To upgrade an electric bicycle lamp using ultra-bright white LEDs, it's essential to power the LED with a constant current source. This ensures that the brightness remains consistent regardless of fluctuations in battery voltage. For optimal performance, choose white LEDs designed for concentration, as they provide better light focus and efficiency.
Most electric bikes currently use incandescent bulbs, which are inefficient and prone to dimming when the battery voltage drops. This can significantly reduce visibility and safety during nighttime rides. Replacing these bulbs with high-brightness white LEDs can greatly improve lighting performance and energy efficiency.
Battery voltages can vary widely. A 36V battery may reach up to 45V, while a 48V battery can go beyond 60V. To protect the LEDs from overcurrent damage and maintain stable brightness, a constant current power supply is necessary. One common solution is to use the LM317 IC to create a 60mA constant current source. White LEDs typically operate at around 3.1V to 3.5V, so for a 36V system, you can connect 9–10 LEDs in series. These can be grouped into four parallel circuits, each carrying about 15mA. This setup helps prevent the entire lamp from failing if one LED is damaged, as the remaining LEDs will continue to function normally.
If an LM317 isn't available, a high-power transistor can be used instead to build a simple constant current circuit. In this case, a red LED (with a forward voltage of around 1.8–1.9V) can serve as a reference. The transistor should have a beta (hFE) of at least 100. If the beta is lower, adjust the resistor value to maintain the desired 60mA output.
When replacing the original bulb, ensure the power supply is compatible. Some systems may use a 15V input with a 5V output at 4A, which results in a 10V drop across the transistor. This can lead to significant power dissipation—up to 40W—so proper heat management is crucial. A suitable aluminum heatsink with a thermal resistance of 0.75°C/W is recommended.
Once the circuit is built, install the LEDs and components inside the existing lamp housing. Retain the original reflector bowl for optimal light distribution. The total power consumption should remain under 3W, yet the luminous flux can exceed 100 lumens. This makes the upgraded LED lamp both energy-efficient and long-lasting, offering a safer and more reliable lighting solution for electric bicycles.
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