Hub dynamo questions

[e-rider]

I've never used a hub dynamo before but I'm considering one for the touring bike. I have a number of questions:

1. Can anyone tell me the difference between these two Shimano XT T780 hubs? The name only differs by "1N" and the description states that one is 6V 3W and the other 6V 1.5W, although the latter is more expensive but appears to put out less power, or is that the power needed as input???

http://www.wiggle.co.uk/shimano-dh-3n72a-dynamo-front-hub/#tabCustReviews

http://www.tritoncycles.co.uk/components-c9/mtb-hubs-c120/shimano-dh-t780-1n-deore-xt-hub-p9068

2. Looking at front light units, they all seem to have different brightness outputs e.g. 15 lux up to 80 lux. I don't understand how if the input from the dynamo is limited, where does the extra brightness come from???

That's all for now thanks

 

[Yellow Saddle]

I think the pricing is a mistake. The 1.5W one was always cheaper than the 3W one.
Get 3W, that gives you enough out put for a good headlight and even a tail light if you want. You may even be able to charge some smartphones or GPSs with the 3W one, depending on the input requirements of the device. Some devices will not charge if they don't receive enough power.
The power is output BTW.

 

[raleighnut]

They are also supposed to have less rolling resistance when the power generated is being used (i.e the lamp is on) due to magnetic 'eddy' currents within the dynamo.

 

[Yellow Saddle]

They are also supposed to have less rolling resistance when the power generated is being used (i.e the lamp is on) due to magnetic 'eddy' currents within the dynamo.

That would defy the laws of magnetism. They have more resistance when the light is switched on.

 

[raleighnut]

Having looked again it is the Shimano HB-NX32 that has higher 'drag' when the light is not switched on, according to the tests on t'iternet performed by Cycle Touring and it is surmised that the other coils are energised by the current generated leading to more drag in another article. Best results came from a SON hub-dyno.

 

[MichaelW2]

1Can anyone tell me the difference between these two Shimano XT T780 hubs? The name only differs by "1N" and the description states that one is 6V 3W and the other 6V 1.5W

2.....15 lux up to 80 lux. I don't understand how if the input from the dynamo is limited, where does the extra brightness come from???
That's all for now thanks

1. All dynamo hubs output 6v/3w. The 1.5w is a mis-print.
2. Lamps convert electricity to light and heat. More efficient ones produce more light and less hot air.

Advanced road bicycle lamps direct the light into the most effective usable area, mostly a rectangular patch or road with a small side illumination. Generic flashlights and off-road lamps produce circular beams.
Busch and Muller are hard to beat and worth the money.