Alternator regulator keeps dying – ls1tech – camaro and firebird forum discussion electricity and magnetism equations

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I am in a unique position where I have access to almost any engineer at Remy, and I have spoken with the engineer who has design control of this alternator. The L-terminal has a maximum rated current of 0.4 Amp. The recommended resistor to use with the L-terminal is 50 Ohm. There is nothing wrong with my resistor of choice. Root cause of problem is something else.

I did a little more sleuthing today with a Remy technical resource. We went down a few trails of thought and both landed on possible issue being rotor over-speed. The associated failure modes of the rotor and brush leads fit my symptoms pretty well.

Turns out the CS130D type alternator used in the F-body cars has a fairly low speed rating compared to other compact brush-type alternators (10K rpm continuous, 12K rpm intermittent). I don’t know my exact pulley ratio but I can see it is in the ball park of 3:1. That means I am turning the alternator up to 21K rpm. So I’m thinking to myself, how does the alternator live on a LS7 Corvette? I found an easy answer to that…. it doesn’t. Corvettes use a Valeo alternator. Even the aftermarket Remy part is a reman Valeo.

I think what I’m going to do is find an alternator with a higher speed rating and see how that rolls. I was told there are aftermarket companies that might upgrade the CS130D with stronger rotors. If so, that would be an easy drop-in replacement without the fuss of changing my FEAD.

Seems that I solved the problem for now. This is an LS swapped car and I had the alternator L-terminal wired to a "Service Engine Soon" light bulb in the dash. It seems there was a poor (intermittent) connection of the electrical connector at the gage pod for the circuit that excites the alternator. It is the old GM green printed circuit board from the 1980’s. I think this was causing the alternator to shut off sporatically.

I want to whip this once and for all and not have to worry about intermittent connections, or deal with the 50 Ohm in-line resistor that is needed for the L-terminal circuit. I moved the accessory wire from the L-terminal to the F-terminal and wired it directly to a switched 12V source (unused circuit I had left over from an add-on fuse center that I made for the LS swap). Dropped a 5A fuse in the circuit and alternator turned on, as it should.

For those that are wondering, the L-terminal requires an external resistor to keep current draw below max allowable specification. Whereas the I/F-terminal has adequate resistance internal to the alternator and can be wired directly to a 12V source.

Seems that I solved the problem for now. This is an LS swapped car and I had the alternator L-terminal wired to a "Service Engine Soon" light bulb in the dash. It seems there was a poor (intermittent) connection of the electrical connector at the gage pod for the circuit that excites the alternator. It is the old GM green printed circuit board from the 1980’s. I think this was causing the alternator to shut off sporatically.

I want to whip this once and for all and not have to worry about intermittent connections, or deal with the 50 Ohm in-line resistor that is needed for the L-terminal circuit. I moved the accessory wire from the L-terminal to the F-terminal and wired it directly to a switched 12V source (unused circuit I had left over from an add-on fuse center that I made for the LS swap). Dropped a 5A fuse in the circuit and alternator turned on, as it should.

For those that are wondering, the L-terminal requires an external resistor to keep current draw below max allowable specification. Whereas the I/F-terminal has adequate resistance internal to the alternator and can be wired directly to a 12V source.