Battery Charger Circuit using SCR

Battery charger is important in electric system as it give back power to rechargeable battery; also circuit is good way in using SCR (Silicon Controlled Rectifier).

SCR is strong, reliable and control well and it have four layers, three junctions and work like switch and rectifier.

Furthermore, small current go to gate turns it ON and stay ON until current goes below certain level, as this is good for AC power control, so its good for battery charger.

Moreover, this battery Charger Circuit using SCR is easy to make with low cost and easy to fix.

Circuit Working:

Parts List:

Components	Values	Quantity
Resistors	330Ω 1/4 watt	1
	22Ω 5W	1
	820Ω 1/4 watt	1
	100Ω 1/4 watt	1
	1Ω 5W	1
	Potentiometer 100Ω	1
Semiconductors	SCR BT151	1
	Transistor BC547	1
	Diodes 1N4001	3
	Diode 1N4148	1
	Fuse 2A	1
	Transformer Primary 230V and Secondary 15V / 3A	1
	Battery 12V	1

To begin with, this article show basic SCR battery charger circuit, as SCR changes AC voltage to DC for charging battery.

When battery is low and voltage drops and then this stop forward voltage going to T1 base through VR1 and D2 so T1 turns OFF and when T1 is OFF then SCR gate get trigger voltage from R1 and D3 and SCR turns ON and start rectifying AC.

Then DC voltage goes to battery through R5 and battery starts charging and 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 and then only small current passes through R2 and D4 for trickle charge and because it uses half wave rectifier it charges battery slowly, but for fast charge we need full wave rectifier.

Also, VR1 let us set voltage to stop charging and this circuit uses 230V to 15V/3A step down transformer.

Moreover, battery can connect with crocodile clips and 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, so 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 and also 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:

• First, gather all the parts as shown in circuit diagram above
• Then T1 collector go to diode D1, base go to center leg of pot VR1 through diode D2 and then emitter go to ground
• After that, connect resistor R3 from positive supply to first leg of VR1, then connect third leg of VR1 go to ground
• Now SCR cathode go to diode D4 and resistor R2 in series and anode go to 230V transformer primary and gate go to diode D3
• Connect resistor R5 and fuse in series from SCR cathode to battery positive and connect battery negative to ground
• Next, connect one 230V transformer wire between resistor R1 and R and then connect second transformer wire to ground

Conclusion:

To conclude, Battery Charger Circuit using SCR is simple, efficient and easy to control, as it help to charge battery safe and keep battery in good condition for many uses.