Sunday, 10 February 2013

Long Term Test: Shimano hub dynamo.

Shimano DH 3N20 hub dynamo on my folding bike
I've just got a Shimano hub dynamo for my little bike, and I fitted it yesterday.
I have a 100mm front OLD on my folder, which is wider than many folders, and is the same width as the front wheel on a "normal" bike, as well being the same size as a child's 20"-wheeled bike.

For those of you with narrow wheels, try this link to a chap who has experience with Shimano DH F7 series hub dynamos with an OLD of 74mm (my Cinzia had an OLD of 100mm, same as a "normal" bike)
Score: 9 out of 10.
  • bought one ready-laced into the wheel, saving a lot of hassle, and at a competitive price
  • fantastic light output when coupled with an LED headligh, particularly when used on a small-wheel bike (I have 20" / 406 mm wheels)
  • no more tyre wall slipping (that happens with a "bottle" dynamo
  • bigger axle diameter than my "old" wheel, so I had to use an angle ginder
  • fitting where cable plugs into hub seems a little insecure, so I taped it just to be sure

It is the bottom of the range model - the DH 3N20.
I got it already laced into a wheel from Dutch Bike Bits, appropriately enough based in Holland. David Hembrow, who runs Dutch Bike Bits, is British, and lives in Assen, so don't be afraid to order in English :-)
It cost me about 51 Euros (about 43 pounds or 68 US dollars)  - you are supposed to oder the little clip-on terminal connector separately (for an extra couple of Euros), but, being a dummy, I forgot. David very kindly sent me a gratis connector in with my order (which had quite a few other things in it as well).
Thanks David - you are a star! (I will settle up with David on my next order!)
The price of the complete hub dynamo/spokes/wheel rim is only about the same as many bike shops charge for JUST LACING UP A WHEEL !!
There is a rather hefty postal charge from Holland to the UK (something in the 25 pounds / 40 dollars region), but if you order several things in the same package, the postal charge barely changes.
(I ordered a the dynamo/ wheel, two stands, two lights, a front rack. and some bits and bobs all in the same order!), so if you are ordering from David, order big and infrequently! (my previous order was three puncture-resistant tyres, a heavy-duty rear rack and a saddle).
Shimano DH 3N20 hub dynamo already mounted and spoked into a 20" (406) wheel. The complete assembly was supplied by David Hembrow at Duch Bike Bits (in Holland, naturally!)

Fitting was more of a trial than it should have been - the axle size on the new hub was a touch larger than the axle on my existing front wheel.

This gave me several choices:
  1. give up :-)
  2. take the whole wheel and hub apart and see if I can get a smaller axle to swap into the hub
  3. get out the angle grinder, and slightly enlarge the slots in the front fork so the wheel would fit.
I, of course, chose option 3.
With just a touch of trepidation (my use of such tools is perhaps described as "occasional"!), I ground out a bit from each fork end, a bit at a time, checking the new axle each time to make sure I took off just enough, and also got both sides level, so the wheel will sit comfortably and STRAIGHT in the two slots.

After that it was fairly easy going. and, more importantly, it works!
I had a few other jobs to do, like fitting a small front porteur rack and a new LED front light, and then I connected the wiring into the existing wiring for the rear light (I like the look of the rear light I have!).
The combination of the new hub dynamo and the new LED light is certainly impressive - the front light illuminates (although flickering a bit) reasonably well when I am just pushing the bike at a modest speed, (perhaps 2 mph, 3kph), and when I get going to a decent speed (about 10 mph / 16kph) the front light is pretty bright.

After completing the other jobs, I taped up the wiring a bit, too, so it can't droop into the wheels or catch on anything.
The connector which joins the wiring to the hub dynamo seems a bit insecure and/or likely to be affected by weather/puddles etc, so I put a bit of masking tape round that, too - and no problems so far!
(the one mark off, reducing the score from 10 to 9 is for the connector!)

