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Thought experiment of rigging solar panel to electric bike, questions about LiFePO4

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  • HarperHurst
    replied
    The math I've done is like this:

    45 Watt Panel with operational voltage of 36V going into an MPPT controller that perhaps isn't even the most efficient one. Say 85% efficiency, even though most of them are >90%. Converting 45W & 36V to say the battery's voltage of ~29V with 85% efficiency is about 1.3 amps at the panel's peak performance. The charger that comes for the battery is a 24V 8A charger, which they claim can charge the battery in 4 hours from a near-dead state. Would my reasoning of saying an average solar charging amperage of 1A vs the 8A of the official charger is 1/8th as fast?

    Mind you, whilst riding the bike I would not be using the motor 100% of the time. Perhaps it would be used with pedal assist to get to around top speed where I take over with just pedaling to keep it at top speed. Once the bike is parked the panel could charge the battery at its fastest possible rate (which would be dependent on parking position, angle of panel and how much sunlight it would receive.) so hopefully it would be back near a full charge by the time I got back to it. (Provided the initial journey wasn't too long and I didn't use up that much of the battery's juice whilst traveling.)

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  • jflorey2
    replied
    Originally posted by HarperHurst View Post
    Another question which came to me (And that should have been my first one) is that can a battery be safely used to power a motor while also simultaneously being charged by the panel?
    Yes. You still need a charge controller to prevent overcharge when stationary though.
    The specific panel I had in mind was a 45 Watt 24V panel. It's measurements are 22x27x3 inches. However; the bike would not operate on the panel's power alone.
    Well, give it a try if you want. I suspect you won't see much contribution from the panel but it probably won't hurt anything. I would advise mounting the panel VERY well to the rack; the panel will see a lot of force on it on bumpy roads.

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  • HarperHurst
    replied
    The specific panel I had in mind was a 45 Watt 24V panel. It's measurements are 22x27x3 inches. However; the bike would not operate on the panel's power alone. The bike has its own 24V 8Ah battery powering a 300W motor which it uses to get to about 15-20 mph (Reviews I have read state that 20mph is impossible off of the motor's power alone, you would want to use the pedal+motor assist to get up to that speed.)

    Another question which came to me (And that should have been my first one) is that can a battery be safely used to power a motor while also simultaneously being charged by the panel?

    (By the way, I HAVE made it through math courses up to Differential Equations as well as Physics 1 and 2. Physics 2 was all the electricity mumbo jumbo which I barely remember. That's why I'm not sure about a great number of things related to solar panels.)

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  • jflorey2
    replied
    Originally posted by HarperHurst View Post
    Say I added a panel behind me on the cargo rack. Say the panel is 22 inches wide, and my body is 16 inches wide. If I created a housing for the panel and controller (Panel being the top) in a shape similar to that of a boat to hopefully maximize C_drag, surely the effects wouldn't be as drastic as you claim? The panel itself would weigh about 10 lb, and the controller perhaps another pound. If the housing were constructed out of something lightweight, perhaps the weight everything adds could be minimized as well? The whole housing would be perhaps 10 inches tall... but I would think that a good amount of the surface area could be neglected seeing as it would be behind a body whilst riding.
    Your body is up high; the panel will be below the wide part of your body. The panel you describe would be about 30 watts, which is about 10% of the energy you need to ride at 19mph even without a panel. With just the 30 watts you could move at about 5mph on a perfectly flat road.

    (BTW a good simulator for such thought experiments is at http://www.ebikes.ca/tools/simulator.html. It does NOT include the drag of the panel.)

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  • SunEagle
    replied
    Originally posted by HarperHurst View Post
    Sunking's post has me thinking a bit more..

    (By the way, I'm currently a junior in Civil Engineering. I had previously thought about air resistance but I figured it would be negligible; many of the calculations I did in a highway design class concerning horsepower required for a vehicle neglected air resistance because it was minuscule compared to all the other forces acting against the motion of a vehicle.)

    Say I added a panel behind me on the cargo rack. Say the panel is 22 inches wide, and my body is 16 inches wide. If I created a housing for the panel and controller (Panel being the top) in a shape similar to that of a boat to hopefully maximize C_drag, surely the effects wouldn't be as drastic as you claim? The panel itself would weigh about 10 lb, and the controller perhaps another pound. If the housing were constructed out of something lightweight, perhaps the weight everything adds could be minimized as well? The whole housing would be perhaps 10 inches tall... but I would think that a good amount of the surface area could be neglected seeing as it would be behind a body whilst riding. If the panel+controller was able to deliver about an amp of current, surely this could counteract any air resistance/weight losses. This would all be reliant on a lightweight and a hopefully more aerodynamic system. If the weather outside isn't good enough to supply more power than what the system could put in, I could also rig a way to just easily remove the system and ride it in its stock configuration.

