I thought I would share a solution to a common problem that people fight.
The solution is Fairly simple. and its a solution that most people overlook because they dont know any better in the first place.



most people will not over extend the amount of voltage/amperage their alternator can put out...
the stock Fbody Alternator is made to do approximately 95-100 amps of current draw maximum.

if you add some electronics to the car(big stereo and subs, electronics for racing reasons, whatever) you start to need more amperage to handle the extra items

Most people can Just upgrade to the Suburban 2500 series Truck Alternator which is made to do 145-160 amps....and their voltage drop issues can be solved

but this Only solves the issue if you are drawing more power than the alternator can Put out....

what if you are seeing a voltage Drop at WOT...and you dont have a bunch of accessories and other junk drawing power... what if you are pretty much Just a stock vehicle with a Modded motor...






My setup was a pretty much Gutted 2001 Camaro, with a racecar motor and a few basic things...stock pcm was replace by a Holley Dominator
I have a handfull of Gauges, and a Dual stage Nitrous System with 2 Nitrou Solenoids, and 2 Purge Solenoids, 2 bottle heaters, dual in tank fuel pump...

Then I switched to a Super Victor Intake, and an ATI Damper.

This is when I noticed my Voltage Drop and the amount of Voltage Drop became a real issue.
at the track, I was seeing solid voltage till 4000 rpm, then it would just drop like a rock....so bad that one pass I saw 9 volts and the pcm shut down which in turn shuts down everything engine related....so I had to coast thru the Finish Line

I had already swapped to the Truck Alternator...and thought I had enough juice...but I wasnt sure...
so I switched to a High Amperage output Alternator from www.powerbastards.com...capable of supplying 225 amps of power and also designed to handle slightly higher rpm's


I was Still having a Voltage Drop at upper rpms...




In my search for a solution to this Voltage Problem...I asked an Old Racing buddy of mine...and he Gave me the answer.


After I told him a detailed list of everything on the Motor and all of my electronics and other accessories....he tells me this....

"well... there is a simple explination

Your Voltage Drop...its probably directly related to the Alternator itself and the Rpm you are spinning it at...I think you are spinning the Alternator too fast "


I am certain that I was spinning the alternator too fast..and I didnt even realize this until my buddy pointed this out

when I switched to an ATI Damper that was back to stock size, I never swapped over to the stock alternator pulley, and to top it off I was also spinning my engine up to 7400 rpm now because of the Single plane style intake...


I was using an Underdrive crank pulley, and an overdrive alternator pulley
between the 2 pulleys, I was still at a stock 3.05: ratio
which was ok.. but I was probably seeing voltage drop at high rpm's....like above 6000 rpm..but I really didnt even notice the small drop I was having because I wasnt spinning past 6500 at the time with my FAST Intake





so...some basic Math

Stock Crank Pulley = 7.625"
Stock Alternator Pulley = 2.5"
Ratio of 3.05:1
which is what you typically see most stock setups at
that means that at 6000 rpm, you would be seeing 18,300 RPM at the Alternator

normally you dont really want to see more than 16,000-18,000 rpm at the alternator.
there are a handfull of alternators that are the exception and can handle a little higher, the LSx Alternators are not one of them






so 7.625/2 = 3.8125:1
x 7400 rpm = 28,212 rpm
WAY over the recommended 16,000 -18,000 rpm

I was seeing voltage drop happening at 4000 rpm...which is roughly the 16,000 Alternator RPM

the solution was actually pretty simple...
I had Bob Ette over at AEI CNC cut me a New bigger alternator pulley...
I did the math, and figured out what it was going to take to get me back down to 18,000 alternator rpm
7400 RPM X 7.625 / 18,000 = 3.1347"
we first went with a 3.5" alternator pulley because I knew I might be spinning to 7800 rpm...
but I wasnt getting enough voltage at Idle RPM... alternator was just spinning too slow to make decent voltage.
so I had him make me a 3" alternator pulley



I now get a full 14v at 950 rpm Idle, and I have no voltage drop at High RPM





Voltage Problem Solved

 

What is the cause of dropping voltage @ higher RPM?
The windings should naturally generate more. Is it a
field-regulator cutout phenomenon, brush-float, ???

 

typically a combo of both...
you basically overdrive the alternator and the regulator shuts down
even the ones that are made to go to a higher RPM will experience problems with Brush Float

With Mine... the Regulator was shutting down...The drop off was sudden and drastic...
My drop was 14v up to 4000 rpm and then It fell immediately to 12v..and then continued to drop as rpm went up...

when it drops steady as rpm goes up, that is brush float......


as you see.. I was experiencing both situations.

 

good...but dammit i never go past the stock rev limiter

 

if you do the math, and you arent spinning your Alternator too fast...
then you very well may need a different alternator...

I honestly cant tell you if the higher amp truck alternator was made to spin 6k or not...the trucks had a different cam and intake which was made for low end hauling torque...

you can try the powerbastards alternator, or you can can try a different pulley

also, you should upgrade your wiring to a bigger gauge than stock
I went with a 1 gauge everywhere except for my starter... the starter is Just 4gauge because the lug is so small that the 1 gauge wire end has too big of a hole to actually connect properly


also, if you are using a resistor or a voltage regulator to do the field wire, get rid of it...go straight to a Light bulb in line on the field wire.
I originally had a voltage regulator doing my field wire on my alternator.. was only seeing 12.5~12.8 volts most of the time except for the first few minutes after the car was started...
when I swapped it to a light bulb, it became a constant 13.5v~14v and never went dont until my upper rpm issues happened.
the light bulb is the right way to go

 

soundengineer,

thanks for this info

can you explain more detail about the light bulb usage you mentioned...?

 

Its for anybody not using the Stock PCM to send voltage to the L-terminal of the regulator
you just use any cheapy lightbulb from any auto parts store with a holder socket and wires coming off of it and Just add it into your wire that goes to the L-Terminal of the Alternator

 

So the lightbulb has the right resistance for the L-terminal circuit, ok I see.

 

At night with the lights on and I go WOT my lights will dim sometimes. The car had 63k miles on it and I went WOT on the freeway up to 120 and the lights dimmed and never came back up Voltage completely fell off and the alternator took a crap. I have a Optima red top and the car didnt even make it back home. Used up the battery and died.....apparently it takes alot of power to run the PCM etc etc etc. and i turned everything off trying to limp back home and it wasn't that far. I did not want to but a auto parts rebuilt Chinese POS on the car so I took my original off and had a local shop rebuild it and put the better diodes etc. in it and put it back on the car. It works perfect but sometimes the lights dim when I go WOT. It doesnt do it every time but still does it regularly. Darn Chevrolet!