2.4W dynamo hubs

[Brucey]

some of these things are possible but they all cost money. And efficiency is a hard taskmaster; often just putting in a smoothing capacitor 'costs' plenty there too.

Years ago I spent a little while designing a circuit (for an SA dynohub) that would overcome flicker (in tungsten bulbs), and prevent them from being overvolted on fast descents. It would also open the door to an easy battery back-up. Well the net result of my endeavours was that I found several new ways of having dimmer lights than normal, nearly all the time. If you don't have much to start with, losing another 10% can be quite noticeable. OK things are a bit different now, but if you asked me to spend money and choose between 'more light for the same effort' or an improvement in some secondary characteristic, it'd be 'more light' every time, please.

I can think of any number of ways of making bottle generators better, more efficient etc but they all come at a cost. And when you look inside a bottle dynamo it is clear that cost was the main driver when the thing was designed. They really are very simple machines; that they work as well as they do is something of a miracle.

If you look at 'better' bottle dynamos (such as the B&M S series) they were notable for two things
1) they were fiercely expensive and
2) they didn't sell that well.

From which you might conclude that most folk who would choose a bottle dynamo in the first place wouldn't value the benefits and advantages that the improved design offered. If you look at hub generators, a SON costs about x10 more than the most basic shimano hub generator but when measured it is only slightly better (that SON generators sell as well as they do is surprising to me; warranty, weight and reputation seem to count disproportionately here and manufacturers of similar products don't seem to be able to charge a similar premium for them). You could 'improve' all kinds of things in a similar way.

So technically speaking I think it is likely to be more difficult than you imagine to do some of these things and that efficiency will probably suffer. In addition I suspect that folk wouldn't pay any premium for such changes, so commercially speaking I think it would be on the back foot from the start.

cheers

[SA_SA_SA]

.....I can think of any number of ways of making bottle generators better, more efficient etc but they all come at a cost....

Err, but the last bit of my last post was about simply increasing the frequency (not efficiency) of hub dynamos at low speed (by increasing poles) and alternatively wondering if the axial SP design would suit rough three phase DC output better than conventional hubs.

I don't want to go back to bottle dynamos, I just want no more flicker than I got from my retired nordlicht bottle from a hub dynamo ie the almost the same flicker performance.

People seem to be willing to pay for Schmidt hubs despite SPs being almost as efficient: maybe schmidt will need a new USP (less flicker due to either rough DC output or more poles ) soon which could trickle down later.....

[Brucey]

more poles/phases = 'better' = more expensive

whether it is a bottle or hub generator

simples

If you don't want your lights to flicker at low speed, you can always turn them off and use battery powered ones instead....

cheers

[SA_SA_SA]

more poles/phases = 'better' = more expensive whether it is a bottle or hub generator

Theres more room in a hub and the problem essentially doesn't exist in any bottle I have used.... More expensive covers an unquantified range. If the Sztvo didn't require 5Hz at 3mph (from memory) then presumably flashing would be even worse.

If you don't want your lights to flicker at low speed, you can always turn them off and use battery powered ones instead....

Thats going a bit far surely .... an add on capacitor circuit/battery backup would retain the car-like availabilty of dynamo lighting (and be by-passable) but if pay 40 pounds ore more for an approved Stzvo lamp its rather annoying to have to do so (and find somewhere to mount extra stuff etc (after designing and building it...).

[SA_SA_SA]

....Years ago I spent a little while designing a circuit (for an SA dynohub) that would overcome flicker (in tungsten bulbs), and prevent them from being overvolted on fast descents. It would also open the door to an easy battery back-up. Well the net result of my endeavours was that I found several new ways of having dimmer lights than normal, nearly all the time. If you don't have much to start with, losing another 10% can be quite noticeable. ....

I recognise that from the days of filament bulbs because I was always wondering how to avoid a backup circuit with a relay (to avoid the relay drive current of simple circuits that power the coil from the dynamo rather than backup battery (that would be the sort of circuitry that needs to keep dry and need more circuit space ): The only way to avoid dimness due to rectifier losses seemed to be to accept a current from the battery even when moving to supply the missing 10%.... I eventually ten years late I made a relayless blocking capacitor circuit which turned out to be more or less the circuit used in a CLC-58 backup (minus the timeout timer) but because I wanted to mount a (bottle) battery backup with battery and circuit and blocking capacitors all in different places. This was pretty untidy compared to a front lamp that does all that for you.....