    The whole point of the project would be to engineer the bike so that it can charge at a decent enough pace while its parked at wherever its ridden to (Say at work) to hopefully top off the batteries before setting off again. (In order for it to be topped off, the initial distance traveled would have to be short. 1-5 miles at most)

    So after what you said, the goals for the project would be this:
    1.) Create a system that can charge the battery wherever the bike goes without having to take the battery inside and plug it into the wall.
    2.) Engineer the system in such a way that it can produce power at the same rate or just barely higher than it costs to have the system mounted on the bike while it is moving. (Either make it so it isn't a burden or can still produce slightly more than what it costs to have it on the bike while its moving.)

    This was written in a hurry, so I'm sorry if I missed some other minute details in my thought process.
    If you checked on the Marissa Muller's equipment you can see she added a wind screen in front of the bike the helps to reduce the drag from the panel on the trailer behind her. It looked like a nice system but I am sure she had to perform a lot of her own peddling over the entire 3200 mile trip.

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  • HarperHurst
    replied
    Sunking's post has me thinking a bit more..

    (By the way, I'm currently a junior in Civil Engineering. I had previously thought about air resistance but I figured it would be negligible; many of the calculations I did in a highway design class concerning horsepower required for a vehicle neglected air resistance because it was minuscule compared to all the other forces acting against the motion of a vehicle.)

    Say I added a panel behind me on the cargo rack. Say the panel is 22 inches wide, and my body is 16 inches wide. If I created a housing for the panel and controller (Panel being the top) in a shape similar to that of a boat to hopefully maximize C_drag, surely the effects wouldn't be as drastic as you claim? The panel itself would weigh about 10 lb, and the controller perhaps another pound. If the housing were constructed out of something lightweight, perhaps the weight everything adds could be minimized as well? The whole housing would be perhaps 10 inches tall... but I would think that a good amount of the surface area could be neglected seeing as it would be behind a body whilst riding. If the panel+controller was able to deliver about an amp of current, surely this could counteract any air resistance/weight losses. This would all be reliant on a lightweight and a hopefully more aerodynamic system. If the weather outside isn't good enough to supply more power than what the system could put in, I could also rig a way to just easily remove the system and ride it in its stock configuration.

    The whole point of the project would be to engineer the bike so that it can charge at a decent enough pace while its parked at wherever its ridden to (Say at work) to hopefully top off the batteries before setting off again. (In order for it to be topped off, the initial distance traveled would have to be short. 1-5 miles at most)

    So after what you said, the goals for the project would be this:
    1.) Create a system that can charge the battery wherever the bike goes without having to take the battery inside and plug it into the wall.
    2.) Engineer the system in such a way that it can produce power at the same rate or just barely higher than it costs to have the system mounted on the bike while it is moving. (Either make it so it isn't a burden or can still produce slightly more than what it costs to have it on the bike while its moving.)

    This was written in a hurry, so I'm sorry if I missed some other minute details in my thought process.

    EDIT: Yes, I'm aware that it would be MUCH more cost efficient to just plug the darned thing into the wall. It just sounded like something fun to do for "stuff" and grins since it was the possibility of making an ebike that potentially never has to get plugged in, provided you only ride it for about a quarter to a half its possible range.

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  • sensij
    replied
    Originally posted by lkruper View Post
    Could an e-bike like the one from the OP make it up a 10 mile uphill grade that starts at 1000ft and ends up at 5500ft?
    Originally posted by jflorey2 View Post
    I don't know; I don't have any experience with such a bike. Mine could do it, but just barely. I have an EMS E+ conversion with a 36V 22AH battery. I've made it to Julian (4200 feet gain, 40 miles) with some pedaling on a single charge.
    Just looking at the energy required to change the elevation, 250 lbf * 4500 ft = 1125000 ft lbf * (3.766 e-7 kWh / ft lbf) = 0.424 Kwh.

    36 V * 22 Ah = 0.792 kWh, so just over half the battery capacity is consumed by the elevation change. The energy required to travel 10 mi at speed is a calculation like what Sunking showed, so if you go slow, or do some pedaling to help, it might work.

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  • SunEagle
    replied
    Solar Adventure Cyclist Travels 3200 miles

    Check out Marissa Muller website. She rode a solar assisted bike more than 3200 miles.

    Leave a comment:


  • Sunking
    replied
    [FONT=Comic Sans MS]Our good old friends Physics and Math will bite you in the butt with reality. You know those two teachers in school whose class you dropped out of. [/FONT]

    There is a very good reason you do not see anyone trying or doing what you want. Thousands before you have tried. When it comes down to moving objects, ones with wheels using motors. or animal power you have to deal with 3 Forces of: Weight, Rolling Resistance, and the biggest of all losses Aerodynamics or wind resistance.

    Let's take your average bicycle and 200 pound man on it for a gross weight of 250 pounds Cross-Sectional Frontal Area of 9/ft2, and inflated rubber tires on a flat smooth concrete surface resulting in a C of Drag = .9 of a bicycle. . To travel:

    10 mph requires .2 hp. For a hub motor that works out to around 180 watts.
    20 mph requires .68. For a Hub Motor around works out to around 600 watts.

