Dynamo system choices

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mercalia
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Re: Dynamo system choices

Post by mercalia »

ConRAD wrote:
cycle tramp wrote:... with any dynamo system, its worth considering not using the lamps in parallel ... use the lamps in series ...

... it works of course ... but you're loosing almost 1W, this conclusion being based on real tests with a dynohub at 20 km/h, from 4.3W in parallel to 3.5W in series !!


if used in parallel do you have to be careful if the front light blows and the full power of the dyno going into the rear?
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ConRAD
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Re: Dynamo system choices

Post by ConRAD »

mercalia wrote:... if used in parallel do you have to be careful if the front light blows and the full power of the dyno going into the rear?

… definitely yes. One 6V/2.4W front light in parallel with one 6V/0.6W rear light makes an equivalent of 12 Ohm (i.e. 15 Ohm in parallel with 60 Ohm, in this case either lamps being tungsten/halogen filament lamps).
As soon as the front light blows, at 20km/h approx, the voltage all of a sudden goes up to something like 16V and as a consequence also the rear light is likely to blow.
At this point you need to protect the rear light with some overvoltage protection, or just stop!!
Different story for the modern LED lights where a dedicated surge protection is already incorporated in the front light.
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fatboy
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Re: Dynamo system choices

Post by fatboy »

Sweep wrote:Since brommies have come up, I'll pop in.

My 5 speed brommie (traveller?,) Came with a rack and a bottle dynamo as its added features, for which a premium was charged. Have never used the rack, but I like it being there and may use sometime. The bottle dynamo was a right waste of time. Positively dangerous since I never knew if the back light was on. I chopped the entire system off and just went to battery lights, which for the use a brompton tends to get is just fine and dandy.


I've, until today, found it good especially as I've upgraded the lights, however snow and a bottle dynamo don't really play nicely together (not very suprising since the bike is an abominable snow bike!).
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Brucey
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Re: Dynamo system choices

Post by Brucey »

mercalia wrote:
did you ever have the B&M one ?


No, and I never will. I have no doubt whatsoever that they are not all the same as one another but certain features are common to all such as

- being mounted where road spray can accumulate crud all over the thing
- if the air currents swirl they carry (salty) water into the bushings
- crappy pressed steel brackets that just fatigue (if they stay tight enough that they don't move...)
- wiring connectors made in substandard materials that are positioned to collect water, poorly strain-relieved, easily corroded etc
- wheels that will (under some condition or other) slip, fall off, or just disintegrate
etc etc

If you think B&M bottle generators are somehow immune to the above then I would suggest you are mistaken.

cheers
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speedsixdave
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Re: Dynamo system choices

Post by speedsixdave »

We have four hub and two bottle dynamos on various bikes. The Axa bottle on an old Moulton Automatic is fine as it only ever goes to the village shop or the pub after dark.The hubs - Shimano 30 and 72, SP8 and a SON deluxe - are great: trouble-free, sufficiently powerful and, to my insensitive body, imperceptible on or off. The other bottle is a B&M S6 on my 'fast tourer', on the front fork cantilever boss. Mostly this bike is ridden in the daylight, and the bottle is fine then except when I fear it will work its way into the front spokes (hopefully irrationally).

Recently I have been occasionally riding this bike to work in the dark (15 miles). Having done this a few times now this winter I can conclude that I really don't like it. It did slip a lot in the wet (on Marathons with a dynamo track) and was therefore mostly useless and unreliable. After a lot of fettling and removing part of the front mudguard it now seems to work fine and does not slip, but is noisy in the dry and excruciatingly noisy in the wet. If I hadn't just spent a fat load of cash on a new Moulton and didn't have a fairly new, fairly good front wheel on the fast tourer, I'd definitely replace it with another hub dynamo. Mostly, if I know it's going to be dark, I ride a different bike.

This is just another sample of one adding to the conventional wisdom, for which I apologise. But I often think a good thought experiment for the practicality of bike parts is, would I fit this to my wife's bike? For bottle dynamos, the answer is a resounding no.
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cycle tramp
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Re: Dynamo system choices

Post by cycle tramp »

speedsixdave wrote:The other bottle is a B&M S6 on my 'fast tourer', on the front fork cantilever boss. Mostly this bike is ridden in the daylight, and the bottle is fine then except when I fear it will work its way into the front spokes (hopefully irrationally).

Recently I have been occasionally riding this bike to work in the dark (15 miles). Having done this a few times now this winter I can conclude that I really don't like it. It did slip a lot in the wet (on Marathons with a dynamo track) and was therefore mostly useless and unreliable. After a lot of fettling and removing part of the front mudguard it now seems to work fine and does not slip, but is noisy in the dry and excruciatingly noisy in the wet. If I hadn't just spent a fat load of cash on a new Moulton and didn't have a fairly new, fairly good front wheel on the fast tourer, I'd definitely replace it with another hub dynamo. Mostly, if I know it's going to be dark, I ride a different bike.


Hope you don't mind me asking, which roller wheel are you using on your b&m dynamo? The standard dynamo came with the usual rubber wheel, however you could up grade it to a wheel which was a wire brush wheel.
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cycle tramp
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Re: Dynamo system choices

Post by cycle tramp »

Brucey wrote:
mercalia wrote:
did you ever have the B&M one ?


