s5 to fd alternator problem
 

I just installed an fd alternator into my s5 fc and im running into a problem. It seems to work great above abour 1200rpm, showing 13.5+, but below 1200rpm it drops off to 12.5 or 12.1 with lights and brakes applied. I have the atkins dual pulley installed.
The only conclusions I can draw are that I may have incorrectly wired it ( I didn't wire a thing, just plugged it in because its LS to LS), I have a wonky regulator, or the pulley is too small.
I need advice though, any thoughts? Was I supposed to wire it a different way?

I read up on the wiring and there were no mods to be done, so that cancels that.
I have a power fc, and a large efan as my only load sources, no stereo. I'm wondering if the fan alone could be the culprit, but I assumed the fd's output would handle it.

bad alternator?

Mine does the same thing.it is on my S4..Parked or stopped at idle my lights are Dim,but touch the gas,they get brighter.I can cruise at 14.5 volts,no problem.
I am thinking Regulator.I am close to an alternator rebuild place to I may take it there.

So does that mean FD's Alternator is direct drop in to S5 with no modification at all ?

cuz I think my S5 Alternator is dying, charging only 13.6-13.8 with headlights on. :(

yea, its drop in for S5.

The FD alt doesn't charge too well at idle, but it should still put out close to 13V over about 900-1000rpm (where the vast majorityof driving is done) it should be putting out 13.5 easily, I get 14+ at pretty much anything past 1200-1500rpm

well, stock FC NA S5 @ idle is like what, 650 or 700 something RPM? thats kinda low IMO

I can go for other ones but for me, FD Alternators are easy to get :)

Thx :)

Is that Atkins pulley an underdrive pulley?

+1. I was thinking the same thing.

sorry to revive a thread from so long ago, and i know its been said that its a drop in install on the s5, but does that also mean no belts, pulleys, etc are needed? if i bought just a fd alternator would i have everything i needed for the swap? and if so, im in the mnarket for one.
thanks in advance,
carrington

since the FD pulley is a serpentine design you need to change it to a V groove belt pulley.
The bore is 17mm.(shaft size)

thanks boss