Battery Charger Circuit using SCR

Battery charger is important in electric system as it give back power to rechargeable battery.

Circuit is good way in using SCR (Silicon Controlled Rectifier).

SCR is strong, reliable and control well.

It have four layers, three junctions and work like switch and rectifier.

Small current to gate turns it ON and stay ON until current goes below certain level.

This is good for AC power control, so its good for battery charger.

Battery Charger Circuit using SCR is easy to make with low cost and easy to fix.

Circuit Working:

Parts List:

This article show basic SCR battery charger circuit.

SCR changes AC voltage to DC for charging battery.

When battery is low and voltage drops.

This stop forward voltage going to T1 base through VR1 and D2 so T1 turns OFF.

When T1 is OFF then SCR gate get trigger voltage from R1 and D3 and SCR turns ON and start rectifying AC.

DC voltage goes to battery through R5 and battery starts charging.

When battery is full, thenT1 base get forward bias from R3, VR1, R4 and D2 and so T1 turns ON.

Now SCR gate loses trigger and SCR turns OFF.

Then only small current passes through R2 and D4 for trickle charge.

Because it uses half wave rectifier it charges battery slowly.

For fast charge we need full wave rectifier.

VR1 let us set voltage to stop charging.

This circuit uses 230V to 15V/3A step down transformer.

Battery can connect with crocodile clips.

We can test circuit on PCB or normal board.

Formulas:

Here are some important formulas for simple SCR battery charger circuit:

1: Resistor Power Calculation

Resistor must handle heat with power it makes.

Use this formula:

P = I² × R

where,

• P is the power in watts W
• I is the current in amps A
• R is the resistance in ohms Ω

Or use:

P = V² / R

where,

• V is the voltage across resistor

2: SCR Gate Triggering:

SCR turn ON by small current at gate.

To find gate current:

IG = VG / RG

where,

• IG is the gate trigger current
• VG is the gate trigger voltage
• RG is the gate resistor for R1

3: Charging Current Calculation:

Charging current depends on rectified voltage and resistor.

Icharge = (Vrectified − Vbattery) / Rseries

where,

• Vrectified is the filtered DC voltage
• Vbattery is the battery voltage for example 12V
• Rseries is the charging resistor for example R5 is 100Ω 5W

These formulas help design and check the charger circuit.

We may need to change values based on circuit needs.

How to Build:

To build a Battery Charger Circuit using SCR follow the below mentioned steps for connections:

• Gather all the parts as shown in circuit diagram above
• Collector to diode D1
• Base to center leg of pot VR1 through diode D2
• Emitter to ground
• Connect resistor R3 from positive supply to first leg of VR1
• Connect third leg of VR1 to ground
• Cathode to diode D4 and resistor R2 in series
• Anode to 230V transformer primary
• Gate to diode D3
• Connect resistor R5 and fuse in series from SCR cathode to battery positive
• Connect battery negative to ground
• Connect one 230V transformer wire between resistor R1 and R2
• Connect second transformer wire to ground

Conclusion:

Battery Charger Circuit using SCR is simple, efficient and easy to control.

It help charge battery safe and keep battery in good condition for many uses.

References:

Battery Charger Circuit Using SCR