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  1. #1
    Senior Member Rob_E's Avatar
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    Bottle dynamos - recommendations/questions

    I've recently realized that my forks are a little too narrow for a hub dynamo, so I'm going with Plan B, a bottle dynamo. But I know nothing. They seem to range widely in price from around $10 to up near $80, and I don't really know what I'm looking for as far as what makes the difference.

    Any bottle dynamo recommendations or warning?

    Also, having read a number of threads on lighting options, I get the impression that a DIY LED system will give me much more light (i.e. "to see" light) for around the same or less $$ than a halogen set-up. If that's the case, that's probably the way that I'd like to go because I like a good DIY project, but, as far as wiring electronics goes, I'm starting with a clean slate knowledge-wise, so if anyone has any references to direct me to or pointers, they would be much appreciated.

    In particular I'm wondering what kind of set up I need to keep my lights powered during a few minutes of stop time. I love the idea of having access to light without having to recharge my battery daily, but I don't like the idea of being plunged into darkness every time I stop, particularly at intersections, where I'd like to remain visible.

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    I am not a fan of bottle generators. Having had a few in days gone by, I returned to using battery lights. I just didn't care for the drag and the loss of light due to speed reduction. There is also the issue of tire wear from the gen's drive wheel.
    I am also not well versed in the electronics realm, but with the new led and cree lights coming out and the long battery run times, for me, it doesn't pay to use a generator.
    There is also the chance that the mounting bracket will gouge your paint.
    Last edited by bobn; 11-03-08 at 12:32 PM.

  3. #3
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    Here are a few links of interest:
    http://www.pilom.de/BicycleElectroni...lectronics.htm
    http://www.nscl.msu.edu/~daniel/sreg.htm
    http://www.myra-simon.com/myra/bike/tips.html

    Don't be afraid to explore these sites, you'll learn a lot.

    Good reading!

    You could start with a 3 LEDs setup. 3 Crees (Q5 or R2 bin) will give you from 400+ lm to 600+ lm depending on the circuit you decide on. As for the drag, the dyno should slow you down about 2 km/h, if your not a racer it is inconsequential. The noise makes it sound worse than it is really. For convenience dynamo can't be beaten.

    Bottle dynamos don't do to well in the snow but this shouldn't be a problem in N.C. .

    Don't bother to power the rear light with the dyno (that's where you need the stand light the most). Use a battery rear light they last a loooong time. The Planet Bike Super Flash seems to be the best for a reasonably priced one.
    Last edited by calina; 11-03-08 at 02:47 PM.

  4. #4
    Senior Member limeylew's Avatar
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    Bottle dynamos - recommendations/questions

    Quote Originally Posted by Rob_E View Post
    I've recently realized that my forks are a little too narrow for a hub dynamo, so I'm going with Plan B, a bottle dynamo. But I know nothing. They seem to range widely in price from around $10 to up near $80, and I don't really know what I'm looking for as far as what makes the difference.

    Any bottle dynamo recommendations or warning?

    Also, having read a number of threads on lighting options, I get the impression that a DIY LED system will give me much more light (i.e. "to see" light) for around the same or less $$ than a halogen set-up. If that's the case, that's probably the way that I'd like to go because I like a good DIY project, but, as far as wiring electronics goes, I'm starting with a clean slate knowledge-wise, so if anyone has any references to direct me to or pointers, they would be much appreciated.

    In particular I'm wondering what kind of set up I need to keep my lights powered during a few minutes of stop time. I love the idea of having access to light without having to recharge my battery daily, but I don't like the idea of being plunged into darkness every time I stop, particularly at intersections, where I'd like to remain visible.
    I have used bottle and bottom bracket style generators for over 25 years and never had the generator fail, although I have had a few bulb failures but not very many.

    A lot of people will tell you that they have a lot of drag and will slow you down. Personally, I have never been trying to set a world speed record in the dark, so I don't let what I perceive as a minimal amount of drag bother me. Also, with a generator system, you will NEVER 'forget and leave your light at home', or have your battery go dead on a ride.

    You will probably be able to get a bottle generator for 'almost' nothing from a friend, a charity, a yard sale, etc.

    It is probably good to supplement your generator system with inexpensive, front and rear, battery lights which you can use for visibility when you stop at a stop sign or red light.

    Here is a place that I have found to have VERY affordable bike lights:-

    http://www.dealextreme.com/products.dx/category.905

    They're not all going to last you for a lifetime but what I have bought has always worked well.

