2.4W dynamo hubs

[MikeF]

there has to be something limiting the voltage in your open circuit tests; probably some kind of clipping diode, but possibly something else.

Keeping track of power is fairly simple as long as the load is resistive, and the current remains in phase with the voltage. However when they are not in phase with one another you can have a true power that is completely different from the (RMS) Volts x Amps value.

ps I have just looked inside a bottle dynamo and there is a diode of some kind across the output. I don't recognise the markings perfectly but they are as follows

- DB (run together as a single character, I think this may be a maker's mark)
- P 709
- P6KE8.2CA

I suspect this is a suppression diode of some kind, eg. containing a pair of Zener diodes back to back perhaps. Possibly presently available hub dynamos can contain the same kind of thing? (they didn't always; some generators were measured to produce up to 100V at speed into an open circuit). Note that when a diode like this conducts, it dissipates power and that effect will be seen as a reduced efficiency (power in vs power out) if all you can do is measure the terminal output.

[edit Farnell list P6KE8.2CA as a bidirectional TVS diode. datasheet http://www.farnell.com/datasheets/2861222.pdf]

cheers

Limits output to 8 volts peak.

[SA_SA_SA]

... because the circuitry in the headlamp can destroy the hub output waveforms suitability for a rear lamp (eg letting hub voltage rise higher or lower) because it is driving the rear lamp(s) from the output of its own switching converter circuitry.

NO, the voltage to the rear lamp is solely controlled by the overvoltage built-in protection present in the ....

I am not talking about controlling (limiting) the passed thru voltage from the hub* I am suggesting the rear lamp is driven from a/part of switching regulator circuitry in a hypothetical front lamp: so there is no direct connection from rear lamp to hub therefore whatever distortion away from a nominal 6V rms (as expected by rear Stvzo lamps) at the hub input side that this front lamp's circuitry causes (in pursuit of efficiency/max power extraction) is irrelevant because it (re)creates a suitable drive for the rear lamp itself.

[Brucey]

er, yeah, but most front lights don't work like that. A few do, but most don't; the rear light is connected directly to the hub when the switch is 'on' and the regulation of the voltage seen by the rear light is because of the headlight parts that are in parallel with the rear light, not in series with it. Exactly as Conrads dwg.

cheers

[SA_SA_SA]

er, yeah, but ...

I was making a suggestion for future improved lamps and perhaps that STvzo might choose to mandate that mode of operation in order allow more flexibilty at about future hub generators.

[Brucey]

I see.

I can envisage them having a whole new, different standard (e.g. like the 1,5W one) but I don't see them revising the extant 3W standard anytime soon. The reason is that if you did so, you would probably render things non-backwardly compatible in an unhelpful fashion, for little gain.

In fact I'm not quite clear what the objective would be of making changes; you can already buy front lights which use dedicated rear lights, rear lights which can be used whilst only the rear light is connected to the generator, etc etc.

cheers

[SA_SA_SA]

I see. I can envisage ....

But that leaves them stuck requiring hubs to have a voltage output designed to suit filament bulbs, thus ruling out generators that might suit LEDs better (or be allowed to be simpler/lighter etc)... and consumers unsure of what DC their dynamo lamps can stand (and requiring manufacturers to make separate E-bike lamps). An electronic LED front lamp needs AC TO DC and voltage conversion circuitry to get the most from the ac hub so why not explicity make them cope with DC as well, but with an output to feed standard dynamo rear lamps retaining interoperability with the past.

I find it annoying that Dynamo filament bulb lamps could be run at full power from DC but running dynamo lamps from DC seems to involve asking the manufacturer and even then I am not sure that (eg Cyos) run at full rated power from DC unlike a filament bulb. So the Stzvo have already reduced compatibility and also accepted 1.5W dynamos only for LEDs etc.

[Brucey]

well I too have wondered about running lamps from DC but in fairness your envisaged uses will only be of interest to a tiny fraction of possible customers. The reason lamp manufacturers don't list DC compatibility is twofold

1) most people are not very interested in this and
2) it is a non-trivial problem.

Most of the voltage regulation schemes employed in front lights only work because the generator won't ever produce more than a certain amount of current and when higher than normal current is drawn the voltage at the generator output droops. This means that you can quite easily design a regulation scheme which only ever has to dissipate a known amount of power. It also allows cheap lights to be made that use low power (~1W or lower) LEDs that come to full brightness at low speeds, even though there may be ~2W wasted inside the lamp at high speeds.

