Question

Draw the circuit diagram of battery charger using SCR and explain its working.

Answer 1

### Battery Charger Circuit Using SCR

Here’s a basic explanation of how a battery charger circuit works using an SCR (Silicon-Controlled Rectifier):

Circuit Diagram:

The circuit consists of the following components:

1. AC Source (AC input): The power supply is typically 220V AC.
   

1. Transformer: Steps down the AC voltage to a lower AC voltage (e.g., 12V or 24V AC) suitable for charging the battery.
   

1. Silicon-Controlled Rectifier (SCR): Used to control the charging process by regulating the flow of current to the battery.
   

1. Diode: Prevents reverse current flow.
   

1. Resistor: For limiting the current flow.
   

1. Capacitor: Smoothing out the ripple in the DC output.
   

1. Battery: The battery to be charged.
   

1. Load: The device powered by the battery.
   

Basic Working of the SCR-based Battery Charger:

1. AC Supply to the Transformer: The AC mains voltage is first stepped down by the transformer to a suitable lower AC voltage. This lower AC voltage is used to charge the battery.
   

1. Controlled Rectification with SCR: The SCR is the key component in controlling when the AC current is allowed to flow to the battery. When the gate of the SCR receives a trigger signal, it conducts and allows current to pass through. Otherwise, it remains in its off-state, blocking the current flow.
   

1. Charging the Battery: Once the SCR is triggered, the AC voltage passes through a diode and is converted into pulsating DC, which is used to charge the battery. A capacitor is used to smooth out the pulsating DC, providing a more stable DC voltage for charging.
   

1. Current Regulation: The SCR helps regulate the current by controlling the time interval at which it conducts. By adjusting the triggering point, the charging current can be varied, ensuring that the battery does not overcharge or receive too much current.
   

1. Preventing Reverse Current Flow: The diode in the circuit ensures that no current can flow backward from the battery to the charging circuit, protecting the components.
   

1. Battery Charging Process: As the battery charges, the voltage across it increases, and once it reaches its full charge, the charging process may be cut off automatically (using a cutoff circuit) to prevent overcharging.
   

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Advantages of Using SCR in Battery Charger:

1. Controlling Charging Time: SCR allows precise control over the charging time, making the charger more efficient and protecting the battery from damage.
   

1. Current Regulation: It helps in maintaining a steady and regulated charging current.
   

1. Cost-effective: SCR-based chargers are simple and less costly compared to other advanced types.
   

In summary, an SCR-based battery charger uses a controlled rectifier to efficiently manage the AC-to-DC conversion and regulate the charging process, providing a safe and reliable way to charge batteries.