Bottle Dynamos

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jb
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Re: Bottle Dynamos

Post by jb »

Carlton green wrote: 30 Jul 2022, 8:46pm
jb wrote: 30 Jul 2022, 7:27pm Our Raleigh Leeds has a hub dynamo so you can get home even if the battery has run out
https://e-motionevc.co.uk/store/product ... id142.html

23kg of bike and a flat battery sounds like bad news to me, but maybe I misunderstand.
Well obviously you wouldn't want to pedal it without power if at all possible but if that last half mile sees the battery cut out at least it can be pedaled back with full illumination, hopefully on the flat.
And I don't think it's any harder to pedal than fully loaded tourer but then again it's not me pedaling it - but I can push from the side :)
Cheers
J Bro
wjhall
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Joined: 1 Sep 2014, 8:46am

Re: Bottle Dynamos

Post by wjhall »


You won't find a current source in a Thévenin equivalent circuit simply because by definition it doesn't have one;... ....the Thévenin-Norton equivalencies can both be used to represent the same network of linear voltage and current sources and impedances at a given frequency, and can also be equivalent to each other via well-known relationships. ... ...
As an example of this, page 6 of Magdowski's 'Modeling a hub dynamo' has ... ...

I appreciate your point here has been that "describing dynamos as current generators is not helpful" but I'm still not sure I understand why you think that.
Good point, I had misremembered Thévenin's Theorem as stating that either current source/admittance or voltage/impedance models could be used to represent any circuit.

Magdowskis paper begins to show why an understanding of the nature of the circuit is useful. In the front lamp failure case 20 V will be driving 0.3 A into the remaining rear lamp load, with fatal results for the old fashioned filament lamps, or anything without effective protective electronics. In a sense the constant current model is usefully pessimistic, although I doubt the difference in time to failure of a filament lamp for 0.3 A rather than 0.5 A is of practical use. The external current will continue to fall as the load impedance rises, tending towards the limiting case of zero for an open circuit. This is where the voltage source-impedance model seems to give a better understanding, I cannot, at the moment, see how the a large internal current produced by a frequency dependent current source corresponds to physical reality.
wjhall
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Re: Bottle Dynamos

Post by wjhall »

wrote:
wrote: ... (Phil Wood hub) with a dynohub. ....
You could buy a dynamo hub and replace the hub on your wheel with it. I did it (on 2 bikes) a few years ago and rebuilding the wheel wasn't that difficult - getting started being the hardest part (I made a jig to hold the hub and rim in the right place relative to each other).


I built a dynohub wheel earlier this month, just laying it on a table according to the Park Tool website instructions. My first wheel build and seems to be satisfactory so far. I did subsequently use old forks and a dial gauge to true it to about +/- 0.3 mm from probably twice that.
220818-0162 SP V-8 Hub Dynamo Build-laced.JPG
However the OP specifically mentioned the hub as a good part of the wheel. There is probably no solution to that, you either bite the bullet and rebuild the wheel with new spokes, or build a new wheel, or use a bottle dynamo, or battery lamps.

The reason for my build was that after forty years of bottle dynamos, during which I thought I had encountered every possible problem, and the solutions, and seemed currently to have a nicely running bottle dynamo, an entirely new problem appeared:

220711-9158 Dynamo less cap.JPG
Which was just too much.

Now I am ready for practical study of the problems of hub dynamos. The one that comes to mind is regreasing the bearings, which presumably needs doing just as often as any other hub, but is now part of a complicated electrical component that is not, perhaps, meant to be user serviceable.
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SimonCelsa
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Re: Bottle Dynamos

Post by SimonCelsa »

This thread has just inspired me to refit the bottle dyno to the commuting bike as it's dark now at 06:15 when I leave home. Still have the summer tyres so have set it to run a little higher than usual. The wheel spins OK and the light comes on so that's the important thing. I note the ridges have worn away from the rubber wheel anyhow so it shouldn't damage the tyre hopefully.

It sounds a little 'clunky', maybe it needs a bit of maintenance but I can't see how to open it without butchering it. I'll have a quick butchers to see if there's any information on You Tube.