The dynamo hub will be brighter at lower speeds on my bike than on a larger bike because I have 20 inch wheel (406mm size), so my wheel turn more times for a given speed than a bike with regular 26 inch (559mm size) or 700c (622mm size) wheels - in fact my wheels turn a bit more than three times compared to two for 700c wheels for the same distance, so the hub dynamo generates a given level of output at 2/3rds the speed!
Of course, the other side of the equation is that my small-wheel setup results in greater drag from the dynamo hub for a given road speed, but I only travel fairly slowly (mostly on cycle paths and sidewalks) so it is more important to me to have more light at low speed than it is to have a higher maximum speed :-)

Update 18th February 2013:
I've ridden to work with the new setup every day for a week, and ... there is SO MUCH LIGHT !!!
Because I have been working long hours, I made 10 trips with the lights on, one where it was a bit dim, and the lights turned on and off a few times (there is a sensor on my new LED light that switches the light unit on automatically when it is dark enough), and only one in daylight.
On the internet, one reads folks who post things like "my new hub dyanamo is great, and I don't notice the extra work at all", etc. etc. ... WELL, I DO!
It seems to me that the effort to pedal at night is similar to that of using my old "bottle" dynamo - which I have previously indicated to be about half-a-gear's worth of effort, but the light from both lights seems better!

So, to summarise so far, the hub dynamo isn't really saving me any pedalling effort, but the back light is brighter at low speeds (which I often use).
The front light is much, much, brighter, but a good deal of the improvement is no doubt due to the switch I made at the same time from a 2.4W bulb to an LED light.
The dynamo/light combination as a pair is fantastic, and I'll be equipping any future bikes I get with a similar setup!

Update 26th May 2013:
I've been riding about with the new hub dynamo setup for 3 1/2 months now.
It is great.
When it is off, there seems to be very little change in resistance (I have done some before-and-after "roll" tests on a section of road on my route home, where I roll a section of it quite slowly, and the hub dynamo seems to have little effect on how far I roll!), but when it is on, the resistance is noticeable (it really shows up in the "roll test" I described above), but compared to my old "cheap" rub-and-hope dynamo setup, it seems, in my informal opinion, to be a definite improvement. My old tyre wall dynamo used to cost me about half a gear in pedalling effort, but the new setup is a good bit less!

And the light!
Coupled with a modern LED light, this setup is great.
For a small-wheel bike like mine, the extra rotations (my wheels go round about 12 times for every 10 times on a 26"/559mm wheel bike) mean extra light, front and back, at small speeds.
(by contrast, a tyre wall dynamo turns an amount proportional to the amount of tyre that goes past it, and is thus directly proportional to speed, rather than wheel diameter).

Update 25th June 2013:
Not much to say - it is the summer, and I ride to and from work in daylight now :-)
I suppose I could mention that the thicker axle (see fitting difficulties, above!) on the hub dynamo gives more strength to support the "Steco" front carrier I have, but that is really a by-product rather than a reason to fit a hub dynamo.

Update 11th August 2013:
An unexpected shift to night work (the company I work for was short on that shift, and my many and varied talents were required!) meant that here I am, using the lights to get to work in the summer!
Again, I am stunned by the amount of light that the dynamo and LED headlight produce at low speeds!
I often cycle at about 10 mph (16 km/h), although I can touch 20 (32 km/h) on a downhill section, and the light produced while moving in the 5 to 10 mph (8 to 16 km/h) range is really good! (note that, as I have discussed above, with small wheels, you get more light for a given road speed, up to the point where maximum output is reached, which is reached at a lower speed, too!)

I would definitely buy another one!
The only note of caution is, as a colleague of mine at work pointed out, you could buy a lot of batteries for battery lights for the cost of a hub dynamo.
So it up to you - I like the "always ready" aspect of a dynamo - the last thing you want to be doing on a cold, dark, morning when you are five minutes late is messing about with finding new batteries for the lights you accidentally left on all night (been there, got the tee-shirt!).
Cost vs convenience - you choose.
And of course, with batteries, there is all the waste, or all the rechanging time and effort for rechargeables ...
I choose the convenience of hub dynamo lighting!

Update, 16th May 2014:
Since the demise of my Cinzia folding bike, the dynamo hub has sat in my garage.
I'm aiming to build a windmill project next with it.
Check back later for progress!

