Portable Battery Charging Pod for E-Bike Trailer

[HollowPoint]

Greetings All: I hope I'm in the right place to be asking for suggestions or insight on how to best setup the project I'm about to describe. I'm not in search of "Free-Energy." I mention this because I know how easy it is for inquiries like mine to go off on various tangents and completely miss the purpose of the original questions.

I'm a self-taught fabricator of sorts. Some might call me a chronic tinkerer. I have no problems fabricating out of metal or wood as I have in my home shop a CNC metal mill, a metal lathe among other equipment, but when it comes to anything having to do with electricity or electronics I'm completely out of my element.

My present project involves building a light weight Cross-Country E-Bike trailer for long distance fishing and hunting trips. Building the trailer is easy enough but I want to incorporate a removable onboard charging pod as a component of this bike trailer in order to be able to run off the bike's primary battery while simultaneously charging my secondary or spare battery as I ride.

As I stated above, I'm not looking for free energy or any other pie in the sky technology. What I had in mind was to use an automobile alternator who's input shaft will be spun by the trailer wheels. Here's my dilemma.

In my mind's eye I already know how it will fit into my trailer. What I DON'T KNOW is how to wire it up. The only point of reference I have for anything like this is my home made two-panel solar charger which goes from my solar panels to the charge-controller I have mounted on the wall of my shop; then from there to the 12 volt battery. From the 12 volt battery to a small power inverter with two electrical plugs into which I connect my radio or my fan or other small electrical appliances.

With this bike trailer Charging Pod I was wanting to use the spinning tires of my trailer as the input power to spin the alternator. I'm sure I could figure out how to do this through trial and error but I'm also sure it might take less time and most likely be less costly if I just ask someone with the experience in electrical work to help me along or at least give me a clue on how to go about this.

The hub motor on my E-Bike is rated at 500 watts and the battery that powers it is a 48 watt 16 amp output. (if I read my manual correctly) The charger that came with this E-Bike plugs into a standard wall plug. The specs on that charger states the following:

Input: 120 volts-3.0 Amps 60 Hz

Output 54.6 volts 3.0 Amps Also, I should state that the symbol for alternating current (Solid line above with short ------ below the solid line) is shown on this Output line.

The battery of my E-Bike is rated at 48 volts.

I've calculated the RPMs on the twenty inch trailer tires I'll be using as they spin a two inch diameter pulley on the input shaft of the alternator and depending on the alternator I choose I believe that it will produce sufficient RPMs at an average of 15 miles per hour to power said alternator. I can maintain that average rate of speed while riding my E-Bike for quite a long ride.

I'm aware that there is most likely some critical information that I may be leaving out here so if you can tell me what that might be I'll be happy to find that info and get back to you with it. For now I'd like to ask any of you who might be inclined give an electronically-challenged novice your suggestions as to what components I would need to connect together to be able to build this E-Bike Charging Pod; and in what sequence of components would you go about using?

I have not selected the alternator as of yet but I do want to utilize the charger that came with this E-Bike unless there's a component that might optimize this project. Any help you would be willing to share would be appreciated.

Following is the CAD rendering of my E-Bike trailer.

https://www.instagram.com/p/CKc2SMUBebH/

Tim M.

 

[Bluejets]

So you have a battery driving a motor , motor then driving a bike which has a trailer, to which you hook an alternator to recharge the battery.
Is that about the strength of it..?

If it is, then No, it won't work.

 

[Harald Kapp]

I should state that the symbol for alternating current (Solid line above with short ------ below the solid line) is shown on this Output line.

Huh?

If it is, then No, it won't work.

I agree.
Assuming you get the connections and stuff all right such that the spinning trailer wheels are indeed charging he main battery. Then this energy stored into the battery has to come from the wheels which in tun are powered by the motor from the main battery. If everything were 100 % efficient, this would amount to a perpetuum mobile. But you have to account for the energy required to get you moving plus the losses in the motor, alternator, charger etc.
You'll get more mileage from the main battery and your legs if you omit the alternator and charger. Less weight, longer distance.

 

[HollowPoint]

Harald Kapp: You're absolutely right. My mistake on the AC/DC thing. I'll use this as a good example of what I referred to when I mentioned that when it came to electricity and electronics, I'm way out of my element.

I can already see that my initial explanation of what I had in mind was lacking some important details. It was not my intention of using one battery pack to power my bike while simultaneously pulling the trailer who's spinning wheels would be spinning the alternator's input shaft and thereby recharging my spare battery.

