Weak = adequate for a complete stocker and Mall crawler. What the stock alt/gen is rated at, and what it puts out at 600 RPMs are two different things. Add accessory lights, winch load and/or Efan load and you can be below where your demand is depending on what accessories are being used.

I'll stick by my observation that the OEM alternator is weak and there are scads of threads complaining about this at many forums. In case of misunderstanding, no I am not talking about at driving speed, I am talking about output at IDLE.

Who said underdrive pulleys are a waste because your alternator is weak???? Seems a simple comment may be taken by some BSer as the reason for whatever they conjecture. Rather than write a discourse, I thought a simple observation and reference that the computer controlled power output already reduced belt load variably accomplishing what underdrive pulleys aimed at mechanically in so far as alternator load.

Just because underdrive pulleys might free up a tiny amount of HP in a street car, doesn't mean it works well for an off road truck where you don't see high rpms for long periods at a time. For those of you who have never left the pavement, never mind.

 

me too,but first;
if ure old,me,u remember the platinum gas saver by various names,,,comes out every 15 to 20 years originally it went on the carb,then in the tank,,,15 yrs the guy gets out of prison ,for false advertizing,tries again.
so ill say it again,if someone has a fuel saver WITH a written guarantee,even spelling out the driving conditions i must follow and the payoff time ,,,ill buy in. there have been posts saying,zero noticeable gains with air intake mods of various suppliers,,,im just sayin

now the facts;
i look in the window and read 12.4 v b4 i open door. i put an external 60 amp load on the batt,volts start to drop. i open door,turn on brights,turn fan full blast,push e brake down, start engine,put in gear. while standing outside i read a minimum of 11.7 at IDLE. btw in neutral idle is apx 600 700. in gear it goes to 800. no matter,in neutral,rpm to 2000 no change. so it bottoms out at 11.7 ,WITH all normal loads at full blast,AND,60 amps external.
now if ure winchin do you need brights,off road lites,and fan full blast,and monsoon crankin.

turn off anything and volts go up to 12+, quickly to 12.9+.
i would not want to push any alt for a long time and overheat it but clearly the h3 alt/gen is totally capable.(my load box was smokin!)

also the horsepower thing is a waste of time. 10 hp dont matter. face it we want seat time,i stole that line from,??. its the drive we like and we do it mostly around 2000 rpm,AND WE ALL WANT MILEAGE. give me some torq there,not 6 hp at 5000 rpm like k+n filters does. the hp gains are at high rpm where we dont go,except for the h3 guy making a 1/4 mile trip in 20-30 seconds! not too many h3 running the strip.
i have no way of running below 600 so an underdrive may lower below 11.7,IF YOU RUN ALL ACCS AND 60 AMPS EXT. i doubt it.

hey for 12 bucks at walmart get a digital meter and see for ure self.
oh normal loads, volts are 14.8,sometime 15.1 at start up charge.

 

Most of that is good stuff.

However, a MM9500 draws 85Amps at NO load, 150A @ 2K, 201A @ 4K, all the way up to 375A at full 9.5K load.

The OEM I5 alternator is rated a 120A peak (2500 RPMs+) and makes no more than 84A at idle, the LH8s are rated at 145A and put out 101.5 at idle (per GM's 2008 Engine Electrical - H3). If you use a parasitic draw test switch with a charging system meter, you will actually see 10-15% less at idle, but let's assume GM is accurate in its ratings. Doh. So just an itty bitty winch pull with everything else off is tapping the system.

I understand duty cycle and note each draw should be short in duration.

Different situation.
I'm not into multiple off road lights, but many are. Lets say somebody ??? has 2 brush guard lights and 6 roof rack lights with 100 watt bulbs. 100 Watts means 8.3A each x 8 = 66.4As for lights alone.

This is why I am not excited about the OEM alternator. Will it work for the average Joe? Sure. Is it weak, yep.

Underdrive pulleys anyone?

 

so,,,the point???
underdrive wont get u 1 amp, ahh so whats the point??

oops forgot,,,"8.3A each x 8 = 66.4As for lights alone. "so u cant use em.

i guess the only answer is a second gen!

 

Owww, my head hurts. What were we talking about?

 

I, too am getting amped up over this topic . . .

 

Do you feel an electric fan(s) is a waste of time too?

 

if it costs more than 50 bucks it probably takes 5-7 years to break even on mpg and the hp gain is not needed

 

I know what you mean about the payback period. I don't have an efan but I wanted to see how effective it could be so I did some before and after testing without the fan (i.e. removed the fan/clutch and the rad shroud).

On a certain long stretch of level road going exactly 40 MPH during both tests (auto tranny, 4th gear, torque converter locked):

With the fan - Instantaneous MPG = 22 MPG
Without the fan - Instantaneous MPG = 24 MPG

I noticed about 1 more MPG without the fan with general driving but this is more subjective.


During Idle at 600 RPM (my idle is lower than stock)

With the fan: engine load in gear = 30.6%; engine load in neutral/park = 27.5%

Without the fan: engine load in gear = 29.4%; engine load in neutral/park = 25.9%

I meant to log instantaneous gal/hr fuel consumption during this test, but I accidentally logged the average gal/hr. I think the instantaneous gal/hr should follow the engine load.

Your load numbers will be different with your stock idle RPM.

I have the ability to dyno the H3 but I ran out of time and had to put the fan and shroud back on.

 

yeah,at 40 u prob dont need any fan so even the dc fan would not be running.

be interesting to compare dc running,with its load,and the stock fan. lots of work!

my dc fan on mustang ,i used an air flow microswitch to kill it when rolling