pulley size and "high output" alternators

[Sprintcar26]

Recently reading about what are being called "high output" alternators, the ads for which recommend against changing the small pulleys they come with, and also indicate that you need to purchase a shorter belt to compensate for the smaller pulley size. Some folks on this site are talking about amps, draw, h/p, and stuff that that goes far beyond my limited knowledge, but I was wondering if these are really "high output" alterrnators, of just regular alts, that are being made to spin faster due to the smaller pulleys? Thoughts?

 

[The_Jeff]

They use a different winding on "high output" alts that peaks at higher RPM at the detriment of lower RPM. So the smaller pulley helps with that.

 

[ctechbob]

They use a different winding on "high output" alts that peaks at higher RPM at the detriment of lower RPM. So the smaller pulley helps with that.

Yep, what he said. Was typing pretty much the same thing.

But at the same time, you can't just spin them to the moon.

Fun story. Back in the late 90's I was in product development for StreetWires/Esoteric Audio. We had a subcontractor building alternators for us. Nice units. All of them came with a 2" pulley. Until we started putting them on GM Trucks/Suburbans/Etc that had massive crank pulleys on them.

We sent a couple fan blades through the hoods of a couple trucks until we had to back off to a bigger pulley.

Ended up buying some hoods......

I forget what rotor RPM they ended up spinning, but it was a lot. The fans would flex, hit the belt or case and frag out. Wasn't pretty.

 

[Sprintcar26]

Got it! Thanks for the info!

 

[Johnny248]

I just installed one a couple of days ago on my truck and happen to have the test sheet in front of me. Does have a smaller pulley, and it shows 137amp @ 650rpm 251amp @ 1800 RPM. I have another sheet at home from my other vehicle that I can post later. It shows the output sweep all the way though the alternator RPM.

 

[Kira]

We sent a couple fan blades through the hoods

You're talking about the alternator's little fan, yes? fan

 

[ironman_gq]

I just installed one a couple of days ago on my truck and happen to have the test sheet in front of me. Does have a smaller pulley, and it shows 137amp @ 650rpm 251amp @ 1800 RPM. I have another sheet at home from my other vehicle that I can post later. It shows the output sweep all the way though the alternator RPM.

Most of the ones I've see top out around 6000rpm on the alternator and depending on crank pulley and alternator pulley ratio that could be anywhere between 2000 and 4000 engine rpm

 

[ctechbob]

You're talking about the alternator's little fan, yes? fan

Yup

 

[Johnny248]

Here is the sheet from the other HO that I have.