OT - generating electricity on a bicycle

[David]

The standard ways are:

a hub dynamo (ridiculously expensive considering I had one on my bike in the 1960s) but this needs a wheel rebuild as well as the purchase of the hub.

a bottle dynamo (which is a pain to get to rub against the tyre when you want it to and not when you don't). Also noisy and perhaps not very efficient.

There was a dynamo a while back which fitted to the frame just in front of the rear wheel and contacted the tread of the tyre instead of the side wall but I haven't seen this around for a while. Cant locate it via Google after a quick search.

I did wonder if there was another way. For example using a disc brake like assembly, with a metal plate rotating through two fixed contacts (just like a disc brake and pads).

For another example, having a light metal cover on the front wheel (like the aero wheels on time trial bikes) and fixed contacts all the way up the front forks.

Both (badly described) methods should provide the basic rotating split ring and metal brushes of a DC generator. I just have no idea how efficient this would be compared to a hub or bottle generator.

Of course, an adverse reaction to water and grit might play a part as well.

Just pondering.

Cheers

Dave R

[The Natural Philosopher]

You could attach a load of neodymium magnets (alternate NS poles) to the wheel rim, and have some coils either side in series.

Bridge rectifier and a cap and its all rubbishy DC for lights. Id use that to charge a battery.

[newshound]

Why? are you trying to provide lights for cycling, or thinking about charging your Tesla Wall while taking exercise on a static bicycle?

In the far east, a charity is converting "dead" bicycles into mechanical energy generators for very light industrial or farming applications, which seems to me to be entirely admirable.

To actually answer your question, the efficient way would be to use the relatively high-tech motor of a modern electric bicycle as a generator.

[Clive George]

Is the right answer though.

The posh ones are expensive, but Shimano make some which are very sanely priced.

20 euro. I wouldn't rebuild the wheel, as you'll need new spokes anyway, so factor in new spokes (16 quid from chain reaction) and rim (15 quid or so?).

It'll give you the most reliable electricity supply on a bike. Pretty much unnoticable when on too, unlike a bottle or a bottom bracket generator. (the bottom bracket ones suffered from being in the worst place for muck on a bike).

[Brian Gaff]

What |I'd like to see would be an exercise bike which could charge up batteries so your efforts are not wasted. I have no bike and do not want to buy one since I cannot ride it on the streets obviously. There is one on amazon which clames to operat of the chain on a normal bik, but fitting it looks like a complete bodge up. Brian

[Tim+]

Sanyo dynapower.

I had one. Crap in the wet as the roller would lose traction with the tyre.

Bit puzzled why you're trying to reinvent the wheel though.

Tim

[David]

Apart from the question "why would I need a new rim" that sounds sensible. I can see that new spokes would be needed.

However there is one minor issue - I was considering it for my Dutch bike which has hub gears and brake at the rear, a hub brake at the front, and so nowhere to fit a hub dynamo.

Which made me ponder.

Cheers

Dave R

[Chris Bartram]

I think the suggestion was to have a whole new wheel built, rather than mucking about with the existing one.

Shame.

What's the intended use? I have to say, I wouldn't bother. Rechargeable lights are good enough, these days.

[Clive George]

Because new rims aren't that expensive and it leaves you a complete spare wheel.

Dyno-hubs are common on dutch bikes, complete with hub brakes :-)

(they'll do a 28"/700c one too, you'll just need to look)

What sort of hub brake do you have?

[Clive George]

Rechargable can be way brighter if you want.

But they still need charging. I prefer a light I don't need to worry about at all, which means hub dynamo. Most of ours are switched on full time.

(On a recent cyclecamping tour we also used it to charge phone and other USB stuff while riding)

[Syd Rumpo]

This is what you need, low voltage, high current...

Cheers

[tabbypurr]

Then skip it & get something decent first.

I can't imagine any scenario where a dynamo makes more sense than a rechargeable battery.

NT

[Chris Bartram]

Yes, I could see that. I don't ride far in one stretch, and in fact gained a really good front light from a friend who found it didn't always last for his commute: it only does an hour-hour and a half or so on full whack (which is far to bright for the road, but ace for a dark towpath).

[James Wilkinson]

Are you one of those annoying pricks who uses lights during the day?

[Clive George]

Any bike used regularly at night. The light is always there, ready, no need to remember to carry anything, charge anything. You wouldn't put up with having to carry a car battery in to charge every day - why do so on a bike?

[Tim+]

Not quite analogous. What does a car battery weigh compared to a rechargeable bike light? I do agree though that for regular after dark use, a dynamo system has a lot to commend it.

Tim

[newshound]

In the 1960's, superconducting motors were developed based on the same principle. The CEGB had one at Fawley Power Station

[The Natural Philosopher]

less likely to get nicked if its built in to the hub

[harry]

Bicycle generators are all AC. Why would they need to be DC? Have you never dismantled one?

[Syd Rumpo]

Interesting, thanks.