Cycling UK Forum

Open circuit voltage from a bike dynamo (magneto) is s lot more than 6V. They are devices that try to push a constant current, so the voltage goes up as the resistance does...and an open circuit is the highest resistance you can get.

rjb wrote: ↑30 Jun 2022, 4:58pm

Nearholmer wrote: ↑30 Jun 2022, 4:43pm Why are they traditionally run on the tyre sidewall?

Couldn’t they be run from the “road face” of the tyre at/near the top, thereby using the bit that is designed to take hard wear?

"Mudguards" is the reason. No mudguards then you could make a bracket to run on the thread.

Wouldn't the tread be more consistently wet in the rain and more prone to causing slippage than running on the sidewall?

Bottle dynamo needs a dynamo track on the sidewall of tire, to run properly. Tire manufacturers begin to skip that track as few people use sidewall dynamos anymore. Without the track, the dynamo may slip even in dry weather.

If they had drive-heads made from tyre-type rubber, no, they wouldn’t slip.m, and the necessary pressure to obtain drive would be low.

Anyway, this is one type of better mouse-trap that the world won’t beat a path to my door if I invent (I suspect re-invent), so all mere musings.

Nearholmer wrote: ↑30 Jun 2022, 10:02pm If they had drive-heads made from tyre-type rubber, no, they wouldn’t slip.m, and the necessary pressure to obtain drive would be low.

Anyway, this is one type of better mouse-trap that the world won’t beat a path to my door if I invent (I suspect re-invent), so all mere musings.

That's contrary to my experience. I put together a bike, still a while ago, and found that my light was unreliable which was horrid as I had a lengthy night commute in serious traffic. I got a new tire with a track, but that track was only half pronounced, with the manufacturer explaining that it was cursory since not many customers kept using sidewall dynamos, and they want to give the tire a sporty look. Only third tire worked well, at least in dry weather. Yeah, I could also use a wire head for the dynamo, but then risking a shorter life for the tire.

Carlton green wrote: ↑30 Jun 2022, 1:41pm I’m a fan of Bottle Dynamos and think them unfairly dammed, but it all depends what the OP wants to do.

If you want anytime drag free electric generation then you’ll have to cough up for a hub dynamo. If in reality more perceived than real a bottle dynamo does suffer a little drag; a bit of light oil might help with that (I believe it does) and so might an extra cap / cover on the dynamo drive wheel (not tried that yet but have some covers ready). I’ve covered loads of night time riding miles with just old style Union Dynamos and never had any bother with them, they just kept working for me as I steadily rode along in all weathers. With the LED lights and bottle dynamos on my bikes I can literally walk pushing the bike and have plenty of light - I find that amazing.

The best advice I can give is to pick a moderately powerful set of lights and then try them out with a second-hand Bottle Dynamo, it’ll be at least a stop gap arrangement and if you really can’t get on with the bottle then it’s no big financial loss.

Have to admit that I'm with Carlton Green...
I've used them on almost all my bike builds (which almost go back for 25 years).

I find them appropriate technology for the times when I use them which is infrequently and occasionally. However when I have used them they've been great and always worked.
This has included a 13 mile bike ride from a ghost hunt in a pub at 5 am in the morning in March (2005) through two snow showers, a 5 mile push/ride off road across the Quantock Hills and a 25 mile ride for some fish and chips in 2015...

If you were building a bike for a 48 hr non stop ride, or a commuter bike for someone who does night shifts then I would recommend either hub dynamo or a quality light/battery set up or even both*.. but if you were building a bike which you may use occasionally sometime in the dark then I'll always fit a bottle dynamo.

I would say that setting up a dynamo driven by a tyre sidewall takes an almost zen state of mind to do it right. Even now, it can take me half an hour and several attempts. The important thing is the piece of string. Can't stress that enough.

Personally I don't understand this 'either' dynamo 'or' battery lights that some bicycle users have adopted. Personally for longer rides in the dark (over 4 miles) I'll always carry rechargeable lights, and there's nothing stopping you from doing the same - dynamo lights for flexibility but backed up by rechargeable lights when you know you'll be riding in the dark.

