I have recently resurrected my push bike for roaming the local villages.
This has a Sturmey Archer dynohub which generates around 12v AC.
Currently this drives a front and back light, both 6v. The bulbs are the kind that have the filaments folded back on the flattened bulb body (rather than the pin type) IYSWIM. They simply push into the bulb holder, not the bayonet type.
Is there an LED equivalent of these that is worth considering? I know I really need auxiliary lighting for after dark stationary periods.
Go for 'proper' modern battery-powered LED lights, the cycling world has all sorts of cycle lights available, from ones that help you see where you're going to 'make a statement' type of flashing monsters designed to dazzle drivers.
Rectify the AC with a bridge rectifier and you will have ~15v DC.
That would drive a chain of 3 power LEDs in series with a 100R 1W dropper resistor at about 300mA (or 1 power LED and a 390R 5W resistor).
You could also charge a nominal 12v NiMH battery pack off the DC supply so that when you are stationary the lights stay on.
Making a DIY LED bulb that would fit into the existing fixures might be interesting an LED with a reverse diode across it and a current limiting resistor in series would work if you can assemble it in the space.
Look for replacement lights with a 'standlight', which is a capacitor that keeps the LEDs running for a few minutes while stationary. 6v AC lights designed to be driven from a dynamo are common, they have the rectification and voltage clamping built in.
Busch and Mueller are good:
formatting link
(in Germany dynamos are more common, in other countries they prefer battery lights. At least pre-Brexit it was often cheaper to buy them from Germany or the Netherlands)
You can try and just replace the bulbs in your existing lights with LEDs, but you'll find the beam angles all wrong, since the diffuser is designed for a filament rather than an LED source. Better to go for a light that has all that properly designed.
At the cheaper end, ebay has plenty of Chinese lights which have an 18650 or similar lithium cell inside and charge off USB. You do need to charge them, unlike a dynamo, but you don't need to charge them that often. Frequently they quote one hour of runtime in peak mode, but you can often get away without using peak brightness and that improves the battery life.
The downside though of those kind of pencil-torch lights is they're often very 'spotlighty', which means you don't get a great beam spread. OK for seeing the pothole immediately in front of you, but not for seeing the road
20m+ in front so you have time to avoid the pothole. The difference with a quality light is the beam spread is better, and if it's solidly mounted to the bike you can align it properly, rather than lighting your front wheel or dazzling/shooting over the top of cars. Many of the cheap ones have flimsy rubber mounts that aren't good for alignment.
On 05/05/2022 10:16, Martin Brown wrote: <snipped>
The dynamo's most likely more of a constant current than constant voltage. Rectify with a bridge made from LEDs, and use a supercap across the bridge output with further LEDs as a standlight.
That has an interesting comment that the WWII-era Dynohubs were initially
12v, and later settled on 6v. If the OP's setup is a 12V antique it may be driving two 6v bulbs in series, rather than the usual arrangement where it's
6v out of the dynamo to two parallel 6v bulbs.
However bike dynamos are roughly AC constant current devices - under no-load conditions you can get the open-circuit voltage to go quite high, but once a load is applied it will drop down substantially. If the OP is measuring the no-load output of a 6v dynamo I'm not surprised it goes to 12v or more. You still want 6v lights for that.
The main issue was when your 2.4W front bulb blew or became disconnected and suddenly your 3W dynamo output was going through the 0.6W rear bulb, which would cause the voltage to rise and that one to blow too. Modern LED dynamo lights have zener diode clamps to absorb spikes like this so it's not a problem.
Long before LEDs, when I was a teenager, I did something similar with ordinary bulbs and some rechargeable batteries, with one of the dynamos the ran on the side of the rear tyre.
But modern LED based bike lights are now so efficient that battery powered ones (rechargeable or not) are quite long lasting.
4Ah D cells @300mA ~ 12 hours continuous use. 2Ah AA cells ~ 6 hours.
The OP might be better off buying something intended for the purpose. NB Rear red LED lights have different voltage drop ~2.2v each (and it makes good sense to make red light efficiently rather than the old style white filament lamp with a clear red filter).
To answer the question raised by Theo, the bike is described as Vintage in posts I have read. It's a BSA Bermuda dating from around 1970.
I was measuring the 12v with no load on the dynamo and assumed that the two bulbs were in series. The lights had stopped working, but this was due to a detached connection and once reconnected both bulbs were found to be fine.
