anyone ever try fitting an alternator to an ebike?

zippinaround

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just wondering if anyone out there has ever tried fitting a truck alternator to run friction drive from the back tire to recharge the batteries for extended range? just an idea that popped into my head maybe it wouldn't turn it fast enough to charge?
 
Power required to turn the alternator at a useful speed (if you need to use gearing, there's added power needed), losses in rectification and battery charging circuitry.

It can take one to a few horsepower to run an alternator, you produce _max_ one-third of a horsepower, your motor might use 100wh to 1500wh to produce it's rated 500w or 1000w output (typical setups anyways) depending on what's going on. But it's gonna go up dragging an alternator around. And now your motor has to work harder... which means it requires more current to produce the same output... which uses more current, which requires more mechanical power to be applied to the alternator to supply that current...

See where this is going?
 
The history of physics is sort of fuzzy in my memory. So I might not have details perfect. But........

Look up (by google, for instance) a fellow named Helmholtz. First name, maybe, Friederich or Ferdinand. Plus I think there's a Von in between. He lived in, probably, the nineteenth century. If not, then the eighteenth. Certainly a German. I'm assuming he lived in Germany.

He came up with three laws of energy that are not seriously doubted by anyone who is seriously interested in the truth to this very day.

The first states that energy --though Helmholtz himself did not realize it, this really applies to matter/energy-- can not be created nor destroyed.

The second states that energy will move on it's own from areas where it is more concentrated to areas that are less concentrated.

The third is less easy to state in a simple sentence or two. But it deals with a concept known as entropy.

(And how am I going to get to the point without writing a long lecture that I'm only very partly competent to write? I don't know yet, but I'll try......)

Entropy is a measure of just how 'diluted' the energy of a system is. That is diluted in the sense of the second law; how evenly spread out the energy is. A closed system --no energy entering or leaving-- at maximum entropy might be viewed as 'dead' in a physical sense. Nothing can possibly happen within that system. No movement, no chemical reactions, etc. Plus there is no way, even in theory, to separate the energy in the system. To put it back to the state where there is energy concentrated more in some parts than in others. So that movement or chemical reactions and such then could take place again, per the second law.

Now imagine a dead battery. This would be an approximate, real world example of a closed system at maximum entropy. It is inert and it will not do the work that we normally expect of a battery. Now in the real world a dead battery does not need to remain a closed system; we can easily pour more energy into it. Using a battery charger, for instance. Or an alternator.

But the third law makes it clear that you must pay a penalty for doing so. No matter what you do it will always, always, always cost you more in energy than you can expect to extract from the system.

So imagine this alternator on your bike and charging your batteries. We can imagine that this setup will give to you X amount of energy from those batteries once they are fully charged. The third law tells us that no matter what you do you will have to pour more than X energy, substantially more in most cases, into that alternator. That energy will have to come from your own legs, perhaps. (Might as well forget that. Humans don't have the power to charge batteries like this in any reasonable time.) It might come from a gasoline engine. But the gasoline burnt would get you further by chain drive off of the engine than it will by charging batteries and having them turn a motor. The third law tells us so.

I guess I don't need to go on. I'll only end up confusing the subject and myself. But I can promise you that if you were to build such a system and claim that you made it work, then every scientist in the world --who is worth the name-- will bet any odds, any odds at all, against you, feeling completely certain that they can count their winnings as money in the bank. And they really, really will be right.

There's a reason I took the time and space to write all of this. It's in the hope that anyone who reads it will grow a bit curious. Maybe google Von Helmholtz and read what they (you) can. Gather an understanding of concepts like the conservation of mass/energy and entropy.

The understanding that I referred to above forms protective armor for the mind. You'll be able to spot horsefeathers from a mile away. You'll be insured a great deal more against fraud. Both literal and figurative.
 
Grade School Science?

Simply ...
Any alternator, generator etc. requires more energy input than it will output!

An eBike that cruises along with a 500w input ...
Add a generator to produce 500w ...
Your battery will be forced to supply the original 500w ... plus an additional 1000w to overcome the drag produced by the generator. After initial start the battery must supply 1000w through the motor to the generator to produce the 500w to power the motor. Effectively ... your battery must supply 2x the energy! 50% for motivation and 50% to spin and heat up your generator (alternator).
So ... add an alternator ... if you want to cut your range in half!


A permanent magnet generator might be 80-90 efficient in turning mechanical energy into electrical.
A series wound generator, or alternator, uses additional energy to power electromagnets, dropping efficiency to 50-60% or lower! Drop this another 10-20% to offset the inefficiencies of a friction drive.
 
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No, no zippinaround.....you shouldn't give up this easy. We need to have a an argument like those physics geeks on that TV show.:cool:

You might challenge us nay-sayers on these grounds, for instance. "Then how come a Chevy Volt uses a gasoline engine to charge a battery? Wouldn't it be more efficient, by your reasoning, to simply have the engine power the wheels directly, like in a conventional car?"

I've been pondering that question since writing that long winded post above. And I think I know the answer. But it's not a lot more than guesswork.
 
Here's a possibility!
Hybrid.jpg

Chris
AKA: BigBle
 
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