As previously mentioned may performance tyres don't carry a dynamo wall strip. But equally many tyres made for commuting or city bikes do have them.

I'd like to extend my personal thanks to everyone who has replied to the original post damning bottle dynamos for being awful. Every time a thread like this appears everyone who has one sells their bottle dynamos cheaply....
My store of 2nd hand bottle dynamos currently look like this. I hoping to add to it sometime:-)

There is a contactless rim dynamo system too, called I think magniclight.

That works rather like a squirrel-cage induction motor, using permanent magnets in the dynamo to induce eddy currents in the wheel rim, which in turn creates the opposing magnetic field to turn the dynamo.

I have a feeling it’s a tad expensive compared with a mechanically driven dynamo though.

Some years back now, but I used a Nordlicht very successfully for commuting. I've just never had the issues that others have.

cycle tramp wrote: ↑30 Jun 2022, 10:24pm I would say that setting up a dynamo driven by a tyre sidewall takes an almost zen state of mind to do it right. Even now, it can take me half an hour and several attempts. The important thing is the piece of string. Can't stress that enough.

Please elaborate

iandusud wrote: ↑1 Jul 2022, 5:39am

cycle tramp wrote: ↑30 Jun 2022, 10:24pm I would say that setting up a dynamo driven by a tyre sidewall takes an almost zen state of mind to do it right. Even now, it can take me half an hour and several attempts. The important thing is the piece of string. Can't stress that enough.

Please elaborate

For what it’s worth I have found it import to align the dynamo spindle correctly. For me correctly is at 90 degrees to the wheel circumference. The dynamo’s spindle (*) axis of rotation should near perfectly align with a taught piece of string from the axle’s centre to the rim. I would check that alignment with the dynamo in the operating position (pulley pressing on tyre).

* Of course you can’t see the dynamo’s spindle but you can make a perfectly satisfactory judgement of where it is using the centre of the pulley, dynamo body and central electrical terminal, etc., as guides.

Those B&M dynamos can have weak catches. My lights kept turning themselves on when I hit a bump in the road.

rogerzilla wrote: ↑1 Jul 2022, 6:52am Those B&M dynamos can have weak catches. My lights kept turning themselves on when I hit a bump in the road.

I’ve not used the B&M ones myself so won’t comment on them specifically. Correct adjustment of the swing pivot (to make use of the travel) and a true running wheel have helped me to reliably use Bottle Dynamos, well that plus a bit of oil and maintenance. The lights turning on by themselves after a jolt (the Dynamo literally springs into action) is rather unusual, but I’d say more a nuisance than actually hazardous. Perhaps your particular dynamo(s) latching mechanism was worn, not quite manufactured correctly or otherwise not perfectly functioning.

As the evenings are getting shorter it must be time to revive this old thread. Everything you need to know (well a lot of it,) about dynamos, bottle hub or otherwise.
viewtopic.php?t=127606

And if you want to build your own led lighting system this is the Bible.
"Dynamo LED Light Systems for Bicycles (electronic circuits)" http://pilom.com/BicycleElectronics/DynamoCircuits.htm

Happy tinkering and soldering.

And if you want to keep it really simple connect a standard 12v mr16 led bulb straight to the dynamo. These led bulbs will have all the necessary rectification circuitry built in and can take whatever current the dynamo generates. Simples.

rogerzilla wrote: ↑1 Jul 2022, 6:52am Those B&M dynamos can have weak catches. My lights kept turning themselves on when I hit a bump in the road.

Damn, that must've been annoying. To be fair I've used one from 2004 to 2012 - I changed it for an axa dynamo bottle because the axa dynamo bottle looked cheaper and I was parking up the bike alot during that time.

During my time with the B&M dynamo I did Lejog, several weekend tours and a few week tours, I took it down canal paths, farmer's tracks, and even road it across the Quantocks a couple of times, all without any issues.

...however my dynamo set up might have been different to yours - my dynamo was fitted behind the front fork at an angle of about 35 degrees, and my wheels were 26 size with 1.75 wide tyres. Both may have made a difference between your experiences and mine.