How to design a rechargeable LED table lamp

In this mini do-it-yourself (DIY) project, we’ll design an LED table lamp that’s battery-operated and rechargeable. It will also feature light dimming so you can adjust the lamp.

There are two basic types of lamps available on the market. A typical one with a 3 to 5-W LED bulb that works on a 230 V AC supply. This one doesn’t usually allow for any light dimming and can only be turned ON/OFF. There’s also a battery-operated, rechargeable LED table lamp. It tends to have less illuminance (brightness) than a typical 230 V AC LED lamp. Let’s design a lamp that includes features from both.

Specifications

• Bright 5W @ 12 V LEDs – to provide sufficient light in a room
• A Li-ion (lithium-ion) battery with a battery management system (BMS)
• The IC NE555-based PWM dimmer for adjustable light intensity
• Lightweight, compact, and portable

It’s easy to build this lamp at home with only a few components as it has simple circuit and wiring connections.

Required components

1. Three bright 5W @ 12 V LEDs

2. Three Li-ion 3.7 V battery cells; 18650 (1200 – 2800 mAh)

3. A triple Li-ion cell case

4. The 3S 10A 12V BMS module

5. The IC NE555, TIP122, and 5 K POT

Circuit diagram
There are two sections of the circuit.

• Li-ion battery pack power supply
• The LED driver circuit with PWM dimmer

Li-ion battery pack power supply
The power supply for the circuit and LED lamp is built using three Li-ion battery cells and a BMS module.

As shown in the above diagram, the three Li-ion battery cells are connected back-to-back in the three-cell holder.

1. The +Ve terminal of the cell holder connects with the BMS module’s B+ terminal
2. The -Ve terminal of the cell holder connects with the BMS module’s B- terminal
3. The single cell connects to the B1 terminal and the two cell connect to the B2 terminal
4. There are P+ and P- terminals for taking output from the battery pack
5. Those same two terminals are used to supply charging input to the battery pack through an external adapter

LED driver circuit with PWM dimmer
The circuit is built using IC NE555, Darlington transistor TIP122, 5 K pot, and few other components.

Circuit operation

• The IC NE555 is configured in a stable mode so it generates continuous pulses of about 1 KHz.
• The 5 K pot connects between discharge pin (7) and threshold pin (6) using two diodes, D1 and D2 as shown in the circuit diagram.
• When the pot value increases, the charging time of the capacitor, C1 also increases, and the discharging time decreases.
• This will increase the pulse width of the output, keeping the same frequency.
• Similarly, when the pot value decreases the charging time of the capacitor, C1 also decreases, and the discharging time increases.
• This will decrease the pulse width of the output.
• The PWM output is given at the base input of the Darlington transistor Q1.
• When the pulse width increases, more current passes through the LEDs connected in the collector, increasing the light’s intensity.
• When the pulse width decreases, less current passes through the LEDs, so the light intensity decreases.

Housing and assembly
As shown in the image below, the PWM dimmer circuit is housed in a plastic box and the LEDs are connected to the circuit using single-core 1 mm² flexible wires. The battery pack with the BMS is fixed at the bottom of the plastic box. One ON/OFF switch is connected on one of the sides of the housing box.

The result is a nice, usable table lamp that can be used on a side table or desk.

• While reading, writing, or studying, turn the pot knob for the full intensity of the light.
• If working on a PC or laptop, turn the pot knob for minimum light intensity.
• Use it as a night lamp by using the lowest intensity of the light.
• For any other type of work, adjust the light as desired, using the pot knob.

Here is a YouTube link for a closer look at this homemade LED table lamp:

 

 

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Filed Under: Electronic Projects
Tagged With: batterymanagementsystem, bms, diy, lamp, led, tutorial
 

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