Author Topic: Another Knowledge Question  (Read 2516 times)

protomech

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Re: Another Knowledge Question
« Reply #15 on: May 31, 2012, 08:28:26 AM »
Many systems are available which partially power themselves through their own operation. These are not perpetual motion machines, because (per the 2nd law of thermodynamics) any energy conversion step produces entropy (heat). They do increase overall efficiency by recovering and making available for reuse energy that would otherwise be wasted.

Hybrid / electric vehicles with regenerative braking are a good example. The motor converts stored electric energy into kinetic energy (motion), and then operates as a generator to convert kinetic energy back into stored electric energy under braking. The electric => kinetic => electric conversion process is typically 50-60% efficient at best .. you always lose energy to heat.

BMW is working on waste heat recovery systems which could provide a small efficiency boost to their cars.
http://www1.eere.energy.gov/vehiclesandfuels/pdfs/thermoelectrics_app_2011/monday/eder.pdf

***

Here's the last discussion we had on energy conversion fun (in this case, using the battery to generate hydrogen from water and using a fuel cell or turbine to power the bike):
http://brammoforum.com/index.php?topic=656.0

Some reading on perpetual motion machines:
http://www.howtopowertheworld.com/over-unity.shtml
http://goaskgrandpa.com/sample09.htm

Some types of things are very long life motion (earth's orbit around the sun, for example). Some types of things are theoretically perpetual motion .. eg current flow in a superconductor. Until we find a room temperature super conductor though.. they require significant energy to bring down to their critical temperature.

Perpetual motion machines are fun to read about. They're a fantastic example of "extraordinary claims require extraordinary proof" .. they're either deliberate deception (peddled by the new generation of snake oil salesmen) or suffer from a genuine misunderstanding or calculation error regarding energy.
« Last Edit: May 31, 2012, 08:41:13 AM by protomech »
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Mithion

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Re: Another Knowledge Question
« Reply #16 on: May 31, 2012, 08:51:58 AM »
It's funny, you spend years around ICE cars and bikes, go to school to learn all about them, and then you get pulled into this advancing technology that has been around for years but is really just starting to be payed attention to. Something about the clean efficiency of electric power trains mesmerizes me while I still love ICE they always seemed like we just stuck with what was just good enough for the moment and it became the norm and we never went back to seeing if there was a better way, until now.

Is it me or does using electromagnetic forces to create rotation and traction make so much more sense than a series of little explosions to produce a reciprocating motion?

Now I gotta learn all this new stuff to keep my own thirst for knowledge full lol!

protomech

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Re: Another Knowledge Question
« Reply #17 on: May 31, 2012, 08:57:57 AM »
Yes, hook up your brain to the firehose of knowledge : )

Here's a good analogy for spacecraft propulsion:
http://en.wikipedia.org/wiki/Ion_thruster
http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29
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Mithion

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Re: Another Knowledge Question
« Reply #18 on: May 31, 2012, 09:26:16 AM »
Another somewhat related question-

What is the storage to weight ratio for most of the EV batteries being used today?

This many kWh capacity battery on average weighs this much...

Shinysideup

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Re: Another Knowledge Question
« Reply #19 on: May 31, 2012, 08:37:27 PM »
Is it me or does using electromagnetic forces to create rotation and traction make so much more sense than a series of little explosions to produce a reciprocating motion?

It's not just you. I test wrote an electric bike (2012 Zero) a couple of weeks ago. Gave it a pretty good run onto the freeway and around a curvy course. Had it out for probably a half hour. Then I got back on my usual ride (TMax) which has a counterbalanced 500cc parallel twin that's very quiet and relatively smooth.

My first thought back on my bike was, "How primitive!" As in, what's all that commotion and vibration and buzzing, and rattling doing down there around my feet? Similar to the first time I heard a dot-matrix printer after first experiencing a Laserjet. Primitive. Soooo 20th century!

So on so many levels, not just sensory, having a motor turn because of magnetic attraction is much nicer than an engine that's trying to reciprocate itself apart. Simplicity vs. complexity. Maintenance issues. etc, etc.

You also asked why manufacturers seem to be pursuing perpetual motion.  A big part of it (other than maintaining the customary feel of engine braking) is that the public is mesmerized with regenerative braking. It's got marketing sizzle.

Not so much steak, however.

I built an electric bike and, apart from "How fast will it go?" The second question usually concerned regenerative braking. On a bicycle, there is such relatively low mass, that the gains are miniscule and it's far more efficient to allow the vehicle to coast freely to recapture energy.

Now on a trolley car or electric bus, especially on San Francisco hills, you've got some serious mass and can recapture some serious electrons. In short, regen sells products, just like carbon fiber bits on non-race bikes. But that's another subject...

