Why no alternator?

[AndrewTO]

So, being the newbie that I am (keep that in mind) i'm looking at all these pictures and seeing sooo many people re-charging their batteries. Okay, it makes perfect sense - use power from a storage device and you'll have to replenish it eventually.

(again, e-NEWBIE here) When I look under the hood of my car I see a battery. I don't do anything to it. Nothing at all. Maybe I wipe the top of it off every once-in-a-while to keep it looking all nice'n'purdy-like, but that's it. The alternator keeps charging it and that's that.

Alternators aren't on e-bikes normally because ..... ?

I can see things like (static) weight consuming more energy to propell the vehicle, same goes with rotational/rotating (call it whatever you want - we all know what I mean here). Personally, I HATE heavy things. In the bike world i'm a weight weenie. It represents reduced efficiency, IMHO, and that's simply sucks. (sorry, pun not intended!)

I can also see added cost, but just as with added weight, the end might justify the means. Spend "a few bucks" up front and sit back and wait for the returns ..... eventually.

Not enough - surely adding an alternator won't be enough to have the masses tossing their chargers (perish the thought!) as the rate of consumption would easily outweigh that of replenishment, BUT ..... i'd like to think this is one of those 'every bit helps' situations.

Ummm, that's all I got. (shrug)

Why aren't alternators being used?

 

[xyster]

Why aren't alternators being used?

In regen(eration) systems, the ebike motor acts as an alternator to recharge the batteries during braking about 5-10% more than without regen.
Separate, small alternators are also used to power bike lights. Save for these examples, alternators aren't used because:
think about how much assist you get with an electric motor. My ebike batteries store the equivalent energy of 5 Lance Armstrongs pedaling in unison for an hour as hard as they can. The motor/controller combo can dump this energy back to the pavement within an hour. So in order to get all that back, even at 100% efficiency, it'd take Lance Armstrong pedaling his butt off for many hours to recharge my bike batteries.

Gas stores more energy per kilo than even the best batteries now. Car engines produce more than enough power to move our multi-ton metal beasts at over 100mph, so siphoning off a little to keep continuously recharged a relatively small lead battery, whose only job it is to start the car and run the accessories, is no big deal. Now if that battery was responsible for locomotion too, the equation would change. Which is why hybrids employ small generators on braking to recharge the main battery just a little just like some ebike systems do.

In real world ebiking, regen systems end up being more pain than they're worth, because, in addition to the extra complexity, you also lose the ability to freewheel (coast). Regen makes more sense for cars because the moving mass is much greater, and so there's much more energy to recoup in stop-and-go type driving.

 

[TylerDurden]

Ja , what he said...


...or in other words: the energy it takes to lug the thing around is more than what you could get back.

8)

 

[fechter]

Well, that spiffy alternator is powered by a big gas-burning engine. Since alternators are not 100% efficient (car alternators are awful, around 70%), you need to put more energy into one than you get out of one. If you've ever noticed, that car battery doesn't stay charged when the engine is not running.

Having pedals that connect to the wheels by a chain can tranfer your body's energy with about 98% efficiency. This is much higher efficiency than any alternator. That's not to say a pedal powered alternator is out of the question, I've thought about a bike where the wheel is powered by a typical hub motor, but the pedals go directly to an alternator that charge the batteries. While this arrangement will be less than 70% efficient under typical conditions, it does have some advantages. You can input power though the pedals when the bike is going too fast for a normal chain setup, even going downhill or when stopped. It also eliminates the need for gears. It allows for flexible component mounting, a recumbent might benefit from such an arrangement.

 

[esr750]

alternators and generators do similar thing - generate electricity from a source of mechanical rotational force. Usually an engine, gas, diesel or steam turns the alternator/generator and you make electricity.

Alternators only produce AC electricity though so to use that electricity in a battery it must be rectified. Yep, your car has a rectifier too.

Your low maintenance car battery only supplies a large amount of current for a very short period of time. 5-10 seconds average engine cranking maybe? That's a much different thing compared to pulling large amounts of current from a battery for 30 minutes or longer.

EV motors will sometimes be configured to provide electrical generation from coasting downhill or pedaling. It's very tricky to manage properly and not burn a bunch of stuff up. So far those gains have been very small in actual vehicle service.