For those of you with narrow wheels, try this link to a chap who has experience with Shimano DH F7 series hub dynamos with an OLD of 74mm (my Cinzia had an OLD of 100mm, same as a "normal" bike)


  1. You could buy a lot of batteries, but it is a hassle to keep them available and fresh, and any battery light that compares to a 60 lux Phillips lamp is going to have a big appetite for batteries. My dyno lights "just work" whenever needed without any planning or testing, etc.

    So I am thinking to equip my folder and found this review through searching, and it still doesn't provide the answer I seek: What is the over locknut dimension (OLD) for this hub? Many folders require a 74 mm width vs the 100mm industry standard.

    1. I thinks it is 100mm OLD.
      I will measure it for you this weekend, just to be sure.
      I didn't go as fancy as the 60 lux Phillips.
      I got a lower power, much lower price, LED dynamo lamp.
      I will check the stats, and post for you, too.

    2. So I checked it for you with a ruler on the hub on my (broken) folder in the garage.
      As with all my "Long Term Test"s, I actually possess the stuff I am reviewing, and I thank you gor your enquiry. I can, of course, time permitting, answer any further enquiries you may have about anything I have written. Just ask away.
      I will update the "Test" above shortly with the OLD information.
      It is 100mm OLD, just like I thought.
      I bought it already in a 406 (20") wheel.
      The same unit is also available in 559 and 622 diameter wheels.
      the 406 version fits 20" kids bikes and velocycles, and SOME small wheel bikes (like mine!)
      the actual "hub" is 60mm across the flanges (by which I mean the raised metal ridge at either side of the hub that takes the spokes).
      BUT the ability for adaptation is significantly reduced by a plastic section which emerges from the right-hand side, which contains the power terminals etc.
      I looked on the Shimano website, and it says lots of interesting stuff, and has "exploded" diagrams, but it doesn't say what the OLD is!
      Anyway, as I said before, it is 100mm.
      Evans Cycles say that a "special" version of a Shimano hub dynamo is available for the Brompton (which I am guessing you have, or something similar, at least!). Link:
      My LED light is a Union UN-4268 35 lux light, which is priced at just under 20 euros (about 16 pounds 50 pence, or 26 US dollars), but the shipping cost is going to kill you. I make an order once a year maximum to get as much stuff in the one shipping rate as possible.
      Anyway, I got my light from Dutch Bike Bits in Holland (which is where I got the dynamo wheel, as well). Link:
      I thought I read that Biologic make a 74mm OLD hub dynamo as well, but I only seem to be able to find 100mm units when I googled it :-(
      SJS (a good vendor of odd bits and bobs, like spokes for small wheelers!) has a top-of-the-range SON dynamo hub in a Brompton-sized hub, but sit down before you look at the price!
      SJS also sell a cheaper shimano based "Brompton" unit, and unlike Evans, they sell just the wheel (and dynamo) rather than a kit with lights etc. bundled in. So it is cheaper.

      Hope this helps.
      Any further questions, just ask away!

    3. I agree with you that one of the BIG advantages of dynamo lighting is the "always ready for use" aspect - it is very handy when unepectedly delayed etc.
      However, one advantage of removable battery lights is that the front light can often be used as a torch for finding the bike in an unlit shed. etc.
      My bike is kept in an unlit garage, and although dimly illuminated by a nearby streetlight, an additional light simplifies things somewhat.

  2. Thanks for the good info. Yes, I am needing a 74mm OLD. My bike is a Novara (REI store brand) Transfer 7. It seems to be made by Tern. Tern sell a dynamo wheel, but the price is high. I have bought things from David Hembrow of Dutch bike bits. The shipping is painful but his prices seem pretty fair. I might use a bottle generator, but worry that it will get damaged or interfere with the fold. The bike did come with nice Schwalbe tires that have a dynamo drive track, so a bottle dynamo should work well and would cost very little to add. A bit more running drag than the hub, but zero when not using the light.