    OK now you want to add weight, and change your Coefficient of Drag to that of a parachute. Panels are not aerodynamic and unless orientated pointed into the sun, is just a Boat Anchor to you. The only thing carrying a panel around is going to accomplish is just cut your range 50 to 75% with all that added weight. What little power a panel can generate is not enough to overcome the weight and drag it induces. In the end just that much more weight you have to carry and increase the distance you have to carry it.

    [FONT=Comic Sans MS]Mr Physics and Math would have taught you the only gain that will come from this idea, is the person selling the panels and batteries to the guy who flunked Math and Science. [/FONT]

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  • jflorey2
    replied
    Originally posted by lkruper View Post
    Could an e-bike like the one from the OP make it up a 10 mile uphill grade that starts at 1000ft and ends up at 5500ft?
    I don't know; I don't have any experience with such a bike. Mine could do it, but just barely. I have an EMS E+ conversion with a 36V 22AH battery. I've made it to Julian (4200 feet gain, 40 miles) with some pedaling on a single charge.

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  • lkruper
    replied
    Originally posted by jflorey2 View Post
    There are several sites around that contain ebike stuff. The forum at Endless-sphere is a great one. Grin Cyclery's site is dedicated to EV's and has a very good dedicated charger that will do nearly any battery chemistry.
    Could an e-bike like the one from the OP make it up a 10 mile uphill grade that starts at 1000ft and ends up at 5500ft?

    Leave a comment:


  • jflorey2
    replied
    Originally posted by HarperHurst View Post
    EDIT: Nevermind. Google was my friend. Just a fancy way of programming the controller to know when to stop charging. Funny this doesn't have it, as everything else I've looked at has this feature.
    There are several sites around that contain ebike stuff. The forum at Endless-sphere is a great one. Grin Cyclery's site is dedicated to EV's and has a very good dedicated charger that will do nearly any battery chemistry.

    Leave a comment:


  • HarperHurst
    replied
    Originally posted by jflorey2 View Post
    Some notes -

    You will probably find you don't want a solar panel hanging off the back of the bike. I've tried it. They are heavy, awkward and are big sails - and the normal amount of pounding that a bike takes will not be kind to the panel. You are much better off with a few stationary panels at wherever you are going.

    It looks like the one above does not have adjustable voltage setpoints, so probably not.

    As long as you can set the charging voltage accurately you can feed the battery directly from the charge controller.

    No.

    That would work for a while, so if longevity is not a concern that can work.

    Very few people have the skill or the patience to manually balance a battery pack. If you want to balance it get a BMS or buy a battery that already has a BMS. There are plenty of them available.
    This answers nearly all of my questions... however I've thought of another from what you said. What exactly are adjustable voltage setpoints, and why are they important for charging the LiFePO4 battery?

    EDIT: Nevermind. Google was my friend. Just a fancy way of programming the controller to know when to stop charging. Funny this doesn't have it, as everything else I've looked at has this feature.

    Leave a comment:


  • jflorey2
    replied
    Originally posted by HarperHurst View Post
    A few days ago I began postulating the possibility of selling my old Kawasaki dirt bike and buying an electric bicycle. I then had the idea of rigging a solar panel to said bicycle. From my own research, I know that at a bare minimum I would need a solar panel (Duh.) and a solar charge controller.
    Some notes -

    You will probably find you don't want a solar panel hanging off the back of the bike. I've tried it. They are heavy, awkward and are big sails - and the normal amount of pounding that a bike takes will not be kind to the panel. You are much better off with a few stationary panels at wherever you are going.
    1.) Would I need to buy a charge controller that is meant for charging LiFePO4 batteries, and is the one listed above able to do so?
    It looks like the one above does not have adjustable voltage setpoints, so probably not.
    2.) Even with a compatible controller, part of me assumes it will not be easy (near impossible) to feed power directly from the controller into the bike's battery. Is my reasoning correct on this?
    As long as you can set the charging voltage accurately you can feed the battery directly from the charge controller.
    3.) If my reasoning in #2 is correct, would it be then be necessary to purchase an inverter and some sort of cable to charge the battery similarly to the way it's meant to be charged?
    No.
    Provided the cells are balanced (and stay balanced after charging) when you first get the battery, or you manually balance the cells (which hopefully stay balanced after charging) there would be no need for individual cell management.
    That would work for a while, so if longevity is not a concern that can work.
    I'm guessing that if you also just perform routine checks to the battery's cells to make sure they're balanced (and balance them if need be) you could completely eliminate any possible need for a cell management unit built into the whole rig. Is this reasoning correct?
    Very few people have the skill or the patience to manually balance a battery pack. If you want to balance it get a BMS or buy a battery that already has a BMS. There are plenty of them available.

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  • HarperHurst
    replied
    It's not really a "problem" per se, it's just the thought of having a bike that could be used for short distances (Off-road as well as on) that wouldn't need to be plugged in often and could go a little further than originally designed if need be. That's it. It's just been a fun idea for a possible project to work on. I just don't know enough about some of the aspects involved to make it a realistic possibility.

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