Mithion

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Re: Another Knowledge Question
« Reply #20 on: May 31, 2012, 08:43:14 PM »
I always wondered that to, why regen braking when all I read about it is that it's very inefficient right now, it always seemed to be that simply coasting and allowing the motor to act as a generator made so much more sense. I don't know how much or less energy is gained when it comes to regen braking vs regen coasting, but it seems that for regen braking your creating heat when it's not needed where you could even combine it and regen coasting and when you obviously have to stop at some point have regen braking also.
« Last Edit: May 31, 2012, 08:46:14 PM by Mithion »

Richard230

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Re: Another Knowledge Question
« Reply #21 on: June 01, 2012, 09:25:15 AM »
My sepex GPR-S had its regen set at 100% and over a typical up-and-down-my-local-hills ride, it would put between 2 and 3% of the power used back into the battery pack, according to my power meter. So you don't get much power back from regen, but it does save a lot of brake pad use - keeping brake pad pollutants out of the environment.    :)
current bikes: 2018 16.6 kWh Zero S, 2011 Royal Enfield Bullet 500 Classic, 2009 BMW F650GS, 2007 BMW R1200R, 2005 Triumph T-100 Bonneville, 2002 Yamaha FZ1 and a 1978 Honda Kick 'N Go Senior.

860

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Re: Another Knowledge Question
« Reply #22 on: June 01, 2012, 01:31:31 PM »
My first thought back on my bike was, "How primitive!" As in, what's all that commotion and vibration and buzzing, and rattling doing down there around my feet? Similar to the first time I heard a dot-matrix printer after first experiencing a Laserjet. Primitive. Soooo 20th century!

I have an SV650, and a decent section of slightly downhill road I ride every day.  I totally know what you are talking about, because I've been simulating what it would be like to ride an EV bike by pulling in the clutch and letting it coast downhill on this section with the engine idling.  It is smooth and quiet and feels great!  Then I get to the bottom and have to rev the engine back up to 5-6K rpm and all the vibration and noise seems so archaic. 


Now on a trolley car or electric bus, especially on San Francisco hills, you've got some serious mass and can recapture some serious electrons.

In real life here in Colorado, regen will be nice for typical canyon carving sessions in the foothills.  Denver is built right next to the mountains, and fun runs typically go uphill a few thousand feet in altitude, and then right back down.  I'm expecting regen braking to have a real practical return in this situation. 

I keep saying that the Brammo Empulse seems to be purpose built exactly for folks living along Colorado's front range.  We can take advantage of the regen, we get a nice tax incentive, we get the EV advantage of no power lost to altitude, and there is even a brewery with a high-speed charging station to charge at! 

Shinysideup

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Re: Another Knowledge Question
« Reply #23 on: June 01, 2012, 04:34:20 PM »
A brewery? Now were talkin' regen!

Car Loss

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Re: Another Knowledge Question
« Reply #24 on: June 01, 2012, 06:52:40 PM »
So you don't get much power back from regen, but it does save a lot of brake pad use

Bingo.  It took a generation or two, but the Prius now has enough regen that a reasonable driver might never change the pads over a reasonable ownership length.  Of course, if you're a rager in Manhattan, then you might need to change pads once. 

Regenerative braking isn't meant to be a silver bullet, and certainly not in every vehicle.  Sometimes, you want a few percent here, two percent there, and the numbers work out. 

Carlos

Richard230

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Re: Another Knowledge Question
« Reply #25 on: June 01, 2012, 07:34:45 PM »
I rode my Zero up a back-road hill today. The fuel gauge lost a bar on the way up and gained it back on the way down. That was the first time I had ever seen that happen.  Of course, a few miles later, I lost the bar again.   ;)
current bikes: 2018 16.6 kWh Zero S, 2011 Royal Enfield Bullet 500 Classic, 2009 BMW F650GS, 2007 BMW R1200R, 2005 Triumph T-100 Bonneville, 2002 Yamaha FZ1 and a 1978 Honda Kick 'N Go Senior.

protomech

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Re: Another Knowledge Question
« Reply #26 on: June 04, 2012, 01:40:42 AM »
Another somewhat related question-

What is the storage to weight ratio for most of the EV batteries being used today?

This many kWh capacity battery on average weighs this much...

2012 Tesla Model S uses Panasonic 18650 cells, 250+ Wh/kg.
2012 Zero bikes are use EIG pouch cells, 175 Wh/kg.
Empulse / Enertia Plus use unknown brand pouch cells, "highest specific energy pack of any EV manufacturerer"
Nissan Leaf uses pouch cells, don't recall manufacturer, 140-160 Wh/kg (have seen different numbers).
1999 Honda VFR800i | 2014 Zero SR
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http://protomech.wordpress.com/