Of the suggestions offered, I think I prefer the option to use the dynamo to charge a battery pack to feed more modern lights.
You do AC to DC conversion, just in the same way you would do it for a hobby 5V supply in the old days. In the old days of digital logic breadboarding, you would use
transformer - bridge rectifier - filter cap - 7805_regulator
That's an example of an inefficient linear implementation of a 5V supply.
You will be replacing that with:
hub/bottle_gen - bridge rectifier - filter cap ==> wide range DC out
That's the very most basic part of it (the three items produce "wide ranging DC" and more circuit is needed than that). The three named components are only "sufficient" under a very special set of circumstances.
My power source on the current commuter bicycle is a 1950's...
Sturmey Archer bottle generator 6VAC 0.5A [Danger: Max Output 100VAC at 0 amps]
All that you need, to start, is a bridge rectifier. I built mine from four individual 2 ampere Schottky rectifiers arranged in the bridge. Schottky improve the efficiency of the rectifier stage slightly. Considering the gobs of power yours has, any old bridge rectifier will do. The limiter is intended to clip output peaks, so the generator never rises to the 100VAC level by accident. You insert zeners in series so "the zeners don't get hot in normal operation", yet the filter cap is protected against the possibility of excess voltage. Your 12V hub might require four zeners in series like that (band "up"). Your filter cap will need a higher volts rating. Because your hub has twice the voltage of my bottle gen. The bridge rectifier, four leg device, have those very symbols printed right on the plastic. Hookup is simple.
+---------+ Generator ~ ------| ~ + |--------+------------------+---------------+ | | _|_/ | | Gen Ground ~ ------| ~ - |--+ / ^ 5.1V 5W --- | +---------+ | _|_/ zener etc V 2.5V 20mA | + | / ^ --- White LED --- 47uF 16V | | "Limiter" | --- filter cap | | --- | - | | V 2.5V 20mA | | | --- White LED | Filter cap to | | | | be placed next +-----+------------------+---------------+ to LED tree!
\__________________/
This section is your "basic unit of light"
The audience members will immediately point out "you idiot, you forgot the *resistor* to protect the LED".
Well, as it turns out, the generators of the day, were constant current sources. On my generator, it approximately wants to produce 0.5 amperes, no matter what. You must be doing around 5 MPH for the output to rise sufficiently for lighting usage.
The voltage drops in my circuit are approximately
0.5V (first bridge rectifier diode) 2.5V LED 2.5V LED 0.5V (second bridge rectifier diode) ------ 6.0V but this is relatively unimportant (efficiency issue maybe) ------
Now the next thing I'm going to do, is put "multiple basic units of light" in parallel. The audience will howl "this will result in current hogging!". Yes, it might... if the LEDs had not been carefully matched on Vf at a fixed If. I set up a test jig, and measured all the LEDs for their Vf. Then, pairs of LEDs, their "total Vf" is the same as all other "basic units of light". I used a spread sheet, to track all my LEDs.
Using 48 pairs of LEDs, uses up the 0.5 ampere being offered. Each LED pair has about 10mA flowing. If the cable for the front light falls off, the 24 pairs sink 20mA each. In other words, by over-rating the lights a bit, if half the load falls away, the second array gets "twice as bright" but nothing burns.
The more LEDs placed in series, the easier it is to tune the Vf of each vertical column of LEDs. If the LED trees were one LED high, this would be impossible to arrange (a single VF isn't close enough). Two LEDs (what I used) is the shortest column that is practical.
The result is, my lighting system has *no resistors at all*. The internal impedance of the Sturmey Archer is the only impedance in the circuit.
The circuit still has *lots* of failure modes. For example, if one LED fails short, the second LED in the stack carries *all* the generator current, damaging the second LED. If your array goes dark and one LED is "blasting out light", you know its mate failed short.
The two stacked Zeners, are to try to avoid blowing the filter caps. If the circuit loses its load for any reason (circuit "rusts out"), the filter caps *might* be the most expensive part of the circuit. You stack enough 5.1V zeners, so that the zeners do not normally conduct. If the filter cap is 35V for example, you might stack four zeners and clamp the max positive rail at 20.4V.
