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Electrical power on tour

Peter Weeks2018-07-30 16:38:22

When touring Jen and I sometimes run out of electrical power for keeping the sat-nav, two phones and the camera charged up.

So, when getting a new front wheel, we specified a Schmidt SON28 dynamo, primarily aimed at charging these devices and also to power front and rear lights. 

One headlight, the B+M Lumotec IQ2 Luxos U Senso Plus, has a USB socket for this purpose, but it has poor reviews for quality and reliability.  Only one I have found. Does anyone have experience with any other headlamps with a USB socket?

The other option I can see is to buy a USB charging device e.g. Sinewave Cycles Revolution USB which converts dynamo power to USB, and separately take power from the dynamo to the lights.

Suggestions and comments welcome!



Peter Weeks  


philip tregear2018-07-31 14:39:43

 i have looked into this. the trick seems to be to place the right sort ( charge through) rechargeable lithium battery of small capacity between the usb out and your devices. All these usb charging devices seem to suffer this problem and the right battery is the fix.It has to be the charge through variety. with this setup your devices will charge and stay on regardless of lo, high or no voltage coming through the system. it also means you can unplug at night to use your lights , using the battery to keep your devices charging if needed. without the right sort of battery between the usb and your devices , devices will either switch off or drain their battery depending on how fast you are going. only rarely will they charge and stay on. I am not an electrician, so i dont follow the physics. but I found this out through talking to touring cyclists and reading about it. it may well be that the dynamo light you are looking at is just as good as the other bits, if you add the battery ( which you will need to add to any set up)

David Hammond2018-07-31 16:39:45

This is what you need.  I have one on my solo and it keeps phone and Garmin charged although it does dim the front light a little if charging at night.  I do also use via a charge through battery as a backup. 

Terry Barnaby2018-07-31 20:42:47

Wow those are expensive for what electronics they have in them. Will have to design and make some to sell :)

I think you are going to be hard pushed to keep two phones, a sat nav and a camera charged up with just a dynamo. The Schmidt SON28 appears to be able to produce 3 Watt's presumably at reasonable cycling speed. A mobile phone will take around 0.2 Watts on average when mainly idle with very occasional use assuming there is a reasonable signal level and that is continuous power drain. In active use it may take about 1.5 Watts.

So some rough figures for 24 hours:

Item Watts Time used Watt hours

Watt hours 5V

Dynamo 3 4 12 9.6
Phone idle 0.215 24 5.18 5.18
Phone used such that it lasts 8 hours 1.3 8 10.4 10.4
GPS rough 0.3 4 1.2 1.2
Good Solar Panel 10W 350.0 x 285.0mm 5 (50%) 6 30 24
  • Assumes you cycle for about 4-5 hours a day.
  • Watt hours 5V is lower due to 80% efficiency of Dynamo/solar to 5V convertor.
  • So you will be able to keep almost 2 phones going if you hardly use them or almost 1 phone if you use it a fair bit.
Might be better to have one or more largish mobile phone battery packs 10,000mA (37 Wh) or more (will keep a mobile phone going for about 7 days or two for 3 days and charge them when you are near mains power. Could charge this with the dynamo and if you had room a solar panel on the rear carrier to get a longer time from it (If its sunny!).
philip tregear2018-08-01 09:09:24

Hi Terry, your table makes a lot of sense. I know nothing about electrics but the consensus of what i have read agrees with you: These electrical interfaces between the dynamo and the device are all much of a muchness and ( in all probablity) utilise very similar circuitry and components. they all require a rechargeable battery as an extra stage. This prevents the device being charged from misbehaving.. I understand, from what i have read, that that battery has to be of a particular type and not large in capacity to enable the charger to work most effectively. such a setup would enable a traveller on a bike in a remote place to keep their sat nav and phone charged enough to navigate, take pics, communicate. This should suffice, especially when weight and space will also be key considerations.

Off the shelf the german light witha usb connection seems to be the best choice, although the risk would be breaking it whilst on the road. Beyond that, perhaps the simplest/ cheapest straight from the hub which I think are about £25.


If you are going to make some, please let me know via this forum what they are/ pics/ price. I would be interested.

PS I run a SA dynamo front hub/ drum brake to a rear and front light. I can switch the front light off but not the rear. This is a commuter bike and, at this stage, I am just interested in making a charging system work reliably and understanding it`s on the road performance. It is my son who does the wild bike tours ( south america etc). I would use what i learned on my bike to help him build the right bike for his next tour ( possibly china).


best wishes