What kind of a bike did this come out of? That's one heck of a large battery for a motorcycle.

 

Sorry Doc, that's not going to work, for me. I need to understand this, not trust someone.

If the alternator needs to make 40 amps to bring the voltage to the proper level, it needs to make these 40 amps, regardless of the pulley size. The amount of horsepower required to turn the alternator (that needs to make those 40 amps) seems like it would be totally independant of the pulley size....

 

Greg it all hinges on TORQUE.......Kibort in 3,2,1.....

 

Porsche actually made two different AC pulleys, one for hot climates (and rear AC) and one for cooler climates.

 

Two different engine fan pulleys. M319 is the 86mm, higher fan speed pulley option. Regular pulley is 106mm.

 

Ok, no prob. Please enroll in your local university engineering program and take 4 years of Electrical Eng studies. I know you'd like two or three sentences that asplain it all but that ain't going to happen. Sorry.

 

http://www.intmath.com/trigonometric...ns/pulleys.php

http://www.tutornext.com/help/pulley-block

http://www.mecheng.osu.edu/vibration...jmes_aug08.pdf

http://www.brainmass.com/homework-he...physics/116773

http://teacher.nsrl.rochester.edu/ph.../FinalExam.htm

Work on this. It should cover everything.

The definitive work on the subject: http://physics.kenyon.edu/EarlyAppar...s_Machine.html

 

I'm taking your word for it Doc, this is as far as I got with this link.
http://www.intmath.com/trigonometric...ns/pulleys.php

 

It's like on your old 10 speed bike, shift into a lower gear, and it's easier to pedal, but you go slower.
On a stock pulley alternator you need to get the RPMs to about ~1000 to get it to charge, but with this
one you'll need to get the RPMs a little higher, but it won't take as much effort to run. On the track,
you rarely get below 3000 RPM, so you don't have to worry about the not charging issue, like on
the street. Also it weighs less, which helps power to weight, braking, etc. Of course, .3 lbs isn't much,
but as you know, it all adds up. Ok, did that help?

Of course, I'm running a 140 amp alternator with the stock pulley just to power all the extra stuff in my car,
but I don't need to worry about weight, since it helps keep the car on the ground at high speeds...

 

Doesn't this go back to the first law of thermodynamics? The one about no free lunch, and energy may change forms but still has to be accounted for.

An alternator, with its output disconnected (and producing no useful energy), spins pretty freely--other than some (small) bearing loss, no energy is being consumed or generated. Similarly, connect the same alternator to a fully-charged battery, no current will flow and there will be no energy consumed or generated.

Now turn the headlights on, and the alternator has to generate 200 watts or so, depending on the lights. That puts a load on the alternator of 200 watts plus whatever the efficiency is, probably around 350 watts total-- that's about 1/2 horsepower. The rotational speed of the alternator doesn't figure into that, except as it effects efficiency-- I am not sure whether that is a big actor, or even which way it goes--better at high RPM, or lower.

So I'm with Greg on this, confused.

 

If you look at alternator output curves they need about 1,000 RPM to start charging but around 2,500-3,500 reach near max output. Spinning faster makes almost no more output. The voltage regulator is the brains and increases the power to the magnetic field to increase the output to meet demand. So even at lower RPM it will increase the drag to induce more output if it is NEEDED. One site stated it takes about 1 hp to make 23 amps 5 hp for 115 amps. All of which would indicate that it is best to start the race car with a booster battery to avoid draining the battery. Running a low amp alternator would limit the maximum HP draw (my 911 had a 35 amp). Also means that a larger pulley is going to make little or no difference due to the output curve the max charging is relatively constant from 3,000 RPM up. So slowing it down by even 50% would have little impact on the output or the horsepower consumed accept at low RPM.

 

If one assumes that alternator output and thus power lost from the engine, rises linearly from 0 amps at 1000 engine rpm to max amps at 3500 engine rpm. then stays the same above 3500 rpm

By reducing the alternator rpm by 1/2 it means max load from the alternator coincides with max engine output at say 7000 rpm. This means the proportional loss is less ie effectively more power available from 2000-6999 rpm.

It will probably also mean that the alternator will last longer as it won't spend most of it's life at or near it's max rated rpm. There has to be additional losses from turning the alternator faster thanis actually needed.

 

I'm with Greg and Jim on this. Unless we are talking about incredibly small +/- differences in the hp required to turn the pulley I just can't get my head around what difference it makes unless the load changes over RPM.

George's comment about the geared bicycle is not the discussion. It's about hp loss. Changing the pulley affects rotational speed and not any measurable meaning hp. (1hp or more)

So, what takes/burns more energy? Running or walking a mile? Measured only during the time of effort it is the same. To me this is what is happening with the pulleys.

My physics is from a long time ago so my ability to noodle on this is only through practical concepts.

Feel free to call me stupid and ignorant. Ever since I was 18 when I thought I was incredibly intelligent and believed I knew everything, its been a steady slide down the slope of humility

 

Carl,
I would love to buy some parts from you but it seems all your developed parts are for high end high dollar race only applications. Is there THAT big of a market for up scale 928 race cars???

I am no financial wizard but it seems you would make a lot more profit by developing improved products for every day street drivers. Throw us daily drivers a bone too please.

Some Examples would be...

Reasonable Blower motor replacement....new includes housing that's not needed and runs $600 plus.
New motor could be used from another car...but which one
fits the fan housing? May need just a replacement bearing
you could manufacture. Every car will need one eventually.
New cam gears...............way too much $$$ now a days. Could be made and sold cheaper and again..
every car will need eventually.

 

Carl's new pulley is much prettier than the ugly stock one.

That's all you need to know.

Move on, bitches.