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Building a High Performance LED Lighting System, Part 3

Flashing high power LEDs - and installing a complete lighting system

by Julian Edgar

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In the first two parts in this series (Building a High Performance LED Lighting System, Part 1) and Building a High Performance LED Lighting System, Part 2) we covered the building of an extremely bright handheld spotlight or bike headlight, and a couple of different approaches to building extremely bright red lights.

In this story, the last in the series, we look at how you can flash high power LEDs, and then install a complete high power LED lighting system on a Human Powered Vehicle.

Flashing High Powered LEDs

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Whever attention needs to be gained, it’s normal practice to flash LEDs. In addition to attracting the eye, flashing LEDs also considerably drops battery consumption.

Let’s look at the second point. If the light has a similar on and off time – say 1 second on, 1 second off – it is said to have a 50 per cent duty cycle. Straightaway, we’ve approximately halved the power consumption of the light! But what if we drop the duty cycle of the flashes below 50 per cent? In fact, what if we run a 20 per cent duty cycle? Now we’ve saved about 80 per cent of the power!

But if the light is off for 80 per cent of the time, will anyone see it? Yes they will – if you make the flashing frequency high enough. In other words, a very short duration flash that occurs rapidly will work brilliantly at getting attention but will have energy consumption far lower than if the light was on continuously.

Therefore, we have a very specific requirement for a flasher module: high frequency, low duty cycle and able to switch at least a few amps (a typical current draw of a high power LED system).

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The best way we’ve found to achieve this is to use the Nitrous Fuel Mixture / Motor Speed Controller electronic kit – available from Jaycar Electronics and the AutoSpeed Shop.

Despite its name, this kit is a very effective light flasher with high power handling, a flash rate adjustable by altering the value of one capacitor and a duty cycle that can be adjusted by turning the on-board pot. We’ve run a full article on this kit – see The Nitrous Fuel Controller - That's Also a Lot More!. The section of that article subtitle ‘Pulsing’ describes the capacitor change that needs to be made.

We used a 2.2uF capacitor that gave a flash rate of about 3 times per second and the on-board pot was set to give a duty cycle (an ‘on’ time) of 20 per cent. Note that both of these values are entirely up to you – to save even more battery power you can go for a shorter duty cycle, for example.

Connections

The Nitrous Fuel Mixture / Motor Speed Controller kit (perhaps we’ll now just call it the High Power LED Flasher kit!) has three connections. Power and earth are obvious (and, incidentally, the kit will work on lower voltages than specified – we use it on ~7.5V) but the ‘out’ terminal isn’t so intuitive.

Loads on the kit (eg the LED you want to flash) are wired between the supply voltage and the ‘out’ terminal. In other words, the module is like a switch that connects to ground to turn the LED on. Keep this in mind and you won’t have too many problems.

Complete LED Lighting System

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I ride the pictured recumbent Human Powered Vehicle, which I designed and built (see Air 150 Recumbent Trike, Part 1.) Much of my riding – perhaps a majority – is at night on unlit rural and semi-rural roads. Good lights are absolutely vital – both to stop being run over by cars and also to spot the wildlife that includes pythons as thick as my arm that lie across the roads.

The headlight must illuminate the road sufficiently for me to be able to ride down hills at up to 60 km/h (lots of steep hills around here) and also be able to attract the attention of car drivers. The tail-lights need to be visible for a long way – at least 400 metres – and experience has shown that side-facing lights are also needed. (Without side-facing lights I feel very vulnerable at T-junctions, where I am riding across the top of the T and a car is approaching at right-angles.)

Finally, I expect to go touring on this machine and want to be able to run the lights in day-time – they’re quite visible even in direct sunshine. To achieve this, a good battery life is needed.

The lighting system consists of:

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The 5W headlight covered in Part 1 Building a High Performance LED Lighting System, Part 1 of this series

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Four 1W side and tail-lights, as covered in Part 2 Building a High Performance LED Lighting System, Part 2 of this series. These comprise two yellow wide-angle lights, each facing sideways (these use 20mm oval-beam collimators)...

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...and two 30mm narrow beam red tail-lights facing rearwards.

There’s also a NiMH battery pack and a control system that flashes the side and rear lights and allows the headlight to be easily switched from being fully on to flashing. Let’s have a look at the battery and the control system.

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The battery is one stick from a current model Toyota Prius high voltage battery pack. It has a nominal capacity of 6.5 amp-hours and a voltage of 7.2V. It has a mass of 1kg and is 285 x 117 x 20mm. The stick was obtained by buying a complete HV battery that came up on eBay at a price too good to refuse. (The other sticks are being used in different applications.)

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The High Power LED Flasher kit is mounted in a plastic box. Front and rear light connections are made via plugs and sockets, allowing the battery/control box to be easily removed as required.

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The LEDs are powered through dropping resistors – all 1 ohm 5W units. The wattage rating is much higher than needed but it ensures that the resistors do not get hot. By using a nominally 7.2V battery, very little power is wasted in the resistors – the system is still highly efficient. The rear/side lights are wired in a series/parallel arrangement (see below for more on the wiring).

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The control box has a large rocker on/off switch positioned in its upper lid. The box is taped to the battery...

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...and then the whole lot placed in this bag that is strapped to the trike. The switch is able to be operated through the soft wall of the bag.

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A second switch is placed on a steering lever to enable the selection of flashing or fully-on headlight modes. Flashing mode is used in well-lit areas and in the daytime, or when the attention of a driver needs to be gained. In night riding it is switched from one mode to the other quite frequently. The side and tail-lights constantly flash.

Wiring

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The wiring diagram is fairly straightforward. Note the fuse placed close to the battery and the way that the headlight can be switched from being connected straight to ground (ie always on) to being switched so that it is grounded through the flashing unit (ie flashing). A single pole, double throw (ie three pin) switch is used for this function. The three 1 ohm resistors can also be seen, as can the series/parallel wiring of the tail and side lights.

Conclusion

While not ultra lightweight, the complete HPV LED lighting system is probably amongst the best in the world for illumination and visibility at a relatively low power consumption. And the techniques covered in this series are also applicable whenever very bright lighting with low power consumption is needed.

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