antique cycle 6v adding led headlamp

I thought this was one of the most active automotive/12v ~ 6v boards on the web. Where's the love?

Well I can't speak for others, but if you can build your unit cheaper than an off the shelf light (let alone 1/4 the cost), then you are way ahead of me. (Not that I can see any landfill with my solution - merely the addition of a dc-dc converter.) And maybe I and others see us researching the answer as negating your exponential learning exercise - even if we did see it as being practical.

Geez, I Thought this was one one of the most knowledgeable and active forums on mobile electronics on the web. MY original post has been met with mostly a loop of E. Morriconi and tumbleweeds. I finally got lucky as hell with a DigiKey phone tech who was willing to overlook their policy against design assistance since he owned some vintage bikes himself. MY old trail bikes. 4vac ~ 16vac unrectified unregulated. 35w ~ 40w max output. For this small a system a bridge rectifier such as this http://www.digikey.com/product-search/en?vendor=0&keywords=GBU10A-BPMS-ND was suggested by the gentleman. Should be a suitable option with a properly sized cap paralleled to smooth out ripple in the the dc output and negate the need to use a battery here since I have no need for accessories beyond head and taillights. The rectifier ought to limit the top end fed to the regulator to 12 ~ 13vdc. Rectifiec Dc/Dc conversion can be as compact and adequate as this... http://www.digikey.com/product-search/en?vendor=0&keywords=941-1042-ND It has an input range of 3.1VDC – 13.8VDC, with an adjustable output range of .6V - 5.1V. This can also deliver up to 30W (6A),.. about half the size and twice the current of similarly priced ebay regulators in this voltage range. This would be a viable option for powering neutral white LEDs as most of them have a forward voltage in the 3.3-3.8VDC range. It may require more than one LED to reach desired light output. Since the DC/DC converter can only output up to 5.1V LEDs would have to be in a parallel arrangement so that their voltages were not additive. But Actually I believe I can find an single LED SMD adequate for my lighting needs. Isn't anyone else keeping pace with these developments? So far, so experimental. Inexpensive enough as a base start to have some fun. But I'm mindboggled at the range available here for LED element options. Any suggestions for me to identify a suitably max lumen/watt neutral +/- 3.x voltage LED from these pages? Before I return his email and overstay his welcome? Dimensions are no concern. Plenty of space to work with. http://www.digikey.com/product-search/en/optoelectronics/leds-high-brightness-power-modules/525140. Anyone care to identify a few prospects for this project from among the dozen or so 3.x volt neutral white LED SMD available either from Mouser, Digikey/Cree, Ebay Cree, or elsewhere? in addition, can anyone offer a size/brand capacitor to use in parallel between the rectifier and regulator? Thanks. C'mon... come through for me guys Sincerely, Brad W

I guess it's been long enough to confirm that in this case, YOU are the SME. Hopefully you'll reciprocate the love in this forum by updating this thread else a new thread with your solution. Certainly if you can do as you say - ie, do the above for much less then the cost of our solutions - it will indeed be a first. As to the cap size required, there is lots of web info for that. Determine what the load current is and what max ripple you want (at the lowest frequency). Then decide if you want ESR or normal electrolytic caps. (Of course dc-dc converters require no "smoothing" caps.) Looking forward to your updates. Best wishes.

Oldspark, despite appearances, my antagonism was purely facetious. Rather backfired. I was only hoping to goad a few here into weighing in but few seemed that interested. Well I can't speak for others, but if you can build your unit cheaper than an off the shelf light (let alone 1/4 the cost), then you are way ahead of me. (Not that I can see any landfill with my solution - merely the addition of a dc-dc converter.) I was not clear about the "1/4" cost part. Obviously LED lights from ebay on up to highly specialized flashlight/bicycle/motorcycle/automobile websites/vendors can range from two USD to many, many hundreds of dollars. In this case I was only referring unit costs, which even diy'ers are highly conscientious about. For the option of choosing among a very wide range of SMDs, rectifiers and regulators from digikey, mouser, and others, I can design something that is 90 percent suitable to my application and learn a great deal along the way. And no doubt spend more time and money doing so than simply buying and off the shelf unit.    I'm most fond of DIY options to needs in somewhat the same manner as one anticipating the travel more than the destination. Most inveterate DIY'ers, having sufficient experience with the (un?)discipline, learned long ago that the time, tools, costly mistakes, almost always bring the costs in well above the off the shelf solution. And that with even no sure promise of greater success with your own attempt in the end. Analogies are countless. Why do so many fish and hunt when the cost of prepared meats in the grocery is infinitely less than the cost of guns, fuel, boats, spending holiday hrs from your job, etc, etc? And there are many dozens of forums expressly populated by doityourselfers. Again, most genuine DIY'ing on the web is rarely motivated by saving money on the overall project as opposed to walking into bestbuy and simply taking the box home. There is a very active community of diy'ers who look upon saving money as a prime motivation as building "Jerry-Built" crap. Duct tape and baling wire done lazily, hastily, and destined for failure.    Yes, I did propose in the fist post that I anticipated adopting an off the shelf bicycle light to the cycle. That's already half way toward diy'ing rather than purchasing a 300 dollar package that is plug and play for many of these motorsports needs. The motorcycle forums, like advrider.com can point me to many of them. In the subsequent couple of posts as I started to learn more from the net regarding color temp options (generally not available in most singular off the shelf units), rapid new LED development, and as I began to get a bit fascinated with the new technology generally, I started getting more interested in some experimentation with mouser and digikey.      I came here misapprehending, it seems, the focus of this forum and I'm sorry for that and coming across as I did. Thanks Oldspark for the ideas you passed on, but I'll let this rest here and continue on with two threads on other forums more specific to lighting, where the direction of my topic has met with more interest. What is an SME:) Probably embarrassingly obvious, but I looked the net over and didn't find the acronym.

