that balance may not be the same for you.)

I also didn't worry about running the engine for a short time with it putting out excess voltage (just over 16v IIRC), as it had already been doing that for a while (who knows how long?) before I discovered the problem, so a bit longer wasn't going to make much difference. The batteries (already a bit knackered due to age, etc.) survived to tell the tale.

 

[VicS]

I have a problem with an alternator which is putting too high a volatge into the start battery. I assume the regulator is faulty. I need to run the engine for a short time before removing the alternator for repair, without frying the battery. So I need to disable the alternator somehow.
Will removing the ignition switch/indicator lamp wires stop the alternator working, or do I need to remove the battery connection as well. The alternator is Hitachi, connections are Bat+, Bat-, L and R.

Yes disconnect both the L & R connections (

If that does not work disconnect the main battery connection ( B+) and insulate the lead ( or remove the lead altogether)

Diagram attached explains why both L and R must be disconnected

 

[Upnorth]

Thanks for all the help. I ran the engine long enough to get to marina. No ill effects (yet). Will try the L & R removal at next opportunity.