Alternator OD pulley for load spikes

[wirelessF]

I have an 02 Chevy Silverado 5.3L with a couple electrical mods. It has the larger 130A alternator and just recently upgraded to OEM Silverado electric fans. When the fans switch on to high under idle there is a momentary idle drop to
I'm thinking of using an OD pulley to increase idle amps to handle the amp spike demand of the efans.

 

[danthaman1980]

I think alternator output is more or less controlled by the ECU on these pickups, so I think any pulley change will be reverse-compensated. However, in your case I think I'd start by installing a capacitor or two (just prior to the fan relays). That should help start your fans without such a huge voltage drop.

 

[JimPghPA]

Just my $0.02 worth of opinion:

Why?

Seriously, why?

If you put a larger diameter pulley on the engine so as to have the alternator spin faster so it can put out more current to keep the voltage up, then you will be giving the alternator more leverage to bring down the engine RPMs even more when the increase in load from the fans occurs. Bring down the RPMs some more any you might get something to act up such as the engine stalling, or maybe even the transmission having some lag when you accelerate due to the internal oil pressure being too low caused by the lower idle?

The voltage dipping to 12.5 for a short amount of time is nothing to be concerned about unless it is causing some kind of a problem with some other electrical component such as you sound system. And most other systems such as sound will have no problem with the voltage being 12.5 Volts. Are the headlights getting so dim during the 12.5 Volt dip that it is a noticeable problem at night?

If there is no electrical component problems during the 12.5 Volt dip then why mess with something that is working just fine the way it is? If it ain't broke don't fix it. If you do you may be setting your self up for problems that may eventually convince you to put it back the way it was before you messed with it.

 

[The_Jeff]

So are you saying this comes stock with a belt driven fan? If so your ECM is probably not calibrated to boost the idle 1/10 sec before the fans kick in.

A custom tune might help, I guess.

Also you say "fans", if there are two identical fan motors you can work your wiring some more and put in a high/low relay that runs them in series for low fan then parallel for high. Once you get them going the fan motors won't need such a power surge to boost up to high.

 

[JethroBodine]

Originally Posted By: eljefino
So are you saying this comes stock with a belt driven fan? If so your ECM is probably not calibrated to boost the idle 1/10 sec before the fans kick in.



+1 Consult your dealer and see if they can reprogram your ECU to handle the larger alternator.

 

[meep]

Do not change pulleys.

The larger pulley is not an amp issue-- the engine RPM is falling BECAUSE the ECU is demanding more output from the alternator. you see, the alt is doing its job.

The ECU may also ramp up alternator output on purpose to reduce electrical spikes and NVH.

using an OD pulley will effectively do very little if the alternator is achieving commanded output. If it's a little short, it will actually pull more load from the engine and drop your idle a bit more, the opposite of what you want. (assuming it's on the crank). An UD pulley on the crank would reduce the symptom but potentially reduce alt output.

I'd leave it be if it were me. big loads happen.

 

[HerrStig]

Starting load on electric motors is higher than running load, (something called "back emf") -- I think I'd look for a way to stagger start the fans, one a few seconds after the other.