Alternators and Electric bicycle

[Innovate!]

Can I connect an 12V alternator to my Electric cycle's rear wheel to recharge my battery simultaneously?

I mean to recharge simultaneously while my bike is driven by a DC motor. The alternator would be connected to the other side of the rear wheel.

The Electric bicycle runs on 250W motor/12V Lead acid battery system. Is it possible? Need experts' help!

[ewmon]

Alternators transform physical power into electrical power. So, the battery would need to provide more power to run the bike *and* the alternator, then there would be losses in the alternator, cables, charging circuit and battery. But, yes, the power that is not lost through these losses would recharge the battery. All you'd effectively be doing is losing power through all the losses just mentioned. Plus, you'd be adding weight to your bike, which would also require more power to move it, spending money on the alternator, wasting your time, etc.

[InigoMontoya]

Can I connect an 12V alternator to my Electric cycle's rear wheel to recharge my battery simultaneously?

I mean to recharge simultaneously while my bike is driven by a DC motor. The alternator would be connected to the other side of the rear wheel.

The Electric bicycle runs on 250W motor/12V Lead acid battery system. Is it possible? Need experts' help!

 

No. There's this thing called the 2nd Law of Thermodynamics.

 

However... Regenerative braking is a nice thing to have on electric vehicles....

[TonyMcC]

To put it at its simplest, the more power you take from an alternator the harder it is to turn. The power you put into turning it will always be less than the power got from it.

By the way, an alternator provides a.c. voltage so you couldn't use it connected directly to a d.c. motor - you would have to rectify its output first - another small source of lost power.

[Moontanman]

To put it at its simplest, the more power you take from an alternator the harder it is to turn. The power you put into turning it will always be less than the power got from it.

By the way, an alternator provides a.c. voltage so you couldn't use it connected directly to a d.c. motor - you would have to rectify its output first - another small source of lost power.

 

 

Tony, i think you've hit upon something here that many people do not understand and it contributes to many of these free energy ideas. It takes power to run a generator/alternator, the more power you get the harder it is to turn, yes you can take an alternator and turn it easily with your hand but it doesn't generate much power at such low output but the more power you get out of it the harder it is to turn. I'm not sure about the exact figures but a alternator on a car takes several horse power away from the engine to generate 12v at the amperage needed to recharge the battery and run the car's electronics that would other wise be used to move the car.

[TonyMcC]

Tony, i think you've hit upon something here that many people do not understand and it contributes to many of these free energy ideas. It takes power to run a generator/alternator, the more power you get the harder it is to turn, yes you can take an alternator and turn it easily with your hand but it doesn't generate much power at such low output but the more power you get out of it the harder it is to turn. I'm not sure about the exact figures but a alternator on a car takes several horse power away from the engine to generate 12v at the amperage needed to recharge the battery and run the car's electronics that would other wise be used to move the car.

Made a silly slip in my post - I don't seem to be able to edit it. You obviously didn't spot it!

The power you put into turning it will always be GREATER than the power you get from it.

Edited February 9, 2011 by TonyMcC

[ewmon]

alternator on a car takes several horse power away from the engine to generate 12v at the amperage needed

Yes, 1 hp = ~746 Watts = ~746 Volt∙Amperes = 12 V × ~62 Amps or 14 V × ~53 Amps (most alternators actually output 14 volts). So, a regular 100-Amp alternator at full load would draw at least 2 hp from the engine, a heavy-duty 200-Amp unit would draw at least 4 hp, etc.

[johnbtes]

Wouldn't the alternator at least make the battery last longer?

 

So for a crude example: Battery under use lasts 3 hours when used with alternator the battery under use lasts 4 hours

 

So not keeping the battery at full charge but charging the battery to extend the time that it is charged enough to be used.

 

Thanks,

John

[JMJones0424]

Wouldn't the alternator at least make the battery last longer?

 

No, because the battery is what is powering the alternator. At best, given 100% efficiency, there would be no difference. Power output from the battery to turn the alternator would equal power input to the battery from the alternator. Under no circumstances, in the situation as you have described it*, will the alternator ever charge the battery more than it draws from the battery. In practice, due to inefficiencies such as bearing friction, heat loss, etc., the alternator will always require more energy to turn it, and therefore draw more power from the battery, then it generates and returns to the battery.

 

 

*Regenerative braking is a way of recovering the energy of the vehicle in motion that you need to shed in order to stop rather than wasting it as heat loss in the brakes. This is wholly different then using a battery to turn an alternator that charges a battery.

[Dr. J]

I have an 80cc 2-stroke engine on my schwin bike. What do you guys think of equipping it with an alternator? I was thinking about putting an electric front wheel on the bike with a battery that I would charge with the gas engine.

[InigoMontoya]

I have an 80cc 2-stroke engine on my schwin bike. What do you guys think of equipping it with an alternator? I was thinking about putting an electric front wheel on the bike with a battery that I would charge with the gas engine.

You run into the same problem.... It will take more energy to drive the alternator than you'll ever get out of it. This is doubly true since you're charging a battery THEN using the energy (each step has it's own losses).

[Dr. J]

I found a low rpm generator that could potentially work for this application. I could place this unit in a housing and run a drive chain directly from the rear axle. Would a small generator like this be powerful enough to charge the battery? Thanks!

