It is currently Thu Aug 16, 2018 7:39 am



Post new topic Reply to topic  [ 46 posts ]  Go to page Previous  1, 2, 3, 4, 5  Next
Author Message
 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Sat May 05, 2012 12:54 pm 
Offline

Joined: Tue Aug 02, 2011 12:08 pm
Posts: 2882
Location: Norn Iron
ECU Model: No ECU
DTAS54 wrote:
stevieturbo wrote:
My issue is simply down to going to quite extensive measures only to yield maybe 3-4bhp under certain circumstances. I just dont feel it is worth the effort, unless all other avenues of power release have already been exhausted


Swapping pulleys and activating an existing feature are extensive measures?


Swapping pulleys, swapping alternators, swapping batteries, Swapping water pump systems, swapping entire power steering systems.

The conversation isnt just about an alternator pulley, and you've already said you yourself have changed all of the above. I would consider that extensive modifications.

And what is the existing feature that's being activated ?


Top
 Profile  
 
 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Sun May 06, 2012 9:45 am 
Offline

Joined: Fri Jul 29, 2011 9:08 pm
Posts: 30
Dwell table. Activating that feature is how the topic of pulley use for parasitic reduction came up.

Thanks for the (intrinsically obvious?) reminder that if we reduce parasitic losses, it should not be at the expense of reliability. It is a valid point, and in fact, the reason the conversation began was to use a DTA feature for that purpose.


Top
 Profile  
 
 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Sun May 06, 2012 3:28 pm 
Offline

Joined: Mon May 10, 2010 5:09 pm
Posts: 214
ECU Model: S80 Pro
Firmware Version: 61
im still interested by this, if the only drag you are reducing by slowing the alternator down is the bearings then why not get rid of the alternator and put a bike one strate on the crank? no belts no more bearings! almost all production bikes have quite large 3 phase alternators running at crank speed (alot more that you run!!) how much current do you need to run the car?

so you can have 14 v at tick over and no extra drag what so ever!


Top
 Profile  
 
 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Sun May 06, 2012 3:46 pm 
Offline

Joined: Tue Aug 02, 2011 12:08 pm
Posts: 2882
Location: Norn Iron
ECU Model: No ECU
How much current will vary.

There is the cars electrics, the ecu, injectors, coils, electric water pump, electric power steering, fuel pump and then some reserve to charge the battery.

In reality that can be a pretty large amount of power required.


Top
 Profile  
 
 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Sun May 06, 2012 6:49 pm 
Offline

Joined: Sat Nov 12, 2011 6:24 pm
Posts: 96
Location: Montreal, Canada
ECU Model: S100 Pro
Firmware Version: 61
lumley32 wrote:
im still interested by this, if the only drag you are reducing by slowing the alternator down is the bearings then why not get rid of the alternator and put a bike one strate on the crank?


Reducing accessory speed from a 2:1 ratio to a 1.5:1 ratio (just an example) for ALL accessories (alt, WP, PS) puts less load on the crank, everyone can agree to that, right? Regardless of electrical load, it takes less horepower to turn the alternator at 12000RPM than at 18000RPM. The alternator is identically electrically loaded at both RPM's but it takes less crank horsepower if you're spinning it slower (it doesn't need to spin at 18k to produce 14V, I think most alts produce 14v around 2500RPM on a 2:1 speed ratio with the crank...). So let's say it takes the crank 2hp less for EACH underdriven accessory, you can easily deduce that you've now got 6hp (with 3 accessories) more than you had before slowing everything down, right?
To add to the debate, if you're changing your stock steel pulleys for lightweight ones (forget underdriving right now), decreasing rotational mass is also a source of horsepower. It's why we use lighweight flywheels and nice aluminum lighweight wheels. No added horsepower at a steady RPM but it's easier to accelerate lightweight pulleys than heavier steel ones, no debate there.
Anybody still doubt this? I'm not saying everyone should do this, no more than I would presume to tell anyone what mods to do to their cars. But it's a measureable fact that underdriving accessories with lighter than stock pulleys will free-up a certain amount of horsepower. How much depends on the quality of the parts, i.e. the amount of reduction in both speed and rotational weight.
And yes, if there was a way for me to mount a very small lightweight alternator directly on the crank without having it stick out a foot past the bumper, I would :D Just not gonna happen without extensive and expensive mods, pulleys are cheaper by a mile I think.
Just my 2 cents.


Top
 Profile  
 
 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Mon May 07, 2012 1:47 am 
Offline

Joined: Tue Aug 09, 2011 2:54 pm
Posts: 318
Location: Stevenage
ECU Model: S80 Pro
Distributor: Roverdose
Simon P. wrote:
Reducing accessory speed from a 2:1 ratio to a 1.5:1 ratio (just an example) for ALL accessories (alt, WP, PS) puts less load on the crank, everyone can agree to that, right?


i dont see it. if the p/s still reaches the same pressure at a slower speed, turning a smaller pulley is more difficalt (same as trying to turn a small steering wheel compared to a big one)

if your using more dwell time on the coils when the battery voltage is low, because of the slow running alternator, surely your using more power and thus more drag from the alternator.

water pump i can see, but not if you do any road driving.

