Using a dynamo to charge your FP

Continuing the discussion from Do you have experience with the Finn bike holder? Alternatives?:

Wow, I really like the idea of using a bike dynamo to charge my FP! :smiley: But is it good for the battery? Plus: Really great would be a way of using a dynamo bikeless, e.g. with a handle to charge your FP on the go!

But let’s start from the beginning: @paulakreuzer, how did you connect the USB cable to your dynamo?


OK so here is what I use:

A Shimano DH-3N20-A dynamo. I can totally recommend it.

A Revolt PX-8166-675 adapter. In theory it’s quite cool because it has an output to connect 2 lights and one USB output for the Phone, but it doesn’t really work well. In reality it can only power either lights or the phone, not both at once.

A nice led-backlight…

…and a really strong front led light.

I can’t recommend the Revolt thing, I’m sure there are better options out there.


Oh, so you are using a hub dynamo and not a bottle dynamo! I didn’t think of this possibility…

I imagine that in place of the Revolt adapter one would only need a female USB cable, cut it open and connect it to the power outlet of the dynamo.

PS.: What I was thinking of was connecting a handle to a bottle dynamo and charging the FP by winding manually. How cool would that be! :slight_smile:

Just like one of these:


Yeah that would be cool.
I’d really like this device with a USB output instead of the light. Although all that spinning probably wouldn’t be good for the cable.


did anybody already try to use the FP2 on a bike for navigating and use the power supply by a hub dynamo?
Off course I have to buy a quite expensive, special recharger for the phone. But I know, that the FP2 reacts weak on some rechargers. So I would appriciate it very much to recive some experiences from other users on that topic, to avoide a misinvestment
Thank you a lot!

I saw some dynamo adapters in bike shops, they seem cool but are quite expensive.
I didn’t try them. They say MAXIMUM value is 1.5A. Is that enough for the FP ? And how fast would you need to ride to reach them ?

Also, the power will be very intermittent, when you accelerate, stop at traffic lights etc… Maybe that’s why you need an expensive regulator, or intermediate battery.

You could use a powerbank that can charge a phone at the same time it is charging. That would give you a steady power supply and could be used in other occasions as well.

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Yes, there are some powerbanks, rechargeable by a hub dynamo, such as the “Dynamo Harvester” or the “Forumslader”, both between 100,- and 200,- €! And again: Did already anybody use such a charger in connection to the FP2?

Sorry I didn’t use a dynamo charger, i hope someone else can advise you.
But as others said, it should not be an issue if you use a cache intermediate battery.
I use a powerbank, charging from regular mains, and it has no problems charging the FP2.

I think the thing is that all power sources other than the wall socket are inefficient in comparison.

If you want to be independent from a wall socket, you should probably get a solar charger. Consider one of the sustainable alternatives, that have been working together with Fairphone: Little Sun or WakaWaka.

PS.: Read more on this here:

I do have solar panels on my houses roof, But I don’t think, that this is a solution for collecting energy by riding a bike. You very often change the direction and you would have to justify the solar collector again and again. And you are depending on sunny weather. Therefor I think a hub dynamo is a much better solution for harvesting electric energy riding a bike. At the german online magazine “Fahrrad Zukunft” there is a very informative collection of articles about that subject (, but of course the rechargeable powerbanks are not tested with a FP2. But it says there, that you can harvest electrical energy more than 5 watts at a bike speed of 20 km/h. The loss of speed for producing the electrical energy is between 0,3 - 1 km/h, depending on the speed and the power consumption of the electrical devices you are running.

The difference, however, is that with a solar charger, you don’t have to provide the energy yourself. :wink:

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Your link and content to the magazine looks perfect to me. Doesn’t it answer your question beside the question about a testing person that you are looking for ?

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May be, I have to be the first one, who is testing it. And I am confident, it should work. On the other side I remember trouble, I have had with charging the FP2, depending on cable and charger. I wouldn’t like to have it with an 150,-€ device again. I could ask Fairphone, but when would I get an answer, if I get a helpful one at all?

(I don’t want to do publicity for any device but I think it’s necessary to mention some model names to describe setup as detailed as possible…)

I’m using a bike with Shimano DH-3N71 dynamo. Attached to this dynamo is a device. With a short cable a FP2 is connected. Starting with nearly 20km/h the FP2 begins to load. The app “Ampere” shows about 50-250mA of loading current. Strange is that the loading current shown seems not to increase when riding faster (tested up to 30km/h). Don’t expect to really "charge"your phone with this setup. Battery percent increased about 1℅ in 20 minutes. But at least you don’t lose energy while riding your bike, so you remain autonomous… :slight_smile:


Hm, I didn’t come on with this stuff until now. I contacted Thomas Tryer, who is manufacturing the ‘Dynamo Harvester’ and he promised to me to send me a harvester for testing with the FP2 for four weeks. I ordered it, but than I didn’t get an answer from him anymore. My be, he has been on the Fairphone forum and read about all the trouble some people did have with charging the phone? And he may think, no news is better than bad news.
But spring is coming and the main reason for me to buy the Fairphone was to get into contact with the world around on our tandem bike tours around Europe, for example to find a place to sleep in the evening. Also it is importand for us, on our journeys to stay in contact with relatives and friends. Until 2014 I used a Nokia C7 phone for eight years, and it is still working, but you know the Nokia story: No service for Symbian phones anymore, when they escaped into the Windows world. For other needs I really wouldn’t need a smartphone.
But now I will try to get another proper charger to use the phone on tours, sometimes without wall chargers within reach for days. The next target is to find out, whether the ‘Forumslader’ does work together with the FP2.

I used a USB-charger on my bike tour for my GPS. I connected this device: to my hub dynamo like in the picture explained. The min-USB connector fit for the GPS and during cycling I could use it without any battery loss.
Back home I cut off the mini USB connector and exchanged it with an USB 2 (female) connector from an USB 2 extension cable I didn’t use. Now I can connect any USB 2 cable to the dynamo. With the switch on the device I can decide whether I use the energy from my dynamo for my lights or for my USB-port.
But I think the best way using it for a smartphone is to charge a power bank from the dynamo and use the power bank for charging your phone. This will make sure you have an constant loading current to your phone.

I got a similar experience to @Volker : [quote=“ff2u, post:15, topic:5660”]
Don’t expect to really "charge"your phone with this setup. Battery percent increased about 1℅ in 20 minutes. But at least you don’t lose energy while riding your bike, so you remain autonomous… :slight_smile:

Sadly I used the setup just ones with my fairphone 1. With a car navigation app opened and the display switched on all the time I even lost percentage from my fairphone battery while cycling > 20km/h.

I don’t think that you can produce enough energy with a bike to charge your phone similar to charging your phone with your computer (with 500mA). Doesn’t matter which product is connected between your dynamo and your phone. Maybe with induction…

Well, I hadn’t mentioned that above. But during my tests I had the screen on, GPS activated and bike navigation (osmand) running. And it did still charge (and not discharge).

Did you use the FP1 oder 2? Maybe I give it soon another try and report my experience with the FP2. I used by the time sygic for the navigation and it was freezing cold. My phone warned me a few timesduring the trip that it is too cold (~0 °C). Maybe that was eating up my battery as well. Nevertheless I don’t think that you can produce enough energy to use AND charge your phone. But if I’m wrong please tell me, because that would be awesome =D

I was using a FP2 at “normal” temp. I may try again and give you more details if needed.