IMG_20221001_150702474[1].jpg
IMG_20221001_150653075[1].jpg
jb
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Location: Clitheroe

Re: Bottle Dynamos

Post by jb »

Bottle dynamos still have their place but the skills to keep them trouble free are getting more into the hobby market I'm afraid. cheap models will only haste their demise.
Annoyingly I have a 'Light Spin' in the shed that is excellent except for the spring and useless roller cap. With an elastic band its performance is second to none. but alas this makes it somewhat impractical for everyday use.
Cheers
J Bro
cycle tramp
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Re: Bottle Dynamos

Post by cycle tramp »

SimonCelsa wrote: 1 Oct 2022, 3:49pm This thread has just inspired me to refit the bottle dyno to the commuting bike as it's dark now at 06:15 when I leave home. Still have the summer tyres so have set it to run a little higher than usual. The wheel spins OK and the light comes on so that's the important thing. I note the ridges have worn away from the rubber wheel anyhow so it shouldn't damage the tyre hopefully.

It sounds a little 'clunky', maybe it needs a bit of maintenance but I can't see how to open it without butchering it. I'll have a quick butchers to see if there's any information on You Tube.


IMG_20221001_150702474[1].jpg


IMG_20221001_150653075[1].jpg
Nice! I like a good bottle dynamo. What I would suggest is periodically checking for the tightness in the clamping bolts. It looks like that fork tapers, and as Brucey's not around to remind everyone, if (and its a big if) the clamp becomes loose, the dynamo may drop on the forks and perhaps even swing into the wheel spokes. However as you've mounted the dynamo in front of the forks (unlike mine), the motion of the wheel is more likely to knock the dynamo out of the wheel spokes rather than into it.
Here endeth the lore according to Brucey verses 2 until 4 :-)
Motorhead: god was never on your sidehttps://www.google.com/search?ie=UTF-8&client=m ... +your+side
Carlton green
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Re: Bottle Dynamos

Post by Carlton green »

The pro’s and cons of bottle dynamos have been endlessly discussed and chewed over. Use what suits your needs and your pocket.

I decided to use bottles rather than hubs because I can buy a second hand bottle that will gives years of use for a tenner or less and because if I need to replace a wheel then I didn’t want to also loose my generator - it’s more resilient to have them as separate items. Fitting a new bottle generator is comparatively easy (I have some identical spares in my store so replacement is a 15 minute job), fitting a new hub generator isn’t comparatively easy (a wheel strip and rebuild is involved).

If you demand the best, use your dynamo during much of your riding or have ‘special requirements’ then have a hub dynamo instead of a bottle. Both routes work but one might suit someone better; what type of cheese suits you best: Wensleydale or Cheshire? I like both but the most important thing is that I’ve got some cheese 🤔.
Don’t fret, it’s OK to: ride a simple old bike; ride slowly, walk, rest and admire the view; ride off-road; ride in your raincoat; ride by yourself; ride in the dark; and ride one hundred yards or one hundred miles. Your bike and your choices to suit you.
drossall
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Re: Bottle Dynamos

Post by drossall »

SimonCelsa wrote: 1 Oct 2022, 3:49pmI note the ridges have worn away from the rubber wheel anyhow so it shouldn't damage the tyre hopefully.
You can buy spare rollers for Axa dynamos.
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SimonCelsa
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Re: Bottle Dynamos

Post by SimonCelsa »

drossall wrote: 2 Oct 2022, 12:01am
You can buy spare rollers for Axa dynamos.
Yes, I think there are a couple in the shed, I'll have to dig them out, perhaps that will solve the light clunking noise. I can handle the whirring/whining but when combined with the clunking it soumnds quite self destructive!!.
rogerzilla
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Re: Bottle Dynamos

Post by rogerzilla »

jb wrote: 30 Jul 2022, 7:27pm Our Raleigh Leeds has a hub dynamo so you can get home even if the battery has run out
That was Gernan law until fairly recently. You couldn't use the traction battery for lighting. I don't know whether this was so you could pedal home in the dark, or whether it was caught by the more general law that only lightweight bikes are allowed to use battery lighting.
Carlton green
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Re: Bottle Dynamos

Post by Carlton green »

