Introduction: Smart Charger for Alkaline Batteries

Have you calculated the number of alkaline batteries we throw every year, around the world. It's enormous... !

The battery market in France is 600 million units sold each year, 25,000 tons and 0.5% of household waste. According to Ademe, this number is 1 billion and 90 million for batteries ... 80% of batteries are not recycled in Europe in 2009.

In France, in 2006, 2 out of 3 piles ended up in the trash: only 9,000 tons of used batteries were collected while at the same time 30,000 tons of new batteries were sold. 80% of the batteries used in Europe in 2009 are not recycled!

We all need to do something to make this change .... for example, to start by reducing the number of alkaline batteries used.

A few years ago, I found a document from a French manufacturer "Wonder" of alkaline batteries that had surprised me. He explained how to recharge them several times ... hallucinating. Here it is.

In summary, here's what you need to respect to recharge an alkaline battery:

  • The terminal voltage must be greater than 1.25V for a 1.5V battery.
  • The battery should be discharged only partially (20-30%) to increase this life and are possible recharge number.
  • When charging, the voltage at the battery terminals must not exceed 1.7V.
  • The charging current must not exceed C / 15. "C" is the theoretical capacity of the battery. for example C = 1100mAh for an R6 battery.
  • A dozen recharge possible if this point is respected.

In 2017, I had enough to throw away the batteries used in the toys of my young children. So I started to test chargers (No. 1 and No. 2) batteries for so called alkaline batteries. But none of them met the load conditions explained in the Wonder manufacturer's document. In the end, the batteries recharged by these chargers were good to throw.

I had no choice then. I had to design one myself.

Step 1: The Functions He Has to Fulfill

  • Charge 4 1.5v AA and AAA 1.5v alkaline batteries.
  • Limit the load to 1.7V per element.
  • Charging current of C / 15, about 80mAh for a 1200mAh / 1.5V battery.
  • Detect if the battery can be recharged.
  • Detect if the battery is fully charged.
  • As a bonus, transmit the voltages of the batteries by serial link.

Step 2: ​The Box

I used a box 4 batteries the cheapest possible, found on Aliexpress to use its mechanical system of fixing batteries and LEDs.

The electronic PCB consists only of 5 resistors for the LEDs and the battery charge. I modify this ultra simple card by cutting tracks to isolate LED power supplies and mechanical contacts to use them.
To be able to integrate the electronic card, I printed a box extension, which sticks on the high part of the box and is screwed on the bottom of the box. The file STL is available here.

Step 3: Electronics

The charger is designed around a 28 pin dsPIC30F2010.
These inputs / outputs will allow to:

  • Measure the battery voltages.
  • Control the charge of each battery.
  • Control the charge state LEDs of the batteries.
  • Transmit voltages by serial link.

The charge of each 1.5V battery is achieved by the PWM control of a transistor 2N2222 (T1 to T4) and a resistor (R2, R5, R8, R11) limiting the current to C / 15, 83mAh. A diode 1N4148 (D1 to D4) protects the battery and the charging circuit from a possible error of setting up the battery in the case.

The values of resistors R2, R5, R8 and R11 can be changed to charge more + or - significant batteries. But be careful not to exceed the heat dissipation power of transistors T1 to T4.

The card is equipped with an ICSP connector to program the dsPIC30F2010.

A LM317 regulator is provided to charge 9V batteries at 38mAh @ 10.2V. But the tests showed that it did not work. I do not use this function.

The analog inputs of the dsPIC measure the voltage across the battery when the transistors (T1 to T4) are in the off state. Thus, we know the voltage at their terminals.

The LEDs (DS1 to DS5) indicate the charge / discharge status of each 1.5V (DS1 to DS4) and 9V (DS5) battery.

The board is powered by a 12V / 1.6Ah power supply.

The 5V is produced by a 12v- 5V DC / DC switching board.

Step 4: Schematic

Step 5: Operation

The status of the LEDs indicates whether the battery is charged / discharged / not rechargeable.
LED off: no battery or battery not rechargeable Flashing LED: charged battery LED on: battery charging

If the LED remains steady after 12 hours of charging, the battery is considered charged. It must be removed from the charger.

Step 6: The PCB

They are designed to charge 4 1.5V batteries and a 9V battery.
Unfortunately the 9V battery charging tests were inconclusive: the 9V batteries are discharging instead of charging. So I did not use this function later, even though the program measures the voltage of the 9V battery and transmits it by serial link.

Its dimensions are: 68x38mm.

The DC / DC power adapter must be configured as follows: solder the ADJ connectors together. Then adjust the potentiometer to output a voltage of 5V. The "5V" pre-setting of the card does not work properly.

Step 7: Nomenclature

  • 1 case for 4 batteries
  • 1 PCB + components
  • 1 power supply card 12vDC / 5Vdc 0.8Ah
  • 1 block 220Vac socket (or 110Vac) to 12V / 1.6Ah
  • 1 case extension (3D printing)

The complete component nomenclature is available here.

Step 8: Serial Communication

The configuration of the communication is as follows: 9600 bauds, 1 start bit, 1 stop bit, no parity.

The output voltage levels are TTL.

Step 9: Do It Yourself

You want to do it, no worries, I propose several kits depending on the budget you want to put.
They are available in the shop of my website.

All files are available here.