When generating electricy (AC or DC) - you put something in - you get something out - but the conversion is not without losses and eventually add-up to more trouble than it would be worth on board a lightweight vehicle. Not that it isn't good stuff to experiment with but it's best for lab excersizes and not practical for everyday use at this time.

Try to think of your legs as an alternator and every good pedal stroke you add to an e-bike journey is that much less electricty your batteries will need to supply. This principle will give you the best overall range with reduced need for charging from an external source.

 

[patrick_mahoney]

An alternator is a motor that has been designed and configured to generate electricity from "work" (a belt that is driven by the motor) - compared with the motors on an e-bike which generate "work" (moving the bicycle) from electricity.

It doesn't work to add another motor to act as an alternator into the system to recharge the battery while propelling the bike forward. The motor would get electricity from the battery which would turn the wheel, which would turn the alternator which would charge the battery. Which is a good idea, but this is a "perpetual motion machine" and they don't work. There's enough friction in the system and other inefficiencies that you would use more electricity to drive the motor than you get back from the alternator and eventually the battery will run out of energy. Since the alternator acts as a "load" on the system, the primary motor output won't translate into as much speed as you would get without this added load. And it turns out that if you calculate it out, you are better just to drive this motor at a lower wattage - by, for example, limiting the current - than to take off some of the power to drive an alternator.


That said, what a lot of people do implement on "e-bikes" is "regen" or regenerative braking. This uses power from the motor when it's not using electricity to load down the system such that it acts like a brake which charges the batteries. The problem with regen systems is that they are inherently more complex than non-regen systems and thus add cost and complexity to the system. There are some threads on DIY regen systems. One of the more familiar examples of a regen system is the braking system used on the Toyota Prius and other hybrids, but it has been used on some e-bikes... most notably the Tidalforce line of electric bicycles.


Edit: Wow. I take 15 minutes to reply to an answer and suddenly there are already 4 other answers. You guys are fast.

 

[xyster]

Edit: Wow. I take 15 minutes to reply to an answer and suddenly there are already 4 other answers. You guys are fast.

Boy, we were all over this topic -- workin' it like bees to honey, coming at the question from different angles, ending with impressive symmetry.

It takes you 15 minutes to write an answer like that, Mahoney? Gotta work on that! Snap to it, boy! Chop chop..... JK.

 

[AndrewTO]

(since Patrick mentioned it - i'm typing this after his reply :lol: )

Okay, i'm getting the idea here - not worth it.

Can't help but "read between the lines" (kinda) and notice that regen systems seem to be almost poo-poo'ed. :? Being the newB that I am I just kinda figured a regen system is the "latest and greatest" and should be a feature that I should seek in whatever route I take. Interesting food for thought! I'll be sure to consider it with my own version of a "hub or not" debate (yeah, kinda didn't know you could build a non-hub system untill about ..... oh, an HOUR AGO! ).


xyster - like the bike, really dig the scooter. Might you be able to share more info on the "Separate, small alternators are also used to power bike lights", please? Thanks.

Patrick - understood that you can't have the bike act as a perpetual motion machine - not looking for that, although interesting. If I didn't need sleep, though ..... :lol:

Thanks to all!

(oh, I already know one reply got in before mine :lol: )

 

[xyster]

xyster - like the bike, really dig the scooter. Might you be able to share more info on the "Separate, small alternators are also used to power bike lights", please? Thanks.

A good place to get an idea of what's available.
http://www.sheldonbrown.com/harris/lighting/generator-hubs.html

Bicycle generators are also commonly called "dynamos", so googling 'bicycle dynamo OR generator' should tell you lots more.

 

[patrick_mahoney]

Can't help but "read between the lines" (kinda) and notice that regen systems seem to be almost poo-poo'ed. Being the newB that I am I just kinda figured a regen system is the "latest and greatest" and should be a feature that I should seek in whatever route I take.

I don't know that I personally look down on regen systems. I think they are pretty neat. But they are more complex which translates to more expensive. Regen controllers for e-bicycles are also really, really hard to find. In fact, I'm not sure that I could even find a link to one that's on sale anywhere.

