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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Thu May 03, 2012 10:53 pm 
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lumley32 wrote:
there is "no" drag on an alternator! (apart from bearings)


The drag from the bearings is real.
I choose to minimize it.

I completely understand that the draw on the alternator is primarily due to the load.

Maybe you are swayed by your famous loom builder, maybe I'm swayed by photos of race motors with huge alternator pulleys. Neither is a valid proof.

I am not suggesting that putting on pulleys alone will be a huge difference, but every little thing adds up.


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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Fri May 04, 2012 2:59 am 
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Wasnt there some little gadget years ago that shut off the alternator from charging at a certain rpm ? Sort of fell into the same league as electric superchargers, magnets in the fuel tank etc

I guess you're also using cogged pulleys/belt and not ribbed setup ? A clutch pullied alternator too ?


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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Fri May 04, 2012 3:44 am 
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ignitionautosport wrote:
And yes, quite right about the parasitic loss though charging - if you want to see, give an alternator full field and see if you can turn the pulley by hand. Feels rock solid.


Ahh, thank you! The penny drops. I've always struggled with the concept of alternators being hard to turn when they are making current, because they free-wheel easily by hand. I guess it's like a motor in reverse?

This would explain why engines slow down at idle when you switch on all the electrical accessories. A good example of parasitic loss :D

On parasitic losses in general, is there much gain in knife edged cranks, windage trays etc etc?

Out of interest, when OEMs dyno their engines, do they measure the power in full road trim, or do they just strap it to the bench tester with no alternator or pumps etc? I've seen pictures and videos of bench testing and some of them have no accessories and the intake and exhausts are obviously radically different to what the engine will see in the car.


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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Fri May 04, 2012 9:06 am 
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stevieturbo wrote:
Wasnt there some little gadget years ago that shut off the alternator from charging at a certain rpm ?

I guess you're also using cogged pulleys/belt and not ribbed setup ? A clutch pullied alternator too ?


Not sure about "gadgets"

The pulley naysayers are helpfully reminding, or perhaps educating those unaware, that the drag increases as the electrical load goes up. This is pretty obvious, and even if you are poking fun Steve, you know it as well.

So, in serious answer to your comments, yes, in fact, as alluded above, many race teams turnoff the alternator at WOT. Interestingly enough, the factory Siemens ECU does this for a bone stock BMW E46 M3 too eek out every last bit at full throttle.

Clutch on alternator is an interesting idea, but the weight and possibility of failure seem to favor a simple pulley on a critical component. I'd rather go the next step beyond WOT switch, and implement a path to only turn on the alternator at a specific voltage.

My neighbor used to be a sponsored motorcycle racer, he did in fact run short races with a total loss system, no alternator at all, just enough battery to last.

I like your thinking on cogged pulley system having less drag. I believe that is the case. On a simple pulley system with just one driven slave pulley, it would be easy to swing that accessory on a bar tensioner, deleting the original hydraulic tensioner from the original (presumed serpentine) belt layout.

On my car's current configuration, I could do just that, I have EPS, EWP, and my aftermarket lightweight alternator is already on a swivel mount, (which allowed deletion of the hydraulic tensioner weight wise, and failure wise)..... So it would be a simple matter of new pulleys......hmmm I like!

Many people have not considered EPS and EWP, so using cogged belts might be challenging, I don't know much about how that sort of conversion would look/work/package. Photos anyone of cogged belts exclusively used with 3 accessories? Sound a mess Steve. Perhaps you were joking, not really trying to help.

Edit: since posting this and looking around I believe it would actually be an easy conversion even with a couple accessories....I like!


Last edited by DTAS54 on Sat May 05, 2012 12:41 am, edited 1 time in total.

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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Fri May 04, 2012 10:31 am 
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VR6Turbo wrote:
This would explain why engines slow down at idle when you switch on all the electrical accessories. A good example of parasitic loss :D

In the case of a race car, getting rid of the loss due to turning on accessories should be what I consider low hanging fruit. Most serious track car owners would remove AC, get rid of radios, redundant wiring and modules for electric seats/windows whatever, and not just for weight savings, but also to reduce all electric draw.

Any electrics drawing current (in my mind) would be items of necessity, and I wouldn't actually consider them "parasitic" in our context.

If it helps the car go faster, it is necessary, not (in my mind) parasitic. The parasitic losses, in my mind again, are losses that might be avoidable, and hopefully can be minimized without loss of reliability, or in the best of all worlds, costing too much.

In this context over-driving a water pump is wasted energy, and turning a hydraulic PS pump when driving in a straight line is wasted energy too.... so these two items are ripe for revision on a track car.
VR6Turbo wrote:
On parasitic losses in general, is there much gain in knife edged cranks, windage trays etc etc?

I do not consider myself expert on all things related to crank design, but some of what goes into a crank is meant for harmonics, smoothness of operation, some of the weight is helpful in the sense of a gyroscope and momentum to preserve longevity etc etc etc... I'm speaking loosely, and not with complete authority.

I've seen examples of race engine builders preaching both sides of the crank lightening arguements, and I think its a very complex subject. Some say you shorten the life of the engine dramatically if you take off too much, but in the interim get many of the benefits of a light flywheel, others disagree and say its a matter of extent, and that you can safely remove quite a bit of weight without compromise blah blah blah. It would be about as useful I think to debate this broadly without reference to a specific engine and crank as debating belt vs direct drive turntables in the audio world. IE... do it right and you're probably OK, do it poorly, and its best not done.
VR6Turbo wrote:
Out of interest, when OEMs dyno their engines, do they measure the power in full road trim, or do they just strap it to the bench tester with no alternator or pumps etc?