When I ride my E-Bike I use mostly peddle power. If one were to create a pie chart of the input vs output of power usage as I ride I can easily say that on even terrain my legs are providing most of the power that moves my bike forward. That would be about 3/4 leg power and 1/4 of the overall power used is coming from my battery pack. Honestly, it varies by terrain.

As you've stated, I get more mileage from my main battery in conjunction with my leg power. In fact I can get in excess of sixty miles on a one way cross country trip this way. That sixty miles takes me a little over 3 hours; closer to five hours depending on where I ride. A younger rider could probably do it a bit faster. (I'm 65)

In my little pea-brain this means that if I were to recharge my spare battery (that battery being depleted down to 20 percent) by simply plugging it into the wall using the charger that came with it, It would take about three or four hours to recharge back to 80 percent.

In about that same amount of time riding cross country, if my DIY charging pod were set up correctly I could achieve similar results.

I hope all of that made some kind of sense. What I want to avoid here is going off on various tangents from the subject at hand. I just want to know how best -from an electrical standpoint- to set up my components AND, what exactly those components would be.

Thanks for taking the time to reply to my inquiry.

Tim M.

 

[Bluejets]

Show a circuit or the model/brand of alternator you intend to use.
I imagine you are aware, if you've ever taken notice of the installation in an auto, that the alternator is geared up, so essentially runs at approximately 3 to 4 times that of the engine.
At a little above idle which is where most alternators normally start to charge, this relates to around 2,000 rpm.
An adult male on average can output approx.1/7hp ( 746/7 = 106W) for a very limited time.
Energy losses from any drive mechanism must also be taken into account as it will eiither have to come from your existing battery or your pedal power.
Question is, which?
I'm guessing the former.

If you want it to come from your pedal power alone, then it would be essential to drive the alternator via your drive chain or switch your main drive off while "coasting"
Problem here is, in order to coast, one has first to build up that kinetic energy and where would that come from....again I'm betting the drive battery.
I can clearly remember the dynamos we used to use on the wheel of our bikes to drive a couple of 6v bulbs, one each for the headlamp and tail lamp. Both only a few watts each. These alone used to require a fair amount of extra "grunt" and not for very long I might add.
I have a feeling your round trip will be extended more than you imagine.

 

[HollowPoint]

The alternator I have my eye on can be seen on the following link:
Alternator 1 Wire Universal Self-Excited 10SI 10 SI 7127-SE - DB Electrical

I'm presently looking at a lighter weight alternators used on either forklifts or John Deere lawn tractors. Weight will be a factor in this build but for the time being the above alternator is my starting point. Human leg power will make up the bulk of the energy expended in the spinning of this alternator.

As for a "Circuit," I have no circuit to show other than the DIY solar panel (two one-hundred watt panels) that I put together many years ago. It includes the two panels, charge-controller, small 12v battery and power inverter. I imagined -perhaps ignorantly- that a portable charging pod like the one I've attempted to describe would include basically the same components but, being that I have miniscule amounts of experience in anything having to do with electricity, I could be completely off base with my assumptions.

I envisioned a similar setup for the charging pod except that in place of the solar panels I would have the RPM of my trailer wheels spinning the input shaft of my alternator. I'm afraid that's the best description I can give at this point.

I too recall the dynamos we had on our bicycles as a kid except that those dynamos sent power directly to the DC light. I don't know if it's even possible to send the current produced by the alternator directly to the battery I'm wanting to charge.

As in my cheapy solar battery charger, I assumed a similar setup. I just have to figure out the best or optimum components wired in the correct order to make this work. Making the trailer is a piece of cake. The charging pod, not so much.

Thanks for taking the time to reply.

Tim M.

 

[dave9]

It still makes no sense, to expend your energy to recharge it, in order to get it back so you don't have to expend your energy.

It is a losing proposition unless your battery is only used to power something at your destination like a flashlight or radio, charge your phone etc, not power the bike. ONE exception might be if you had a very low charge rate to reduce drag and the only purpose of the battery was to get up a particularly steep hill, so you can spread out your energy expenditure from peddle power rather than having to exert yourself all at once for the hill, and if you can do that, you still don't need to do it, can just not use the main bike battery until the hill, saving it because you were exerting the extra energy from peddle power anyway.

You seem to not recognize that peddling to recharge the battery without a big hill scenario as mentioned above, is going to be harder than never having any batteries at all for assistance. You do seem to want free energy.

Okay I just thought of one other exception. If you have substantial downhill travel where you have to keep applying brakes for safety, then you could reserve charging for use during this scenario, where this essentially becomes regenerative braking, but still if you only electrically disengage the alternator from charging the battery, it will still have additional drag compared to not spinning it at all, would need a clutch of some sort for engagement.