    1. David Hembrow's prices are often VERY GOOD INDEED, but the shipping cost means I make a few BIG orders, rather than lots of little ones, like folks do with Amazon :-)
      David's price for that hub dynamo mounted in a wheel is unbeatable, but only if you have a 100mm OLD! Many local bike shops will lace any rim to any hub (if the hole count is the same), but the charge too much for it!
      That's why I bought David's wheel.

      Novara Tranfer 7?
      Sure about this?
      I googled it, and a "regular" style bike, rather than a "folder" came up.
      Sure you have a 74mm OLD?

      Bottle dynamos vs hub dynamos
      It is all about physics.
      1. Drag
      a) When in the off position, a bottle dynamo has NO DRAG WHATSOEVER.
      b) A hub dynamo, even though I was unable to measure it in practice :-) must have some, simply because if you turn the bike over and spin the wheel, it doesn't spin as freely!
      Conclusion: depends if you ride at night much! If yes, then a hub dynamo is clearly superior. For about 6 months every year, I use lights to get both to and from work, so, I ride at night quite often!

      2. Power output
      the rotating "head" of a bottle dynamo, sitting on the wheel rim, moves at a speed proportional to the road speed of the bike (if on a bigger wheel, the wheel is turning slower, but, for each rotation, more tyre passes under the dynamo "head", which balances it out)
      the hub of a hub dynamo rotates at a speed which is proportional only to wheel rotation, not road speed (the bigger the wheel, the slower the rotation for a given road speed).
      Conclusion. If you ride a small-wheeler like I did, mostly at modest speeds, then the power output from a hub dynamo is FAR GREATER.

      3. Dynamo slip.
      a) a bottle dynamo is likely to slip a bit in the rain, and if you ride in the winter and get slush/snow on the wheel, the bottle dynamo will slip a LOT, and you will notice the loss of light output! (two winters ago I cycled right through it with a bottle dynamo, and I have a Schwalbe Marathon tyre, with the same dynamo track on it as you do)
      b) hub dynamo = no slip in snow and rain = good light output throughout.
      (I cycled right through last winter with the hub dynamo, and it was FAB!)
      Conclusion: If you cycle in rain, and especially slush/snow, a hub dynamo is clearly superior.

      4. Efficiency
      a) bottle dynamo = low to medium (more modern dynamos are better!)
      b) hub dynamo = medium to high (although in my case, with the small wheel, the efficiency increase showed up as more light rather than easier pedalling! - see the comment 2) above about power output.
      Conclusion: depends how much you cycle at night!, and whether you cycle on cycle paths or unlit country roads - for a small-wheeler on unlit country roads/tracks, a hub dynamo is clearly superior

      5. Cost
      a) bottle dynamo = cheap
      b) hub dynamo = expensive.
      Conclusion: Depends much do you cycle at night. If rarely, then a hub dynamo is an expensive addition, and the money could perhaps be best spent elsewhere (my wife rarely cycles at night, and just has battery lights for the very few times she needs them - she has one of David Hembrows nice "rack-mounted" battery units screwed on the back, and a removable cheap supermarket front light with rechargeable batteries. But she rarely uses them! that's why we didn't get her a hub dynamo as well!)

      Hope this helps

  3. do you plan to use your hub dynamo to charge other appliances such as telephone?

    1. not at the moment.
      sometimes I think I should fit a switch so I can switch the power from the lights to a battery set, then use the battery set to power devices - but I haven't yet implemented such plans.
      i guess it depends how long one wants to use the devices away from "mains" power.
      certainly for cycle camping, it would be a great idea.
      but then I don't log every inch I cycle either, and I have a fairly low-power smartphone (so the battery lasts a decent time) - folks with something power-hungry, who like to leave the GPS turned on all the time, while having the screen at maximum brightness, and running some apps in the background, would find their need greater than mine...
      something like the BUSCH + MüLLER E-WERK would cover such a need if ever I had one:

  4. thanks for the reply and link

  5. I have a 3N20 on my cargo bike, it a solid reliable units, and I have nothing but praise for it, its main advantage is that it is a hub dynamo, and as such is quiet, reliable, and unnoticeable!