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

BUT

• 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!)

Verdict:
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)