Brammo Owners Forum
General => Off Topic => Topic started by: Mithion on May 30, 2012, 10:35:13 AM
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If you hooked up an alternator to the output shaft of an electric motor would it work as a generator to at least recharge a battery a little bit? I was reading that the alternators on big trucks and buses can produce up to 300amps.
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I expect protomech will be able to expand on this, but basically it sounds like you're looking at a regenerative braking system that would be separate from the motor itself. I think the drag that something like that would place on the motor would be counter-productive to the amount of energy produced.
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I see what your saying, maybe instead of a direct connection to the output shaft there could be an alternator connected freely to the wheel where the motion from the spinning wheel rotates the alternator. This way the electric motors are propelling the vehicle and that very rotating motion they create is spinning the alternator which is creating the recharge to the battery.
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Brammofan is right. The first law of thermodynamics says that this would not work:
http://en.wikipedia.org/wiki/First_law_of_thermodynamics (http://en.wikipedia.org/wiki/First_law_of_thermodynamics)
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Makes sense, but what if the system were externally cooled somehow to reduce the created heat?
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In this case you are trying to harness kinetic energy, which would in turn slow down the bike, and on top of that a percentage of that returned energy would be lost as heat (battery charge and motor waste heat)... so you have diminishing returns at both ends, loss of kinetic energy and waste heat. Now if there was a way to harness that waste heat, then you may have something. Regenerative breaking works because you WANT to remove kinetic energy to slow down, even if it is not 100% efficient its better than just losing all that kinetic energy to brake friction which produces more waste heat.
A 100% efficient motor would produce 100% kenetic energy and no heat...
Now that I think of it, both the Zero and Empulse have simulated engine breaking... so, they already do this, even though its wasteful. Protmech or BrammoBrian can probably explain this much better.
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Well...lol... Guess I won't be the guy to figure out perpetual motion!!! :0)
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Certainly an alternator could recharge the battery by converting kinetic energy back to electrical energy. In fact, both on the 2012 Zero bikes and the Empulse the main traction motor can do this by acting as an alternator. No need for the weight and complexity of a secondary alternator.
However, you will always, always get less energy out of the system than you put in, once you account for all inputs. For example, if you start at the top of a tall mountain you can recharge the battery somewhat through regen braking. At the bottom you'll likely have more charge than you started with ... so what happened? You lost the potential energy from having the bike at the top of the mountain ... and in practice you'll regain roughly 25% or so back into the battery pack .. so you can perhaps ride 4 miles down, then use that regained charge to ride 1 mile back up.
So where does the rest (roughly 75%) of the potential energy you started with go? It's lost as resistive heat through the motor, both in regen and power modes; heat in tires as they grip the road; heat in the forks and shocks; friction heat in the wheel ball bearings; sound; drag and turbulence through the air; the headlight and other onboard electronics; etc.
Similarly, you can slowly accelerate from a stop to say 25 mph, then slowly regen brake your way back to 0 mph. You won't regain > 100% of the energy used in acceleration, or even close to 100%; over a short distance (immediately braking once you hit 25 mph) you might see 50% regeneration.
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Ok, so basically when it's all said and done- the energy required to run the alternator included in the system is more than the energy the alternator would produce anyway so this not worth it.
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Just to toss in a little motorcycle history into the discussion, my first "full size" motorcycle was a 1963 Yamaha YD3 touring bike (complete with accessory legshields and 16" whitewall tires). It used a "dynamo" installed on the end of its crankshaft (the clutch was on the other end) that first acted as an electric starter when you pushed the starter button and when the engine started running, it reverted to a electric dynamo and generated electricity to recharge the battery and operate the ignition and lights.
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Kind like the hub dynamos used on bicycles
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The older Honda Goldwings operated in a .. somewhat similar fashion. Separate starter motor and stator to operate the electrical system. Have to pull the gas engine (http://www.goldwingfacts.com/1200statorreplacement.htm) to change the stator.. seems most people report the change interval is about 20k miles (stator gets caked up with oil, not sure what Honda was thinking there). Rather labor intensive.
Friend bought a 1984 aspencade, he's replacing the stator system with an external alternator (http://donaldantiquerototillers.com/Alternator.html). Seems like a lot of work, but oh man those bikes have a bunch of electrical gadgets on them.. even the old 1980s bikes.
@Mithion exactly like that.
And to bring it somewhat full circle.. you can basically use a beefed up motor to drive the rear wheel in the same way to turn a bike into an ebike.
http://www.electricbike.com/friction-drive/ (http://www.electricbike.com/friction-drive/)
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So would hub dynamos have any benefit on an electric motorcycle or are not even worth the power they would generate? I was picturing using Hun dynamos to power the lighting system so the batteries can be fully used to power the motor and ecu only
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No. The batteries would still be powering the lights indirectly. Think about it this way: if the bike doesn't move, the dynamo doesn't turn. How does a pedal bike move? The human turns the pedals. How does an electric bike move? The battery turns a motor. Therefore the human (or battery) is indirectly powering the dynamo..
You can do this two ways:
Battery => DC/DC converter => 12V lighting system
Battery => motor controller => motor => dynamo => 12V lighting system
DC/DC converter is probably 90-95% efficient.
Motor controller is probably 97+% efficient.
Motor is 85-90% efficient typically.
Dynamo (kinetic energy to electric energy) is probably 60-70% efficient (http://en.wikipedia.org/wiki/Hub_dynamo) at low speeds, and gets much worse at high speeds unless you could build in some type of variable resistance.
Worst case vs best case, 90% vs 97% * 90% * 70% = 61%.
There's some debate about dynamo lights vs battery-operated lights in the pedal bike community as well.. though this may be done with the introduction of affordable LED headlamps. You could even have a hybrid battery/dynamo (or capacitor/dynamo (http://www.myra-simon.com/bike/dynamos.html)) setup, as in a ICE motorcycle or car .. which would give some of the advantages of both along with increased weight.
http://nordicgroup.us/s78/experts.html (http://nordicgroup.us/s78/experts.html)
Here's a review of various hub dynos for a pedal bike, take a look at the power requirements (page 3) to operate a 3W (nominal) headlight:
http://www.bikequarterly.com/VBQgenerator.pdf (http://www.bikequarterly.com/VBQgenerator.pdf)
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All makes sense. So from what know/read/etc, what's does the industry seem to be looking into in terms of research for that seemingly unobtaibable perpetual motion machine? That electric system that powers and recharges itself from its own operation etc...
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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 (http://www1.eere.energy.gov/vehiclesandfuels/pdfs/thermoelectrics_app_2011/monday/eder.pdf)
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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 (http://brammoforum.com/index.php?topic=656.0)
Some reading on perpetual motion machines:
http://www.howtopowertheworld.com/over-unity.shtml (http://www.howtopowertheworld.com/over-unity.shtml)
http://goaskgrandpa.com/sample09.htm (http://goaskgrandpa.com/sample09.htm)
Some types of things are very long life motion (http://en.wikipedia.org/wiki/Perpetual_motion#Low_friction) (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.
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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!
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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/Ion_thruster)
http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29 (http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29)
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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...
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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...
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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.
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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. :)
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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!
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A brewery? Now were talkin' regen!
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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
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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. ;)
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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).