 

[xyster]

The bionx is advertised as having regen:
http://www.greenspeed.us/bionx_motor_bike_kit.htm

" GENERATION
Bionx offers four levels of power generation. Regenerative braking activates when the rear handbrake is used. It is possible to charge the Bionx battery pack by pedaling against motor resistance. Generation mode makes it harder to pedal so its often used when going downhill. Please note that the generative mode does not replace the existing brakes, but considerably increases braking quality, especially on extended downhill runs."

 

[patrick_mahoney]

The bionx is advertised as having regen

Ok. How about one that's just a controller by itself? For added challenge.

I spent a while searching and I found one, but the link had died.

 

[Lowell]

Increases braking quality? Perhaps that should read 'increases braking'. I have yet to see a bicycle regen system that was progressive, and for those of us with higher speed bikes, that's important. Braking down hills shouldn't be a problem anyways with modern disc brakes.

 

[xyster]

How about one that's just a controller by itself? For added challenge.

Riding just the controller would be a challenge! I suppose you could attach wheels to the bottom, connect the wheels to a little RC motor, then wear the batteries in a back pack

Uhmmm...I don't know of any separate bike-size BLDC motor controllers with regen. For regen on brushed motor systems there's options like the 4qd (which I tried on my scooter, but found the regen downright dangerous, and then it died and I returned it.)

http://www.4qd.co.uk/prod/index.html

 

[Nimbuzz]

Just to clarify, I use regen everyday on my Tidalforce M750X but I ride over a small mountain. On my 4 mile downhill runs the regen gives me very helpful "increased braking" and some noticeable recharge on the batteries. I don't really want to live without regen and don't ride my Crystalyte over the mountain for the lack of it.

This is an unusual case (over a mountain) and for most, on flatter terrain the regen benefits might be negligible. The system is more complex, millions of dollars went into R & D for the complete drive and regen system, making it too sophisticated for some home repairs. Mine works perfectly and I love it.

The Bionx system looks very interesting and the regen might have value in the hills too.

A Prius gets better mileage in the city than the hiway because the regen adds up in stoping a 3K lb car over and over again as do my downhill runs. It's still only a 10% recoup and gets much maligned. However it is the beginning of an emerging technology and the maligners might be much like those that attacked the first autos. You think auto pollution is bad -- think of the Rocky Mountain sized pile of horse manure we'd have if we'd stayed with them!!

Besides, I really like putting on my brakes and knowing that I am creating my own energy -- I'm not saving the world -- it's just plain fun!

 

[esr750]

Getting a motor to push current back into a battery isn't the hard part. The hard part is controlling it so that it doesn't cook the battery pack or fry other components if/when the battery is already full and the regenerative energy has no where else to go.

TidalForce produced a great system that does work (as long as the batteries survive) but unless you live in a mountainous area, it ain't gonna provide any real benefit.

As computing power increases we'll see more use of regen but also more of it's application problems. It's great to shoot for the stars but you gotta get over the mountains 1st - my advice, stay simple, learn fundamentals, practice what you learn. A practical design will always be a pleasure to ride/use compared to something that sounds great on paper but isn't much more than a lab test.

 

[Mathurin]

Regen controllers here. If you look under crystalyte kits, there's a part about controllers, and number 2 is regen type, FWIW.

 

[Jay]

Besides, I really like putting on my brakes and knowing that I am creating my own energy -- I'm not saving the world -- it's just plain fun!

Nice to read that I'm not the only one! I bought some relays & wired up a regen brake setup last year, knowing full well it was not worth the complexity, on a purely practical basis (I live in a flat area & hardly use brakes anyway). But I got a great energy-geek thrill out of pushing the button and feeding energy into my batteries.

I removed the regen circuit when I switched to NiMH's, out of worry that the cheap relays (or my crappy wiring job) would fail and short the batteries.

 

[tailwind]

Here is link to a streaming audio talk given by Max Mosley from Formula 1.
He talks about the introduction of regen braking in the F1 cars from 2009 onwards and how F1 can accelerate the development of this technology for use in hybrid vehicles.
The section to listen to is from 8:00 - 20:00.

mms://wmv0.cambridge-iptv.com/iws-iptv/mm_keynote_msport_business_forum.mp3