 

http://www.windstreampower.com/443540_PMDCG.php

 

 

 

 

 

You run into the same problem.... It will take more energy to drive the alternator than you'll ever get out of it. This is doubly true since you're charging a battery THEN using the energy (each step has it's own losses).

 

 

 

[InigoMontoya]

I found a low rpm generator that could potentially work for this application. I could place this unit in a housing and run a drive chain directly from the rear axle. Would a small generator like this be powerful enough to charge the battery? Thanks!

 

You're missing the point.

 

The question isn't whether or not a generator could charge the battery. It could. The question is whether or not doing so would be an efficient use of the gasoline in question.

 

Let me try a different approach.....

 

Suppose you have a big rock. We'll say it weighs in at 100 pounds. The rock is sitting in your front yard. You want it moved to your back yard. Which of these two scenarios would be most efficient:

 

A) Picking up the rock, putting it in a wheel barrow.... and moving it directly through your side yard into your back yard.

 

B) Picking up the rock, carrying it by hand, walking all the way around the block, through the back yard of the guy who lives behind you, and then heaving it over the back fence into your yard.

 

 

If you vote 'A', then skip all the generator/battery BS and just power your bike with the 80 cc motor you already have.

 

If you want to impress girls with your manly muscles (even if all the guys think you're an idiot), then by all means vote 'B' and use the generator to charge the battery to power your bike via electric motor (Rube Goldberg would be proud!).

Edited October 2, 2012 by InigoMontoya

[ewmon]

I have an 80cc 2-stroke engine on my schwin bike. What do you guys think of equipping it with an alternator? I was thinking about putting an electric front wheel on the bike with a battery that I would charge with the gas engine.

InigoMontoya makes a valid point about your idea being inefficient because you would convert the engine's mechanical power into electrical power, charging the battery, discharging the battery, and then back to mechanical power, and each step involves a loss. Plus the added weight of an alternator, voltage regulator, battery, motor controller and electric motor.

 

However, depending on the equipment you use, your *peak* power output could be much higher than what your 80cc engine could produce, and this peak power could be used for climbing hills, fighting headwinds, passing, etc. So, if you travel lots of ups and downs or often have headwinds, your idea might benefit you so you're not crawling up hills or against the wind. Also, like the Chevy Volt, you still have battery power if your engine quits or if you run out of gas (so it's like having a reserve). It'll also give you electric power for lights, radio, etc.

[Spyman]

You're missing the point.

 

The question isn't whether or not a generator could charge the battery. It could. The question is whether or not doing so would be an efficient use of the gasoline in question.

Maybe you are missing the point, while I agree with all arguments against perpetuum mobiles there is a slight possibility that Dr. J missed that part of the thread and only wants to charge the battery for normal use with lights and stuff. There is no mentioning of any DC motor powering that bike, which likely is converted with a simple engine kit that don't have a built in generator for external electrical components like the lights.

 

Standard motorcycles have generators charging the battery and powering electrical equipments and for that purpose the gasoline is efficiently used.

 

EDIT: Scratch that since in my second read through I googled "electric front wheel" and found out that it in fact is an electric motor with the purpose to help powering the bike.

 

 

I found a low rpm generator that could potentially work for this application. I could place this unit in a housing and run a drive chain directly from the rear axle. Would a small generator like this be powerful enough to charge the battery? Thanks!

 

http://www.windstreampower.com/443540_PMDCG.php

You need a generator that is adapted to your battery voltage or otherwise something will likely get damaged.

 

But that generator seems capable of charging a standard 12 VDC car battery - if used wisely since it doesn't have any electronics protecting it against overloading or overheating. Also it is not sealed against outdoor weather and needs to be enclosed.

 

EDIT: As noted in my above edit I agree with InigoMontoya about the ineffecient use of the gasoline, your driving range will get much shorter.

Edited October 2, 2012 by Spyman

[InigoMontoya]

By the way...

 

I meant to say it earlier but failed....

 

That's a sweet set up on your existing bike, Dr. J.

 

Did you build it or buy a kit or...??

[Dr. J]

Thanks for all the helpful advice I built the bike from a kit, but recently bought some better parts that I will be installing shortly. I will upload some pics when all of the new parts are put on. I don't like the wheels that come standard on these bikes. I always upgrade to the manic mechanic sprocket adapter with thicker gauge wheels. I also put a larger gas tank, performance carburetor, and a new seat.

 

One last question before I give up on the hybrid bike technology. What if I had a switch that would activate the generator only going downhill. I live in Irvine CA and there are a fair amount of hills on UCI campus. Then gravity could do the work instead my gas.

 

-Dr. J.

By the way...

 

I meant to say it earlier but failed....

 

That's a sweet set up on your existing bike, Dr. J.

 

Did you build it or buy a kit or...??

[InigoMontoya]

One last question before I give up on the hybrid bike technology. What if I had a switch that would activate the generator only going downhill. I live in Irvine CA and there are a fair amount of hills on UCI campus. Then gravity could do the work instead my gas.

 

Now you're on the right track but let's take that step just a little bit further....

 

Rather than turning on the generator when you're going downhill, just use it anytime you want to slow down. Congrats, that's called "regenerative braking" and it's why hybrid cars get good gas mileage in stop/go conditions.