I often explore the countryside with my smartphone saddled on my bicycle providing GPS information. This is battery-intensive so I would like to charge the phone while riding.


  • Not using secondary batteries. Must tap bicycle motion, vibration, solar energy or anything similar
  • Must not make the bicycle sensibly slower: most energy-efficient solution wins
  • Output can be plugged into the smartphone's Micro-B USB slot
  • Under 100 USD

Micro-B USBSmartphone on bicycle

  • How flexible are you on that $100?
    – Andy
    Commented Sep 24, 2015 at 14:26
  • Also, what kind of brakes do you have on your bicycle?
    – Andy
    Commented Sep 24, 2015 at 14:30
  • @Andy: Can be double if really necessary, but I hope not. Commented Sep 24, 2015 at 15:25
  • @Andy: My brakes are exactly like this: sheldonbrown.com/images/vbrake-overallsm.jpg Commented Sep 24, 2015 at 15:26

2 Answers 2


I recommend Siva Cycle's "The Atom".

The Atom - Siva Cycle

This product mounts to the rear wheel. Siva has good instructions on how to install it.

The Atom - Mounted to rear wheel

Using this, it can charge constantly via USB. I use it to charge my HTC M8 while using it's GPS features. It also has a battery pack, which you can use for power while away from your bicycle.

One very important note: This does not work with disk brakes. You indicated that you have rim brakes. This means you won't have a problem with your current bicycle. It is something to remember, though, when you replace the bicycle.

Siva has the product for sale at $130. Amazon has the same price. It is weather resistant to IP-4 standards. This protects you against splashing water.

I have not noticed any slow down while using this. Installation took me about 5 minutes.

  • Do you have any comparison with solar solutions?
    – Adam Wykes
    Commented Aug 10, 2016 at 23:12
  • @AdamWykes Solar solutions likely need quite some surface area and will be rather heavy. That said, in a sunny climate and if it only needs to work in great weather conditions and say in the 6 hours around noon, then it might be feasible.
    – Nobody
    Commented Aug 11, 2016 at 0:02
  • Yeah my own investigations of solar have revealed its limitations. I was wondering how this solution stacked up. Andy's answer was very helpful, but I was hoping he'd put in something about how much cycling it took to fully charge his phone.
    – Adam Wykes
    Commented Aug 11, 2016 at 1:53

The best, most energy efficient solution would be a hub dynamo.

A basic model of hub dynamo would be something like the Shimano DH-3N31, available from about €30. There are more expensive models, which are lighter weight, and a bit less drag. But you probably won't notice much difference anyway, unless you are riding a fast, lightweight bicycle. Note the DH-3N31 is only suitable for rim brakes, there are similar models that work with disc brakes (eg Shimano DH-3D32).

You would need to get the hub dynamo built into a wheel. You could rebuild your existing wheel, to replace the hub, or maybe easier just to buy a complete dynamo wheel. Cost from about €75, depending on what sort of hub and spokes you want etc.

Then you need something to take the power output from the dynamo, and convert it to a USB output. A good option would be the Busch & Müller USB-Werk, for about €65. This has a built in cache battery, so it can supply constant power to your phone, even if you slow down or stop.

There are also dynamo powered lights, with USB output. This could be useful if riding after dark. Though they are more expensive. eg Busch & Müller Lumotec IQ2 Luxos U, for €120.

  • Thanks! Would you mind adding one or two pictures to make the picture immediately understandable? Cheers :-) Commented Aug 13, 2016 at 13:11

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