Ive had Nelsons fan harness and a set of F-body e fans on my truck now for a few months and im starting to notice that at night time when the a/c kicks on and the fans turn on High that my light will dim a good bit, at a stop I can also watch my volt gauge slowly drop down until i accelerate, does this happen to anybody else?
not sure if its time for a bigger alternator (not sure what mine is rated for) or just a new oem one.

 

Yes it happens to mine. I am using 05+ fans with a Black Bear harness controlled by the PCM for both highs and lows and the PCM turns the fans on with the AC as needed. When I first put mine on my fan temp on/off settings were too low and they were coming on needlessly even around town and it would always pull it down to the 12.5-13 volt range, especially at idle. After adjusting the settings and finding out the fans move so much more air on low than the stock clutched fan could ever dream off I have mine setup to where under normal circumstances they never go any higher than low speed. If the temp gets above 215 they will turn on high however. For good AC operation low was more than sufficient. I've idled it at Sonic when its 110 degrees for a good 15 minutes and it would blow in the low 40s at idle. One thing I did do though was bump my idle speed up by 100 rpms both in gear and in park. It seemed to even out some of the voltage fluctuation at idle and made the AC cool a little better. I still have the stock 105 amp alternator and after getting it all set right it never drops under 14 volts according to the gauge but testing it at the battery shows right around 13.75 volts.

 

Alt and/or batt...google "the big 3" and do that also

 

I have seen symptoms very similar to yours before when e fans were added to a truck that didn't come with them in which case the truck just had a 105 amp alternator. I would be willing to bet that you've just got a 105 amp as well. IMHO I think it's time for a higher amp alt.

 

☝Ditto.

 

I don't have e-fans on my truck but they have been on my todo list for a while. I did recently do the Big 3 Upgrade and holy sh*t what a difference. I can roll both windows up and down without my lights diming and they move faster. I am willing to bet the big three would help your situation out! Just look how small the factory wire is from the altenator to the power distrabution block on our trucks. It might be a 10ga wire. I replaced mine as well as a few grounds and a power cable going to the fuse box to 4ga wire. BIG DIFFERENCE!!!!

 

anybody have a part number of what vehicle i can get a alternator for that has a high output than 105 amps?

 

I have an 02 Silverado with e-fans with nelson harness and nelson tune and i had the same issue with the lights dimming and my truck has power everything and the amps for the Alt is 105 and i upgraded to 130amp from a Tahoe or Suburban. A GM parts tech told me that it would fix and should fix the dimming issues, which its better than before, the dimming isn't that bad but better! Give me a few and i can get the pn# from the Alt at lunch.

I just want add that, if you upgrade to this Alt, it does have a bigger pulley than stock, so your stock belt may not work! I tried to change my belt last weekend and the new stock belt doesnt fit, its like 1/2 too short so from the research i found out it should be 93' inches overall to fit correctly or swap pulleys or get a March pulley which will work as well.

 

ok thanks, ill probably just swap pulleys, or would a tahoe/ suburban belt fit? hmm

 

did you try the belt for the trucks that came with the 105amp alt that may do the trick.