8550 alternator

I assume my 8550 came from the factory with a brushless niehoff alternator, but had a delco on it when I got it last year. That alternator went out on me one Saturday afternoon while seeding last year. I got a Wilson replacement for it from a NAPA guy who was about to close for the weekend and shoved like a 65 amp alternator at me to get me out the door, saying that was all he had. That one already went out this year, and I replaced it with a 105 amp one. Son was out seeding the other night, and said the alt light was coming on again, so I told him to quit for the night, and I'd see what it does the next day. So the next day, I am on some flat ground, and so I was toodling along and didn't have it quite at full throttle, and not even realizing it wasn't quite full throttle, and the alt light started flickering on again. I shut the AC down, and that didn't help. Then I cracked the throttle wide open, which wasn't too much more, but then the light went out and stayed out, even with turning the AC back on. Now the original alternator pulley has been changed to each new alternator, and I am wondering if the pulley may be too big, and the alternator isn't spinning fast enough. When I got this last alternator, the pulley that came on it was probably half the size of the tractor original, but the guy I got the alternator from, said stick to the tractor original pulley, so we did. What would happen if I put that smaller pulley on? Is there such a thing as over speeding the alternator, or could it help, without hurting anything? If I am correct, the tach runs off the alternator, and that indicates to me that the alternator is running too slow, because full throttle only reads about 1900 RPM's on the tach, and the tach isn't always working, either. As far as stuff drawing juice, I have an electric lift pump on there for the fuel that is pretty hefty (don't know the exact draw of it}, there is an electric seed clutch on the air seeder, have a Case IH/trimble auto steer, and AC. And lots of lights, but only that one time when my son was running it after dark. There shouldn't be issues with this situation, should there? Any ideas? Thanks, Darrel

BTT

Here is a picture of a Delco CS130 alternator I put in place of a niehoff.  I used the original pulley.  I find them at the U Pull it junkyards for 25 to 30$, just look for one that looks new.  I usually pick up a few if I am there, good to have a spare.  I have replaced the Delco 10SI with this and it does read a little slow on engine RPM, about 125 RPM's.  When I replaced the niehoff the RPM's are right on.  It has a 4 terminal connector.  I use P for the tach, L for the alt light, and F to power the field.  Do not use the S terminal.

Would, could a Neinoff from an N5, 6 & 7 work on a 7000 and the 8550?

Edited by Unit3 - 03 Jun 2017 at 5:56pm

I guess my main concern is just wondering if it will be OK to put the small pulley on the alternator I now have on it, or if that will make the alternator spin too fast. I am pretty sure that wouldn't be a problem, but just thought I'd check. Darrel

Doubtful that you would spin the alternator too fast. Consider that an automobile engine spins at twice the speed of a tractor engine. My only concern with too small a pulley is the possibility of belt slippage.