Super Bright Rechargeable Light With Unique Timer Circuit

My target was to build a bright lighting system that keeps mosquitoes away, requires no fixed wire to be connected to mains, and is aesthetically pleasing.

I had two surface-mount LEDs lying around and thought of using those. The lights work at 48V, so I used two boost regulators to boost the voltage from a 12V battery pack. (I had to modify the boosters since the default output is 35V max)

I also made a timer circuit using NE555 to turn the light off if it is kept on for a long time. The circuit also ensures 0A current drop when not used.

When plugged in to charge the battery, a relay system swaps the light connection from the battery to the power supply for faster charging speed.

With powerful Lithium batteries(total 5500mAh), this device can run the LEDs for 2.5 hours at fixed brightness.

Hardware components:

• 2 x 18W surface mount LED LINK
• 6 x 18650 battery LINK
• 2 x 3 battery spacer LINK
• 2 x Push button LINK
• 1 x 12V 5A SMPS power supply LINK
• 1 x Power cord LINK
• 3mm PVC board LINK
• 2", 0.5" screws

Soldering Iron and Glue gun

Circuit components:

• 2 x boost regulator LINK
• 1 x BMS circuit 12V 20A LINK
• 1 x battery charge indicator LINK
• 1 x NE555 timer LINK
• 1 x 7805 voltage regulator LINK
• 1 x BC547 transistor LINK
• 2 x 1k resistor LINK
• 1 x 10k resistor LINK
• 1 x 0.47ohm 5W resistor LINK
• 1 x 100ohm resistor LINK
• 1 x 100k potentiometer LINK
• 2 x 1n4007 diode LINK
• 2 x 12V relay LINK
• 1 x Bridge rectifier LINK
• 1 x 47uF 25V capacitor LINK
• 1 x 10uF 25V capacitor LINK
• 1 x 1uF 25V capacitor LINK
• 1 x 0.1uF 400V capacitor LINK
• 1 x 5pin JST connector LINK

The main idea is simple:

• The device is powered by 6 lithium Ion batteries connected in series and parallel in 11.1V configuration
• The On button turns on the timer circuit, which then turns on a relay, forming a loop. This keeps both the timer and main circuit powered.
• The voltage from the battery is boosted using two boost regulators to supply to the LED panel.
• When the power supply is connected, a relay disconnects the whole circuit from the battery and connects it to the charger. Ensures faster charging speed.

After drawing the block diagram, I came up with this schematic. It required a lot of testing to finalize the design.

• Section 1: This small capacitor power supply is required to turn a relay on during charging. This was necessary since connecting the BMS directly with the SMPS power supply will continue to draw current. This circuit ensures the battery is only connected to the charger when plugged in.

• Section 2: 3 batteries are connected in series to produce the desired 12V with the other 3 batteries in parallel to increase charge capacity.

• Section 3: This is a timer circuit in a monostable configuration. the capacitors C4 and R3 give a short pulse when powered on, triggering the timer circuit. This circuit would turn the LEDs off if not turned off within 20min. The time can be adjusted using the potentiometer RV1.

• Section 4: This forms a loop with a switch, relay, and timer when the power on button is pressed. This ensures 0A current drop when not in use.

• Section 5: Manually turning off the button is turning the transistor Q1 off by applying a negative voltage at its base. This breaks the loop, and the circuit is turned off.

• Section 6: I have use two XL6009 booster module to boost the 12V to 45V DC. I had to hack the module to increase its output from 35V to 75V max.

I bought these 6 high-quality batteries and connected them with BMS(battery management system), as shown in the diagram.

The BMS ensures:

• Over voltage protection
• under voltage protection
• short circuit protection
• equal voltage in all the cells

Battery spacers are used to keep the batteries in place.

The default Xl6009 booster module can output a max of ~35V, but the LEDs require higher voltage. I could buy a booster with a higher rating, but I found a simple hardware trick to hack the module.

According to the datasheet, the feedback is connected to two resistors, R1 and R2. The ratio of these two is used to determine the output voltage.

Vout = 1.25*(1+R2/R1)

Thus, I replaced the resistor R2 with a 330ohm resistor. By varying the resistor, I can get a practical voltage of up to 75V!

However, this method also introduces noise at the output, so it is unsuitable for sensitive circuits. For my LEDs, this is more than enough.

When I press the switch, the ne555 turns on and triggers high. After a designated time, the output of the IC goes LOW and turns off the power flow.

This timing is done by charging and discharging a capacitor connected to pin 6 of the IC.

Note that ne555 in monostable configuration requires an initial trigger for activation; this is done by a small circuit consisting of capacitors C4 and R3. This provides the initial pulse required, as you can see from the gif.

To learn more about how ne555 works check out this post from amandaghassaei : https://www.instructables.com/555-Timer/

I have used 5mm PVC boards to place all the components. I had to reinforce it since the batteries are quite heavy.

Used a few 0.5cm self-tapping screws to hold the components with the board. Occasionally used hot glue to place some components. For the battery pack, I used two cable ties to hold them firmly.

The capacitive power supply is connected to the power input of the SMPS power supply.

The battery is not directly connected to the SMPS power supply since it will deliver the excess amount of current. The BMS also allows this current since its limit is 20A. Thus a 0.47ohm 5W resistor was used to limit the current.

Modeled the design using Sketchup. Took precise measurements of the components to make them compact.

I used 3mm PVC board to make the control box. It is easy to cut using an anti-cutter.

I made a 2D diagram in Illustrator and printed it on A4 paper to make the sticker for the box.

A wood in the middle separated the control box and the circuit box. I had to drill a portion of the wood to pass the connecting and power wires. I used some 2-inch screws to hold the boards in place.

The LEDs are attached at an optimal position for maximum spreading of light. They come with brackets, which makes the installation easier.

To keep the wires neat, I used 5mm cable pins. Finally, I used hot glue to cover the circuit box. The control box is also attached using 5-inch screws.

The table top hides all the components and I am quite satisfied with how it turned out!

And done! The project turned out to be much more complicated than I thought. But I learned a few valuable things.

I tried to make it as durable as possible, hopefully it won't disappoint ;))