Leece Neville alternator diagnosis, continued

[Compu Doc]

I'm back with another puzzle about this alternator.
What the _____ is going on now? I can't afford to wreck my new CAT batteries or get stranded.

Since the alternator's on-board regulator is activated by the third wire 12 VDC feed, I am at a loss as to why revving the engine causes the alternator to suddenly wake up.

Appreciate suggestions, as always

If the alternator that you put on has a diode trio you do not use the wire activated by the 12VDC wire. My original alternator did not have the diode trio and my replacement alternator did. The first thing I did was call the place I got it at and asked them if the third wire needed to be installed and they said no and not to use it. A simple blip of the throttle started the alternator. In the image the black thing is the diode trio with the wire on it next to the regulator. If yours has that then the alternator probably is not working right because you have the third wire installed. If that is the case you might have fried something. The alternator in the image is what is known as a self excite alternator which means it does not need any current to turn itself on.

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[pybyr]

Thank you everyone for the suggestions.

When I said I'd replaced the diode trios, I mis-spoke; I'd replaced the rectifier bridges, both positive and negative. It's not the self-excite, and relies on the 12VDC wire to 'wake up' and power the regulator/ field.

The alternator has been flaky as heck today- started out charging normally, then not at all, then again, then not at all.

Seems to get more erratic as things warm up.

I've never seen power rectifiers act intermittent- they seem to either work or fail, so I am thinking that either the new regulator has gone flaky or else the field winding in the rotor goes open when it warms up.

I hope to heck it is the regulator, not the rotor winding.

At this point if it is the regulator, then I would definitely like to change over to a fully outboard adjustable regulator.

I like the concept of external rectifiers, as it does get them into a better cooled setting, but I sort of dread all the cabling- I know how to do it electrically, just don't want one more rat's nest.

 

[franklin2]

I am assuming this type alternator uses the same circuit as the regular alternators on these trucks, that is it's brought "online" by the signal from the instrument cluster. I had a problem with mine, and I found I was not getting the battery light always when I first turned the keyswitch but didn't start the engine. Turns out it was bad connections in the cluster, and sometimes I would get the excite signal from the cluster and sometimes I would not. Cleaning all the connections in the cluster fixed it.

When I was having problems, mine would do the same thing, and work sometimes when the engine was revved. It would slowly come to life like yours. I think that may be caused by residual magnetism in the unit self-exciting the field in the alternator, giving it some output.

 

[Compu Doc]

When mine would charge and then not charge I got a replacement alternator. Upon taking the old alternator out I noticed the small nuts holding the regulator in came loose. On the E series Fords you can't see the regulator. Not knowing if that was the actual cause of my problem or not I changed out the alternator anyway because the old was under warranty but the one thing I did do and have done since is double nutted the regulator screws.

You may want to see if the nuts are loose on yours also and if they are double nut them. A loose regulator can cause problems as the brushes are losing contact with the armature.

 

[MIDNIGHT RIDER]

I will add that the Leece-Neville 110-555s that I use are self-exciting.

They are also externally regulated WITH the external regulator being mounted right on the back of the alternator.

As a general rule, the alternator self-excites and immediately begins charging as soon as the engine comes to life, with no blip of the throttle required.

About one time in fifty, a slight throttle blip is necessary.

 

[pybyr]

I will add that the Leece-Neville 110-555s that I use are self-exciting.

They are also externally regulated WITH the external regulator being mounted right on the back of the alternator.

As a general rule, the alternator self-excites and immediately begins charging as soon as the engine comes to life, with no blip of the throttle required.

About one time in fifty, a slight throttle blip is necessary.

Thanks, but I don't see any way that L-N could be shoehorned in where the unit is located on the IDI in front of the fuel filter bracket. It's possible to get the various L-N models set up to be self-exciting. At present I would settle for it exciting at all!

 

[pybyr]

When mine would charge and then not charge I got a replacement alternator. Upon taking the old alternator out I noticed the small nuts holding the regulator in came loose. On the E series Fords you can't see the regulator. Not knowing if that was the actual cause of my problem or not I changed out the alternator anyway because the old was under warranty but the one thing I did do and have done since is double nutted the regulator screws.

You may want to see if the nuts are loose on yours also and if they are double nut them. A loose regulator can cause problems as the brushes are losing contact with the armature.

thanks- when I had it out to change out the rectifiers, I put toothed washers between the posts and the terminals for the rectifiers...

 

[Compu Doc]

thanks- when I had it out to change out the rectifiers, I put toothed washers between the posts and the terminals for the rectifiers...

I would check it out anyway. Mine had lock washers and it came loose before it was double nutted.

 

[pybyr]

I would check it out anyway. Mine had lock washers and it came loose before it was double nutted.

Thanks- does sound like it could be an explanation. I was under-impressed with the solidity of all of the regulator attachment and terminals when I had it out before, given the supposedly legendary L-N robustness.