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  1. #1
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    Question about batteries and voltages

    I've been dabbling with the idea of an Ebike setup. I was thinking of going more of a tadpole trike, but same concept. What I'm wondering is can you run an alternator as a charging source through a converter to step it up from 12v to 36v or 48v? Or could/would it be better to run an inverter setup to either charge a 48v bank of batteries or a 12v battery with some kind of inverter/converter direct to the motor? Thereby being able to run the alternator direct to the battery and convert the voltage between the battery and motor?

    Sorry, I know the thought is sort of scatterbrained, I'm trying to think low cost at the same time as efficient and I'm fairly sure the two are mutually exclusive.
    ~Chris.

    On a long enough time line the survival rate for everyone drops to zero.

  2. #2
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    The amount of complexity involved in adding an alternator and/or inverter setups, does not justify, the added cost/weight..

    You're better off buying a decent battery to start with and forget the rest.

    For the cost of an alternator and a decent inverter, you could just buy a decent battery.

  3. #3
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    Now mind you, I AM run something "close" to your idea..
    I have a HUGE 12v LiFePo4 (60Ah) battery that I use an inverter and a 36v charger to recharge my 36v battery while I'm running, but it's about 80% efficient.
    (I got the 60Ah 12v for a THIRD of it's normal price - $125 instead of $375 AND I already had a 200w inverter).

  4. #4
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    While I haven't researched this idea too much, I saw a couple of videos on youtube about people generating around 300 watts with alternators connected to bikes. So, my idea was, instead of running a regular drivetrain with chain to wheel, I'd thought I'd just use an electric motor (probably a hub motor) and run the chain to the alternator...

    I have a spare alternator kicking around as well as an inverter. The bike itself will be a ground up build, frame and everything... ATM I'm not too concerned about weight, as much as I am about the possibility of it working at all..

    Thanks for the reply .
    ~Chris.

    On a long enough time line the survival rate for everyone drops to zero.

  5. #5
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    You need a gas engine to run the alternator...
    It's not like you energize the alternator and it starts running and automatically produces energy..
    You need some form of engine to actually keep the alternator running and pedaling just ain't gonna do it.

  6. #6
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    The first link is something along the lines of my idea.. Its actually pretty cool to see someone else has already done it.... Around 2:45 in the first video you get an idea of the alternator application...

    http://www.youtube.com/watch?v=eknnz...eature=related

    Second and third link are just a couple examples that a peddle bike can power an alternator.

    http://www.youtube.com/watch?v=kVAZIDFMRXY

    http://www.youtube.com/watch?v=T3JPZ...eature=related

    I'm not sure where you got the idea that you need a gas engine to spin an alternator. What you need with an alternator is an initial charge make the alternator produce electricity.. which is fairly easy to come by since its connected to a battery... You can actually use an alternator in a wind turbine setup as well, provided you have enough wind to spin at the required RPMs...
    ~Chris.

    On a long enough time line the survival rate for everyone drops to zero.

  7. #7
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    Let me rephrase....
    You need a gas motor to run the alternator to get any Kind of USABLE energy out of it.
    I think you haven't figured out, that us (normal) humans can't produce Large amounts of continuous power for any length of time...
    Generating the voltage is NOT the issue.. Generating AMPERAGE is..
    The second you started pedaling with the alternator engaged to the battery and you have to provide a certain amount of amperage into the battery, that alternator will start to bog down and you won't be able to pedal.

    If just hooking up an alternator that you could power with just pedaling and provide enough "juice" for charging a battery, was easy (or efficient), then EVERYONE would do it.

    Most Tiny dynamos for regular bikes produce about 6w or 12v .5a. Scaling it up will get you more amperage, but then the energy needed (pedal power) to create larger voltages/amperages will have to scale up too.

    P.S. I didn't even look at those videos yet, but I'm sure none of them show someone pedaling easily to generate voltage above 12v or amperage above an amp. Let's say best case scenario for power generation by pedal power at a reasonable/continuous level (meaning a well trained athlete) is probably 60w, or 12v 5a, or 48v 1.25a..
    Most motors/electric bikes use about 20wh/m, or about 2.4a at 48v.. Factor in (BEST case scenario) of 90% efficiency (which is really, probably closer to 75%) for your power generation by pedaling is 1.1a, so effectively doubling your range with HARD PEDALING and charging up the battery, BUT you could probably just get double your range by pedaling hard in the first place..

