Should I go dynamo, or stick with batteries? And if dynamo, DIY or commercial?

[fyrstormer]

I've never heard of a bike light with an AC generator. Interesting idea.

this is one of those areas where YMMV definitely applies!

My first design was a basic arrangement like this with AA NiCads. The NiCads got overcharged and died an early death.

My second design had a very nifty pwm'ed regulator for charging the AA NiCads, and a regulator for driving the headlight. It didn't kill the battery, but there just wasn't adequate capacity in the winter. This was a result of it being very difficult to charge a nicad in very cold weather and the almost constant need to power the headlight (dark in morning and after work).

Both of those problems sound like symptoms of inadequate battery capacity. But yes, switching to LEDs (and possibly adding a buck circuit between the generator and the batteries to prevent overcharging) makes things a lot easier to manage because of the lower power consumption.

 

[GlowBike]

I think they're all AC these days (Schmidt, Sanyo, Shimano, modern Sturmey-Archers like the X-FDD that I'm getting ... hey, they all start with "S", just like mattress companies. Weird). Anyway, that's why all the circuits on pilom.com have bridge rectifiers in them.

 

[Steve K]

I've never heard of a bike light with an AC generator. Interesting idea.

I've only ever seen AC bike generators. It's certainly the simplest and cheapest design; just spin some magnets inside of stationary coils of wire. To do a DC design either requires brushes or a rectifier assembly.

Both of those problems sound like symptoms of inadequate battery capacity. But yes, switching to LEDs (and possibly adding a buck circuit between the generator and the batteries to prevent overcharging) makes things a lot easier to manage because of the lower power consumption.

well, if you are taking more energy out of a battery than you are putting in, then it doesn't matter what the battery capacity is. Eventually, you'll drain it. The worst case scenario might be some urban riding, where you pedal for a block (taking 5 minutes), sit at a red light for 5 minutes, pedal a block, wait 5 minutes, etc. If you are trying to keep a 3 watt headlight fully powered for that whole time, the battery will eventually get drained.

My first design, which just continually charged the battery, could have been solved with a much bigger battery. For a charging current of 0.5A, you'd need a 5 A-hr nicad to tolerate that sort of continuous overcharge. For a nimh, it would need to be bigger since they aren't as tolerant of trickle charging. I used to power a NightRider headlight with a 4 A-hr pack made of D cells, and that's a very hefty battery to be carrying around in order to justify not using a charge regulator. I use voltage limited charging on the AA nicad in my standlight designs now, and it's quite simple and gentle to to nicad. It doesn't try to reach 100% charge, though. It's a compromise that works for me.

Steve K.

 

[Lynx_Arc]

I've only ever seen AC bike generators. It's certainly the simplest and cheapest design; just spin some magnets inside of stationary coils of wire. To do a DC design either requires brushes or a rectifier assembly.

Alternators are cheaper and offer more power at lower speeds. I think the reason they were not common till later is that there wasn't a huge interest in bike lighting at that time I think only a few companies made lights and they were not cutting edge. The light I got was nothing like the high end brands out there that still used generators but it stomped them in output due to the superior performance of the alternator itself allowed for it to run at lower speed levels and the battery light switching on at low speeds was nice not leaving you in the dark when you stopped.

 

[Steve K]

Alternators are cheaper and offer more power at lower speeds. I think the reason they were not common till later is that there wasn't a huge interest in bike lighting at that time I think only a few companies made lights and they were not cutting edge. The light I got was nothing like the high end brands out there that still used generators but it stomped them in output due to the superior performance of the alternator itself allowed for it to run at lower speed levels and the battery light switching on at low speeds was nice not leaving you in the dark when you stopped.

I'm not clear about what you mean when you use the term "alternator". That's not an engineering term, and as far as I know, only has a meaning in the context of automobiles. In autos, the alternator has a built-in rectifier bridge and a voltage regulator that operates by controlling the field current. Maybe the late LightSpin incorporated some of these functions, but not anything currently in production such as the Schmidt or Shimano dynamos.

What was the specific dynamo/gen/alternator that you had such good results with?

Steve K.

 

[Lynx_Arc]

I'm not clear about what you mean when you use the term "alternator". That's not an engineering term, and as far as I know, only has a meaning in the context of automobiles. In autos, the alternator has a built-in rectifier bridge and a voltage regulator that operates by controlling the field current. Maybe the late LightSpin incorporated some of these functions, but not anything currently in production such as the Schmidt or Shimano dynamos.

What was the specific dynamo/gen/alternator that you had such good results with?

Steve K.

The original generators had windings and contacts set up to make DC output only they were incapable by design to output AC. An alternator puts out AC from the coils and uses rectifiers to convert it to DC. The first automobiles used DC generators (typically 6v). I think some of the first alternators used external rectifiers and many use or used to use external regulators also. So alternator is related to the coil/brush/contact design and not the final output from the back.

http://en.wikipedia.org/wiki/Electric_generator

 

[Steve K]

Does anyone out there have a bike dynamo that produces DC output? I'm having a hard time believing that such a device would exist because there's no need for DC on a bicycle. Although... I have seen an old (mid 40's?) Raleigh catalog where they showed a dry cell battery used for a standlight. They would need DC for that, and that pre-dates most semiconductor applications. They would have had a DC generator for that. For such an exotic application, the cost of the brushes and commutator contacts would be tolerable.

