3 Watt LED Bike Light Experiments
June, 2008, Rev e
Michael Krabach

Contents

Introduction
Synopsis of Experiments
Prototype 1 - Resistor Controlled Prototype
Prototype 2 - Triple Cree with large heat sink
Prototype 3 - Double Cree with Individual regulators
Prototype 4 - Single Cree and regulator
Prototype 5 - Single Cree and regulator
Prototype 6 - Triple Cree revised heat sink
Prototype 7 - Triple SSC in C Mag-lite Head
Prototype 8 - Triple Cree in D Mag-lite Head
Prototype 9 - Prefabricated 3 LED Mag-lite Head
Prototype 10 - Red flasher with Wide Optic Lens
Prototype 11 - Yellow flasher no Optics
Prototype 12 - Red flasher no Optics
Prototype 13 - Red flasher two LEDs
Prototype 14 - Triple Cree with 8 deg Optics
Prototype 15 - Red flasher two Cree LEDs
Prototype 16 - Red flasher two LEDs Clear Case
Prototype 17 - Auto 12 v clearance light
Light and Beam Measurements
Conclusions, Recommendations, and Further Speculations
Summary Table and Parts Sources

Prototype 13 Red Rear Multi-mode Flasher with Two LEDs

This flasher was an attempt to not use the regulator (DX SKU-7882) with a trim pot to reduce the voltage suitable for a single red LED. By using two red LEDs in series to share the output voltage, a similar regulator (DX SKU-7302) could be used that is designed for LEDs with a forward voltage of 3.7v. The DX-7302 is advertised as a 5 mode control but it really has 17 modes, exactly as DX-7882. The red LEDs used are the DX SKU-11017 which are no-name brands as far as I can see. They appear to be only 1 watt, and the actual LED die is only the size of the Cree red LED. This is seen in the comparison first photo below. The Cree is on the left, no-name on the right. The regulator in the second photo, the DX SKU-7302, comes with the output wires attached. The third photos shows parts used. Different than previous prototypes, a plastic shim (green notebook cover scrap) was needed to raise the heat sink plate above the battery compartment lip so the the LED stars could sit flush on the plate. The LEDs must be bonded (Arctic Silver Thermal Adhesive) in the centerline of the plate otherwise the beam pattern will not focus properly through the cover. The clicky switch is under the right LED. Both screws holding the heat sink plate down must be used, because the clicky switch pushes against the plate on that side.

(Directions to configure modes and groups.)
(1) Low, Med, High, Fast strobe, SOS
(2) Low, Med, High
(3) Low, Med, High, Fast strobe, Police strobe, Med strobe, Slow strobe, Beacon strobe, SOS

The DX-7302 is rated at 500 ma. I measured 53, 290, 325 ma on Lo, Med, and Hi for battery current on the steady modes. Across the LEDs (each LED drops the voltage) it is 2.9v, 3.5v, 4.3v for Lo, Med, and Hi in the steady modes. On police (warning) strobe, which uses the Hi level, it will last for over 24 hours with freshly charged NiMH, or alkaline batteries. The (no load) battery voltage (not LED voltage) can run down to less than 0.9v and the flasher will still (though dimmer) work, but if turned off will not restart. This is a great improvement over Prototype 10, 12 which only lasts 6 hours. The beam pattern is similar to overlapping diamond patterns and not as good as Prototypes 10, 12. Since the LEDs are offset to the sides of the flasher, the cover plate optics distort the pattern. The beam is not as bright as the other flashers because the LEDs are less than 3 watts, but the beam has a greater all round visibility. This makes a suitable for clipping on clothes or bike bags where the flasher might not be orientated straight back. This is a problem for commercial flashers that have narrow beam patterns.