I know this has been discussed many times but I could not determine the correct fix for my application. Hopefully you guys can help(as if I have any doubt ;))!!!

Here's the setup: '71 Chevelle. Powermaster 130CS 100A Alternator. Regulator correctly bypassed. 8g charge wire to horn relay. "S" Red wire to alt output. "L" brown wire to dash. Auto meter volt gauge connected at horn relay used for readings.

At idle (900 rpms) voltage drops to 12.5 and lights dims. Once electric fans (dual 14" 20A draw) kick on they will drain the battery pretty quickly (Yellow Top Optima). At about 13-1500 rpms, voltage jumps to 14+ and all is well in the world. I'm running a belt drive system so I can't go with a smaller Alt pulley.

Are there any other tricks to get the alternator to increase output at a lower rpm? Thanks!

You could move the "S" wire to horn relay, I assume this is where fans get there power. If they get power from the battery or junction block you should move it over to horn relay along with the "S" wire. It may help some but your problem does seem to be rpm related. You can use a smaller pulley, just need to get a shorter belt.

So instead of the S wire attaching right at the output, I should have it extend down to the horn relay as well? I'll give that a try.

I contacted the manufacturer of the belt system and unfortunately they don't have a smaller alternator pulley for the belt drive kit.

Thanks

bummer, I just bought a CS130 today at the local Kragens. Are you using relays on those electric fans at all?

You should look at the MAD wiring diagrams as well. I'm in the process of doing all the wiring on my elky.

http://www.madelectrical.com/electricaltech/chevymain2.shtml

I'm running a belt drive system so I can't go with a smaller Alt pulley.

Are there any other tricks to get the alternator to increase output at a lower rpm? Thanks!

There are several diff sizes of alt pulleys for serpentine belt systems available. What diameter alt pulley, and what dia crank pulley are you using now?

Most likely your alternator isn't turning fast enough. http://www.powermastermotorsports.com/power_pulleys.html

It's a COG drive with a 2" belt or some people call them gilmer drive system rather then a serpentine system. I will see what I can find from another manufacturer but my ratio is coming in right at about 3:1. I'm going to give moving the S wire a try once this rain quits!