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smurf hunter 11-16-07 10:19 AM

Shimano Nexus Generator Hub
I started reading Sheldon Brown's site about generator hubs. I've done a bit of wheel building, so the prospect of replacing my front hub or a new wheel doesn't intimidate me.

My bike setup is a Kona Dew (hybrid) which has 700c Velocity Deep V rims on 160mm disc brake shimano hubs. I see there's a nexus dyno with centerlock disc mount - which is what I'd want.

Some newbie dyno hub questions:

1) how do I decide on light options? 1, or 1+secondary? Schmidt, Lumotec?
2) what practical impact does a dyno hub have for normal bike riding?
3) can the power generated be used for other things, such as recharging USB devices or cell phones?

I'd be willing to spend $150-200 for hub/lights plus the cost of new spokes (I'm sure the hub flanges are bigger, so this is an excuse to get some nice DB spokes).


n4zou 11-16-07 12:41 PM

I run a dynamo and use 4 Ni-MH batteries as a current and voltage regulator. I use the batteries to supply clean power for the LED lights or USB port and devices connected to it. The batteries effectively regulate the voltage. As the voltage produced by the dynamo approaches the rated voltage of the battery pack a high impedance load is imposed on the dynamo so voltage is never higher than what the batteries are designed for. I use 4.8-volts as the voltage is consequently regulated at about 5.2-volts with the dynamo engaged. This is well within the standards set for USB ports. The dynamo provides a relatively constant 500mA at its rated speed and above. The batteries will absorb excess current produced by the dynamo using it as recharging current. Care must be taken not to overcharge the batteries. You can calculate how much time to disengage the dynamo per hour using the trip time feature on a Cyclocomputer. Determine how much excess current is recharging the batteries versus current draw with the dynamo disengaged. My two LED lights draw a combined 380mA leaving 120mA of excess current used for recharging. 120mA is also the suggested slow recharging rate for Ni-MH batteries This is about right when traveling in city traffic with stops but is too much recharging current when traveling on highways without stops or hill climbing where speed drops below 8 mph. In these situations I simply disengage the dynamo for 15 minutes of every hour of constant 10+ mph traveling.

In the event the batteries become completely discharged the dynamo may be used to rapidly recharge the batteries at the full 500mA current produced by the dynamo by opening the light control switch and no USB devices plugged into the USB port. 500mA is also the suggested rapid recharging current for Ni-MH batteries.

USB ports include a 5-volt power supply to power USB devices. By adding a USB port to the circuit USB devices like GPS units and some Cell phones designed to be powered and recharged via a USB port may be plugged in for operation and recharging from the 4 Ni-MH batteries. Care must be taken not to overcharge the device and the batteries. Pin 1 is the positive +5 lead and the wire color is red. Pin 4 is DC ground and the wire color is black. The other two wires are data wires and are not used or necessary. These wires may be removed.

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