Batteries have the slightly alarming characteristics that the output voltage varies with the state of charge and the current delivery may be almost unlimited. This is 'not good at all' if the voltage exceeds the regulated voltage inside the light, and the practically limitless current is discharged into the regulation circuit.

I don't think it is realistic to expect lamp manufacturers to build a much more expensive regulation circuit on the off-chance that someone might want to plug a battery into it. However I do think there is a small market for dynamo lights that can be optionally powered by (say) a regulated 5V USB type battery/power supply instead, and this is a much more manageable problem.

if you have a regulated DC power supply with an adjustable current limit, you can test most front lights (for 5V DC drive compatibility) quite safely; first measure the AC current drawn by the front light at speed. Then run the lamp at a (5V max) DC current not in excess of half this. If the light comes to full (or acceptable) brightness at 5V and you are not using the current limiter, then you have succeeded. Otherwise some modifications to the circuit might be required.

cheers

[SA_SA_SA]

"Brucey wrote: well I too have wondered about running lamps from DC but in fairness your envisaged uses will only be of interest to a tiny fraction of possible customers. ...."
The reason lamp manufacturers don't list DC compatibility is twofold
1) most people are not very interested in this and
2) it is a non-trivial problem.

Most of the voltage regulation schemes employed in front lights only work because the generator won't ever produce more than a certain amount of current and when higher than normal current is drawn the voltage at the generator output droops. This means that you can quite easily design a regulation scheme which only ever has to dissipate a known amount of power. It also allows cheap lights to be made that use low power (~1W or lower) LEDs that come to full brightness at low speeds, even though there may be ~2W wasted inside the lamp at high speeds."

SA_SA_SA replied in non-italics:
But
1) getting more than 1 Watt at front (while leaving proper 6V for rear lamp) ie 2W+ in current up-market front lamps does require more complicated circuitry for which a switching regulator of some form seems best and assumes least about PSU, this now seems rather similar to a 40V E-bike lamp.....:
2) higher voltage (> 6V) E bike lamps (usually 40 V DC max I think) will require switch mode step-down circuitry.

3) Cheap lights can continue to be wasteful as long as they cope with 4.8V-6V DC or dynamo AC (Some are already marked as dynamo or 6V E bike compatible).
But electronics tend to get cheaper so why shouldn't these become obsolete in the fashion of halogen headlamps. I still think the Stzvo is too tolerant of annoying* front LED flicker so dealing with that might hasten their end a bit anyway. (*epileptics may use other words)

"4) I don't think it is realistic to expect lamp manufacturers to build a much more expensive regulation circuit on the off-chance that someone might want to plug a battery into it. "
High voltage and high power E bike lamps are priced in the same region as their Hub dynamo cousins so merging them seems possibly both realistic and a benefit to all. Microcontrollers are rather cheap now.

Thus making the same lamp work on dynamos and high voltage E-bikes is good for both customers and manufacturers (less lamp variations in factory / less 'which model do I need' and less variants needed to be stocked in shops). Also allows customers to reuse a lamp from an expired/resting E-bike on hub dynamo and vice versa. B&M have a large amount of variants of each lamp for shops to stock: reducing that seems good to me.

"Batteries have the slightly alarming characteristics that the output voltage varies with the state of charge and the current delivery may be almost unlimited. This is 'not good at all' if the voltage exceeds the regulated voltage inside the light, and the practically limitless current is discharged into the regulation circuit. "
But a lamp designed for high voltage E-bike DC has to cover a wide voltage range any way and any shunt regulator (for hubs) would be set above its specified maximum voltage (eg 40V) at a level that protects the circuitry. The regulator design would be different anyway as it is not regulating to a nominal 6V rms anymore (cos the rear lamp is not directly connected to hub as in my OP). If E bike front lamps drive rear lamp then it would further reduce stock/variants because that would remove the need for special high voltage E-bike rear lamps (and standard dynamo lamps which are 6V DC E-bike compatible seem to be cost effective cos they already exist).


"However I do think there is a small market for dynamo lights that can be optionally powered by (say) a regulated 5V USB type battery/power supply instead, and this is a much more manageable problem."

I could live with that but it presumably needs an extra pair of input terminals / socket (or else current regulation more advanced than the resistor of the Axa Picos) which made me think it was less of a go-er for manufacturers. (NB tern sell a 5V USB powered DC only front lamp (40lux) I think)

"if you have a regulated DC power supply with an adjustable current limit, you can test most front lights (for 5V DC drive compatibility) quite safely; first measure the AC current drawn by the front light at speed. Then run the lamp at a (5V max) DC current not in excess of half this. If the light comes to full (or acceptable) brightness at 5V and you are not using the current limiter, then you have succeeded. Otherwise some modifications to the circuit might be required.!"
I don't want to modify an approved lamp and would rather the manufacturer specifically said it was OK.