By contrast, cars do need DC to run the ignition system. Before semiconductors were common, the easiest way to generate DC was with magnets for the stator and the winding on the rotor. The brushes allowed the commutation to produce a DC (with a lot of ripple) output. The downside of brushes is that they wear out and need to be replaced.

Steve K.

 

[ttoshi]

The lighting of the IQ Cyo Sport is good--all the light is lighting the road, so beams on a wall won't tell the story. I would not get the Cyo R unless you are only going under 15mph the whole time. My issue with the Cyo is that the beam width is about 1 lane wide. If you are going straight, there is plenty of light to go 30 mph, but once you start to turn, you are not illuminating where you are going effectively, since the beam will start pointing in the other lane or along the side of the road. On an upcoming night ride of mine, I will probably supplement the Cyo with a bar-mounted flashlight for the fast twisty descents.

Toshi

 

[Bobblehat]

...... Although... I have seen an old (mid 40's?) Raleigh catalog where they showed a dry cell battery used for a standlight. They would need DC for that, and that pre-dates most semiconductor applications. .............
Steve K.

Possibly this little gem ........ the smaller picture shows the components ..... now there's a miniature rectifier for you :huh:

http://www.sturmey-archerheritage.com/index.php?page=history-detail&id=64

or even this one .......

http://www.users.globalnet.co.uk/~hadland/fsu.html

Still outputting AC from the hub though!

 

[Steve K]

hey Bobblehat, that's some pretty neat stuff! Didn't know that diodes were that common at that time (although I'll assume that they were germanium diodes in those days).

I dug through my files and found the pages from the 1947-1948 Raleigh catalogue that discusses the dynohub and the lighting system with the "accumulator". You can start here...

http://www.flickr.com/photos/kurtsj00/7224472424/in/photostream

The fact that they boast that there are no brushes makes me assume that some dynamos were built with brushes.... and I still don't understand why anyone would, unless using batteries in a standlight was not uncommon.

Steve K.

 

[Bobblehat]

hey Bobblehat, that's some pretty neat stuff! Didn't know that diodes were that common at that time (although I'll assume that they were germanium diodes in those days).
..............................................................................
Steve K.

Could even have been copper oxide or selenium rectifier in those days, certainly the old "plate" type.

Glowbike ... I stopped at Pilom's circuit 7 too ...... 2 x xp-g/reginas and about 400 lumens OTF once I'm over 10mph, and it seems enough for commuting and cycle/canal path use. Low speed output is reasonable too.

 

[GlowBike]

Glowbike ... I stopped at Pilom's circuit 7 too ...... 2 x xp-g/reginas and about 400 lumens OTF once I'm over 10mph, and it seems enough for commuting and cycle/canal path use. Low speed output is reasonable too.

Thanks, good to know. I think I'm going to start with an XPG, a white XPE and a red XPE from ledsupply, the classic simple DIY using square aluminum tubing and Carclo optics. At first I was intimidated by even this much DIY, but after more research I'm pretty comfortable with it. I also have an old dead stereo receiver lying around that should hopefully be able to donate a capacitor to the cause.

Actually, before I even do that, as another experiment I'm going to try out one of these 4-LED MR16 bulbs that I bought from DealExtreme a couple of years ago (I hope it's OK to post the link ... if not, mods let me know and I'll remove it). I've already tried it out as a bike light (with a 12V battery) and has OK throw, at least no worse than my XML. I'm sure it's far short of the claimed 360 lumens, but it certainly more than half that and fairly bright. I also have one in my 12VAC desk lamp so I know it can handle AC. Some reviewers claim it will work down to 6V or so, one even says it works with a (bottle) dynamo, so since I already have one mounted in a bike lamp holder I might as well try it.

It's not well enough focused for me to use as my winter commute light and the LEDs aren't the most efficient, but I can't resist trying it out. If it works decently I might get a generator wheel for my wife's bike and use this as a no-cost headlight.

 

[GlowBike]

FWIW, I finally got around to posting pics of my existing nailbender XM-L based setup on the "show us your ..." thread.

 

[GlowBike]

Finally got this done a couple weeks ago. Front hub is the Sturmey-Archer X-FDD (drum brake/dynamo).

Light is the $8 4-LED MR16 unit that I mentioned above, mounted in a venerable Optronics housing using two L-brackets from Ikea that I had lying around. Shroud is cut from an old water bottle, partially lined with metalized tape to throw a little more light down and keep from killing my night vision too much.

The light actually works surprisingly well. Handles the dynamo's AC just fine since it has a built-in bridge rectifier. Throws out enough light to see by starting about 3mph, loses most of the flicker and reaches most of its brightness by 5mph, gradually increases to maximum by 7-8mph. (This is with 20" wheels). Not much throw, and doesn't light the road enough for riding in the rain, but it is probably spraying out 200-250 lumens (LEDs rated for 360lm total) and sufficient for dry-weather riding. I'll stick with this setup for now, and won't bother trying to build something more powerful until the night riding season approaches in Oct-Nov.

I'd post a beamshot but that's tricky with a dynamo light! Here it is standing still in the daylight instead.