No, and I never will. I have no doubt whatsoever that they are not all the same as one another but certain features are common to all such as

- being mounted where road spray can accumulate crud all over the thing
- if the air currents swirl they carry (salty) water into the bushings
- crappy pressed steel brackets that just fatigue (if they stay tight enough that they don't move...)
- wiring connectors made in substandard materials that are positioned to collect water, poorly strain-relieved, easily corroded etc
- wheels that will (under some condition or other) slip, fall off, or just disintegrate
etc etc

If you think B&M bottle generators are somehow immune to the above then I would suggest you are mistaken.

cheers


However i have. I used it from 2004 to 2011, when it was removed, still working, and placed in a box for safe keeping (i then used a cheaper Axa dynamo purchased second hand from this site). During this time and over 10,000 miles none of the above happened. The steel bracket didn't move in use & did not fatigue. The wire brush roller did not slip or break up (& this included a 3 am ride back home (at 5 am) through two snow showers, following a ghost hunt) and the wiring (fitted by myself) worked without issue, the dynamo (positioned behind the front fork blade, below the height of the mudguard has not got covered in crud & the bearings survived. Even after 10,000 miles the bottle dynamo did fail, i would have simply swapped it for a replacement. No one is saying that bottle dynamos are perfect, but they can be cost effective & simple to replace
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speedsixdave
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Re: Dynamo system choices

Post by speedsixdave »

cycle tramp wrote:
Hope you don't mind me asking, which roller wheel are you using on your b&m dynamo? The standard dynamo came with the usual rubber wheel, however you could up grade it to a wheel which was a wire brush wheel.


I don't mind at all, Cycle Tramp. It's the standard rubber wheel. Are there disadvantages to the wire wheel? If that's the solution to slipping in the wet, should the wire wheel not come as standard?

Thinking about it mine might be a 6 rather than an S6. Whichever was the cheaper one.
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ConRAD
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Re: Dynamo system choices

Post by ConRAD »

speedsixdave wrote:... thinking about it mine might be a 6 rather than an S6 ...

... I think they are all the same ... though each one bearing a different StVZO certificate (K133/K134) ... (?)

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Brucey
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Re: Dynamo system choices

Post by Brucey »

the basic 'dymotec 6' has (had) plain bushings and basic electronics, whereas the 'dymotec S6' had ball bearings and clever electronics to reduce drag at speed. I think they were both built using the same housings hence the dual ~K marks.

Although some folk report good reliability with the dymotec 6 there are others who report (e.g. in this thread) that they got a single winter's use out of one. 'YMMV' indeed.

cheers
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fatboy
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Re: Dynamo system choices

Post by fatboy »

I've used AXA HR dynamos and I got a fair life out of them. I think the old ones are better (with the metal wheel). When my plastic version failed I took it apart (as you do) and it was mainly a rusty brown and I don't know how it had gone around at all! The plus bit of a bottle is that when it fails it's a lot easier to fix. I much prefer hubs over bottles but would rather a bottle dynamo over battery lights, but just my opinion!
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speedsixdave
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Re: Dynamo system choices

Post by speedsixdave »

I see the 'basic 6' is still on sale at SJS. £36, which is neither particularly cheap nor particularly expensive. Slightly more than a 'low-end' hub, slightly less than a mid-range hub. But there's another £8.50 to add to that if you want the wire roller...
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Brucey
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Re: Dynamo system choices

Post by Brucey »

speedsixdave wrote:I see the 'basic 6' is still on sale at SJS. £36, which is neither particularly cheap nor particularly expensive. Slightly more than a 'low-end' hub, slightly less than a mid-range hub. But there's another £8.50 to add to that if you want the wire roller...


and postage of course.

NB they are no longer manufacturing this dynamo so once the extant stock is gone that will probably be it.

cheers
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ConRAD
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Re: Dynamo system choices

Post by ConRAD »

Brucey wrote:... they are no longer manufacturing this dynamo ...

... ohh, sounds good to me, perhaps one day will it become something rare ?

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cycle tramp
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Re: Dynamo system choices

Post by cycle tramp »

ConRAD wrote:
Brucey wrote:... they are no longer manufacturing this dynamo ...

... ohh, sounds good to me, perhaps one day will it become something rare ?

Image


Yes.. and may be worth some money to the right person...
... at the moment the only two advantages that bottle dynamos have over hub dynamos is that they are cheaper and easier to replace.
All this will change in ten years time, due to economies of scale, when bicycle makers can't sell a bicycle without a hub dynamo...
...already we're seeing expedition bicycles produced with hub dynamos so the rider can charge their phone, their camera and even their laptop (so they can update their on line twitter feed and blog site)...
...racing cyclists who use electronic gear shifting will be the next customers in line for hub dynamos, simply due to the fear of there gear shifting batteries losing power mid race..
...and after that are general commuters who expect their bicycle to have the same 'contectivity' as their cars, and expect to charge and use their electronic devices while cycling...(like using an app on your mobile phone to follow a route that you have planned, without the fear of getting lost)
...once laced into a wheel hub dynamos are easier to fit than bottle dynamos, so they'll be some savings on the cost of the dynamo hub itself, but that cost would also be driven down by the bike builders and because dynamo hubs will be everywhere.. you'll be able to get them off the shelf, should your old one fail...
..as a result, market demand for bottle dynamos will drop and everyone will stop making them, leaving a potential market for second hand bottle dynamos...
Eventually the number of tyres on sale with dynamo tracks will cease as tyre makers up date their moulds..
...even worse there may even be a reduction in the quality and range of 'non dynamo front hubs'...
However, as the number of bicycles using dynamo hubs increase... it becomes harder to argue against the introduction of 'day time running lights' for cyclists.. and by the eleventh year 'day time running lights' become uk law...
Last edited by cycle tramp on 3 Mar 2018, 5:32pm, edited 2 times in total.
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