[Brucey]

Regulating a battery voltage of 40V down to 6V with an acceptable efficiency is pretty straightforward. As I explained previously regulating hub dynamo is not; as for the rest of it, well, if you think it is simple, have a go. I anticipate that you will find it is not.

I think that B&M are very happy to sell a plethora of models; that way they have all the bases covered. Most people buying lights of this type would begrudge buying features they don't need, and every 10p extra you spend on electronics normally bumps the retail cost up by a quid or so.

cheers

[SA_SA_SA]

Regulating a battery voltage of 40V down to 6V with an acceptable efficiency is pretty straightforward. As I explained previously regulating hub dynamo is not; as for the rest of it, well, if you think it is simple, have a go. I anticipate that you will find it is not.

But the battery backup in Dec 1994/Oct 95 Wireless world* did that (well from 27-ishV to 6V ): I just don't see how it is beyond the resources of honours degree electronics employee/subcontractors** to do that from 40V. They make the effort once and then its in the bank so to speak....
My idea proposed the voltage regulation is at the high voltage (40V+ a bit side) so the step down circuitry is similar to battery apart from perhaps some extra mcu? electricery and supercaps to avoid flicker at low speeds.

**a level above me

I expect an expensive lamp (ie not a 0.5/1 Watt cheapo one) to have done this work for me: but at the moment they have not. they haven't even avoided low speed flicker. I have always preferred brutally simple circuits for homemade dynamo stuff as I don't want to handle potting compound type stuff to waterproof complicated circuits but I expect a bought lamp to be designed well....
Plus any complicated circuit built by me is going to be large and require a box outside the front lamp when an off the shelf solution is neat inside the front lamp itself and the modified front lamp will be unapproved....

I suspect shops are less keen on B&Ms myriad options (they have to guess what to stock, more options == more chance of customer getting the wrong thing etc etc) and I still think there is a cost involved in too many unnecessary variants (time switching between product variants on line, mistakenly using wrong package, mumbling customers (and hence shops) etc).

* a voltage doubling rectifier (cascaded type) clamped to 27V followed by a LM2575 step down regulator to 6V (which trickle charged 4 ni-cds for backup when stopped. The LM2575 was held off until Smoothing Caps had reached a bit more than 20V Dc.


NB that NX10 seems to have a 6V diode clamp (rather less than the approx 8.4 peak of a 6v rms sine wave) which presumably explains why I saw a claimed that it cut in sooner than other after market ' dynamo regulators'.

[Brucey]

I think you missed my point; Like I said regulating down from 40V battery voltage to 6V is not difficult; trivial in fact, and you are not worried overly about efficiency because you have power to spare there. However if you are using batteries (especially smaller ones) the method of regulation would be different between battery and generator uses. The generator (be it bottle or hub) is not like other sources; you might as well have two separate circuits (at twice the cost?) as build one which would cope with either and have good efficiency.

As I mentioned previously, I don't think that people will pay lots more for features that they are not going to use.

The things that trouble you may not be the things that trouble other folk. Your expectations of what is good, bad and reasonable in a (cheap?) bike light might be vastly at odds with what others think.

For example flicker at low speeds; I happen not to find this so much annoying as useful. In essence you have the choice of

- some flickering
- steady glow worm lights powered by the generator
- steady lights powered by a battery backup

The last option is always going to be less efficient, more expensive, and less reliable. The second option also (for example the least reliable part of a back light which has a built in standlight is the standlight feature). I actually think the flickering is an advantage; it makes the bike more visible when you are pushing it.

Remember you never get owt for nowt when it comes to electronics; efficiency matters and anything that adds cost or reduces efficiency/reliability for no real benefit is better avoided.

cheers

[Brucey]

it occurs to me that a good analogy is wondering why there are so many different sorts of bicycle and whether or not it would be a good idea to have one that was fitted out for derailleurs and hub gears just in case you preferred one to another. Sure, such things exist but they are not mainstream models; most people plump for one or the other rather than pay more and have the choice.