I used ceramic capacitors for a distributed filter. At the time, they were "priced to clear" at Newark (Element14/AVNET). I really should have bought two or three times as many, as the price rose 5X the year after. They are no longer practical at this point. As you would expect, not in stock either. If you lived in Japan, these would be easy to get. But not here.
formatting link
By placing the ceramic capacitor right next to the LED column, the impedance of the distribution cables is taken out of the circuit. If you "clump" all the capacitors at one end of the bicycle, an inferior level of ripple will be seen in the light output.
The purpose of using ceramic SMT caps in a project like this, is there are no legs to break off. A natural choice would be the usage of an electrolytic. They have legs. It takes only
*one week* of bicycle vibrations (pot holes) to break a leg off an electrolytic capacitor. You might use potting compound to fasten the body of the electrolytic to the PCB, but I'm not interested in testing the reliability of those capacitor legs any more.
The LED diodes are an inherently low-impedance load. The front and back light on the bicycle are joined with 14ga lamp cord. The bicycle frame is not relied upon for any purpose. The electronics are insulated from the frame. One leg of the generator output, is tied to bicycle frame (normally), so we have to assume the bicycle frame has AC on it. Do not touch any of the DC part of the circuit, to frame.
I pick up both "~" outputs of the generator, as close to the generator as I can get, then use my decent wire to run to any other conversion boxes on the bike.
Your hub is a 12V circuit, likely 1 ampere output, The circuit will need to be fiddled a bit, to make best usage of the power. You could use four LEDs in a stack, which is 10V approximately. The LEDs are 2.5V, because the current flow is so low in each column.
0.6V (first bridge rectifier diode) [More total current, more Vf in schottky] 2.5V LED 2.5V LED 2.5V LED 2.5V LED 0.6V (second bridge rectifier diode) ------ 11.2V but this is relatively unimportant (you want it sorta close to 12V or so) ------
We could put five LEDs in a stack, and the generator output current will drop a bit.
I use two identical white LED arrays in the design. One on front of bike, one on back of bike. The back one *points downward*. It lights the retro-reflectors on my pant clips.
The front one points ahead.
To incorporate both red LEDs and white LEDs on the same lighting circuit (different Vf), screws up the whole concept and requires the placement of resistors in the circuit. I can only build a circuit with no resistors, if *all LED stacks track in behavior*. Once you mix white LEDs and red LEDs, you have to rethink array stabilization. Resistors are good for that.
I tried "big" LEDs at first. The lighting output was inferior. I could barely even see the road, using a 3.5W Star emitter for the front. I had to redo the hardware and switch to 20mA LEDs, and use a fifty LED bag of LEDs for the front and a fifty LED bag of LEDs for the back. The bags are matched on color and Vf (there is a sorting machine at the factory, no two bags exactly the same kind of thing). I further match them, by testing each LED individually.
Why an array ?
"No optics needed".
If you buy 20mA T1-3/4 white LEDs with a 10-15 degree lens
formatting link
on each LED, you just place those in an array (4x12 LEDs) and point all the LEDs in the same direction. The beams overlap and you get a "relatively smooth cone of light" where the light hits the road. If bicycle cables are in front of the array, their shadows are blended out. No mirrors or other crap, need be placed on or near the LEDs.
The LEDs at the time were 20 cents each, a hundred LEDs was 20 bucks. The whole project probably cost 5x that amount. The LEDs are not your only expense.
On the front light, you need to place an aluminium plate behind the array, to protect your eyes from the light. If you don't do this, you'll find out the hard way what "wash out" is. Shining the LED light into your eye, ruins your night vision. I added the plate, after using the light for a while. It might be even better, if the array had a polarizer out front of it.
*******
You can reduce the circuit complexity a lot, if you can find a commercial lighting solution, and you know its volts and amps. You will need
where the DC regulator is selected for the volts rating of the light. You still need to protect the DC_regulator with the stacked zeners, so if the light cable disconnects from the "converter box" you put together, the VAC does not grow to the 100VAC level. This could blow portions of your circuit not rated for such voltages. The circuit may not be as efficient as mine, but then, you have more electrical power to work with... and still see the road. So if the regulator throws away 30%, so what. Your hub should be an *excellent* power source. Mine is merely adequate.
My lighting has been running for three years now, and other than stuff shorting out in the rain one day, it has worked well. I have placed enclosures around things, as the weather dictated (so the shorting does not happen a second time). No capacitors have snapped off, because all the ceramic caps are afloat in a sea of solder. Soldering those mothers was a bitch.
