antique cycle 6v adding led headlamp

This magneto is nominally 6v. I've measure 4v to 16v through the rpm range. Max output is 35 to 40watts.

It has a separate lighting coil but no rectifier or regulator. Headlamp and taillamp only. Not street legal.

6v lamps are dim to too often blown. 12v lamps are uselessly dim but last longer.

Rather not add a battery unless it is a significant benefit.

From the reading I've done so far LEDs are the only way to get significantly improved candlepower out of the headlight.

This is what I'm contemplating. I hope someone can offer more expert advice on the direction I'm looking at.

common as dirt full wave rectifier to give me dc at the start.
https://www.amazon.com/Amico-Single-Bridge-Rectifier-KBPC5010/dp/B008DEU18G

Adjustable Regulator so that I can recharge the batteries at the ideal level required of them.
https://www./itm/LM338K-Linear-DC-or-AC-6V-30V-Out-DC-4-5V-28V-5A-Voltage-Converter-Adjustable-/221039147321?pt=LH_DefaultDomain_0&hash=item3376f5b939

Kit for 23USD that supplies a headlight and batteries. Rated 1200 top lumen, probably more like 800 in reality, but 15x what the 6v 21w incandescent that is in there presently is giving.
https://www./itm/SecurityIng-1200Lm-CREE-U2-LED-Mini-Cycling-Bike-Light-Torch-Battery-Pack-US-/161074476663

No doubt there are major oversights to my plans. Since there is amazingly little info on the web for this type of application I'm starting at the bottom of the learning curve.

I did not want to add the year make or model since that information generally tends to distract from the topic when questions of completely non-oem retrofits are concerned. The info provided is perfectly adequate without such distractions such as "why on earth would you want to do that to xxxx bike?" "I wouldn't bother" etc. Yes, I've heard all of that before. And it's pure distraction.

But for conformity's sake with the rules, it's a pair of 1981 single speed 50cc Puch mopeds (again,not to be licensed for the street).

IMO forget the linear voltage regulator, use a switching type buck-boost dc-dc converter. There are several in webland based on the LM2577 etc for a few dollars (3 Amps max).

You may need a higher current version.

This is what I’m contemplating. I hope you might offer more expert advice on the direction I’m looking at.

common as dirt full wave rectifier for dc output.
https://www.amazon.com/Amico-Single-Bridge-Rectifier-KBPC5010/dp/B008DEU18G

Adjustable Regulator, as you suggested, so that I can either run led directly or recharge the batteries at the ideal level required of them.
https://www./itm/DC-DC-Step-Up-Down-Boost-buck-Voltage-Converter-…

So I’m searching for a maximum brightness single LED SMD that I can experiment with within the existing reflector and pressed glass diffuser lens at different angles, depths, and possibly even mounted on the inside of the glass lens, heat xfer epoxy, facing rearward toward the reflector for optimum road lighting pattern.

3.X ~ 4.X volts. form factor size is not critical. Something like this unless a larger element is a better candidate.
https://www.digikey.com/product-detail/en/XRCWHT-L1-R250-00901/XRCWHT-L1-R250-00901CT-ND/1923198

I’m a complete beginner except for a couple of days of web research.
Would anyone offer some help as to how to set this up? Just connect the rectifier between the coil output and the regulator, adjust regulator for 4dc in, 4vdc out, and connect direct to LED SMD? Could it be that straightforward? Would it be better to incorporate three eneloop 1.2v rechargeables or even a 4v lead acid battery?

Another off-the-shelf option is this headlamp recently purchased from Home Depot, package of two for 9.95. It incorporates a surprisingly bright, easily adequate for my needs, Cree XB-D element with three aux leds together running on three 1.5v alkaline aaa cells, 4.5vdc fitting the needs of this project quite well

Pics of the innards...




I hope I can get some advice here.   I'd really like to get this put together in some way that I can get max brightness out of this antiquated 4vac ~ 16vac magneto.

link to regulator should be
https://www.aliexpress.com/item/DC-Boost-Buck-Converter-Input-4-35V-Output-1-25-25V-0-4A-Constant-Current-Voltage/556745984.html

And link to Home Depot headlamps
https://www.homedepot.com/p/High-Power-LED-Headlamps-2-Pack-HD12OTB52/203409159#.UgxDlaw6Wmx

There are 2 distinct aspects to a project like this, namely:
- powering of the LED(s)
- charging of the batteries.

As I recall, the original proposed light was a self contained LED with LiPo battery with a DC input (to charge the LiPos).
In that case the dc-dc converter merely supplies the correct DC voltage and the light unit looks after the LED and battery charging.