 

[Bluejets]

I too recall the dynamos we had on our bicycles as a kid except that those dynamos sent power directly to the DC light. I don't know if it's even possible to send the current produced by the alternator directly to the battery I'm wanting to charge.

That is how it usually works.
Given it is a 1 wire unit, without any further details, ( a bit iffy) one would assume that is all which would be required.
I would tend to use a fuse link of some description between the alternator output and the battery.
You do realise you linked to an alternator which has 63A output maximum...??
Bit of an overkill.

I'd be more inclined to look at the alternators used for model aircraft which would be more appropriate.
Something along the lines of 1A output.

Dave, it appears the two battery systems are isolated, however, the energy has to come from somewhere. If kinetic user has produced, fine, but defeats the purpose as you say.

 

[dave9]

Your linked 63A alternator is far too large for peddle power. Recognize that an alternator like that, does not respond linearly to RPM increase, rather falls off a cliff at low RPM so you would have to spin this heavier than necessary alternator, that much faster to get it to produce decent current at same load on you as a smaller alternator spinning faster.

To put it in perspective, I imagine you need upwards of 1HP to get decent output from it. I don't think you can peddle to produce 1HP for long at all. You might be able to achieve 1/3HP for a couple hours if you're quite large and healthy, but that is only spinning an alternator, not going anywhere too!

 

[Bluejets]

You might be able to achieve 1/3HP for a couple hours if you're quite large and healthy.

Not so.
The average male can output approx. 1/7hp for a very limited time.
This has previously been covered elsewhere in this forum I believe.

As the video shows, this bloke produced 0.021kWh of energy which is 21Wh....which is 1750mAh in a 12v system. And this guy is built like a brick s***house.

Found the link here.........

 

[HollowPoint]

I suspect, perhaps incorrectly that most here are not long distance cyclists. This seems to conjure up only images of the presumed inefficiency of putting together such a project and, more tangents that lead one off of the original project.

I'll try to word my inquiry just a little bit differently.

If we can put aside the "Loosing proposition" perspectives or "Not worth it" points of view (even though they may be valid to professional and non-professional electrical engineers) and just focus on the build itself:

Imagine you were tasked with building such a portable charging pod that will in fact be powered by the spinning wheels of a trailer and those trailer wheels will be spun by a combination of peddle power and battery power; what would be the sequence of electrical components that could get the job done?

The electrical specs of my E-Bike were listed in my original post along with the specs of my battery pack and the OEM charger that came with this E-Bike.

Would it be an alternator of appropriate size and spec spun by trailer tires of optimum diameter in conjunction with an optimum diameter input pulley to that alternator which allowed for sufficient RPMs to create sufficient current; followed by a charge controller of some sort which in turn connected to the battery or other component or, would it be some other set of components in some other sequence of connections that would be better suited for this application?

I know that engineering logic might state that this is a loosing proposition. What I'm asking here is to put aside that logic just long enough to consider what components and in what sizes or configurations might work together to build a portable charging pod for a bicycle trailer? Don't stifle your own creativity by focusing on all the reasons you may think such a project is not doable.

Hope that makes sense.

Tim M.

 

[Audioguru]

A guy used a computer fan to be the generator to light LEDs on his bicycle. It did not work until he used a HUGE fan that was difficult like dragging a fully open large umbrella around.

 

[dave9]

Not so.
The average male can output approx. 1/7hp for a very limited time.
This has previously been covered elsewhere in this forum I believe.

As the video shows, this bloke produced 0.021kWh of energy which is 21Wh....which is 1750mAh in a 12v system. And this guy is built like a brick s***house.

Found the link here.........

1/3rd HP is about 250W. If he is peddling this contraption around, on top of already peddling around gear, he has to have bicycle legs. Even so, it would take most of the enjoyment out of it, how slow he was going to get an RPM drive ratio for an efficient charge off such a big alternator.

During a bicycle race, an elite cyclist can produce close to 400 watts of mechanical power over an hour and in short bursts over double that — 1000 to 1100 watts

https://en.wikipedia.org/wiki/Human_power

Granted this is wikipedia, but others have measured their output for various reasons and 300W does not seem too hard to do for an hour for a cyclist.

Suppose you produce 250W going towards charging, and 50W towards propulsion, so you are traveling roughly 1/6th as fast while charging as you would have with 300W but not charging, given similar pedal effort (ignoring wind resistance, which he can't really but it won't be enough difference, then add weight of extra water and food for how long it will take). I guess at 2-3MPH he would get there eventually, except 50W doesn't account for addt'l needed going uphill, but possibly an electrical disconnect would provide enough relief of load for that.

