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Background
Most of the cycling I do now is in the dark, as our local mountain biking group Knobblies usually meets one evening a week, and for most of the year there isn't enough daylight to get much done, so lights are a necessity.
A couple of years ago I bought a set of halogen lights (known in the UK as the Electron EHP310, the previous version of the EHP315), with separate 5W spot and 10W flood MR11 bulbs powered by a 6V 4.8Ah NiMh bottle battery, which gives around 2 hours use on full power. These were fine to start with, as I'd never ridden in the dark before and they fitted in well with everyone else's halogens. (I've never been sure about the quality of the bulbs though, as they always seemed dimmer than other peoples halogens of a similar power.) A couple of guys had been developing Luxeon V lights which were bright enough to easily drown out the halogens, and lasted much longer on smaller batteries.
Around the middle of 2006 one of these guys made a bunch of Luxeon V lights for most people in the group, and the other started playing with Luxeon K2s which didn't need to be driven with such a high voltage. I thought they'd be the perfect match for my 6V bottle battery - no point in it going to waste...
So I passed on the offer of having a Lux V light made for me, as really I wanted to make something myself, and thought a K2 would be the answer. However, various things got in the way, and apart from buying a cheap Luxeon III LED head torch from Ebay to help out, I didn't end up doing anything about it until early 2007.
Design
Searching for "DIY LED bike lights" on the interweb produces lots of hits, and I eventually ended up finding the MTBR lighting forum and CandlePower forum where there are a lot of people building their own bike lights. I found out about the recently available Cree XR-E and Seoul Semiconductor (SSC) P4 emitters, which seemed to be a significant improvement over the K2s in terms of light output and power consumption. As they were relatively cheap compared to things like the Luxeon V, it made sense to have more than one, especially as two at a low current are more efficient than one at high current, and produce less heat.
The typical light output in Lumens and power consumption of various white LEDs that I was able to find:
| 350mA | 700mA | 1000mA | 1500mA | |
|---|---|---|---|---|
| Luxeon III | - | 65 (2.6w) | 80 (3.9w) | - |
| Luxeon V | - | 87 (4.8w) | - | - |
| Luxeon K2 (U-bin) | - | - | 100 (3.7W) | 130 (5.8W) |
| Cree XR-E (P4-bin) | 80 (1.1W) | 136 (2.4W) | 176 (3.7W) | - |
| SSC Z-Power P4 (U-bin) | 100 (1.1W) | - | 240 (3.7W) | - |
Looking for drivers led me to LuxDrive. Two LEDs are more than the 6V I had available, so I was looking for a boost driver, which I knew would be slightly less efficient than a buck but not by enough to really worry about. I also found out about TaskLed and their range of boost and buck drivers that allowed much more control than the basic LuxDrive drivers, by being able to select different drive currents and have things like flashing modes.
However, to drive the LEDs at a low current using just one driver would probably end up needing a lower voltage than the battery, which could end up getting difficult to control. The alternative was two controllers, one for each LED, but that puts the cost and complexity up. Pretty much everyone else in the group was using packs of 8 NiMh AAs without any problems, and the latest high capacity AAs could give me just as many Watt Hours as my bottle battery. It just has a cheapo transformer as a charger so you never really know if its fully charged or not, and if anything went wrong with the individual cells it could end up being difficult to replace any bits. So, I decided that 8 AAs and a buck controller would do. I didn't really consider LiIon batteries, due to the higher cost and care needed with charging and discharging them, and the small difference in weight isn't going to be noticeable.
So I had to choose a buck driver - 3021 (with optional potentiometer brightness control) or nFlex/bFlex. With the bike interface added recently, the TaskLed drivers ended up being the obvious choice.
I had decided to go for Crees instead of SSCs, mainly because I was a bit dubious about keeping the jelly lens on the SSCs clean, especially with this being my first attempt where there would be a lot of messing around and chance of damage. I would probably choose SSCs for a second attempt when I knew exactly what I was doing, as other people have found them to be quite a bit brighter.
There are several choices of lens/optics for the Crees, including Khatod, the square Ledil, and L2 Optics. I went for the L2s, as with their clip-on diffusers they would allow me to change the beam widths until I found the right spread of light, rather than having to change the whole lens. Various people had suggested 10-15 degrees for bar mounted lights, but I didn't really know what would work for me so thought the flexible solution would be the best for now.
My initial thought for a case was a small aluminium box, something like this, which would act as the heatsink and should be fairly waterproof to start with. Searching for a few days I wasn't able to find anything that was the right size - they were either just too small to fit two LEDs and lenses in, or was far too big and would end up being mostly empty.