    It's a matter of basic physics.. Energy in MUST be greater then energy out... (unless you've developed a superconductor that works 99.9999% efficient at room temperature - and even THEN it's only energy in = energy out.)

  8. #8
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    I'm glad you didn't look at the videos yet, it just goes to show the amount of respect you have for others opinions or ideas. As for yours, I'll be happy to test it soon. Further more, to summarize the second video I believe, the person on the bike (who as far as I could tell wasn't that smart based on his set up) clocked his output at 300 watts with a multimeter. FWIW, thats approximately 21 amps if you assume the alternator is putting out 14+ volts, which, most car alternators do. (Thats 300 watts / 14 volts = 21.43 amps, see I can do basic math too...)

    I'll never understand everyone being so quick to hide behind "basic physics" whenever they think they are encountering a perpetual motion idea. and I love the statment "If just hooking up an alternator that you could power with just pedaling and provide enough "juice" for charging a battery, was easy (or efficient), then EVERYONE would do it." Yeah, because its that easy to peddle to get from point A to point B.. yet the majority of people are too lazy for that and need to take a car... So of course they'd sit at home and peddle their asses off to watch TV.. Are you insane? This isn't perpetual motion, and it isn't easy. Its a hybrid system that combines the stored energy of a battery and the energy output of human work. Would it be anymore efficient than running a chain to the back wheel and using an electric hub motor as an assist, I don't know. The only difference is that this relies more on the electric motor and keeps the batteries charged for a longer period of time. Will they eventually die, well, I guess it will come down to either them or the person peddling.... One will out last the other.

    Honestly, I'm not even sure why we are talking about this, as it has nothing to do with my original post.. But, I guess you couldn't get past your idea of what I was asking to actually read what I asked... Which, by the way, I've answered already anyway. So, Good day.
    ~Chris.

    On a long enough time line the survival rate for everyone drops to zero.

  9. #9
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    LOL....
    To try it out is SIMPLE!
    Take a 36v ebike with regen (gives about 36v 6a or close to your 14v 21a) and while it's regenerating, try to pedal, you'll realize FAST, that's it's not so "easy".

    P.S. I watched that second video... LOL.
    You see that setup.. He's using the ENTIRE CIRCUMFERENCE of that wheel to generate that amount of power... It's like using a 80t to 5t crank..

    Can't wait for you to try and report back your findings...


    P.P.S. I will stand by my original statement.. (with a small addition)...
    If pedaling using a generator would produce a usable amount of energy EVERYONE (who uses E-BIKES) would do it.

  10. #10
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    Also to convert 12 to 36v with a buck converter (with an isolated output) is gonna cost you at least $300
    (all the eBay ones you might see for $15 are non-isolated.)

    So alternator charging a battery at 300w (ain't gonna happen with human power on a bicycle crank) would produce 21a, then inverter at 90% efficiency would produce 270w or 36v 7.5a. That would definitely power the hub motor, however your probably using 400w of human power (IF it was possible to pedal at 400w and turn an alternator fast enough to generate 300w out of it - which really ISN'T possible, but IF it were) and get speeds of let's say 20mph out of your hub motor..
    OR
    Just pedal a bicycle with gears at 400w and the bicycle moves at 20mph with human power.

  11. #11
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    Quote Originally Posted by noxyce View Post
    While I haven't researched this idea too much, I saw a couple of videos on youtube about people generating around 300 watts with alternators connected to bikes. So, my idea was, instead of running a regular drivetrain with chain to wheel, I'd thought I'd just use an electric motor (probably a hub motor) and run the chain to the alternator...

    I have a spare alternator kicking around as well as an inverter. The bike itself will be a ground up build, frame and everything... ATM I'm not too concerned about weight, as much as I am about the possibility of it working at all..

    Thanks for the reply .
    If you can generate 300w of power (or any amount for that matter), it's better to apply it straight to the wheel. You'll lose energy when you go through the alternator, the inverter, the battery, and the electric motor. Not to mention, you'll be carrying the extra weight of the alternator and inverter. If you just want to charge your e-bike batteries when you don't need to move at the moment, then finding a e-bike with regen is better since you don't have to carry extra components.

  12. #12
    Watching and waiting. jethro56's Avatar
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    I get people asking me if I can charge my battery while pedaling. I say "I guess I could but why would I want to?"

  13. #13
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    The problem stems from people basically wanting "free energy" and I'm not talking about a conspiracy type thing, either.

