3 to 9W VPG … variable power generator

[ConRAD]

.. just wondering where and when the universal “3W” standard power size, commonly used for bicycle generators, did it come from.
With a few exceptions indeed, e.g 2.4W Shimano and 6W-12V B&M, most of generators on the market today are rated 3W (nominal power).
Now 3W, I guess, are good enough for modern lighting systems and reasonably acceptable for charging small electronic gadgets … but nothing more !!
Induced backdragging produced by a 3W hub dynamo is commoly deemed as something not to worry too much about, so why not to make available at this point more powerful generators just in change of a bit more dragging ??

Concluding … why only 3W ??? … why not a 3 to 9W variable power generator?

[Brucey]

it is zer chermans' fault; they 'decided' that 3W was the correct amount of electricity for bike lights and then created an enormous market for them by mandating that every bike weighing over 12kg had to have a generator making 3W by law.

Meantime the Dutch (unlike us hapless Brits who effectively killed off the original SA dynohub when it was agreed that we should use 3W too.... ) happily use 2.4W dynamos, and always have done.

The thing is, the generators are tested to make 3W into a 12 ohm resistive load. Most of them make a different amount of power into a different load. If you use a suitably reactive load many '3W' generators will happily produce 6W or more.

It is not something for nothing though; you do have to pedal harder!

cheers

[SA_SA_SA]

it is zer chermans' fault; they 'decided' that 3W was the correct amount of electricity for bike lights and then created an enormous market for them by mandating that every bike weighing over 12kg had to have a generator making 3W by law.

....us hapless Brits who effectively killed off the original SA dynohub when it was agreed that we should use 3W too....

When did that happen?
The BS I have only specifies generator voltages against the manufacturers specified load*: so presumably never forbade the dynohub with compatible bulbs/lights.

I thought it was ze Chermans fault for not buying SA dynohubs (cos their 3W rule forbade them). A pity they did not think of allowing a SA dynohub for be seen lights, with either an extra battery or 3W generator front lamp to be used as needed for seeing.

I wonder if the 70cd front cutoff limit in the BS was an attempt to keep out German dynamo lamp competitors to the UK's dimmer preferred be seen front lamps.


*unless I missed a change.

[rualexander]

There are a few 1.5w dynamos now available which also now meet the German regs I believe.
e.g. http://www.bike-discount.de/shop/a99322 ... wwodNgIACQ

[Brucey]

it is zer chermans' fault; they 'decided' that 3W was the correct amount of electricity for bike lights and then created an enormous market for them by mandating that every bike weighing over 12kg had to have a generator making 3W by law.

....us hapless Brits who effectively killed off the original SA dynohub when it was agreed that we should use 3W too....

When did that happen?
The BS I have only specifies generator voltages against the manufacturers specified load*: so presumably never forbade the dynohub with compatible bulbs/lights.
.

I have never seen the paperwork. What I do remember is in about 1982, Dynohubs going NLA on new bikes, and being told that was the reason why. Maybe they said they intended to do that and thus plans were made accordingly... In ~1984 an LBS wound up selling off its old stock of GH6's; they could no longer legally equip new bikes with that generator, they told me, so they had to go. I bought several.

SA got halfway through making a new 3W Dynohub (several times over... pictures in Tony H's book IIRC.) and then quit trying. I have no idea why; probably a chronic lack of investment, a lack of confidence in the basic idea... who knows? Maybe they were busy redesigning the 5s hub (again... ) or something. I have little doubt that in the climate of the time bike manufacturers would have beaten up SA on price so maybe it wasn't deemed viable. If the bike manufacturers had actually spoken more to people that used bikes instead then they might have got a different answer. Dynohubs were a popular point-of sale upgrade in the LBS near me at the time; I rarely met anyone who had used one that wanted to use anything else, certainly not for town use.

cheers

[SA_SA_SA]

I have never seen the paperwork. What I do remember is in about 1982, Dynohubs going NLA.....
cheers

1982 would still have been the era of BS3648 which I have read (in pdf form) at a public library: I didn't notice anything more onerous on dynamos than in BS6102/3 (read in both recent pdf and paper form). BS3648 only required a 0.25cd max from a rear lamp.

Perhaps CJ will know......

That Tony H book sounds interesting, a pity it seems unavailable: I wonder if he could sell a pdf version?

NB in the SA historic website the XAG 3Watt prototype ungeared dynohub is marked ISO6742 so perhaps it would still have fallen short of German voltage vs speed requirements. (http://www.sturmey-archerheritage.com/index.php?page=history-detail&id=141). I think they also made an earlier geared prototype. According to CJ there was no interest in the XAG from manufacturers.

[Mick F]

How much power is required from the rider to produce 3W from a dynohub?
Can't be much more than 3W, and that figure is tiny when it comes to the leg power from the rider.

Why not fit 2W dynohubs front and rear and have a 4W system?

[james01]

There are a few 1.5w dynamos now available which also now meet the German regs I believe.
e.g. http://www.bike-discount.de/shop/a99322 ... wwodNgIACQ

Interesting. Presumably the strict German lighting laws have been amended accordingly. I imagine that with efficient modern LEDs, 1.5 watts would give reasonable lighting for general utility cycling. Presumably buyers will need to be offered a special range of low-consumption headlights and rear lights. I've just done a quick search and can't find any information to guide buyers to suitable lights.

