DIY Lithium Battery Charger from E-Cigarette Controller

If you're interested in making a small current charger for lithium batteries using a disposable e-cigarette's controller, this article is for you.

First, disassemble a disposable e-cigarette to get a few small lithium batteries and controllers. Besides the airflow switch function, these controllers also have lithium battery charging control capabilities, which can be used to build a lithium battery charger.

The controller has three solder points:

· The black wire connects to the battery's negative terminal or the 5V power source's negative terminal.

· The blue wire is the output when used as an airflow switch and connects to the heating wire; when used for charging control, it connects to the 5V positive terminal.

· The red wire connects to the battery's positive terminal (note that the black wire connects to the casing, and the LED also connects to the casing). There is an LED indicator that shows the output signal when used as an airflow switch and indicates the charging status when used as a charger.

The internal structure is simple.

Some of these controllers use a 5-pin chip.

Prepare an unused U-disk like the one shown below:

Pry it open.

It has light guide holes.

Remove the components.

The back is damaged.

Remove the damaged part (you can use a hacksaw blade to saw it slowly).

Scrape off the copper foil.

Solder the airflow switch. The black wire connects to the U-disk (5V) negative terminal and the negative terminal of the battery being charged (using alligator clips). The red wire connects to the positive terminal of the battery being charged (using alligator clips). The blue wire connects to the positive terminal of the U-disk (5V, power input for the charger).

Reassemble and wrap with tape. Attach two alligator clips, which makes charging these small batteries more convenient.

Charge the battery (using a USB port from an integrated machine). The indicator light turns on, showing a current of 244mA. Although this is the output current at 5V, the charging current is essentially the same.

As charging continues, the current gradually decreases.

Continue charging until the battery voltage reaches 4.1V, at which point the indicator light will turn off, but there will still be charging current.

Keep charging until the battery voltage reaches 4.2V, at which point the charging current will be minimal.

Try another airflow switch. Use one U-port and solder flying leads.

Charge it. This charging current is slightly lower at 210mA. Different controllers have varying charging currents.

According to online information, 5-pin chips in e-cigarette controllers vary, including S085, S082, etc., but their basic functions are similar. The specific features are as follows:

· ASIC design

· Low static current in power-saving mode (<3uA)

· Includes short circuit protection (SCP)

· Includes undervoltage protection (UVLO)

· Includes over-temperature protection (OTP)

· LED working indicator function

· Wide voltage charging (4.5-6V), with excellent charging performance and safety

· High precision in charging voltage detection error (within 1%)

· Comprehensive battery protection features

· Uses trickle charging when the battery voltage is below 2.7V, large current charging when above 2.7V but below 4.2V, and constant voltage charging when close to 4.2V

· Simple and low-cost external circuit application

Additional features include:

· When powered on, the LED flashes three times, then immediately enters power-saving mode.

· During normal switch activation (i.e., smoking), the LED gradually brightens and dims.

· When the internal control switch is activated for more than 5 seconds, the LED flashes twice and the output is cut off.

· During normal switch activation, if there is a short circuit (output resistance less than 1 ohm), short circuit protection is activated, the LED lights continuously for two seconds, and the output is cut off.

· During charging, the LED remains on, and when fully charged (VDD > 4.1V), the LED automatically turns off.

· Voltage detection occurs before output load current; if the voltage is below 3.1V, the LED blinks 10 times, and the output is cut off.

Overall, this is quite effective. As an airflow switch, the output current can reach 2A. For charging control, the chip integrates a charging control circuit with a wide charging voltage range: ordinary chargers and USB can be used for charging the chip, with a recommended 5V (4.5V~6V). When charged to 4.2V, the IC's internal protection activates. During charging, if the lithium-ion battery voltage is <2.7V, it uses trickle charging to avoid damaging the battery and ensure safety. Above 2.7V, large current charging starts, and as the voltage approaches 4.2V, the charging current gradually decreases. The charging voltage detection error is within 1%. The LED is on during charging and off when fully charged (VDD > 4.1V).

Completed.