    Like I originally said, it would be A LOT of work (re:energy) to get the system to produce the wanted energy the OP is hoping to get out of it. Problem is, your wasting your leg power (energy) to get inefficient power to the motor. You might as well just pedal along with the motor/batteries and drop their energy consumption, thereby getting a net gain WITHOUT the inefficiency of what he's trying to accomplish.

    As Jethro kinda said, why would you want to use an inefficient setup rather than a more efficient one?

    If you pedaled with 300w and just used regular bicycle technology you get about 285w of power out (95% efficient).
    With the bicycle "system" the OP wants, it's prolly about 40% efficient...
    Why would I want to get 120w out of 300w of power?
    Answer: I wouldn't!

    P.S. I know there are some people out there that will say, "Well if the tour de france" people can pedal with about 500w of power and get speeds of 40mph.."

    Here's the thing..
    Their bicycles weigh about 12lbs! 120psi, 1" tires and Lycra / aerodynamic riding plays a HUGE role.
    Last edited by Sangesf; 12-29-11 at 12:29 PM. Reason: Grammatical fixes.

  14. #14
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    I appreciate the inefficiencies... I'm well aware of them. This is not some idea to change the world or invent some great new product. Its a project because I like building stuff and seeing what I can accomplish. On paper is it less efficient? Yes. Is it a different idea that seems like it would be fun to build? To me, it does. I'm glad you enjoy thinking in your box, I hope you found a good interior decorator to make it nice and comfortable. Personally I like screwing around with stupid ideas and trying to see if there is something someone missed. Its the building process that's fun for me, not necessarily the outcome. I don't expect much, but I don't see the harm in trying. If nothing else I get to learn about electrical systems and expand my horizons. Something you should try sometime.
    ~Chris.

    On a long enough time line the survival rate for everyone drops to zero.

  15. #15
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    You have no clue, what I've done..

    If you want to try it out for fun or as a learning experience, then all the more power to ya!
    (pun intended)
    Just realize that given best case scenarios, you're not going to be getting the results your wanting.

    People told me I was nuts using a 12v 60Ah battery to power an inverter to run a 36v charger to charge a 36v 10Ah battery while using my ebike.
    I am nuts!.. And, like you, I had the equipment already and no funds to buy an additional battery, so it worked out well... it's inefficient as he'll, but it definitely works and effectively doubles my range although I'm using 500wh of energy to produce 360wh extra..

    Let me get you the details of my setup...
    (Borrowed from one of my posts on another site)

    1.) 12v 60Ah line for accessories.
    (12v-30a fuse on positive side going to main accessories line)
    Which by the way is also connected to a 200w inverter that has a 36v charger connected to it so I can charge my 11s battery (#4) "on the go".

    2.) (same 12v battery)/12v line, inline, with a "33v" battery, setup on a switch to go from 36v to "48v".
    (12v-30a fuse on positive side going to switch).

    3.) 24v battery (2 SLAs) in series with the (same) 12v battery/line.
    (32v-30a fuse on positive side going to controller - [controller draws less than 30a - technically 20.9a max])

    4.) "33v" battery (11s LiFePo4) on aforementioned switch (see #2 above).
    (32v-30a fuse on positive side going to controller - [controller draws less than 20a - technically 17.6a max])

    P.P.S. After my first 2 years of using/building e-bikes and blowing countless controllers, chargers, batteries, etc... I've learned to fuse ANYTHING that can short out!
    Last edited by Sangesf; 12-29-11 at 10:37 PM. Reason: Gramatical fixes

  16. #16
    Senior Member geebee's Avatar
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    The losses going from generating the power to then run the rear wheel are massive even using the best of the best, on flat ground you will move maybe, first slope you will stop.
    Its been attempted many times over the years.
    Oh and putting out 300w for any length of time is pushing it for the average cyclist especially when you figure in the losses to the alternator (just googled 50 to 60% at partial load) that means 600w to get 300w output and then losses to the motor lets be generous say 80% efficient, so 240W to the ground from 600w imput.
    I have used a power meter when riding, you will not put out 600w, 100w is meant to be an average fit adults output.
    Whoops I forgot the inverter, charger, battery and gearing up to working Rpm's of the alternator losses.
    Last edited by geebee; 12-30-11 at 05:27 AM.
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  17. #17
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    Sangesf, it is good that you are putting the correct information for people reading this other than the OP. OP, go ahead and try to build this before insulting Sangesf who was trying to save you some time. Efficiency losses in reality are always much higher than on paper.

  18. #18
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    If you think I was insulting him, I apologize. That wasn't the intent. I've just seen things that make me think there are ways of making it work. Not even watching the videos and dismissing the idea, seemingly out of hand, just doesn't strike me as very respectful.