I'm not sure there are any standards. Similarly when a manufacturer posts a weight for an engine, it is not easy to determine if its got oil on board, ancillaries on board, air box, air filter, harness, DME, oil cooler etc etc etc... makes comparing numbers across generations or different competition difficult.


Last edited by DTAS54 on Fri May 04, 2012 2:48 pm, edited 2 times in total.

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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Fri May 04, 2012 11:46 am 
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By clutched alternator pulley, I mean the modern ones where it's a sprag/ratchet/whatever you want to call it where it applies drive only in one direction.

Like a bicycle crank is best description. Not sure if it would offer any benefit.

And the fact you are almost dismissing the cog drive means you really havent researched it that much. Cog drives are common place to reduce drive loads. The belts are more efficient, and require almost no tension.
Tension which would sap power, and also apply loadings to the bearings etc on anything that is driven by the belt..

On a more humorous note...what about removing the alternator altogether and covering the roof/car with solar panels of similar weight ? lol

or less humorous, have an electronically controlled alternator that only charges below a certain throttle opening, below say 4000rpm, and on the overun.

Would that be best of both worlds for a track car, as there will be a fair amount of track time seeing those conditions, so you would still get a fair amount of charging


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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Fri May 04, 2012 2:45 pm 
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stevieturbo wrote:
By clutched alternator pulley, I mean the modern ones where it's a sprag/ratchet/whatever you want to call it where it applies drive only in one direction. Like a bicycle crank is best description. Not sure if it would offer any benefit.

Well then: Thanks for suggesting something you're not sure would be beneficial. Maybe someone does know the answer.
stevieturbo wrote:
And the fact you are almost dismissing the cog drive means you really havent researched it that much. Cog drives are common place to reduce drive loads. The belts are more efficient, and require almost no tension.
Tension which would sap power, and also apply loadings to the bearings etc on anything that is driven by the belt..

Did you read my post? There is no "fact" that I almost dismissed the cog drive Steve. If you read my post, there is nothing dismissive in there about cogged belts. Heck, I LIKE the idea and said so. Don't know how to have made that more clear up above.....

From above, I conclude that you too are in the camp that acknowledges that the typical serpentine belt driven systems we're talking about have real parasitic loads from tension and loads on the bearings, and that it is real enough to consider switching to something less parasitic. Quickest and easiest is my first choice, pulley size changes. I do like the idea of an HTD set up though.

I appreciate your support for the idea that there is parasitic loss inherent in the common stock automotive crank pulley/serpentine belt system going to the alternator. I take it that you are now a convert and understand why reducing this loss would be desirable on a dedicated track car?
stevieturbo wrote:
or .... have an electronically controlled alternator that only charges below a certain throttle opening, below say 4000rpm, and on the overun.

I agree obviously, I turn off the alternator at WOT. I don't think using 4000 is any improvement over what I do. Seems I would get more charging, less risk of running low if I have the alternator on at all rpm short of WOT. Am I missing something?

WRT cogged belt drive:

I actually know a bit about the cogged gears, but don't claim to be expert on them. I learned a while ago about the HTD being lower resistance than the older Gilmer etc...

In fact I designed and built a one-off drysump for one of my race engines that had just one simple HTD belt from crank to drysump. I had EPS, EWP, as well as the alternator driven off the driveshaft (prop shaft for Brits) at lower rpm, with weight transferred to the rear of the car etc.....The version before the drysump spooked people because it was apparently beltless....unless one looked in the back seat!

I was always tempted to make a silly show of pulling a couple used belts out from under the hood, closing and pinning the hood, throwing the belts to the side and saying loud enough for people to hear.... "Hell, I don't need any belts, screw those, just wasting power" and get in and drive away....

Thanks for the real suggestions, the tongue in cheek ones are amusing, and maybe someone can chime in on modern clutch bits


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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Fri May 04, 2012 5:24 pm 
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Quote:
By clutched alternator pulley, I mean the modern ones where it's a sprag/ratchet/whatever you want to call it where it applies drive only in one direction. Like a bicycle crank is best description. Not sure if it would offer any benefit.

OEM use them to reduce harmonics/vibration. for some you can get solid pulleys as replacements, but then the brackets and such break from the vibration and alternator falls off...
In a race engine situation I am not sure if there would be any advantage - also I have only seen them in normal size multi-rib micro-v, not that it is difficult to modify with the right gear.

My thinking (only a theory) is that the alternator load would hold it hard against the one-way pulley the majority of the time so any gain would be in longevity of mounting and internals not getting such a hard time perhaps from harmonics. It's not something I've looked into, have just replaced a couple on cars recently as they crap out and either lock up or free-wheel. I think for any gain, it may not be worth it from a reliability point of view - however that is subjective depending how much you value any potential gain as discussed...

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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Fri May 04, 2012 6:13 pm 
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I'm certainly not a convert. It's obvious various things have drive loads, friction, whatever.

But as I clearly said at the very start, is it worth sacrificing reliability for these barely measurable gains ?
Not a chance. I certainly wouldnt want a system that had massive voltage fluctuations, nor would any professional race team.

If anything, switching the belt drive to cogs would be a more sensible move than underdriving the alternator to an extent it no longer charges properly whilst retaining the ribbed belt.

Saving weight and reducing drive loads is all good and well. But when it has massive compromises and complications elsewhere, it isnt worth it. Unless you really are at the last extremes of all engine tuning and chassis tuning and stuck behind strict rules in whatever race series you race in.


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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Fri May 04, 2012 6:33 pm 
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In a racecar under-driving your alternator (or waterpump for that matter) means that at normal (racing) operating conditions it will be more reliable. Very different to a street car's requirements, as you know. There is a balance of course between gains and reliability.
I also sway on the side of reliability, however others may not care as much about that and instead prefer the gains they may get.

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