Mount alternator on top of back tire?

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

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!

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.

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?

*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.

Hi George - Of course you CAN try whatever you want. But you asked us "Whadyathink???" I think it's not going to be very efficient either, but that is not really a priority for you. One thing I would suggest is that you think about doing this on a trike or quad. I think you're going to have serious balance and braking issues with all the weight you are talking about. Then you could sit down low in a comfortable seat and carry lots of weight too (groceries, etc) There are lots of trikes and quads out there (both pedal and powered) for you to look at. Let us know how it all comes out. jd

If you ran a second (as in ,harbor freight Greayhound motor/to alternator)motor t power the alt.,???

Hi George – What some of us referred to in earlier posts as frictional losses are really the magnetic drag you mentioned in a previous post. There are friction losses of course but they pale in comparison to the magnetic drag the generating device (alternator) would cause. As long as you realize you need the gas motor (or pedaling) to get you up to the top of the hill or to coasting speed or to turn your alternator, you will be fine. My question now is – why bother with the alternator at all? A brushed motor will act as a generator if it is being spun and isn’t drawing power. There are controllers made that have a regen circuit so they can redirect that power into the battery. In a regular car, that’s what the voltage regulator does automatically – it senses the voltage in the battery and charges it if necessary. In a hybrid car, regen can be used to slow the car. The magnetic drag can be that strong. You will already have an electric motor attached to the bike, so why add the extra weight and complexity of an alternator? Just use the motor that will already be turning and available for generating electricity to keep your battery pack charged. If you have an adjustable regen circuit you have electric brakes as well.

There are a few things you can think about that might help you plan things. 750 watts equals about 1 hp. Volts times amps equals watts, but you can turn that around into watts divided by volts equals amps. A 750 watt motor at 36 volts will draw just below 21 amps at its rated wattage. I’m pretty sure a 20 ah (amp-hour) battery pack would run that for just under an hour. There are meters you can put on your bike (Watts Up, Cycle Analyst) that can tell you how much power you are using. I don’t have one but I have run my 350 watt ebike on a 24 volt 12 ah battery pack for 15 miles/90 minutes pedal-assisting all the way and had battery left. 350/24=14.6 amps, so obviously I wasn’t drawing full power. You should probably think about how fast and far you want to go on battery so you can figure how much epower you need. Then you can figure the motor and battery size. The weight of the rig will also figure into that.

Also, you could be thinking about a way to disconnect the gas engine from the driveline when you are on electric power. A freewheel sprocket will do that, but then you will have to figure a way to start the engine. Electric start would work but will add weight. A manual clutch would let you jump-start it but I don’t know if they make them. You could use belt drive with an idler pulley. Friction drive would seem to be perfect for that. Drop it down while you’re moving to start the engine and run on gas. Lift it up for electric. Also you could pull the hinge pin, disconnect the throttle and pull the whole unit off, leaving just the electric if you wanted. A brushed hub motor probably spins easily when not generating but would act as a brake when regen is activated, so that’s what I’d think about for electric power. I’d probably want both gas and electric powering the rear to avoid any possibility of an end-over or “fork-torque” issues. As I suggested before, I’d seriously consider a trike or quad. For stability, if I was thinking trike I’d go with 2 wheels up front and front steering. More complicated but much safer IMO. Rear drive would work but then you have the motor right behind the driver’s head, depending on how low the driver sits. Lots to think about… - jd

I think this is a great idea and look forward to see you get it done. I am 'estupid with math so I have to build some thing to find out what I don't know, I don't know. Ya know? lol

Just thinking and typing out loud here, but instead of st8 up friction, how about a MB sprocket/ rag joint on the front wheel and mounting the alt above? Easy mount options.

I can't find it, but have a thread (or mabie just a post) rack mount some thing like this, Building your own generator. then use a standard ebike kit

the word of the day is "entropy".

The reason why they changed over from GENERATORS to ALTERNATORS in the old days,is because alternators will charge at LOW rpms. ATTN;This is common knowledge.A car engine that is idling is NOT high r.p.m. If your alternator in your car is not charging while the engine is idling,then IT IS BROKEN!! the FAULTY DIODE inside the alt.must be removed and replaced with a new one.If the voltage regulator is faulty,then your battery goes dead, and your car does not start.

If the system could be set up to run only while your going downhill or even with a wind, possibly it would be feasable.