It is rare to find a car these days without some mechanism for charging a cell phone. After all, phones need charging all the time and we spend a lot of time in our cars. But what if you spend a lot of time on your bike? Five teens from Lynchburg, Virginia decided to build something to charge their phones from pedal power.
This isn’t a new idea, of course. Your alternator is charging your phone in your car, and bikes have had alternators connected to them for lights and other purposes. According to the team, you need to pedal about 4 miles per hour to get enough voltage to charge the phone. You can go faster though, because the circuit has a regulator. We especially liked how they determined the speed versus the voltage using a tachometer and an electric drill. We also liked the 3D printed parts such as the handlebar mount that you could probably repurpose for other things.
Our only thought would be to use a boost/buck converter so that even lower voltages could generate enough voltage to charge the phone. Sure, the current would be less — there’s no free lunch — but at least you could get some charge.
Perhaps the best thing though is contemplating a summer camp like this and watching the enthusiasm of the team in the video below. When’s the last time your face lit up like that when a project started working?
We’ve seen bike chargers like this before that did use a DC voltage and a boost converter. We’ve also seen a bike powered up with solar cells. It would be fun to connect one of these to an exercise bike so you could feel as though your exercise was accomplishing something.
It frustrates me when you see people trying to learn about things like this, but they are constrained to think about voltage. You need to think about power. Did they measure the output voltage open circuit (no load)?
A regular “bottle” style bicycle generator gives nominal 6V AC. I get full voltage at about 1 MPH, though the current is pretty low.
I think what you need to do to improve the low speed performance is to add a PFC circuit.
Industrious students, great to see. Thanks for the write up.
I take the opposite approach: I use a 5v USB rechargable battery pack in a little waterproof top tube bag to power 6v LED dynamo lights (good ones work perfectly, cheap ones sometimes don’t), satnav, and phone recharging.
The USB charging pod used as a cache battery is useful if you start out charged. It would probably be easy to wire up a smart circuit to prioritize charging the phone(or other device) first and then switch to charging a cache battery then let the phone pull form the cache battery when moving slowly up a hill. Another smart function is to pause for a set number of seconds and then restart charging as some older phones would always step down to and stay at the lowest amps before undervolt charging setting of the charge session (probably to save wear on an overloaded dumb-ish wall wart). Most everyone also knows about shorting USB data pins or at least having a switch to short them as many phones won’t even begin charging without that.
I recommend a good hub dynamo the best being the SON brand() though I am just fine with a Shimano, you can drag perhaps 30w or maybe more, I haven’t tried, from a good hub dynamo and it wont strip the rubber from your tires. I suggest only a hub for everyday power and save the others as an expedient for emergency lighting such as when you get caught out later than planned or have to make a quick night run to a shop and want more than or a backup to an LED flasher.
To clarify the charge pause I mention in the above post is an event in a DIY bicycle smart charger control program which resets charging on a timed basis or perhaps begins when the device is drawing less than optimum power form the dynamo and/or cache battery system. Again some phones might step down to lowest power step before undervolt to protect weak wall-wart chargers never having in mind that a bicycle dynamo charger might still show charging while slowly pushing up hill and continuing to charge at maybe 0.05mA even when you get a rare downhill run which which could have easily supplied 3 amps to a phone and also 2A to a cache battery or more. Also might insert a few lines to try shorting USB data lines if the charger program doesn’t detect charging.
The circuit doesn’t need to be very smart. You can monitor the dynamo output voltage. If it is above a certain threshold, then charge the cache battery as the charger isn’t loading the voltage down. Think of it as a shunt regulator – only drawing as much to maintain the voltage level. The output can go o a boost regulator which is diode Or with the dynamo output BUT set a bit lower than the threshold so it doesn’t try to do silly thing like charging itself from its own boosted output.
On 2nd thought, if the cache charger is before the diode Or at the dynamo it won’t see its output. Still having it set just below the threshold would introduce some hysteresis to prevent changing modes when everything is at same level.
DIY kits for such have been available for *ages*: http://www.forumslader.de/automatiklader/
Nowadays there’s also commercial versions, like from B&M: https://www.bumm.de/en/products/stromversorgung/parent/3610/produkt/361bw.html?
And? I built a lot of things at that age that I could have bought as a kit or off the shelf probably for less money. But that isn’t really why you do it. We could talk about the educational value, but look at their faces when it works — it is just the thrill which is great. This is how great engineering careers start, not by buying a bunch of kits. In the Devil’s DP Dictionary they define algorism as the feeling you get when your code runs. We need a similar word for electronics.
For me, I’m glad to see they built their own. Their next version will be better and over time even more exciting things.
Climate change models are based on faulty AlGore-isms!
B^)
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Don’t get me wrong, I do think their project is cool. It’s just that it was portrayed as a new & novel idea – which it wasn’t.
At that age nearly 10% of everything you see each day and over 50% of what you build, think, or create are new and novel to the person who is experiencing it.
Do you have any idea how many campfires have an entire group around them that thinks they are the first to notice that some sparks are longer lasting than others in height, some are brighter, some are both, and some are neither?
I usuakku find myself telling people to grow up, but you need to grow down a little and see life with excitment again.
“…and bikes have had alternators connected to them for lights and other purposes.”
Pedantic Man here: They’re using permanent-magnet generators, not alternators. Dynamo hubs, more and more common in cycling, seem to be built on permanent-magnet stepping motor architecture and are DC generators as well.
I’ve thought about attaching a generator to the idler sprocket on a 10(?) speed bike, instead of having the “bottle” grinding against the sidewall of one of the tires, but as that sprocket is one of lowest things on a bike, it would certainly be hit by a lot of water/dirt.
Bottle generators are f#$@ing terrible, and yes, they’re designed to generate 6VAC.
Generator hubs will, under proper load, generate about 6VAC as well – but open-circuit, at speed, they can generate close to 100VAC.
You are correct in that getting power out of generator hubs efficiently is tricky, and there are a bunch of designs out there that are pretty sophisticated.