Summary: Whatever you do, remember the bad behavior of the generator under no load. Protect your electronics downstream of the generator, so nothing bad happens. It's not really a 12V hub. it is a "0V to 100V death machine" and requires defensive design in the circuit. Many cheap components, aren't rated for these conditions. The Zener clamp column, attempts to tame the circuit, if the load disappears (the cable snaps or a cretin cuts the cable while you were parked)
Stick a meter on the 1000VAC range, crank the wheel at speed, and check the open circuit gen voltage, as part of your project preparations. The manufacturer of the generator, should have made sure the insulation on the device, can withstand open circuit conditions.
Once you get above 30MPH, the output of the generator starts to drop. So even though it is inherently a CC circuit, the available CC at high rotational speeds, is down a bit.
You can get more than the rated output of the generator, by using a series cap. The size of cap required, varies with wheel speed. It's unclear what impact the extra heat inside the hub would have, on reliability. I do not use this technique on mine. 3 Watts is fine with me.
"Using a series cap to boost output" [Cap properties TBD]
If you are going to only draw 20mA from the supply you might as well limit the current with a high wattage resistor and use much cheaper less beefy standard Zener diodes.
Rough values
R = 470 ohm 1/3W (20mA approx) R = 220 ohm 1W (50mA approx)
Zeners can then be standard 300mW types in both cases.
High power Zeners are expensive and increasingly rare these days.
A bit more care needed with the computations and heatsinking if you want to drive higher power LEDs at 300mA or 0.5A.
BTW 6mm White LEDs will run fine at 50mA and about 4.2v voltage drop. (a 4v voltage drop is more typical for a white LED - not 2.5v)
You can check these things with a meter. You don't have to leave it to chance.
You can also connect ceramic power resistors, and measure the V and I with that fixed load, to give you some idea of what it can make. This pre-supposes you have some idea what the output is, and want to make a little chart for yourself, for prediction purposes.
These are the style of power resistor I might use for a home project. They come in various ohm values and are handy for a quick test. (In school labs, we might have "load boxes" with rotary switches for fun things like this.)
formatting link
Because the generating device is constant current, once the speed is between
5 MPH and 30 MPH, the output should be pretty stable. V=RI. Inverting the bicycle, would allow you to make a scheme to provide excitation (it's harder to make a front wheel turn at a constant speed for this testing).
The old incandescent bulbs, didn't care. DC or AC made them work. As long as the voltage level was correct for the job.
LEDs are DC only. The small LEDs have a 5 volt max Peak Inverse Volts rating (PIV). Large power LEDs *do not* allow reversal. The large power LEDs sometimes even contain a reverse protection device inside, intended for transient/ESD protection. Even working with the little LEDs, it's quite possible you might inadvertently reverse the polarity and damage something (if the voltages involved are way more than the 5V accident rating). The LEDs in your computer (which are the small ones), the nice thing about the 5V PIV, is you can reverse the cabling when assembling a computer, and there will be no damage to the T1 3/4 LEDs on the case.
*******
You can see if you head over to Wiki, even they're a bit confused. Showing some waveforms in the article, might have helped pass on info about pulsating AC and pulsating DC waveforms. In the old days, a pulsating DC could be "cleaned up" with a battery as a cheesy form of regulation.
formatting link
# "alternating current"
formatting link
# bottle dynamos, hub dynamos
"The name is conventional as these are small permanent-magnet alternators, not <=== AC self-excited DC machines as are dynamos"
formatting link
"direct current generators which use exclusively the self-excitation (self-induction) principle to generate DC power."
"commutated direct current electric generator"
[See the section entitled "Commutation" as for how DC is possible] It is pulsating DC, and needs to be filtered.
formatting link
"A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current."
The commutator in your electric hand drill, complete with sparks, shows you why commutators are a bad idea. Like slip rings, they can wear out, or a groove can be worn in the surface, or a piece of grit in a carbon brush can make a mess. Good commutators are so thick, they can be turned down on a lathe. But that's only on big electric machines. Not fractional horsepower style devices.
My bicycle bottle generator, has no commutator or slip rings, which would have been the least reliable part.