[RickH]

I came across some interesting stuff about someone trialling using an ExtraWheel trailer fitted with a hub dynamo for extra power on the Thorn forums (link here).

Rick.

[Brucey]

1982 would still have been the era of BS3648 which I have read (in pdf form) at a public library: I didn't notice anything more onerous on dynamos than in BS6102/3 (read in both recent pdf and paper form). BS3648 only required a 0.25cd max from a rear lamp.

That Tony H book sounds interesting, a pity it seems unavailable: I wonder if he could sell a pdf version?

NB in the SA historic website the XAG 3Watt prototype ungeared dynohub is marked ISO6742 so perhaps it would still have fallen short of German voltage vs speed requirements. (http://www.sturmey-archerheritage.com/index.php?page=history-detail&id=141). I think they also made an earlier geared prototype. According to CJ there was no interest in the XAG from manufacturers.

I have a copy of Tony Hadland's book and it mentions that 'falling demand and (to a lesser extent) inability of existing designs to comply with standards' caused them to cease production of the GH6 in 1984. The standards mentioned are BS6102 and the ISO DP674 standard. It isn't stated if the problem was really with the generator or the lamps themselves. If merely the latter then I got my wires a bit crossed.

The XAG was a 30-pole generator with ceramic magnets. It looks to me that they made it small enough to fit in a hubshell that would otherwise accept a 70mm hub brake- exactly what I'd have chosen to do. SA claimed it was four times more efficient than a tyre driven generator.

Around that time you could buy a cheap Union or Soubitez generator set for about ten quid and a set of the rather unwonderful 'wonderlights' was about the same. A set of Every-unreadys was ten or twelve quid I think. A Sanyo or Soubitez roller dynamo was around £15 to £20. A hub generator was over £20 and the lights came extra. I guess the hub generator would likely still be working today (I have much older ones than that even) but maybe that wasn't apparent at the time.

In 2008 Hilary Stone sold a prototype XAG

http://oldroads.com/tool_date_rss3.asp?QuestionID=24466&db=eng

heaven knows where he got it from!

BTW it takes between 5W and 7W input power to make 3W output using a hub generator. So an average hub generator needs about 6W. Some models drag as much when the lights are off (too many eddy currents) but the best generators drag about 1W when the lights are off.

1.5W generators don't necessarily need special lights; LEDs pretty much just make light pro-rata with current.

Dutch spec generators make 2.4W and are often (e.g. in SRAM and SA versions) noticeably less draggy than the 3W versions.
Original SA dynohubs make 1.8W. Ad hoc measurements indicate ~3-4W drag on load and ~1-1.5W off load. Anywhere from 1.5W output upwards is plenty for town riding with modern LED lamps IMHO.

It doesn't take that much more money (or weight) to make a 3W generator vs a 1.5W generator, so two 1.5W to 2W generators would be more weight and cost than is necessary. Unless they are each separately rigged to produce DC (using separate rectifiers), then combining the output of both would be difficult.

Hub generators can be 'external type' (i.e. use a hubshell that would take a drum brake in a similar opening, where the hub is still a functional hub when the generator assy is removed) or 'internal type' i.e. where the hubshell is assembled around the generator, removal of which does not leave a viable hub. Most modern designs are 'internal' type.

IMHO there is room enough to fit an 'external' type hub generator on the left side of the rear hub in most bikes with rim brakes. Rear hub brakes are more of a problem, but with the right design I think a rear disc brake and generator would be easy enough to include.

cheers

[SA_SA_SA]

I wonder why they didn't use an alloy brake hub shell for the front GH6 dynohub.
I wonder if anyone has tried fitting the GH6 internals into such an alloy front brake shell.

[NATURAL ANKLING]

Hi,
The way to do away with no load drag is to dispence with permanant magnets, and use a electro magnet armature, but it would need brushes, vary easily controlled output....................

[ConRAD]

Hi, the way to do away with no load drag is to dispence with permanant magnets, and use a electro magnet armature, but it would need brushes...

... you've perfectly got the point ... nevertheless I still do prefer permanent magnets to "sparking" brushes

[Brucey]

I wonder why they didn't use an alloy brake hub shell for the front GH6 dynohub.
I wonder if anyone has tried fitting the GH6 internals into such an alloy front brake shell.

I think it will fit into a 90mm brake shell, leaving enough room for a magnet ring with a ~10mm wall thickness. There isn't really enough room for a standard GH6 armature in a 70mm brake shell; not with magnets as well, anyway.

cheers

[[XAP]Bob]

IMHO there is room enough to fit an 'external' type hub generator on the left side of the rear hub in most bikes with rim brakes. Rear hub brakes are more of a problem, but with the right design I think a rear disc brake and generator would be easy enough to include.

Would it be possible (and/or desirable) to put a set of magnets on a disc rotor, and then have the electrics in a "fake calliper".
Good rotation, strong magnets, no dodgy twisting motion to get away from with the wires. Many bikes have the capacity - I'm sure disc pads could be added as well if really needed. Could be run on the rear wheel (with a rim brake, or on a fixie etc) or on either side of a front wheel (yes it would need a new hub shell)

Close tolerances are attainable, and it could even be "dialled out" for daytime racing...