...But the reason the Wireless World voltage doubling rectifer followed by switching step down regulator appeal(s)/ed to me was that the designer claimed that operating at the higher voltage of 30 Volt-ish (and less hub current) compensated for the solid state losses by reducing I2R losses at the dynamo coils ( a 15% efficient union 6701). He claimed his ni-cds never needed topped up.

I now have 2 dyno hub wheels (and a wheel stand) so some experimenting may happen but I still feel it should be unnecessary for mid and upper price lamps ....

[ConRAD]

... but the last bit of my last post was about simply increasing the frequency (not efficiency) of hub dynamos at low speed (by increasing poles) ...

But unless you increase the overall volume and weight of the hub it means to get magnets closer one to each other with consequent drawbacks on the magnetic circuit, additional mechanical problems due to a further reduced airgap between rotor (magnets) and stator (coil+laminations), higher coil reactance, etc.
A standard hub with 26 poles (eg SON28) at 20km/h on a 28” wheel already produces 34Hz approx* (i.e. 8.5Hz at 3mph), much more so far than the you suggested StVZo requirement of 5Hz at 3mph.
3-phase might be a solution or …. if you really don’t like flikering just mount a toggle switch on you handlebar and go on battery, you don't need to change light!

* 20 km/h is 20000/3600 m/s that divided by 2.150 m (28” wheel) makes 2.58 turns per second, i.e. 2.58 X 13 (couples of poles) = 34 Hz (approx).

[SA_SA_SA]

I thought the wireless world(became electronics world)* circuit would generate more interest....


*It was the 'highest brow' UK electronic magazine in newsagents at the time...

[ConRAD]

... I thought the wireless world... would generate more interest ...

"Poles&Wires" ... hopelessly and desperately calling for "wireless technologies" !!!

[nigelnightmare]

I realise that on the face of it this question has an obvious answer (which probably already appears on the forum, but the search function is no help here), but…

Will a 2.4W hub adequately power both front and rear LED lights?

I ask because these hubs (eg the 2N35) seem to be available at much lower prices than the 3W hubs I've always bought in the past.

Additional details for context: it'll probably be used with a Cyo Premium and some sort of Topline rear, on a touring tandem (so the additional drag and weight of an entry-level hub isn't really concern, but output at very low speeds when climbing perhaps is).

If not, no biggie… might just take the battery route anyway, given that it'll only see occasional use and the front wheel already has a perfectly good conventional hub in it.

I run an AXA 70 luxx headlight with a B&M seculite plus with a Sturmey Archer X-FDD 2.4W
and I find no difference in light output compared to the same lights run by either the SON or the Sturmey Archer X-SDD 3W.

All are plenty bright enough to see on unlit roads and oncoming traffic DIP their headlights, so I'd say they think they're bright enough as well.

All are on 406 20" wheels so I have good light from around 2.5-3mph (it would probably be 4-7mph on a 700c wheel).

In my experience the answer is YES it will power both front & rear LED lights.

[SA_SA_SA]

... I thought the wireless world (Electronics World)... would generate more interest ...

"Poles&Wires" ... hopelessly and desperately calling for "wireless technologies" !!!

?
Does this mean you don't like the circuit?

[ConRAD]

... does this mean you don't like the circuit?

... I like I like, but which one exactly ?!

[SA_SA_SA]

... does this mean you don't like the circuit?

... I like I like, but which one exactly ?!

This one
"...battery backup in Dec 1994/Oct 95 Wireless world*...
* a voltage doubling rectifier (cascaded type (so no floating generator needed) ) 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 rectifier output capacitor had reached a bit more than 20V DC."
.....
"...But the reason the Wireless World voltage doubling rectifier followed by switching step down regulator appeal(s)/ed to me was that the designer claimed that operating at the higher voltage of 30 Volt-ish (and less hub current) compensated for the solid state losses by reducing I2R losses at the dynamo coils ( a 15% efficient union 6701). He claimed his ni-cds never needed topped up(on rereading its more implied)."

[SA_SA_SA]

I wonder if a 1.5 to 2 times increase in frequency would do:

would 42 poles be feasable economically I wonder?