MTB Dynamo and USB power

Doing epic multi-day rides brings many challanges, one of which is how to get some power for your gizmos if your bivying out away from civilization night after night.  The lack of phone is almost a positive but sometimes it can keep you sane and might save your life one day, but If your a numbers geek like me you have to keep your Garmin powered up day after day.

There are USB powerpacks that run on AA batteries but I fancied building a more versatile on bike system. Thanks for the Inspiration from Endurance racer Rob Dean and his Deanamo.

Lots of funky colours - but black was cheap

So I purchased a Shutter Precision SP-8 disc brake dynamo  from inteligent design cycles Ebay shop which has some impressive spec and looks superb compared to the Shimano and German competition.  When it arrived it’s a bit disconcerting as the hub feels super stiff and notchy as you can feel the magnets grabbing the coils as they pass, After AJ cycles built up the Stans Arch29 rim onto it, it was barely noticeable and spins on fine.

The Dynamo output is 6v AC which is easily rectified and smoothed to produce some DC for lighting power, and a simple 5V regulating circuit gets this down to USB power. As I’m still messing about with this all the electronics went in a sealed box; which could easily be halfed in size, but I wanted to leave room to tinker in future. The JackPlug MK1 is born.

JackPlug power system

The waterproof switch is in the Dynamo output line so it can be switched off when unloaded, which according to the makers results in only 0.5Watt of drag on your cycling, it also stops the capacitors charging up to high levels too. That and the socket were robbed off an old Lumicycle lamp. The socket allows a direct connection to the lights. The top lead is the Dynamo connection plug which is not the best looking bit of kit, so I sealed it with self-amalgamating tape.

The other flying lead is the secondary USB power where I’ve utilised some superb sealed waterproof plugs and sockets I was donated off some light and motion lamps. Homemade adaptor plugs then allow connections to the normal USB mini plugs or Iphone plug. It’s intended that in use one connection charges the handlebar mounted USE Exposure Diablo while the other feeds the Garmin, or phone, or external battery pack which will sit safely inside my frame bag. Phone can also be charged whilst the Garmin is powered as another option.

Good Socket
Super plug and sockets

The box is cable-tied to the bike headtube out of the way at the moment. I think I’ve got a pretty versatile system. I can mix and match what I’m powering or charging. Initially I’m also charging a Duracell Lithium Battery pack (which incidently comes with a neat short USB lead) which gives you stationary voltage/charging use too.

It only takes about 4 mph for the USB power to be active but of course it’s off when stationary. This causes a slight problem with the USE Diablo as the light charges quite happily while its on (green LED flashing) but the Smart Port Tech then wants to switch off the light when the charging voltage is removed; just when you want the light at gates etc.

This is easily overcome at the moment as you can easily get enough light on low power from the lamp to cover a summer nights riding. Charging a simple Piggyback battery mounted neatly on the bars instead of the lamp can boost the range and allow the use of higher light settings, and then you can charge either or both back up during daytime running. Another option could be to  use Exposures 3.5v to 5V step up lead and use your light system as your battery backup power for your Garmin or phone.

The lighting part is just a stop gap at the moment, as I seem to have no spare time, and the final plan will probably be a combination of a very old tired MaxD LED light and smaller internal battery with my dynamo circuit built inside. But the option to run some cheap LED units direct from the unregulated 6V is also a plan.

The first big test is next week, the Cairgorm loops will be a tough test of the ruggedness of the sealing and if it’s going to be “raced” then only the weak will stop at night 😉 or maybe I’m being optomistically stupid! More on that soon.

Duracell USB power
handy little USB power pack 1150mA Hr and 0.5A output

Oh final note to myself really, if I’m feeling flush we could always go the top dollar route and get one of these SuperNova E3. It’s neat, very light and powerfull, takes 6v AC input and with stationary backup of 7 mins too, top kit. Lets see what USE come up with to rival it.


4 thoughts on “MTB Dynamo and USB power

  1. Thanks for the kind mention 🙂

    I’ve owned a Supernova E3. I sold as I was so disappointed with the light for technical off road use, the standlight is a “be seen” light only for 7mins, not a light to see with. Having seen the specs, I’d strongly recommend the new Exposure light when it comes out, it’s designed for proper off road use, not just a bright urban commuter light.

    Nice project, neatly executed, love your tidy connectors to give it that pro finish. Good work 🙂 Dynamos are the future!

  2. Hi,
    Lovely work and well written. Thanks.
    I wonder if you can share with me where I can get hold of DC regular to AC.
    Searching the web for some time and its not easy to find.

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