    Here are a couple more videos, maybe its something worth trying, maybe it isn't... Either way, its educational and entertaining...

    http://www.youtube.com/watch?v=k5y12...eature=related

    http://www.youtube.com/watch?src_vid...&v=v1p8JYO9ojs

    http://www.youtube.com/watch?annotat...&v=TAgkouFmplo

    Oh, and my name's Chris.
    ~Chris.

    On a long enough time line the survival rate for everyone drops to zero.

  19. #19
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    Quote Originally Posted by Sangesf View Post
    You have no clue, what I've done..

    If you want to try it out for fun or as a learning experience, then all the more power to ya!
    (pun intended)
    Just realize that given best case scenarios, you're not going to be getting the results your wanting.

    People told me I was nuts using a 12v 60Ah battery to power an inverter to run a 36v charger to charge a 36v 10Ah battery while using my ebike.
    I am nuts!.. And, like you, I had the equipment already and no funds to buy an additional battery, so it worked out well... it's inefficient as he'll, but it definitely works and effectively doubles my range although I'm using 500wh of energy to produce 360wh extra..

    Let me get you the details of my setup...
    (Borrowed from one of my posts on another site)

    1.) 12v 60Ah line for accessories.
    (12v-30a fuse on positive side going to main accessories line)
    Which by the way is also connected to a 200w inverter that has a 36v charger connected to it so I can charge my 11s battery (#4) "on the go".

    2.) (same 12v battery)/12v line, inline, with a "33v" battery, setup on a switch to go from 36v to "48v".
    (12v-30a fuse on positive side going to switch).

    3.) 24v battery (2 SLAs) in series with the (same) 12v battery/line.
    (32v-30a fuse on positive side going to controller - [controller draws less than 30a - technically 20.9a max])

    4.) "33v" battery (11s LiFePo4) on aforementioned switch (see #2 above).
    (32v-30a fuse on positive side going to controller - [controller draws less than 20a - technically 17.6a max])

    P.P.S. After my first 2 years of using/building e-bikes and blowing countless controllers, chargers, batteries, etc... I've learned to fuse ANYTHING that can short out!
    Sounds like an interesting project. If you had started with something like this instead of, what seemed like, such a negative tone, my responses would have been much more receptive. All too often I'm confronted with people who think because it hasn't been done, or because it is out of the norm, it can't be done. I understand the limitations and the inefficiencies, and I appreciate you trying to protect me from them. What my original post was looking for was something I'm less familiar with, and that's electrical products. Anyway, I'll continue to dabble and see what I can achieve. Even if I have to reinvent a few things as I go, its the exploration that is the fun part, especially when you get lost along the way.
    ~Chris.

    On a long enough time line the survival rate for everyone drops to zero.

  20. #20
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    It always amazes me after all this time how people write on the internet. We know by now that it is really easy to be misunderstood because we can't see tone. If you think someone is just being negative, I find it works (if they are not just a troll) to ask them a direct question to explain what they meant, explaining that I am a beginner. In person we can quite often see the impact our words have since we have developed language in person for tens of thousands of years. Most of us on forums love the subject and are here to help, not shoot down ideas.
    In this case many of the suggested ideas have been tried and we that have played with electrics for some time keep hearing from people who think electricity is magic so you can get energy for free. So anytime someone heads in that direction, it is easy for us to assume that is where things are going.
    Good luck with your experiments and keep us informed.

  21. #21
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    It took me all of 5 minutes googling pedal power generator and found this...

    http://www.lowtechmagazine.com/2011/...enerators.html

    This is a very good article.. Give it a read...


    P.S. Didn't care whether the OP was being rude or whatever..
    Any time I'm on a (new) forum and I ask questions, the first thing I look at when getting a responses is to see how many posts the author has written and that usually gives me the idea whether he prolly knows what he's talking about or not.
    (hint hint)

    A quick google usually works out the best.

  22. #22
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    For whatever reason, probably personal baggage of my own, we've gotten off on the wrong foot. As I've said, I appreciate the attempts to explain why what I'm thinking about is a waste of time. For whatever reason you think so, be it personal experience or academic study, I'm thankful for your help. I'm sure you have better things to do than watch a couple of videos online and explain to me why what the video shows is not really happening. It is after all, not your problem, its mine. So, I've asked for some information, you have supplied me it to the best of your ability. Thank you.
    ~Chris.

    On a long enough time line the survival rate for everyone drops to zero.

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