Taking inspiration from "The Achesalot" 1" square aluminium tubing design (like many people), I remembered that I had a length of thick (4.5mm) U section alloy in the garage, which was just deep enough to fit a lens in. Unfortunately it was too narrow for them to go in sideways, but putting them in lengthways gave space to fit the driver in and a couple of connectors or switches.
As far as connections went, I wanted a power switch for the batteries so that everything could be isolated, a power connector in the case to avoid ripping wires out by accident, and a separate push switch to control the driver, which would be on its own lead so that it could be as close to my thumb as possible rather than mounted in the case.
To attach all of this to the handlebar, I was going to use the clamp from my halogen lights, as it was fairly secure and had a hole in the top that could be bolted straight to the case so should be easy to modify. It is also available on its own, so I could buy a spare if I wanted to use the halogens again for some reason.
Last was sorting out a front cover. I already had a big sheet of clear polycarbonate (Lexan), so was going to just cut a rectangle of that to fit on the case, sealed with a bit of inner tube and possibly some silicone or sticky foam to take up any irregularities. The main problem was working out how to attach it. I could have put some small screws in the corners, either to nuts glued to the case or with threads tapped into the sides, but that would all be a bit fiddly and I didn't want to end up stripping the threads of tiny screws or bolts. As the polycarbonate is fairly thick, I decided on a big bolt through the middle. This should allow enough pressure to seal the edges, and if the cover starts to distort too much some sort of metal support can be attached over the front.
So, around the end of April 2007 I started buying the bits I didn't already have - an nFlex (which would be a better fit in the rectangular box than the round bFlex), a couple of Cree XR-E P4 stars, matching 6 degree L2 lenses with a selection of diffusers to give different choices of beam shapes (8, 16 and 8x25 degrees), batteries, a small camera case to hold the batteries, and various connectors and other bits to join it all together.
I had also decided that with this improved bar light my cheapo head torch would need upgrading as well to be any use, so got a single Cree for that, with another L2 lens and a LuxDrive 2009 Super High Output Micropuck (500mA) driver. I haven't got round to building this yet though...
Construction
First was checking the polarity of the LEDs, as there were reports of some being put on the stars the wrong way round. Thankfully mine were the right way round. I also made sure that the star was electrically isolated from the emitter, as it would be in direct contact with the case which would be connected to the battery negative. While using a multimeter to check the connections, I found that it supplied just enough current to light up the LED, showing the structure of the emitter. It was still too bright for the camera to take a clear picture though!
Next was wiring the LEDs together, as this determined the size of the case. Using some multistrand wire I already had that is probably much thicker than it needs to be, the two LEDs were joined together and given leads to connect to the nFlex and allow for some early testing using the Micropuck and an AA battery. It took a few attempts to solder onto the stars, as if it wasn't heated up enough the solder would just peel off the connection pad and I didn't want to damage the emitters at this stage through melting them. Hopefully the vibrations while riding doesn't dislodge the wire, as they will be a tad awkward to re-solder once everything is crammed into the case...
Then the lenses needed modifying. As they aren't really designed to fit onto stars there is no provision for the wires, so some of the plastic needed removing. This was done using a Dremel type tool and a needle file, by gradually grinding it away until it allowed a flush fit onto the star. As the wiring to each star was different, the lenses had to be different as well.
Once I knew the exact size of the LEDs with lenses attached, it was time to make the case. After many measurements to make sure it was right, a length of the aluminium was hacksawed off and filed square, and two side pieces were cut out then filed to shape.
Next a few holes needed drilling. The socket for the power lead, the socket for the remote push switch, a hole in the bottom for the handlebar clamp, a hole in the middle to bolt the cover on with, and a tiny hole at the top for a 3mm power LED. Both of the socket holes needed recessing to allow them to sit flush, as they weren't designed to go in something quite this thick. The socket for the switch couldn't actually be clamped in place using its own nut as the thread was far too short, so I ended up making a clamp that would be rivetted to the case, which needed yet another hole.
Once the case had been sorted out, the LEDs could be attached to the nFlex and then the two connectors could be added, as I knew the positions they needed to be in to fit into the case. This was very fiddly to get right, but eventually I got it all put together. I forgot to take a picture with the switch socket attached, but it was soldered on before things went into the case. Some thin strips of sticky foam were added later to the top and bottom edges of the nFlex. It is just nipped between the case and the cover, so this should provide a tiny bit of cushioning and hopefully stop it moving around.
Now it was finally time to do some proper testing. Clipping a variable DC power supply onto the power socket wires and using the switch on the nFlex board, it all sprang to life and seemed to work fine. Not being heatsinked properly yet, I only tested it at the lowest current and never for very long.