    Hope this helps you.
    Lewis.
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  5. #5
    Zoom zoom zoom zoom bonk znomit's Avatar
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    Quote Originally Posted by Rob_E View Post
    In particular I'm wondering what kind of set up I need to keep my lights powered during a few minutes of stop time. I love the idea of having access to light without having to recharge my battery daily, but I don't like the idea of being plunged into darkness every time I stop, particularly at intersections, where I'd like to remain visible.
    I've build a few led systems using hub dynamos and circuits from pilom.com.
    Supplementing with a decent long running blinky is a good idea. People are using supercapacitors too(good for a minute or two, enough for intersections). See this thread for some discussion on longer run times..
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  6. #6
    Senior Member Rob_E's Avatar
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    Thanks for those links, calina, they look to be very helpful.

    Quote Originally Posted by limeylew View Post
    I have used bottle and bottom bracket style generators for over 25 years and never had the generator fail, although I have had a few bulb failures but not very many.

    A lot of people will tell you that they have a lot of drag and will slow you down. Personally, I have never been trying to set a world speed record in the dark, so I don't let what I perceive as a minimal amount of drag bother me. Also, with a generator system, you will NEVER 'forget and leave your light at home', or have your battery go dead on a ride.
    I had a cheap bottle dynamo back in the day and it suited me very well until I accidentally kicked it into my spokes and it disintegrated.

    The battery issue is exactly what I want to get around. I've had several incidents already where I've been out later than I expected and had no light, or I had my light, but it ran down before I got home. Also because battery-driven systems are almost always made to be taken off and recharged, they are almost always easy to remove with no tools, which means I'm be cautious of leaving them on my bike. A bottle dynamo and associated light could be bolted on in a more "permanent" fashion, making it less likely to wander off on its own or be forgotten by me. Plus no one seems to want a bottle dynamo anyway.

    bobn, thanks for pointing out some of the pitfalls. I'm not worried about drag. I tend to ride heavy, slow bikes and am none to light/fast myself, so I'm guessing the dynamo drag will be the least of my worries. I have considered tire wear. It's one of the reasons I'm thinking bottle dynamo rather than a roller. I'm guessing that unless I run my bottle dynamo all the time and let it push against the tire fairly firmly, the tires will probably wear out at the road contact area before they wear out at the sidewall. But certainly if that is contrary to others' experience, I'd like to hear it. At any rate, once I decided to go with a bottle dynamo, I also figured I should go with the Marathon plus tires (I had been considering the Big Apples, too), because the Plusses have a stiffer sidewall which, combined with the dynamo track, should handle the abuse of the dynamo better, I would think.

    I do like the idea of a back up battery lights. I have already been thinking that a good LED flashlight would be a good addition to my tools and could double as a headlight in an emergency as well as my current battery-driven rear light. But I would like to keep them for emergency use and not have to be taking them off the bike every time I park it, so I will have to check out znomit's link on setting up some kind of standlight capacitor system. Or possibly a rechargeable battery set-up than can catch some of the spill-over and power the lights when the dynamo cuts out.

  7. #7
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    You just beat me to the CPF link .

  8. #8
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    I am curious if anyone has experimented with the drag factor of a bottle generator. I'm not trying to be agumentative because you have the final say as to what you do. And that's fine with me.

    Try spinning the wheel without the bottle gen. and time the rotations to stop. Then put on the lights with the bottle gen engaged and time the rotations again. I would do it but don't have one hooked up. Just curious as to the outcome.

  9. #9
    Scott n4zou's Avatar
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    Bicycle Dynamos are very simple devices. Here is a photo of one taken apart.

    This was a vintage dynamo. The glue holding the magnet to the shaft had dried out allowing the shaft to spin freely in the magnet. All modern dynamos use rare earth magnets and 8 poles. The vintage dynamo above only had 4 poles so it's drag was much higher. Because there is less drag from modern dynamos slippage and tire damage is all but eliminated. Mine works fine even when the tire is wet. Snow is the only problem I have encountered with slippage. Because of the dangers involved with night time riding you should always have a backup light available. I carry a battery operated flashlight and handlebar clip. It's also handy just in case you need to work on the bike. It's really hard to work on your bike with only a dynamo headlight!
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  10. #10
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    Spinning the wheel won't tell you much, it doesn't have a lot of inertia by itself.

