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DIY high power daytime running light for ebikes

Published: 03 October 2020
Last updated: 04 January 2023

For my e-bike on solar energy, the Maxun One, I developed daytime running lights (DRL). These are mounted inside the rounded corners of the two solar panels. The challenge was to produce the maximum amount of light with low power consumption.

DIY high power daytime running lights for ebikesDIY high power daytime running lights for ebikes

Flashing light on solar bikeFlashing light on solar bike

Flashing light reduces the power consumption

See also my article about the Bontrager Ion 200 RT teardown:

Bontrager ION 200 RT dismantledBontrager ION 200 RT dismantled

There are used 16 white and 16 red LEDs from CREE at a power of 110W totally. This power cannot be used continuously because the LEDs are not cooled and will get too hot. For visibility however it is sufficient to flash the LEDs. I found out that an on-time of just 10ms is sufficient. With a period time of 450ms, the duty cycle is 2,2%. The average power consumption is so reduced to 2,2% * 110W = 2,4W.

CREE power LED for daytime running lightCREE power LED for daytime running light

Why daytime running lights?

Cars are an increasing danger to cyclists. This is because the motorist is distracted by operating the abundant of electronics in the car, such as navigation, smartphone, etc. A car sometimes looks like an airplane cockpit, with the difference that in an airplane there is a co-pilot to operate everything.

Circuit description

Daytime running lights for ebikes circuit v5Daytime running lights for ebikes circuit v5

The LEDs are controlled by a 65V 1.5A analog current adjustable buck LED driver, the TPS92513HV. The ATtiny3217 microcontroller generates the pulse pattern.

The white LED bar of 8 LEDs needs a voltage of 27V, the red bar 22V. Since the minimum battery voltage is 30V, the LED bars have to be connected in parallel and not in series. No additional series resistance is required because the LEDs have sufficient internal resistance to distributed the current evenly over two LED bars.

To reduce the Attiny3217 current consumption to 2mA, it has to be used on 5MHz and 3,3V.


You can download the files on GitHub HERE.

LED bar design

For the white LEDs, I use the XPEBTT-01-R250-00U80, which has a luminous flux of about 300 Lumen at 1A. The LEDs are mounted at an 1mm thick aluminum PCB designed by myself. When bending the aluminum PCB, care must be taken to avoid hairline cracks in the copper traces.

Daytime Running Light in transparant tubeDaytime Running Light in transparant tube

Hardware LED overload protection

If the LEDs are continuously used at 1A for more than 10 seconds, they become too hot and may break down. Because the LEDs are glued into the panels, they can never be replaced. Therefore, to be sure that overloading can never happens, an extra hardware protection circuit has been added by IC2. Overload protection via software is not safe enough. Note that I have not tested this circuit yet.


The software detects when the battery is fully charged. Then the flashing pattern changes, so that we can see from a distance when the battery is full.


The pcb is sealed with heat-shrink tube:

PCB sealed with heat-shrink tubePCB sealed with heat-shrink tube

Prototype version v2

Here's the schematic of the prototype v4. No PCB has been made yet for the final version v5.

Flashing light circuit v2Flashing light circuit v2

Flashing light pcb v2Flashing light pcb v2



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