LED Electric Bike Lights

Most electric bicycles use incandescent bulbs as the light source of the headlights. Due to the large variation in battery voltage, the bulbs are often in an undervoltage state, and the dim light greatly reduces the safety of night riding. The circuit for modifying electric vehicle lights with ultra-bright white light LEDs is shown in Figures 1 and 2.
Since the maximum voltage of a 36V battery can reach more than 45V, and the maximum voltage of a 48V battery can reach more than 60V. Therefore, the headlights must be powered by a constant current to ensure that the brightness of the light does not change with the battery voltage and to ensure that the LED is not burned by excessive current. Figure 1 connects the LM317 to a 60mA constant current source to power the LED. The working voltage of a white LED is about 3.1V~3.5V. Therefore, electric vehicles with 36V batteries can use 9~10 LEDs in series. The 4 groups in series are connected in parallel, and the working current of each LED is about 15mA. The reason why every 4 LEDs in series in the figure are connected in parallel with wires is to prevent the influence of the brightness of the light when a certain LED is damaged. In this way, when one LED is damaged, the current of the three LEDs connected in parallel increases to 20mA, while the current of the others remains at 15mA, which does not affect the brightness of the headlights. White light LEDs should be selected as spotlight-type. Although the battery voltage may be as high as 60V, which exceeds the maximum input voltage of LM317, the voltage difference of LM317 does not exceed 20V because the LEDs in series have a voltage drop of 30~40V. Its maximum power consumption is only 1.2W, so no heat sink is required.

If you can't find LM317, you can also use a high-power transistor to form a constant current source. The circuit is shown in Figure 2. The LED1 can be red. The forward voltage drop is about 1.8~1.9V. The B of the transistor is better to be greater than 100. If β is too small, the resistance R can be appropriately reduced to ensure a constant current of 60mA.

Remove the original bulb, design a printed board according to the size and shape of the lamp, install the LED and related circuits, fix them in the lamp, connect the power cord, and keep the original reflector bowl. The power of the lamp does not exceed 3W, but the luminous flux is more than 100 lumens, which is a real long-life energy-saving lamp.