The power LED was glued into the case with extra long leads attached, and the self adhesive lenses were carefully stuck onto the main LEDs, after making sure the emitters were as clean as possible - there had been a lot of dust around while modifying the lenses. Two patches on the inside of the alloy case were gently ground away to provide a clean and slightly textured surface, and then the LEDs were glued in place using some epoxy metal. It was only put on a couple of the star's tabs, with heatsink compound thinly spread on the rest of the star. I wasn't really sure whether the glue would conduct heat or not so didn't want to stick the whole thing down. No photo of this, as the glue set after five minutes so there wasn't time!
While the glue was curing, I made a start on the remote switch. I had originally planned to use a microswitch attached to the bottom of the handlebar, but ended up using the tiny eject button from an old video recorder (which was also the source for the 3mm power LED) as this could mount flush onto the back of the bar and be easier to reach. It was conveniently attached to its own small PCB which would make mounting it to the bars a bit easier, so I just needed to attach the wires and file off the sharp legs and solder from the back of the board. The other end was wired up to a 2.5mm mono jack. I haven't properly sorted out a cover for it yet, so its just got a bit of inner tube glued on the back to cover the switch contacts, and its in a small plastic bag to keep the rain off. Something more permanent still needs sorting out...
The battery end was also sorted out. A rocker switch was attached to the battery holder, spade connectors were fitted to the switch wires, the PP3 connector was taken to bits to attach the main wire directly to the terminals, and then the wire was cable tied to the PP3 connector to provide some strain relief. A velcro strap is used to make sure the batteries don't come loose, as this can be a problem with this type of battery holder. This all fits in the case with slightly too much room to spare, but it was the best fitting case I could fine without hunting round for weeks. The case is attached to the stem using more velcro straps through the belt loop.
Before gluing the sides of the case in place, I thought I'd better do a final test using the batteries and the remote switch. As soon as power was applied the LEDs lit up, but pressing the remote switch or the nFlex's on-board switch didn't do anything. Bugger... After a bit of investigation, I figured out the problem - the remote switch was wired up the wrong way to the nFlex. Ages ago I'd worked out that SWB hole on the board was connected to the supply negative, but had forgotten this when wiring it to the socket and did it the other way round. As the ground of the socket is in direct contact with the case and therefore the battery negative, this stopped the switch from doing anything and must have been confusing the nFlex. After a relatively quick swap round of the wires on the socket (a bit more awkward to reach with the soldering iron now) it all started working properly, and thankfully I didn't seem to have done any damage to the nFlex!
Last was gluing the sides of the case in place, using the same epoxy metal as before. While these were curing the front cover was cut and filed to shape, a hole drilled in the middle of it, and the rubber gasket cut from a section of old car inner tube. Also, a small alloy disk was made to fit in the handlebar clamp, as the screw to attach to the original light wasn't long enough to be used, and I didn't have any long bolts that were narrow enough to fit through the original hole.
Once the glue had had enough time to cure, the clamp was attached and the cover fitted. I had decided to initially go with the 8 degree and 16 degree diffusers, which would hopefully produce a bright centre area with enough side spill for peripheral vision. Now it just needed some proper testing to check that it wouldn't overheat, but there wasn't time for that...
In use
...because the first use of the lights was only a few hours after the sides had been glued! A fantastic night ride in Thetford Forest with the local biking group, where thankfully the light held up and there were no problems at all. I played safe and only ran it at 750mA to reduce the chance of any overheating, but this produced far more light than the old halogens did, with a much more even spread of light compared to the fairly patchy MR11 bulbs. The air temperature got down to around 13C during the night, and regular checks of the case showed that it only ever got slightly warm when on full 750mA brightness, so the case seemed to be doing its job.
One thing I did notice was that compared to everyone else's Luxeon V and K2 lights, the Crees seemed very white, almost the same kind of difference there is between halogens and any LEDs. I wouldn't say it affects how well the light works though.
The next ride was a few days later, but just a local one. I'd set the nFlex up to 1A but was planning to keep checking the temperature again, just in case. The forecast was for light rain, so I'd added a bit of sticky tape around the top and sides of the cover as the inner tube didn't look like it would be totally waterproof. It was dry to start with, but the light rain actually turned out to be a thunderstorm. Again, the light was fine, never getting too hot and seeming to be waterproof enough. Since then its never been dark enough to need the light much, but as the nights are getting shorter now it won't be too much longer until it gets more use.
Beamshots
All shots were taken with the same (digital) camera settings (1 second, F3.3, ISO 100) so should have been fairly representative, but the halogens have come out a fair bit darker than they are in reality, probably something to do with the difference in colour between them. I would say that 15W halogen is darker than the LEDs at 350mA, but not massively so.
No light
Halogen 5W
Halogen 10W
Halogen 15W
LED 350mA
LED 500mA
LED 750mA
LED 10000mA
Parts
The parts I needed to buy:
The other bits that I already had:
bravenet.com