Drew


Top
 Profile  
 
 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Mon May 07, 2012 5:37 am 
Offline

Joined: Fri Jul 29, 2011 9:08 pm
Posts: 30
Roverdose wrote:
Simon P. wrote:
if your using more dwell time on the coils when the battery voltage is low, because of the slow running alternator, surely your using more power and thus more drag from the alternator.Drew


The beauty of this concern is that it doesn't matter for a track car.

Remember, we choose a pulley set up that is fine at WOT, and in fact several 1000'rpm below that.

It's only at the very low rpm that we might want some compensation, there we don't care if there is a slight increase in draw on the alternator....it will most likely be paddock driving or very slow in the track. In any event at those low rpm, if we want to go faster, the answer is more throttle, and it's not an issue to lose a small bit to the alternator with longer dwell....

Actually, we are still trying to get the real data we need for the table, either via bench testing or from OEM. Side benefit is that more likely than not, we will be able to reduce dwell at the regulated voltage compared to the one-size-fits-all figure we are using. Might help longevity, probably immeasurable load improvement.


Top
 Profile  
 
 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Mon May 07, 2012 9:21 am 
Offline

Joined: Mon May 10, 2010 5:09 pm
Posts: 214
ECU Model: S80 Pro
Firmware Version: 61
as i see it, if you take 300w from an engine then you loose 300w from output! volts, amps, BHP are all derived from watts! your hp on the dyno may well go up, but you will loose else where, toque for example!

i dont see how changing the speed of bearings can make them any more efficient.

but either way the alternators i use in or race bikes are about 120mm diameter and 30mm thick, how much power dose your car use?


Top
 Profile  
 
 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Mon May 07, 2012 2:53 pm 
Offline

Joined: Tue Aug 02, 2011 12:08 pm
Posts: 2882
Location: Norn Iron
ECU Model: No ECU
Simon P. wrote:
Regardless of electrical load, it takes less horepower to turn the alternator at 12000RPM than at 18000RPM. The alternator is identically electrically loaded at both RPM's but it takes less crank horsepower if you're spinning it slower (it doesn't need to spin at 18k to produce 14V, I think most alts produce 14v around 2500RPM on a 2:1 speed ratio with the crank...).


I'll throw a spanner in the works here.

I'd agree that yes it may take a small fraction more power to maintain 18k over 12k, no load.

But the alternator will always be under load, so you cannot ignore that. So is it easier for the alternator to generate adequate power at low rpm or at high rpm ?

A bit like riding a bike. Is it easier to pedal in a high gear, or a low gear ? Turning it a higher rpm might actually require less effort overall than spinning it slower.

Anyone actually tested torque required to drive an alternator under load at various rpm's ?


Top
 Profile  
 
 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Mon May 07, 2012 4:36 pm 
Offline

Joined: Fri Jul 29, 2011 9:08 pm
Posts: 30
lumley32 wrote:
as i see it, if you take 300w from an engine then you loose 300w from output! volts, amps, BHP are all derived from watts! your hp on the dyno may well go up, but you will loose else where, toque for example!

i dont see how changing the speed of bearings can make them any more efficient.

but either way the alternators i use in or race bikes are about 120mm diameter and 30mm thick, how much power dose your car use?

I think some of the discussion is now contaminated by some cross talk...

I think there is a general consensus that everyone understands that when we generate electricity through an alternator that it takes HP to do that.

I don't believe any "pulley advocates" for lack of a better term believe that we are changing the electrical draw on the alternator... that makes no sense.

But imagine you had crappy high drag bearings in one alternator, and another of same electrical properties, but with expensive made from unobtainium bearings that had almost no rolling resistance. Which would you choose for a race car. (assume they cost the same, and have the same reliability for the sake of simplicity) Obviously the lower drag version.

As a pulley advocate, what I'm saying is, if we create "all things equal" in terms of reliability, why not turn the alternator less in the range where we want more power to the wheels. Less turns has to take less energy.

Steve,

Yes, it may be a bit harder to turn, but the analogy needs one more consideration, we don't need to turn it at the same speed. Ie its really hard to ride a bike at the same speed with the wrong gear, but slow down, and its not that hard....we're changing the resulting rpm and gear ratio...not just one.

A better way to look at it would be you're pedaling furiously, hardly getting anywhere....ie wrong gear ratio, wasted energy... but you gear down, and can pedal less at the same speed even, and waste less energy.

It is almost intrinsic to the idea of this pulley discussion that we are indeed turning the alternator much faster than we need to at the rpm we race. Remember, at idle these alternators can generate enough current to run AC/radio/electric fans blah blah blah.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 46 posts ]  Go to page Previous  1, 2, 3, 4, 5  Next

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Theme designed by stylerbb.net © 2008
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
All times are UTC - 5 hours