It sounds a little 'clunky', maybe it needs a bit of maintenance but I can't see how to open it without butchering it. I'll have a quick butchers to see if there's any information on You Tube.
As far as I know the AXA’s are the best but they’re also effectively sealed for life units. The tubes of rubber (moulding sprues) sticking up from the tyre’s sidewall won’t be helping matters much. They’re perhaps not the best but I like the old Union type roller dynamos, they’ve been durable for me and the roller comes off (unscrews) so you can dribble a little light oil onto the shaft - rotate it a bit and invert the dynamo for a while to let the excess oil return out. Rubber caps for the Unions are available and cheap; I’ve not used mine yet, I don’t ride particular fast so haven’t bothered to pursue their advantages.
Don’t fret, it’s OK to: ride a simple old bike; ride slowly, walk, rest and admire the view; ride off-road; ride in your raincoat; ride by yourself; ride in the dark; and ride one hundred yards or one hundred miles. Your bike and your choices to suit you.
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Sum
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Re: Bottle Dynamos

Post by Sum »

wjhall wrote: 1 Oct 2022, 12:55pm Magdowskis paper begins to show why an understanding of the nature of the circuit is useful. In the front lamp failure case 20 V will be driving 0.3 A into the remaining rear lamp load, with fatal results for the old fashioned filament lamps, or anything without effective protective electronics. In a sense the constant current model is usefully pessimistic, although I doubt the difference in time to failure of a filament lamp for 0.3 A rather than 0.5 A is of practical use. The external current will continue to fall as the load impedance rises, tending towards the limiting case of zero for an open circuit. This is where the voltage source-impedance model seems to give a better understanding, I cannot, at the moment, see how the a large internal current produced by a frequency dependent current source corresponds to physical reality.
In reality a constant current source will cease to provide a constant current when faced with sufficiently large load, but then even a 'pure' constant current source will be defeated by an open circuit, just as voltage source will suffer voltage drop when sufficiently heavily loaded or short-circuited. However, the fact that such things have their limitations doesn't prevent them from being what they are when under nominal conditions.

Magdowski's paper gives a very good understanding on how the dynamo in question lends itself to being a closer approximation to a constant current source rather than voltage source when driving a typical load. It's also shows how good that approximation is and where it might break down, for example when cycling at low speeds, or when the dynamo is connected to too high a load (such as several headlamps in series). A blown bulb is another example, although not as of practical use as you say.
wjhall
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Re: Bottle Dynamos

Post by wjhall »

... ... wrote: 1 Oct 2022, 3:49pm ....
It sounds a little 'clunky', maybe it needs a bit of maintenance but I can't see how to open it without butchering it. I'll have a quick butchers to see if there's any information on You Tube.
...
There is indeed a video on (1) how to open your Axa-HR, although I cannot see any reason to do so unless it has gone open circuit.
They look like this:
210505-965 Axa-HR Disassembly-repair basic elements.JPG
(This is a fifteen year old one that had failed open circuit, possibly a long term result of the contact tabs in that generation being too thick for the female spade connectors and me using too much force. The one shown with the self detaching cap was only fifteen months old, so refunded under warranty. It had thinner contact tabs.)

Removing the cap as shown in the video seems to be unncessary, in fact until the cap of mine separated of its own accord I would have thought it impossible and unwise. Perhaps he was demonstrating his strength.


(1) https://www.youtube.com/watch?v=DrZRAvjgCJg
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andrew_s
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Re: Bottle Dynamos

Post by andrew_s »

wjhall wrote: 2 Oct 2022, 9:28pmpossibly a long term result of the contact tabs in that generation being too thick for the female spade connectors and me using too much force.
It is possible to adjust female spade connectors to give a more appropriate level of grip on the male half of the connection.
Either squeeze gently with a pair of pliers (mole grips are good), or poke a suitably sized screwdriver in and waggle it to open them up.

I adjusted the spade on my Edelux front light - loose enough to just pull off if I forget when removing the wheel, but not so loose that fitting them becomes awkward (the one you fitted first lifts off when you try to fit the second).
wjhall
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Re: Bottle Dynamos

Post by wjhall »

wrote: 2 Oct 2022, 10:16pm .... ....
It is possible to adjust female spade connectors to give a more appropriate level of grip on the male half of the connection....
...
Indeed, I did, but only after trying pushing harder as the solution, and squeezong is a somewhat random operation. There do also seem to be two thicknesses avilable in female connectors of that width although I think the tabs were thicker than either. The second I bought, about fifteen years later had thinner tabs, similar to those on B& M lamps which slip in perfectly.

It is nevertheless a dynamo manufacturers job to design tabs that fit a specified connector.
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