PDA / GPS bike mounted USB charger

December 27th, 2008 by Arend Leave a reply »

An update on this post is found here and a step by step guide is posted here: (still a work in progress)

I love to go on holiday by bike. And as a tech nerd I can’t be bothered by plain paper-maps!
Having a GPS-mapping application like OziExplorer on your bike makes navigation very easy.

The problem however is with the rapid draining of the battery-powered GPS / PDA.
Especially mobile phones / PDA’s have a very short (battery) lifespan, often no more then a couple of hours when the display is always on and a GPS-application running. Normally I just dragged a lot of AA aka penlite batteries with me and powered the phone with a simple battery holder like this one:
4_aa_battery_holder1

Of course this isn’t the best solution and I was looking for better alternatives.
Then I stumbled upon this genius, hub-dynamo driven “Bike mounted USB Charger” on an English bicycle forum.
The idea is quite simple. You take a HUB-Dynamo (Shimano DH-3R30) (I ordered one from ebay for less then 40 euro).
The hub-dynamo generates an alternating current that needs to be rectified and the voltage output should be regulated to 5 volts for USB powered devices.

The hub-dynamo:
dscf2834

These are the parts you need, available at any electronic (parts) store.
D1 – D4     1N5818
C1             2200uF   16v
C2, C3       470uF     63v   Low ESR
C4             .47uF      Tantalum bead
C5             22uF       Tantalum bead
R1             47K         .25W

Solder the parts according to this schematic:
dynamo1sbp

And there you go, you have the best energy- efficient charger, all done with green energy!

This is my effort. It still needs some good housing and connectors but it works perfectly:
dscf28291

For more detailed information visit the bike forum at http://yacf.co.uk/forum/index.php
Many thanks go to Simon Galgut for providing the electronic schematic.

20 comments

  1. T says:

    Brilliant work. I’m curious how it performs for you. Have you thought about adding batteries?

  2. Arend says:

    It works quite well. It even charges the onboard battery when driving at a reasonable speed (20 km/h). But I haven’t tested it with my new HTC Desire yet. This phone will consume a lot more energy and is known to even drain the battery when connected to a regular car charger (500 mA) instead of the HTC OEM version rated at 1 Amp. Adding batteries might be needed now.

  3. Matthijs says:

    Could you mail me a pic of the bottom side of the printboard? And could you tell me to which pins of the USB socket I have to connect the + and ground?

  4. Phil Waud says:

    Thats really simple!

    If I connect 4 AA rechargeables between the +ve and -ve before C4, will I be able to charge them from the hub and run my iPhone 3GS?

    Sorry to ask, but Ive been trawling sites for hours and my head is spinning!

    Phil

  5. Arend says:

    I’m working on a step by step guide in this post:http://www.arenddeboer.com/diy-hub-dynamo-usb-charger/

  6. BoVis says:

    Dag Arend,

    leuk ontwerp ! Maar ik kom er net achter dat ik een LM 2940CT 12 V ic heb. Ze bestaan in verschillende uitvoeringen, en ik moet dus de 5V hebben ..

    grtz,
    Boaz

  7. BoVis says:

    Hij doet t !
    thanx !

  8. BoVis says:

    For a garmin Nuvi 1000mA is required. Is there a simple modification possible ?

    garmin nuvi GPS:
    http://pinouts.ru/GPS/garmin_nuvi_power_pinout.shtml

  9. Arend says:

    The hub-dynamo is the limiting factor, a 3Watt hub can only generate 500mA.

  10. Cage says:

    Could you mail me a pic of the bottom side of the printboard? And could you tell me to which pins of the USB socket I have to connect the + and ground?

    • Arend says:

      Totally missed your reaction, do you still need it ? In the first paragraph I have a link to a step by step guide for building this. It shows you how to connect things up.

  11. Adam says:

    I have a Garmin eTrex 20 that has a pretty decent battery life (I get about 23 hours with the backlight off on a pair of cheap AA batteries) It will run off of USB power, but once that power is removed, it will automatically shut off versus switching over to the on-board power. Would adding a decent sized capacitor in series with the USB load help alleviate the on-off associated with stop and go biking? My EE knowledge is rusty at best… I just enough background to get me into trouble.

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