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This page describes a home made high power LED bike light. The light body is made on a home made computer controlled CNC milling machine, and anodised using a home brew anodising line. The electronics we again home built, and include a microprocessor to control the light to allow various flashing sequences, low battery warnings and power levels. The main drive to do this wasn’t necessarily to save money – like many such projects, it often costs more to produce something at home than it does to go out and buy one, however, I enjoy building stuff, and also did hope to save some money along the way! |
This project started out as a scuba diving torch, but with the idea to also make it usable as a bike light. It is designed to withstand reasonably serious pressures, and I’ve taken an initial prototype to 70m. I hope to test it to around 15 bar to allow for deeper dives. However, winter arrived, and the dive season ended before I managed more than a couple of dives with the prototype, so I converted it into a bike torch as I cycle to work and back in the dark at the moment.
There were also a few other reasons for changing this over to a bike light – the first version had a couple of machining issues that I wanted to clear up. I’d made some of the cuts a bit square, which left some sharper edges than I’d like. For a bike light, this doesn’t really matter, but the dive torch has to survive in a harsh environment, and I wanted to eliminate the sharp corners as the anodising doesn’t take so well on 90 degree corners.
As mentioned above, this light is designed to be small, but also to be taken to depths in excess of 100m, where water pressure will crush lesser torches. High power diving torches tend to be extremely expensive (upward of 500 pounds, and sometimes exceeding 1000 pounds!), so while saving money wasn’t a major driver, it clearly should be easily possible! When diving deep in UK waters, it’s often very dark and a good torch is essential. I’ve been using a 10W HID torch for quite some time, and while it’s OK, I wanted something better. This unit is designed to be as bright as an 18W HID, and is an umbilical torch with a separate battery canister. The diver would attach the torch to his hand using a “Goodman Handle” to leave both hands free during the dive.
All openings are o-ring sealed, and the switch uses a magnetic reed switch so that another hole in the case is not required. The switch can then be mounted on the PCB inside the housing, and the magnet mounted inside the switch outside the housing. This actually makes integration of the light much easier as well.
The body is machined out of 6082 aircraft grade aluminium and measures 61.5mm diameter, and 74mm long (excluding the switch and cable gland which are another 10mm or so). I’ve fitted a Garmin Vista GPS handle bar mount to it so that I can quickly attach and release it from my bike. Once machined, I put it in a tumbler for a couple of days to debur and work off some of the machining marks, following which it is anodised to prevent corrosion and to allow it to be coloured. I thought blue looked pretty cool, and the button for turning the light on and off was died red.
The electronics is a custom designed unit. It is a boost converter, which requires a battery voltage less the LED voltage. It also requires 5 volts to run the microcontroller, so for a 7 LED system, this essentially means the battery must be between about 7v and 18v. I may change the design to a buck-boost design to allow LED voltages lower than the battery as I’d like to use it for 3 LED systems as well. The software monitors the battery voltage and the temperature. If the voltage drops below a set level, the LEDs will produce a short flash every 15 seconds, and the power will be reduced. If the battery voltage drops below a second low voltage limit, the unit will flash twice every 15 seconds. If a third voltage limit is exceeded, the unit will be powered off. As the temperature rises, the LED power will be reduced to prevent damage to the LEDs and electronics. For a moving bike, the light should keep cool so will remain on high power, but it is protected in the event it does get hot.
The light uses the Polymer Optics 7 LED optics, with 7 P5 bin CREE LEDs. These aren't the brightest available, but I bought these a little while ago, and this project has taken about 4 months to finish, and LED technology is coming along in leaps and bounds. Current LEDs are probably about 30% brighter for the same power now!
I custom built a MCPCB (Metal Clad PCB) by milling out the PCB, and also milling out a PCB holder. The thermal path of the LEDs is directly connected to the aluminium PCB holder, thus providing a direct path to the heatsink, and the electrical connections are soldered to the PCB, thus easing the integration.
The following are a few shots of the completed unit. As I build up the next version, I’ll take a few more during the build phase…
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This shot shows the internal components being fitted into the light head. This shows the home made MCPCB, the electronics, and the optics. The red wires are for programming the microcontroller. They go to a small connector on the board and will be removed once I’ve got the software ironed out. |
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This shows the electronics fitted into the head. The cavity in the head has been milled to provide a snug fit for the electronics. The high power switching components are only a fraction of a millimetre from the case, which helps the thermal management. The component in the top (above the yellow capacitor) is the temperature sensor – this is placed close to the LEDs and power electronics. |
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This shot of the front showing the main o-ring, and the LED optics. The front bezel and cover glass are held down with 8 stainless steel screws. |
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This show from the side shows the completed unit. The Garmin handlebar quick release adapter can be seen on the bottom of the light. |
Performance
Ok - so (arguably) it looks good, but what about it's performance? The following pictures give a comparison of my light compared to a couple of other lights that I have to hand. This sort of thing is always going to be a little subjective, but at least this gives an idea of its performance.
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 CREE LED torch
Single P5 LED |
 10W HID
Custom Divers torch |
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 The beast!
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Move your mouse over the pictures of the torches on your right to see the beam from that torch. |
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Possibly I should have made these all a little brighter, but it gives an indication as to the brightness of the torch. The trees are around 25 yards away from the camera at the end of my garden (actually, in the neighbours garden) and the shed is maybe 15 yards from the camera. All photos were taken with the torches aimed about 1/2 way up the tree. With the newer LEDs that are now available, this will be really bright!
