Efan + Charging system

[89VORTEC]

My 89 pickup has a 2 speed ford e-fan (only using low), a 140A cs-130D alternator, and a 900 cca battery. Also have an additional 6 gauge wire from the alt to the battery.

Heres the problem. My digital gauge shows that i'm barely charging (its not lying either) when i have headlights, a/c on high, sub hitting. During the day with a/c and sub, no problem, but when i add headlights into the mix i have charging problems at low rpms .... with a 140A alt...what gives? I do have the smallest available pulley on the alternator. Charge comes back up when rpms come up, but i dont like to see that bargraph gauge in the "low marked" area. I like to see it at 14, or one bar below ... not 4 bars below ... Any ideas?

[89VORTEC]

oops i guess this should have went into the vehicle specific forums instead of the engine forums. mod(s) please feel free to move it if you'd like

[Mikz86TA]

What volt is the gague reading? What kind of gague is this? Start here. Also its best to verify with a quality meter like a Fluke.

[jharrison]

First question is do you have underdrive pulleys? I understand you have a smaller alternator pulley that aftermarket companies love to claim brings you back up to stock. If you do I honestly I wouldn't be surprised if it isn't charging all that well. I have the March power & amp series underdrive pullies with the smaller alt pulley (supposably to bring the charging level back to stock) and when I had the electric fan or when the stereo was cranked up my charging voltage would drop considerably. I guess what i'm getting at is that I haven't been convinced that the smaller pulley gets the alt spinning back up to stock speeds.

I have noticed that at idle charging and cooling abilities have dropped some. Just above idle everything's back to normal. Keep in mind though that i'm down in Texas where the average temp is 90+ degrees with no less than 50% humidity. Charging, cooling, and battery life here is always an issue. I have been playing around with this problem and have come up with only one solution for charging. There are a few companies that offer alternators that have a much higher output at idle than stock and quickly ramp up as rpm's come up. They are expensive, but usually it's either that or leave the stock pulleys on and still install a smaller alternator pulley.

Capacitors really help out in this department when it comes to high powered stereos. Don't stick with the typical recommendation of 1 Farad per 1000Watts. You can always safely add more. More capacitance = more available amplifier power that doesn't have to be taken from your battery.

[nomaboy]

thats normal. the 140 is rated when the alternator is at a cirtain rpm. naturally when the alt. is spinning faster it is going to have the ability to produce more power than at idle. i wouldn't worry about it, as long as it charges with some rpm. mine with efan, lights, sub at idle sits at 12 volts. if i rev it to 700rpm it jumps right back to 14ish. if you figure that the total amp draw with all that stuff on is probably 50-60 amps then it makes since that the alternator can't keep up at low rpm.