Ride Bike, Charge Phone

Spring is coming to the northern hemisphere, and soon it’ll be nice enough outside to tool around town on your bicycle. But bikes don’t have power outlets, so phone charging on the go will require forethought and charged-up battery packs. It doesn’t have to be that way. You’re working to make the bike move, so why not make the bike work for you?

If you’ve ever used a motor as a generator, then you can see where this is going. That’s the underlying principle behind [Creativity Buzz]’s bike-powered phone charger. As the bike wheel turns, the rim comes in contact with a small wheel attached to the output shaft of a DC motor. Cranking the output shaft of a motor with permanent magnets inside will induce a small voltage, and here it is amplified with a DC-DC boost converter and output to a USB jack.

As long as you can find a way to secure the phone to the bike frame, or use a long cord and good cable management, you’re in business. Wheelie past the break to watch [Creativity Buzz] build it and give it a stationary test run. While you wait for bike-riding weather, you can still use this kind of charger by turning a crank.

49 thoughts on “Ride Bike, Charge Phone

          1. I had a permanent magnet alternator on my bike when I was a kid and that was many decades ago. What would be interesting would be to put a mechanical latching mechanism on the alternator and a solenoid to engage it. The solenoid could be triggered by a micro controller that that does things like read an inclneometer, look at what gear you are in, and your cadence, and wheel speed. If you are in a low gear with a slow cadence it would be a good time for the alternator to disengage as you are probably working. Ditto if it sees you going up hill. On the flip side, if you are not pedaling and have good wheel speed or are going down hill, that would be a good time to engage the alternator. It could be tuned to be as un offensive as possible. That would be a neat spin on 1950’s or earlier tech.

      1. I think I’d rather have a few permanent magnets glued to the sidewall and a pickup coil on the frame with no physical contact anywhere. Probably wouldn’t make as much current, though.

      1. Check out a company called PowerFilm.. http://www.powerfilmsolar.com/

        They have very lightweight solar panels.. Not Glass based. Plastic film can be rolled up, segments folded and even shot at and still give power out.. Plus you can take the system along with you when you get off the bike. Hiking, at the beach, etc.

    1. The best case monocrystalline cell the size of a cell phone will have about a half watt output. Then you need direct sun and you need to point it directly at the sun. Off angles don’t receive nearly as much power as you think they would. Then you need to completely and evenly light the solar cell or you receive no useable output power. So let’s say you manage to get about 100 mW output from the cell. That’s great – it will charge your 10 Whr phone battery in 100 hours, or about 10 days, assuming 10 hours a day of sun.

    1. That’s what I did – made a bridge rectifier and added a beefy 35V cap (50V would be better, my hub generator has 32V spikes, but it’s what I had at hand). Then, I added a cheap Chinese DC-DC converter that converts 6-24V to 5V. 3d printed a case and it’s held up just fine (I added a 3.5mm jack socket to the bicycle so I don’t have to add the rectifier to the bike, where it might corrode).

    2. I were thinking the same thing.
      It sure would be easier to use a pre-existing generator/dynamo.
      Then add a bridge rectifier (since all such generators I have seen outputs AC), and a handful of capacitors and using a simple buck converter to get the needed 5 volts.
      And since these wheel generators aren’t typically able to produce more then 10-20 volts, then we don’t really need anything more then some 20-40 volt rated capacitors.

      1. With a buck converter you have to do some MPPT. This generators are normally more current source than voltage source. So the easiest and most reliable solution could be a shunt regulator or a normal linear one.

  1. This is a fantastic design being a bike rider myself over 4 hours daily. I am hopeful that if this design is in place or about to i would appreciate any information regarding purchase of one of these charger set ups. Also would be willing to assist with trials if needed

  2. That wheel looks pretty thin, will it have impact on the tyre? Looks to me it’ s like connecting cutting disc to wheel. Older dynamos had much thicker drum that was connecting generator to wheel, but on the other hand they had much more resistance to turning than this DC motor. Also, I’m not sure how those step-up modules behave when input exceeds 5V, output will probably follow input.

    1. Yep. narrow contact and just a bit above the center line. the skew will help tear the rubber inward as the slot forms.
      If you manage to keep the wheel pressesd against it, the tire(tube) will blow out along the groove at some point.
      Kudos for looking around and utilizing your available items, Just don’t crash yourself in the process. :(
      I can speak from (sorta ancient)experience about bike crashes and road rash.
      Plus it Sucks when your bike gets bent up!
      If nothing els, move the contact wheel out to the tread edge. More meat to work against there.
      Of course then there’s mud and water.
      Sigh… the wider wheel improves things.

  3. There was a time, when bikes had a dynamo to run the light. 6V AC. With bridge rectifier, a cap and a regulator you get 5V. Mine has it even in the wheel hub, no drag when no power is needed. Some people think they are “environmentally conscious” and use button cells to power their bike lights! Just stupid.

      1. The real answer is that neither bicycle headlight coin cells nor bicycle dynamos are causing a significant environmental impact. At that point it’s just a pissing contest to debate who is greener.

  4. I like my commercial dyno-hub, hand built wheel, and long life tires because drag, durability, and longevity over hundreds or thousands of miles matters.
    There is a time do DIY and a time to look for a well engineered system that will allow your bicycle wheel and tire to last long distances.
    This is a great hack similar to one I did in the 90s when I had no money but wanted to charge batteries for my 2m radio because back then I took incoming calls to a pager and called out on the autopatch.
    If you don’t have a built in dynamo for your bicycle this hack or another tire dynamo is a great way to have a cheap non-permanent so zero drag contingency charging system for if you begin hear the sad low battery boops from your phone.

  5. If you ride mountain bikes, like i do, neither tire pushing dynamos nor hub dynamos are an option. The dynamos pushing against the tires wont work with the big knobby offroad tires and usually slip or block up as soon as you get a bit on the muddy/dirty side of the trails. The hub dynamos, at least the ones i’ve seen so far, are not made for off road bikes. We usually run thru axles on the front fork because the quick release stuff is just not made to take the abuse and they are pretty dangerous if they decide to quickly release on a bumpy road.

      1. Thanks for the hint, never saw them at any local store before. Just checked some prices; 4000 taiwan dollars is around 110€, and prices of online shops around here seem to be more in the +200€ range. I’d rather take my usb powerbank and move a bit more weight i guess…

  6. I think using the small sprocket used for chain tension could be attached to a generator/dynamo. Although in that case it will be hanging low on the bike and face its own share of dangers.

  7. It just cannot work for a longer time because there is nothing to pull this gear to the tire (spring or something like that). Also there can be problem with sufficient power – I tried something like that with cheap side mounted dynamo with some rectifier, cap and regulator and power was too small – the phone was turning on display and drying battery faster than without this “charger”. Now 3W hub-mounted dynamo (with the same circuit) is doing the job and is also more quiet.

  8. It is, by the way, an insanely stupid idea to hook up a phone to a power source as unstable as a dynamo. So much so, that the guys behind german “Forumlader” http://www.forumslader.de/automatiklader/ have written books worth texts on where the problems are with that and how to fix them. tldr, you need a pack of rechargable batteries and a whole lot of smoothing capacitors if you dont want to kill your phone.

    I’m sorry to say it, Kristina, please stop posting these articles. This crap belongs on Youtubes trending page, but not on a blog that regards itself towards a hacker/engineer audience.

    1. Thank God I see a bit of common sense here. Potato cell children on Youtube have shown us that phones will show signs of being charging when plugged to almost anything but that doesn’t mean that they will charge the battery to its full state or that the battery life expectancy won’t suffer due to the ugly discontinuous current excursions.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.