Mount alternator on top of back tire?

Whadyathink??? If you made a jig like they test alternators in the parts store on top of where a bike rack goes will it charge your batteries to run lights and extend the distance of your hub mount motor? The exact setup I am concocting (In my head) is 3 deep cell batteries and about a 2 gallon tank mounted on a trailer to end up with a hybrid bike. Alternators with a serpentine belt drive have pulleys about the same width as a bike tire. This would be much the same setup as the roller drive engines utilize now. I figure a mile has 5280 feet and a bike goes roughly 25 MPH so that's 25 X 5280 = 13200 feet per hour
13200 feet / 60 minutes = 2200 feet per minute
I am assuming most pullies are < 1' in circumference which means 2200 RPM

If I get 100 MPG and I bought quality deep cell batteries I would venture to say between 3-400 mile range might be possible.

I have seen claims of a penny a mile on electric consumption anyone have real figure on that?

Gas even at $4 a gallon equals to about 4 cents a mile at 100 MPG.

kidcrash, Addicted To Bikes and me were playing with this idea in the chat lounge...was fun guys!

The added drag would reduce the efficiency of the setup - to what extent I'm not sure. While yer not proposing the fabled "perpetual motion" machine, your numbers may not be as beneficial as they seem on paper.

However - having a true hybrid, both gas AND electric and using the gas motor to help recharge the electric is an awesome idea! Instead of an alternator set up as friction-driven... I wonder about the belt drive rim set-up the Wizzers use?

I built one with a 33cc 2stroke friction drive and a 'Zap' electric drive, the Zap would act as a (somewhat weak) generator when it was engaged but not powered. As I didn't use the electric much unless I was downtown - the batteries always remained topped off and ready to use. I have no idea if the hub motors generate when spun, some motors do - some don't... It's sometimes referred to as "regenerative braking" with electric vehicles. I don't remember the difference... brushed/brushless mebbe? *shrug* ahh... I forget lol

The only problems I had with that setup was the usual woes of rack mount friction drives. Although - if you were to pursue your idea, I'd recommend a much smaller unit than your standard automotive alternator. There are tiny lil ones sometimes found on motorcycles (I believe the Honda Goldwing may be one), even some of the friction generators found for bike lighting are 12v and would help trickle charge during daytime use. Of course you would need a regulator if you weren't using an alternator - which usually have them built in.

Despite many stories to the contrary, it's actually quite difficult to spin an alternator fast enough to generate a charge. The "I wanna make a wind generator" is a common example of the problems involved with drag/RPM. If yer determined, there are many small DC engines that work quite well as generators and are smaller/lighter... but I haven't looked into those myself.


Don't mind me... I'm jus babbling a bit and musing lol

Hi George - The idea of using forward motion to turn any type of generating device needs to be tempered by the realization that the amount of power used (or generated) will come off the top of your power source (as drag, as BarelyAwake noted) It won't matter whether you turn the generator/alternator by the wheel or directly from the power source. If you're drawing a little current, like to run efficient LED lights, it won't create much drag. But if you are trying to charge 36 volts of discharged deep cycle 20ah SLA in a short time, the drag will be enormous. The concept of "regenerative braking" demonstrates this - a Prius can be stopped in a short distance just using regen. The power gets dumped into the batteries, but it is effectively drag on the wheels and that's what slows it so quickly. "They" say 750 watts is one hp so for every 750 watts you are generating, yer little China girl is going to have 1 less hp to push you along. Lack of efficiency will push that in the wrong direction even farther. If you were pedaling, it would feel like one of those slow-motion bad dreams.

As long as you are going with gas you should probably go with the minimal amount of generator and battery that you would need, and it might be best if the electric motor you use could double as your generator. Just a few thoughts - jd

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In theory there is no difference between theory and practice. But in practice, there is - Yogi Berra

George,
I've thought about close to the same rig, but just to charge my lighting battery for my china bike. haven't found one that was small enough, self contained, and CHEAP enough on my meegger paycheck!

Well it's still in the planning stage but check this hybrid setup out:

Motorized Bicycles Detail Page

George, you have to consider the fact that a car alternator works great in a car because it has a powerful gasoline engine turning it at thousands of RPMs and it's mainly keeping the battery charged to run the car's accessories and to occasionally turn the starter for a couple of seconds. An alternator has to be turning at X number of RPMs and requires a certain amount of amps before it can even start charging. It's not likely your bike could even achieve that minimum RPMs. As jcdburg said, the drag would be enormous. You wouldn't gain anything and would lose a lot. Plus, you'd be chugging around that heavy trailer? People are dreaming up these schemes continuously and some even propose the usual propeller on the handlebars and all that kind of stuff. The bottom line is, none of this stuff is remotely close to being worth the trouble on a bike and the only hope there is for ebikes is the miracle, 5 minute charging, 100+ mile range batteries that are always "just around the corner". The primitive SLA battery will just have to do till then or just use a gas engine. That Staton setup is nifty, but you're still better off and much more efficient overall by just using a gas engine as the bike's power source in the first place. Hybrid cars and hybrid bikes are two different animals but I realize a lot of people just want to be able to say they have a hybrid bike even though it's the epitomy of innefficency.

o.O

starrunner - while it's true a car's alternator may be too much for a project like this, hybrid (tribrid lol) bikes like what is proposed here aren't unheard of - or even " the epitome of inefficiency". Even I have built one.

They may be a touch on the heavy side, but if you read my first post in this thread or even dig around on this forum you'll find variants on the theme that are rideable and valid. The only other major setback for these is price.

george n texas wasn't proposing the tiresome perpetual motion scheme, and while it was armchair engineering and the math may be off - the concept has potential, if perhaps with different components.

Without people pursuing what others naysay - none of us would have motorized bikes of any type.

I talked to an engineer at work about something like this and he shot it down because of the drag on the motor and that using an alternator would make it a perpetual motion machine of sorts. Plus you gotta consider the amount of RPMS that the alternator spins at just to put out the volts and amps to run a car. Would a 26" bicycle wheel do the same even if you are expecting less output?

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*sigh*

Yes - perpetual motion is a waste of time to consider, yes a car alternator is too big/excessive drag, yes the RPMs are out of reasonable range.

No - all the ideas presented here aren't unreasonable, please (re)read the previous posts.

I still don't know what's not gonna work about this whole idea. Here's the thing I KNOW from being a trucker...when you are fully loaded 80K pounds if you can let the darn thing fly downhill staying off the brakes you get very close to the same fuel miliage as when empty...a lot of the drag comes from wind resistance and stopping an starting. The main advantage to my design is to give you more torq for starting and stopping as well as the ability to stealthily go thru towns unfriendly to gas engines on these things. I don't care if the contraption weighs 1000 pounds you could even compensate for that in electric trailer brakes and placing the electric motor as well as about as large a fuel tank and pump on the push trailer. In addition to the advantage of being able to start without peddling you also have the advantage of a power unit that could hook up to most any bike in a flash. (ever see anyone run outa gas?)

I understand one fact I did not know before which is relevant, the fact that the magnetic effects of an alternator creating amperage and voltage creates drag much as two like poles of a magnet repel against one another. Here's some fodder for you cows to chew on...the bullet train rides on top of such a field, harness that and you will have done something for sure!
Not a bird or plane, just Shanghai's new Maglev, the world's fastest train

"it's the epitomy of innefficency." starrunner

Don't hate me cause I'm beautiful LOL