    A poor bottle dynamo is at worst 33% efficient. If you use it at 3 W, you will have to provide an effort of 9 W (at higher wattage, efficiency will improve). Since at around 25 km/h you provide about 75 W of power and 6 W are lost due to the friction of the dynamo, your speed will decrease about 2 km/h due to the extra friction. You will also lose 1 km/h to the light. That's about a worst case scenario, a good dyno will do better.
    Last edited by calina; 11-03-08 at 08:12 PM.

  11. #11
    Senior Member Rob_E's Avatar
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    Quote Originally Posted by bobn View Post
    I am curious if anyone has experimented with the drag factor of a bottle generator. I'm not trying to be agumentative because you have the final say as to what you do. And that's fine with me.

    Try spinning the wheel without the bottle gen. and time the rotations to stop. Then put on the lights with the bottle gen engaged and time the rotations again. I would do it but don't have one hooked up. Just curious as to the outcome.
    I don't yet have a generator to test, but I accidentally did a similar test today. Last night I opened up my 3 speed hub to put a little more oil in. I overtightened it when I put it back together and noticed that when I spun the wheel it wouldn't spin freely like it had prior to my messing with it. Giving the pedals a couple of turns and then stopping sent the wheel spinning maybe one more rotation whereas before it had spun fairly freely. I was tired of messing with it, so today I rode it that way. I could definitely feel the drag, especially when coasting, but, other then worrying about what I was doing to my bearings, it didn't impede my ability to get home. I'll be fixing it before taking it out again, but I didn't find it to take longer than normal to get home, I just had to pedal a little more often. I'm not going to intentionally introduce drag for no reason, but when it's there, I think it improves my cadence.

    If you're really worried about drag, it seems like a bottle dynamo is a good compromise. Unlike hub dynamos, you can remove all drag from a bottle dynamo when you're not using it, although when you are using it, I believe the drag is a little more. I believe I did see a study where someone compared many aspects of various generators, including bottle dynamos and hubs, and drag was included in that study, I think, but I can't find it right now. I've read too much dynamo info in the past 24 hours and can't remember which link is which.

  12. #12
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    Ive used cheap Union bottle dynamos, expensive Nordlicht ones and Shimano dynohubs.
    There is a big difference between old-cheap and modern-quality bottle dynamos but just as important is the mounting bracket.
    Clamp-on mounts are useless, they can't counter rotational forces well, they slip around under the spring load and get knocked into spokes. I have a seatstay braze-on tab on my touring bike and use the Nordlicht to power front and rear lamps. The braze-on and mount should be as short and stiff as possible to maximise grip. A rubber ring and Marathon tyres combine to give slip-free operation that does not cut up the tyre sidewall.
    I use a dynohub on my daily commuter which is fantastic, especially with a modern Lumotec Fly IQ LED lamp. For touring, where I only use the light for short evening rides or in emergencies, the sidewall is a better option.

    I have powered Lumotec and Hella lamps and they are both better than old 1970s Union ones. The Fly IQ with senso and standlight is much brighter.
    When you make your own lamp unit, can you maximize the efficiency of the reflector like in dynamo headlamps? You only have 3w to play with so you cant spread it around ober the road but you do need some peripheral star pattern for safety.

  13. #13
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    With LED lights and a bit of tweaking you can easily reach 5W and over.

  14. #14
    Senior Member Rob_E's Avatar
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    My understand (admittedly not very thorough) is that one of the reasons to go LED is that you can achieve much higher brightness (lumens) from the same amount of wattage, so even with only 3 watts to play around with, you may actually end up with light that's much brighter than the previous standards.

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    Quote Originally Posted by Rob_E View Post
    My understand (admittedly not very thorough) is that one of the reasons to go LED is that you can achieve much higher brightness (lumens) from the same amount of wattage, so even with only 3 watts to play around with, you may actually end up with light that's much brighter than the previous standards.

    You are right. Two Cree R2 at 500 mA should give you around 280 lm at the emitter but you might as well use 3 LEDs and get 420 lm, your dynamo will provide the required voltage. Look it up on Martin's site (Pilom).
    Last edited by calina; 11-24-08 at 02:16 PM.

  16. #16
    Zoom zoom zoom zoom bonk znomit's Avatar
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    I think it tops out around 12W.
    I'm running 4 and 5 leds and estimate around 30W halogen equivalent.
    Look here http://www.velociped.ch/docs/Dynamo-...leich_2008.pdf and see the E3(led) vs E6(popular 3w halogen).
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