*******
With the hub or bottle options on bicycles, when selecting incandescent bulbs, you need a bulb that draws "just the right current". If the incandescent bulb draws too little juice, the bulb "burns out when you go down a hill". If the incandescent bulb draws too much juice, then the bulb will be too dim for car drivers to see you.
When changing the old incandescent bulbs, you had to go through your "drawer full of bicycle bulbs", until you found the exact right one for the job. You sweep the hardware store, the bicycle shop, for these things. The "shape" of some of them, hinted they might be the right type, but you still had to read the legend printed on the base! No incandescent bulbs with a lens on the front ("penlight"), was ever the right type.
I nearly got run over one night, because the incandescent bulb I was using on front and back, wasn't bright enough. (This means the resistance of the bulb was slightly too low.)
That's when I started the LED replacement project. It was the shock of nearly getting run over, that provided the incentive. My array lights are much brighter than the old incandescents. By a country mile.
I used to have a sealed beam on the bicycle (this is close to it, but not quite)
formatting link
but... I burned that out going down a hill one night (one of the steepest hills in that city). A policeman pulled me over five minutes later, for "no light", and I'm thinking to myself "he's never going to believe my story". Now, that was a nice light, but buying a second would require fitting something to tame it. Since the bulb had no decent structural fittings on it, you *glue* the bulb to a fat dowel and bolt the dowel to the bicycle. The screw terminals are only for electrical connections, not mechanical.
That's certainly the terms used when referring to cars, but bike ones are normally known as dynamos and, in all likelihood are AC - why have the additional complication of a commutator and brushes or a rectifier, just to drive filament lamps that are equally happy with ac or dc?
But you would only DIY it, if you cannot find any ready-made solutions. You don't exactly save money by building these yourself.
The main benefit, is never having to worry about batteries. I have nothing to charge. Having had battery lights before on a bike, I did not want any batteries on there. Stand light or no.
*******
Yes, the first attempt, with high power LEDs, used extruded cylindrical finned heatsinks.
| | <=== Copper pipe cap | | | ===== | <=== Star emitter, thermal paste to copper cap +-------+ || || || | <=== Extruded heatsink with radial fins || || || | || || || | || || || | || || || |
That's overkill for the power involved at the moment, and I can't feel any heat in the metals. I use that for "kitchen mood lighting" and it runs all day long. There are two of those, running off a wall wart and a small circuit board. So the materials were not wasted. I found a use for them. It's just, as a bike light, it sucked. The output pattern was not useful in any way. Missing from the diagram, is a poly-carbonate silvered mirror, which sits around the LED and reflects the light out the front. It was tailor made for use with the Star scheme (or so they claim).
With the array of small LEDs in the successful version of the project, no heatsink is necessary. There is free air circulation around the LED legs. (You leave the legs on the LEDs, and the LEDs mount in a drilled plate about an inch from the circuit board.) Since light leaks out on all sides of the project, car drivers can see you more easily from the side.
The "Star emitter" is a high power LED having nothing to do with Star packaging particularly, which is soldered to an alumina circuit board (the Star). The alumina is part of the thermal path. They mount all sorts and brands of LEDs on those plates now. But in small, hobbyist, quantity.
When you get someone else to mount the power LED for you, you don't have to worry about damaging the LED your own self. This is just an example of one available this year. The older ones were white, and there's different wiring patterns for the quad LEDs (which is what I used, was a quad, and the quad is uncommitted wiring with eight contacts). With the quad, you can make a 3.2V LED, a 6.4V LED, a 12.8V LED. The quad LED, all the dies have matched characteristics, so you can do series-parallel combos if you want.
formatting link
formatting link
Since you rely on middle men or small shops to do a Star for you, you don't get an infinite choice on materials. They mount whatever is "popular" at the moment.
The first example there, the LED is well suited to hobbyist use. It's some of the SMT ones with contacts on the bottom, it's better to get someone else to do those for you.
On the second Star example, the LED electrical contacts are on the bottom, plus a heat slug.
|||||||| <=== electrical (+)
|||||||| \ |||||||| \___ Supports heat transfer |||||||| / into the thermally conductive substrate
|||||||| <=== electrical (-)
Working with power LEDs is a bit different than the ease of working with T1 3/4 sized LEDs. Most of the work on the LED array version, is... "boring". Lots and lots of holes to drill with your hand drill. Ugh.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.