Portable charger for cyclists- Powers and charges small electronic items and is operated simply by p

[bonj2]

Errr ten miles.

oooh wow double figures. mine's 28.

 

[bonj2]

But what at what percentage of effort does it stop becoming noticeable? 1%? 5%? 10%

Let's say someone is cycling along, not particularly hard, and generating 150W of power. Let's assume 95% of that gets to the bike - 142W. Now let's say that the dynamo uses up 5% of that power - 7.1W, and let's say the dynamo is 85% efficient - 6W.

A Cree LED can generate 130 Lumens/Watt (I think some can do 200 Lumens/Watt now) so you could get up to 780 Lumens from that 6 Watts.

780 Lumens is a lot of light, considerably more than most bike lighting systems. I'm not sure how many Lumens you feel you need for riding in the dark; I guess it depends how fast you want to go.

My guess is that I'd be quite happy riding in the proper dark with a decent 3W light, which would take 2.5% or less of the power I was putting in to the bike.

A 5% drop in power equates on average to a 5% drop in speed, slightly more in fact due to wind resistance.
Why would I put up with a 5% drop in speed when I can ... er, let's see... NOT put up with a 5% drop in speed?, for no discernible disadvantage?
it doesn't matter how MUCH light can be generated from a dynamo, the fact is, ENOUGH light can be generated from a battery, which is no heavier than the dynamo, and doesn't slow you down...
If there was some trade off, such as that batteries were really heavy, or cost many hundreds of pounds, then I might be able to see the merit in dynamos, but none of those is the case, so I can't.

 

[bonj2]

Or you could go the whole hog, be revolutionary and design something that takes its energy from the bike's braking system.

Induction brakes. There's research going on at the moment into them, for cars,lorries etc primarily but obviously could then be applied to bikes, but I think a workable prototype is quite a way off.

 

[bonj2]

Thanks again for the replies everyone.

I'd like to get a better idea of what sort of cyclist uses a dynamo. It seems like the more likely market for a dynamo would be touring, holidaying cyclists or commuters who are not overly fussed about a little extra weight; as opposed to racing cyclists who pay a premium to save on weight and wouldn't want the extra drag.



What sort of cyclist are you bonj?

One that wants free-rolling wheels and thus not to be slowed down by some stupid contraption invented by a mad scientist in a shed, and one that wants ligths that don't get brighter as i speed up and get dimmer as I slow down, and possibly even switch off when I stop.

 

[PrettyboyTim]

A 5% drop in power equates on average to a 5% drop in speed, slightly more in fact due to wind resistance.
Why would I put up with a 5% drop in speed when I can ... er, let's see... NOT put up with a 5% drop in speed?, for no discernible disadvantage?

It's not going to be a 5% drop in speed though. At higher speeds the the vast majority of the power goes into overcoming wind resistance, which is roughly proportional to the square of the velocity. At 20mph, a 5% decrease in power would result in maybe a 2.5% decrease in speed.

If there was some trade off, such as that batteries were really heavy, or cost many hundreds of pounds, then I might be able to see the merit in dynamos, but none of those is the case, so I can't.

But there is a trade-off. You never have to worry about battery management, for the cost of half a mile an hour in speed. I don't suppose you'd want that if you're racing, but I doubt most of us would notice the difference.

 

[snorri]

I'd like to get a better idea of what sort of cyclist uses a dynamo.

I had a dynamo fitted on my touring bike about 10 years ago, the lights have always worked when I needed them, and give sufficient light to cycle at (my!) top speed in pitch darknesss. I have done absolutely no maintenance on dynamo or light fittings and they still function as good as new. There is a noticeable drag with lights on, but as I am not touring great distances at night, this is more than acceptable when balanced with the nil maintenance. It would be interesting to try one of these hub dynamos with less drag, but I worry a little about power output and also the extra expense of having it built into the wheel.
I tried to use rechargeables in a lighting set on my utility bike, but found them hopeless. The bicycle was not used on a daily basis at set times, and I found it impossible to get into any sort of routine of recharging the batteries. As a result when I needed the bike at short notice the batteries were often flat or only partially charged and failed at some stage in my journey. Much of my cycling is on unlit roads, so I need lights to see more than to be seen.
It's horses for courses, and it's dynamos for me!

 

[Arch]

"One that wants free-rolling wheels and thus not to be slowed down by some stupid contraption invented by a mad scientist in a shed, and one that wants ligths that don't get brighter as i speed up and get dimmer as I slow down, and possibly even switch off when I stop."