Likewise you don't often see (say) folk using chain drive but buying a more expensive frameset that might work with belt drive instead.

cheers

[SA_SA_SA]

"Brucey replied: in italics:
"I think you missed my point; Like I said regulating down from 40V battery voltage to 6V is not difficult; trivial in fact, and you are not worried overly about efficiency because you have power to spare there. "
Surely, battery users are more worried about efficiency given that wasting power is unnecessarily reducing run time, whereas dynamo regulation is just heating up a semiconductor (eg the old fashioned 7V5 backtoback zener clamp to modern transistor one on the E6) with the power you don't want? and is needed because not enough LEDs are available to convert available power to light compared to a battery LED lamp which takes only what it needs minus conversion losses.

I am not convinced that the extra regulation on top of E bike battery circuit is so sure to be so prohibitively expensive in mid and upper price lamps against extra flexibility for manufacturer shop and consumer (DC operation is also useful in case of hub failure) / reduced stock / simplfied consumer choice etc. Leaving out the ability to work on DC and AC seems to possibly be a case of spoiling a ship for a ha'p'orth of tar (manufacturers seem quite good at this...)
(See ending equine reference though.... )


"For example flicker at low speeds; I happen not to find this so much annoying as useful. "
But I don't find it useful and find it mildly annoying because I don' t wish to annoy pedestrians (and epileptics) it makes me think of the film speed but with speed in single figures....:
my bottle dynamo front LED was acceptably bright at low speeds without annoying flicker when riding or wheeling therefore flicker from a hub is entirely pointless to me and annoying:
I can't build an approved lamp myself.....

"As I mentioned previously, I don't think that people will pay lots more for features that they are not going to use."
I never suggested paying lots more Non-annoying-Flickering at walking pace is not a feature, it is what Stzvo should require IMO.... If I buy an expensive mid/upper price lamp I shouldn't have to wonder how to add an external circuit/battery backup to stop it flickering when this wasn't a problem with a bottle (NB I don't want to go back to bottles).

However, I feel I am selling an expired equine mammal

[Brucey]

I don't think it is reasonable to assume that e-bike users (who are pushing out 200W+) are going to be worried about a watt or two if their conversion to 6V for powering lights is less than perfectly efficient.

However many of the other things would significantly increase cost and/or losses when running from a generator, where every watt is hard-won, more or less. And that is if they are even feasible at all, which is far from clear to me.

As for bottle dynamo powered tungsten lights not flickering at low/walking speeds... well yours must have been different to mine.

cheers

[SA_SA_SA]

1) I don't think it is reasonable to assume that e-bike users (who are pushing out 200W+) are going to be worried about a watt or two if their conversion to 6V for powering lights is less than perfectly efficient.

2) However many of the other things would significantly increase cost and/or losses when running from a generator, where every watt is hard-won, more or less. And that is if they are even feasible at all, which is far from clear to me.

3) As for bottle dynamo powered tungsten lights not flickering at low/walking speeds... well yours must have been different to mine...

1) But why would they get less efficiency than from a step down regulators 80 to 90-something%? A range of 6 to 40 hardly allows a resistor or linear regulator?

2) I don't see how: a switch mode current source (perhaps with some extra (mcu?) intelligence ) is what I would choose to get 2+W out of a dynamo whilst lighting at low speed (and Mr SWHS made his own switchmode psu for experiment to compare with commercial front lamp drivers).

3) I found a bottle needs to be driven really slow to flicker and then, with filament is dim and bearable but like the much slower but brighter flickering(more pulsing really) of a hub powered front filament lamp which again I find bearable to view due to the long time constant (No I don;t want to back to front filament bulbs either ).
My hub variant Herrmans HOne S was acceptable to me with a Nordlicht bottle, so I just want a circuit to stop it flickering at slow cycling speeds with a hub.... that circuit should be in the lamp.....Grrrr
My home city is full of hire bikes with hub powered Picos/Echos being wheeled / walked slowly on pavement: these give brief bright (ie low mark-space ratio) cold/neutral white flashes and are totally unlike a hub powered halogen bulb and annoy me, so what epileptics think of them I don't know.

If we agree to differ on the previous above ideas:---

4) A different tack maybe: any affordable way to increase poles by say 4 in a claw pole hub?
e.g. I once took apart a dud cibie bottle and instead of a ring of separate magnets it seemed to have a solid ring of magnetic material around the coil:
a)for the same diameter could this be magnetised into more poles than same size ring of discrete magnets:
b) what is the maximum number of claws(ie setting maximum poles) that could fit around a shimano hub's stator?
I wonder if SP dynamos axial layout would make a 3 phase clawpole generator (with 3 star configuration rectifier diodes built in) easier for rough DC ?.....