Talk:Hub dynamo

Non-light usage
Hub dynamos can be used to power more than just lights. For example, some automatic shifting systems for bicycles are powered by a hub dynamo. In addition, they can be used to re-charge mobile phones, iPods, GPS devices, etc (see BioLogic ReCharge). Citeoplasm 03:16, 7 August 2007 (UTC)

hub dynamo for braking
I wonder if I can use some stronger hub dynamo as a magnetic braking system for downhills. When you need to brake immediately you just press conventional brake.--Martian742 00:44, 29 September 2007 (UTC)


 * Find out how much power it supplies, then dump the power into a resistor. For a 3W generator at 6V, you'd need to dump half an amp. That means a 12 ohm resistor with a power rating of (duh!) 3 watts. Connect this through a switch in parallel with the lights. When this switch is on, the dynamo will be at it's most resistant. And your lights will probably dim a lot, or go off!


 * To be honest, 3W isn't much power from a bike wheeling downhill. You'd need to work out how much energy, in watts or joules per second (converting between the two is simple) you want to dump. Get a dynamo with that much power output, then fit a resistor that will suck enough amps at the dynamo's voltage. For 6V, divide the wattage by 6 to give current. Divide 6 by your current to get the needed resistance, in ohms. The resistor needs to be the same wattage rating as your dynamo, or a bit more for luck.


 * I think in practice though it would turn out too expensive to be practical, and a dynamo that can produce, say, 60 watts probably doesn't exist for bikes. The standard is 3W. A 60 watt motor driven by the wheel would work, or a motorbike alternator, but I'd guess these would need a high RPM to work, so you'd need gearing for a bike. All in it'd be a bit of a mess, but prove me wrong. I guess that's why, for the low energies involed, they stick with friction brakes. 188.29.164.99 (talk) 00:23, 5 September 2013 (UTC)
 * could that type of hub be designed to 300% or more resistance to be applied for bracking so you could conserve your friction brakes for emergencies on longer tours for example? 173.180.34.118 (talk) 23:12, 21 April 2023 (UTC)


 * This is not quite how the generators work. They're not really limited to 3W, that's just the standard power that's given.  In reality, both their current and voltage - and power of course, vary with both speed and load. (See: http://www.mikrocontroller.net/attachment/14850/BikeLight.pdf - look in particular at figure 4.  Also: http://www.ihpva.org/HParchive/PDF/hp49-1999.pdf, in particular page 9 figure 5.)  The current is mostly limited to 500mA, but the voltage varies with speed/rpm, and it also varies depending on the (electrical) load applied.  If you can apply more electrical resistance, you can increase the power output (to some limit, of course).  So, no, you couldn't use a bike hub generator to act as a 60W brake, but you probably could get one to act as a 6-8W brake.  Kjmclark (talk) 19:17, 13 August 2014 (UTC)

Electrical Characteristics
Does anyone know the electrical characteristics for the hub dynamo? Can you model it with a thevenin or norton equivalent one port, where the current/voltage source and the resistor are functions of the rotation speed? I assume there are different limits where the different brands and models of hub dynamos will break, for different speed and load, but are there any general "don't":s? Is the output sinus-shaped (or close to), or is there a lots of big harmonics? --Petter, 130.236.56.173 (talk) 17:49, 26 January 2011 (UTC)


 * Note for the one with the same question, until the question has been better answered: From the first graph on |this page, it seems the Norton equivalent one port works, where I ~= 0.37 A and R ~= 6.5* Ohm*s/m is a fairly good approximation. From an efficiency point of view, I rather believe in the Thévenin model, because the wheel rotates easier without any load. --Petter, 130.236.56.173 (talk) 22:59, 26 January 2011 (UTC)

How to link to Dutch page?
In Dutch is Hub Dynamo is Naafdynamo. This one is redirected to a chapter of Fietsdynamo (Bike Dynamo) (it was consolidated). How can these words (Hub Dynamo and Naafdynamo) be related in WikiPedia? Fietsdynamo is already linked, and let it jump to the heading Naafdynamo on the Fietsdynamo page seems not possible. What to do? WritersBlok (talk) 21:55, 18 July 2013 (UTC)

Efficiency figures
While I appreciate the efficiency figures I don't think it should be implied that they are a function of speed. They are almost certainly a function of RPM and probably load and perhaps other factors, but not speed of the bicycle. 75.119.225.176 (talk) 02:46, 10 December 2013 (UTC)

Shimano Models
The sentence referring to Shimano dynamo hubs desperately needs an update, the models mentioned have been discontinued since at least the early 2010s... I could help by providing some of my own experience, but it would mostly be without references. Is that OK? I think it's against wikipedia policies. 2A02:3100:5BA9:B00:14BD:AB1F:BB1D:4806 (talk) 15:14, 5 May 2024 (UTC)