LiPos as with any Lithium battery requires a specific charging method else explosion or fire can result, hence you want to avoid that.
Other battery types have their own charging methods.
And the battery charging voltage will be different to what the LED(s) require, so 2 distinct voltage sources are required (unless you use whatever method the "light" uses to control that).

Combined with the hassle needed to mount LEDs and lens them, buying a ready made unit seems a sensible way to go.

buying a ready made unit seems a sensible way to go.

By that do you mean the Home Depot unit pictured above or any of the dozens and dozens of bicycle headlamps available on the web?

That practically negates the whole exercise. I don't want to be constantly removing, recharging, batteries as the light output gets dimmer and dimmer. I want to use the lighting coil on the engine to keep the unit fully lit and stable enough to get max life out of the LEDs.

I was recently recommeded a list of parts from DigiKey.
I should be able to draw 3 to 3.5 amps from this coil.
For this small a system a bridge rectifier such as this
https://www.digikey.com/product-search/en?vendor=0&keywords=GBU10A-BPMS-ND
should be an option with a suitable sized paralleled cap 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. And the rectifier ought to limit the top end to 12 ~ 13vdc.

Dc/Dc conversion can be as compact and adequate as this...
https://www.digikey.com/product-search/en?vendor=0&keywords=941-1042-ND
It has an input range of 3.1VDC – 13.8VDC, and an adjustable output range of .6V - 5.1V. It can also output up to 30W (6A). This could be a viable option for powering 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.

Probably the most difficult decision to make is identifying the ideal neutral white +/-4000K from among these pages
https://www.digikey.com/product-search/en/optoelectronics/leds-high-brightness-power-modules/525140

Anyone else would like to weigh in here. I'd appreciate it.
From there is the toughest choice. An ideal candidate, or pair of candidates (in

svejk] wrote:

---

don't want to be constantly removing, recharging, batteries as the light output gets dimmer and dimmer.

---

You won't. The dc-dc converter plugs into the light's external DC power socket.

The progress of these LED SMD's is almost on a monthly acceleration curve.

Diy'ing this with digikey or mouser smd's affords me the opportunity to experiment with precisely the pattern spread, Kelvin, manufacturer, mm width and length, etc, for 1/4 the cost of an off the shelf flashlight, the majority of parts of which I would be landfilling anyway.

So just what is the 'latest and greatest' 3.x volt LED SMD available from these vendors today in near to a 4000k spread that is optimal for trail riding conditions (about 120 degrees)?

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
https://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...
https://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.

https://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...
https://electronics.stackexchange.com/questions/80148/how-to-calculate-ripple-smoothing-cap-for-vintage-motorcycle-led-headlight-conve

IMO that voltage reg may have too low an upper voltage but its current capability is good.
Otherwise maybe units like Auto DC 3-35 to 1.2-30V Boost Buck Converter 12V 24V solar voltage regulator charger circuit (2A max) or others based on the LM2576 etc.


The XM-L2 LEDs have viewing angles of 120° which IMO is way too wide tho I haven't analysed the spread.

The cap size is based on the lowest generating frequency (times 2 assuming a single-phase "alternator" fully rectified - ie, the period between 2 fully rectified peaks) and then whatever voltage sag is permissible (ie, total current and minimum operational voltage).
But the dc-dc converter should look after any ripple in the rectified supply provided it's above the converter's minimum operating voltage.

Hope you're sitting down. Here comes another silly question. Actually I think that's why I'm coming off a bit of a blowhard here, since I really don't know a damn thing about what I'm talking about.

IMO that voltage reg may have too low an upper voltage but its current capability is good.

Again, surprisingly difficult to web search optimal arrangements for two or more LEDs. I was working under the impression that wired in parallel, three 2.9v LEDs would still draw 2.9v. That's why I anticipated no problem with that regulator. It's suspiciously tiny by the way... about 1cm x 1.5cm x .5cm.

If it's not too complicated, can you explain what you, and a few others, seem to be suggesting to regulate the CURRENT fed to modern high powered LED's rather than the voltage?

Well, you would not have parallel LEDs if (limited) power is an issue. You would series them into the highest series voltage string you could have to suit the supply voltage.
If you used switching current limiters on both or for all, that's different, but I'm assuming a single supply voltage (eg, 12V) with analog current limiters (resistors etc).

I'll simply state that LEDs are current devices. Their output is not regulated by voltage, but current. And max current is the critical parameter wrt LED life. (Their voltages vary even off the same production die.)


And BTW - use Schottky diodes for rectification. They'll have under half the voltage drop of regular silicon diodes.