Nickel-Cadmium (Ni-Cd) batteries are really popular in many electronic devices because they have a high energy density and can be recharged.
However, the usual ways to charge them can be slow and not very effective which might shorten the batteries lifespan.
To tackle this problem a super fast charger circuit for Ni-Cd batteries has been created using the MAX712 integrated circuit.
This new design not only charges the batteries quickly and efficiently but also keeps the Ni-Cd cells safe during the charging process.
The upcoming article will take a close look at this circuit including how it is designed, how it is built, how it works and the math behind it to help everyone understand how it functions.
Circuit Working:
Parts List:
| Component Type | Value/Specification | Quantity | Notes |
|---|---|---|---|
| Resistors (1/4W unless specified) | 22k | 1 | |
| 68k | 1 | ||
| 220Ω | 1 | ||
| 470Ω | 1 | ||
| 150Ω | 1 | ||
| 1Ω 1W | 1 | ||
| Capacitors | Ceramic 0.01µF | 1 | |
| Ceramic 0.1µF | 1 | ||
| Electrolytic 1µF 25V | 1 | ||
| Electrolytic 1000µF 25V | 1 | ||
| Semiconductors | IC MAX712 | 1 | |
| PNP Transistor 2N2907 | 1 | ||
| Diode 1N4007 | 5 | ||
| LED 5mm, 20mA | 1 | ||
| Battery | Ni-Cd Battery | 2 |
The advanced Ni-Cd battery fast charging circuit has a few important parts that work together.
It includes a bridge rectifier, a voltage regulator, the MAX712 fast charge controller chip and a power transistor that helps control the charging current.
This circuit takes an alternating current AC input of 6V to 9V and changes it into a steady direct current DC output which is great for charging nickel cadmium (Ni-Cd) batteries.
The first thing that happens is the AC input is converted into DC using diodes D2 to D5 which make up the bridge rectifier.
After the AC is turned into DC the voltage is smoothed out with a capacitor C4 which is 1000µF.
This helps get rid of any bumps in the output.
The IC MAX712 chip is in charge of the whole charging process keeping an eye on the voltage and current to make sure everything runs smoothly.
This chip helps the batteries charge quickly while also preventing overcharging.
The time it takes to charge and how well it works depend on a resistor R1 and a capacitor C2.
There is LED1 that lights up to show if the batteries are charging.
The power transistor Q1 controls the current going into the battery pack.
To help manage the current even more there are resistors R5 and R6 that help direct the current to the battery.
Formulas with Calculations:
To design your own Ni-Cd Battery Fast Charging Circuit you need to use the below mentioned formulas with calculations:
Charging Current (Icharge):
Icharge = Vout / R
where,
- Vout is the output voltage of the regulator
- R is the current limiting resistor
Charge Time Calculation:
Tcharge = (1.4 × Cbattery) / Icharge
where,
- Tcharge is the charging time in hours
- Cbattery is the battery capacity in mAh
- Icharge is the charging current in mA
Example:
If a 1000mAh Ni-Cd battery is charged at 500mA the charge time will be:
Tcharge = (1.4 × 1000) / 500 = 2.8 hours
Power Dissipation in the Resistor:
P = I² × R
Example:
For a charging current of 500mA and R5 = 1Ω
P = (0.5)² × 1 = 0.25W
A 1W resistor is used for safety.
How to Build:
To build a Advanced Ni-Cd Battery Fast Charging Circuit following steps need to be followed for connections of the circuit:
- Gather all the components as mentioned in the above circuit diagram.
- Connect pin 1 of IC1 MAX172 to pin 16 of IC1.
- Connect pin 2 of IC1 to positive of Ni-Cd batteries, connect cathode of D1 diode from pin 2 of IC1 and connect the anode of D1 to collector of transistor Q1.
- Connect pin 5 of IC1 to pin 15 of IC1 .
- Connect one end of resistor R3 from positive supply and other end of resistor R3 to pin 5 of IC1.
- Connect pin 6 of IC1 to pin 12 of IC1.
- Connect pin 7 of IC1 between resistors R2 and R1.
- Connect resistor R2 one end from pin 16 of IC1 and the other end connect to pin 7 of IC1, connect resistor R1 one end from pin 7 of IC1 to capacitor C1 one end.
- Connect pin 8 of IC1 to pin 15 of IC1 through LED1 and resistor R4.
- Connect pin 11 of IC1 to one end of capacitor C1 and other end to C1 to one end of resistor R2.
- Connect pin 13 of IC1 to GND of the circuit.
- Connect pin 14 of IC1 to base of transistor Q1, connect the collector of transistor Q1 to pin 2 of IC1 through diode D1, connect the emitter of transistor Q1 to positive of circuit .
- Connect capacitor C3 and resistor R6 in parallel from pin 14 of IC1 and between positive supply of circuit and emitter of transistor Q1.
- Connect positive of Ni-Cd batteries to pin 2 of IC1 and negative to pin 6 of IC.
- Connect one end of resistor R5 to negative of Ni-Cd battery and other end to GND of circuit.
- Connect positive of capacitor C2 from pin 15 of IC1 and negative of C2 to other end of resistor R1
- Connect positive of capacitor C4 from positive of the circuit and negative of C4 capacitor to GND of the circuit.
- Connect positive of diodes D2, D3 and D4, D5 which are as bridge rectifier to positive supply and negative of diodes to negative supply
- Connect the AC input of bridge rectifier with the 6V to 9V AC inputs
Conclusion:
The Advanced Ni-Cd Battery Fast Charging Circuit that uses the MAX712 IC is a great way to charge Ni-Cd batteries quickly and safely.
It charges the batteries fast which means you wont have to wait long and it also helps the batteries last longer.
You can adjust the charging current and time to fit different sizes of Ni-Cd batteries.
This charger is perfect for people who love electronics want to build their own battery chargers or need backup power solutions.