Bonj, have you ever ridden a bike with a modern hub dynamo? They create virtually no drag. (I'll admit, my old bottle dynamo does, but it is old, and all we had to hand when building the bike). I very much doubt a hub dynamo would affect your performance in any way you could actually notice.

Also, a decent modern light has a standlight, so they don't go off when you stop.

I have a dynamo on my winter bike, because it's more likely to be ridden in the dark, and it means I always have my lights there, and to hand, and no worries about batteries running out. My summer bike, I have battery lights, because I need the lights less. Once I get my tourer built up again, I'll have the bottle dynamo on that, but if I ever get the money together, I'd swap to a hub dynamo.

 

[Arch]

Oh, and I did read a couple of months back about one of the bigger companies (Shimano? Sram? B and M? can't remember) already planning or trialling a dynamo charger. It was in the same issue of the Indy that plugged dynamo lights as a fancy new gadget....

 

[MajorMantra]

They're already around for cars. I was talking about bikes.

Given that a charger is something you'd only want on a long journey like a tour, and that this kind of cycling requires relatively little braking a lot of the time, I doubt you'd recover a useful amount of energy.

Matthew

 

[Davidc]

A hub dynamo makes so little difference to the running of a bike that I can't tell if its on or not. I've used one for lights and to charge batteries for years - the last box got nicked with its bike though and I havent rebuilt yet.

When the new one's done I'm happy to let anyone have the details - the potential market's too small for it to have any commercial value. The AC from the dynamo goes through a schottky bridge rectifier before use, and then either runs lights or charges batteries.

The circuit fits in a box with a lights on/off switch on it. When off a small NiMH battery in the box charges to give 'standlight' operation (about 50 minutes) and the rest of the power goes on a wire to the rack. If I feel the need I use a pack (not primarily for this but it works) which has a 3.5AH 6V NiMH battery and a DC-DC converter (bought from Farnell) which produces stable 5v at up to 1.2A. I have a lead for my sat nav if I'm going to use it for longer than the 4 hours it lasts on its own battery (and another lead for charging my phone, but as that stays charged for 3 days it never needs a recharge when on the bike)

The total worldwide market for people wanting to recharge gadgets while on a bike has to be so small that any idea of a commercial device must be ill conceived.

The sort of cyclist who uses a dynamo is one who wants lights available all the time - just like house or car lights - without thinking about batteries.

 

[bonj2]

They're already around for cars. I was talking about bikes.

well they're obviously not efficient/cheap/small/good enough for them to be mass produced. They're still working on them I think

 

[bonj2]

"One that wants free-rolling wheels and thus not to be slowed down by some stupid contraption invented by a mad scientist in a shed, and one that wants ligths that don't get brighter as i speed up and get dimmer as I slow down, and possibly even switch off when I stop."

Bonj, have you ever ridden a bike with a modern hub dynamo? They create virtually no drag. (I'll admit, my old bottle dynamo does, but it is old, and all we had to hand when building the bike). I very much doubt a hub dynamo would affect your performance in any way you could actually notice.

Also, a decent modern light has a standlight, so they don't go off when you stop.

I have a dynamo on my winter bike, because it's more likely to be ridden in the dark, and it means I always have my lights there, and to hand, and no worries about batteries running out. My summer bike, I have battery lights, because I need the lights less. Once I get my tourer built up again, I'll have the bottle dynamo on that, but if I ever get the money together, I'd swap to a hub dynamo.

You can prattle on for as long as you like about how little drag they create, or how unnoticeable it is, but the fact is batteries don't create ANY drag, so they're clearly always going to be better!
If you can invent a hub dynamo that creates a negative amount of drag, i.e. it actually powers me along, then I'll consider it!
The only advantage you seem to be able to come up with is that you might forget to replace/charge the batteries and they might then run out. Well, just don't forget!

 

[hackbike 666]

oooh wow double figures. mine's 28.

28 one way? I just about manage ten miles and im slow.

7 day commute is it?

 

[bonj2]

28 one way? I just about manage ten miles and im slow.

7 day commute is it?

no, but it probably would be 5 if i didn't have other things to do in the evening./

 

[hackbike 666]

28 one way then?

Yes years ago I could have managed that but not now with the seven day stints I do and shifts come to that.

So what do you do? Three commutes a week?

I have only missed one commute in over six years because I stayed at work during the snow.

Have you got a light bike and all the lycra?