Sorry - SME = Subject Matter Expert. And not that I saw system costing $300 etc. Even 3500 Lumen automotive LED arrays are under $100, and I was expecting some of the smaller bike oriented units like the one you lnked. And whereas years ago I may have considered DIYing my own lighting, I can't see myself doing it now with the releasing of so may ready built set up with adequate heatsinking, matched reflectors & lenses, waterproofing etc.

We're actually closer to agreement on this than it would seem. The automobile led arrays are probably internally regulated for 12 volt systems that are relatively (compared to an old motorcycle) stable, rectified, and with plug and play bases to plug the LED units into. The bicycle options are designed around 12vac wall transformers to recharge their batteries. No matter what, I'm still going to have to adapt something to any "off the shelf" option with most or all of the parts I've mentioned. That's not really very much diying really. I'd quickly abandoned any notion of adapting leds to my existing reflector or coming up with a reflector of my own. Thats got to be off the shelf in some fashion, a whole flashlight or flashlight bulb/reflector assembly (never have seen a reflector alone for sale) since so much engineering goes into containing the pattern, depth, and angle of led lights. There are, like i mentioned kits for specific models of motorcycles. They are very very costly. If your motorcycle costs twenty grand, it's not unreasonable. The bikes I'm working with might move on craigslist for 150 dollars or so. In any case, there are none that I'm aware of that even remotely suited to such a small 6v magneto.

I see a front end buck-boost dc-dc converter as being key in this as it can boost sub-6V (maybe from 3V) and buck over 12V (some up to ~34V) to whatever voltage is optimum. If it were a single LED (string) it could even be designed to provide a constant (ie, maximum) current which is what high power LEDs require. (Well, all LEDs, but it's "critical" for newer high power LEDs.) But for several LEDs (strings), IMO analog current limiters are fine since they'd be fed from a constant voltage source. Though 2 transistors & 2 resistors etc can be used, I like the LM317 which only requires 1 resistor, is self thermal limiting etc, AND cheap. As I recall, the 317T (T0-220 package) handles up to 1A or 1.5A. PS - "normal" reflectors won;t work as LEDs are unidirectional, hence why each requires its own reflector.

Oldspark, I appreciate very much the ideas you've entertained with me here. I don't know how interested you might be in pouring over a little of the other input I've gotten on this... I have a hunch that you are... but may I link to another thread in another forum that has frankly confused me more than clarified anything. I also have a couple of transcripts from some pretty lengthy "online chat" sessions with digikey techs. My original order, in fact, was suggested by "none other than" Nick D. Olson Product Manager, Semiconductor Group Digi-Key Corporation. He actually seemed a little interested in how i managed to get his email address. It was provided me in my first digikey chat session since that tech seemed especially interested in what I was trying to do. So Mr. Olson was gracious enough to list specific parts for me and I placed the order. A pair of XMLBWT-00-0000-000LT50E4CT-ND   LED NEUTRAL WHITE XLAMP SMD A regulator NE12S0A0V06PNFA MODULE POWER DC/DC POL 6A A rectifier GBU10A-BPMS-ND ...and a recommendation that "As for a capacitor, basically anything in the micro-Farad range should work; more importantly however the voltage rating should be higher than the maximum voltage on the output side of the rectifier." What followed, from other forum inputs, including what i believe you are observing above, is that at idle this magneto drops as low as 4vac. After losses incurred by the rectifier and capacitor, a "brownout" in all but unavoidable without some form of boost. Could you scan mouser or digikey for the animal that you've described? Digikey's search function, especially, is hard on anyone who is even a bit uncertain of what they need.

Sorry, that thread link... http://electronics.stackexchange.com/questions/80148/how-to-calculate-ripple-smoothing-cap-for-vintage-motorcycle-led-headlight-conve