 

[dave9]

If you have 20" trailer tires and are going 15MPH (which you won't be, as already stated due to more energy used for alternator drag than forward propulsion) that is only 252 RPM. You need to increase that tenfold for a typical generator's sweet zone.

Next, if your alternator is an automotive type for 12V system charging, will produce around 14.(n)V. You probably don't want the extra bulk and inefficient of an inverter to power your existing charger, so instead a switching boost circuit to raise the power to the 54V input the battery uses, and if the charge monitoring and termination circuit is built into the charger, then you'll need to develop one to put in series between the boost circuit and battery.

If 3A charge rate is sufficient, the good news is it's only 165W after losses instead of 250W or 300W as I'd mentioned in previous posts, but again this is after losses, so could still be more than 200W input from peddling. It would seem more reasonable to target a 1A charge rate rather than 3A, and (picking a round number) a 10A alternator.

 

[Bluejets]

Yes but he still has to drag his own weight around AND it is a limited period of output, i.e. cannot be sustained at your theoretical figures.

It still comes down to any energy will have to be in excess of the above AND as already proven, maximum output is 1/7hp which is a tad over 100w regardless of what voltage you run the system.
Not much left to charge a battery after any losses as well.

Whether the Op likes it or not, it still all hinges on free energy bulldust to get anywhere.

 

[HollowPoint]

A guy used a computer fan to be the generator to light LEDs on his bicycle. It did not work until he used a HUGE fan that was difficult like dragging a fully open large umbrella around.

I like the fact that he did it regardless of any of what some might consider down sides. I suspect he did it this way because he was using components that he was familiar with.

I can't help but imagine all of the ground breaking ideas and inventions that have been stifled by well meaning and experienced people who offered up all of their reasons for why this or that idea would was not going to work, rather than thinking a little harder and outside that proverbial box of man-imposed laws or principles.

Have you ever noticed how in just about any field of endeavor those that make a name for themselves in those fields are the ones who didn't constrain themselves by staying inside the box? I have to believe that most folks who pursue higher learning do so because they have dreams of being the ones who come up with the next greatest thing; only to not follow through with those dreams because the higher learning they pursued had drilled into them all the reasons why their ideas wouldn't work.

I can recall some of my previous projects where I went into them not knowing very much about what I was getting into. When I went online in search of wisdom and to look for answers or suggestions or options as to how to proceed I would always get three distinct types of replies.

First and foremost would be the well meaning replies from a purely engineering perspective. Replies telling me why my ideas wouldn't work based on logical established laws of physics and engineering.

The second form of reply would be from good folks telling me of a friend or acquaintance or even their own project, how they managed to go about it and failed or succeeded to some extent but ultimately gave it up.

The third type of replies were mostly from lurkers who perhaps in the back of their minds had thought of doing something similar but for some reason or other never followed through. They would reply after I had posted my results; the ups and the downs of my efforts, the trial and error it took to complete my projects, etc..

These home projects I allude to included working with carbon fiber in gunsmithing, making injection molds, modeling extended 3D printed rifle magazines, fishing lures and Match-Grade-Trigger components for air rifles. Those members of the third types of replies would contact me after I had finished and field tested my projects to tell me that they had been following this project cause it was something they or someone they knew had tried and failed at; or only achieved partial success.

Several of the first group also contacted me. Some of them would state that they thought it couldn't be done or hadn't thought of doing it the way I had gone about it and others of them would reply on the same ongoing forum thread to voice their disbelief and insinuate some kind of fraud or deception.

I know there are guys here that are the same kind of dreamer and chronic tinkerers that I am. That's the main reason I go looking for wisdom or answers or suggestions on dedicated forums like this. It's rare that it ever pans out for me but I still ask. It's a part of the learning curve. It's just another rung in that ladder of success.

Many thanks to everyone who took the time to offer up a comment or suggestion. I'm off to do some trial and error and some video tutorial watching. I may be back to resurrect this thread whether I succeed of fail after I've depleted all my options.

Over N Out

Tim M.

 

[HollowPoint]

Not so.
The average male can output approx. 1/7hp for a very limited time.
This has previously been covered elsewhere in this forum I believe.

As the video shows, this bloke produced 0.021kWh of energy which is 21Wh....which is 1750mAh in a 12v system. And this guy is built like a brick s***house.

Found the link here.........

This guy is a lactic acid storage facility. Long distance cyclist have a different physique all together but I get your point.