V-belt Limit

[Tungsten]

Doing an alternator swap has got me thinking what the theoretical limit is for the power transfer of a single groove v-belt. I heard they can transfer up to 2.2 hp, which for example should be good for a Maxima 90 amp alternator but I don't know if anything more is possible without the belt slipping at high rpm. Anyone have any ideas?

[RJSquirrel]

How is the value of 2.2 hp arrived at? That seems low given that v-belts are used on commercial lawnmowers, and also, older automotive A/C compressors use a lot more power than 2 hp and they are powered by a single v-belt.

 

That doesn't seem right, of course if it is, it wouldn't be the first time I've ever been wrong...

 

Any feedback from those who have installed Quest/Villager or Mean Green alternators (and actually load them) regarding issues with belt slippage?

[Tungsten]

I don't know how it's derived but there should be a formula on how it is done. Something to do with belt length maybe? That's the reason for my post... There is a reason that industrial stuff uses twin V-belt pulleys or serpentine pulleys with multiple V-belt grooves. I have never seen a single V-belt used on anything powerful or relatively high output. For really high output stuff, belts are not even used. Those things are all powered by a tractor PTO shaft.

[Precise1]

http://www.ecae.com/alt1.html

 

140 amp alternator with a single V pully. It's not an issue.

Many people have swapped in 125 amp Quest alternators and switched the pulley to single V without issue.

As for theoretical power transfer limits, I suspect it is complex with many variables such as belt length, belt contact area, belt composition and material quality, belt speed, pulley diameters, etc...

 

B

[MY1PATH]

I run a 180 amp alty and I know a guy with a 240 amp ambulance alty. No belt slippage...

Now the flex limit of a v-belt you use on your truck is a 2in diameter pulley and the grip to turn heavy resistance deteriorates quickly at 2.5"

So any V-pulley over 2.5" (pathy is 3"?) will run whatever alty you throw in there.

[Tungsten]

A little off topic but suppose the belt can handle the load, I doubt the factory wiring is made to handle 240 amps. That would also be a good amount of rotating mass at 5000 rpm!

[MY1PATH]

A little off topic but suppose the belt can handle the load, I doubt the factory wiring is made to handle 240 amps. That would also be a good amount of rotating mass at 5000 rpm!

 

I never said it was a pathy running 240 amps. And no, the pathy wiring does not support more than ~90 amps but it does not need to.

Hypothetically You could hook up a 1,000amp generator and not hurt a single wire because you are increasing the available amperage but you are not increasing the draw. A pair of 60watt headlights still draw ~10 Amps No matter what kind of alternator you have.

When you install a big alternator the only thing you should think about upgrading is the wires from the alty to the battery (charging harness) a dead battery creates a demand higher than a stock alty can provide and so the bigger alty will heat up your charging circuit Stock charging circuit supports 120 amps for short durations. All new loads, Lights winces etc should be attached/relayed directly to the battery so your not increasing the draw across anything stock aside from the charging circut.

[Mr.510]

The figure I had always heard was that a typical automotive application V belt could reliably transfer about 7hp. Given that I've worked on many machine tools with two similar belts on slightly larger diameter pulleys transferring 30hp all day long with nearly instantaneous acceleration and deceleration I would guess that's pretty close. The bigger the pulley diameter and the steeper the V-belt's angle the more traction and therefore the more power that can be transferred. My slidebed wrecker has a GM 250amp alternator that's turned by a belt of the same approximate size as a Pathy belt.

 

When thinking of inertia of an alternator at 5k rpm remember that the general rule of thumb is that an alternator spins about 3x crank speed. So when my VG510 hits the rev limiter the alty is spinning about 24,000 rpm. And yes, I've thrown the windings off the stators of a couple alternators with such shenanigans.

[Tungsten]

I guess for a Pathfinder, a 90amp alternator should be light enough to spin at 20,000 rpm without self destructing while still keeping the stock wires to the battery from melting in case of a dead battery.

 

Good info there!

 

Mods: Request for sticky!

Edited November 25, 2011 by Tungsten

[MY1PATH]

BTW I'm not running an upgraded charging harness with my 180a and it does cook fuisble links from time to time. Like after I run the stereo for 8-10 hours and then start it up to go for a drive.

Or foolishly charge two deep cycle welding batteries with it.

[adamzan]

I melted part of my harness at the alternator. I don't know how or what happened but the only way I noticed was that in the rain my wipers moved real slow and at night I couldn't see because the lights were so dim. I was running a 90A maxima alt. It was charging just enough so that I could still drive.

 

The stock harness is actually 2 wires soldered into 1 connector.

Edited November 25, 2011 by adamzan

[Tungsten]

yeah i think i'll stick with 90 just to be on the safe side to prevent things from melting

i think the fusible link should melt before the harness at the alternator

and i don't want the winding coming apart when the engine is doing 5000 rpm

[Kingman]

Put a 130A Quest alternator in it.

[Tungsten]

yeah but that needs more custom work

i was even fine with the 70 amp one and am only going to 90 amps because of a higher output at idle which improves reliability