Dual Battery Charging Circuit

Did anybody’s device ever had no battery but have other batteries with just wrong size? then this post will show how to make a Dual Battery Charging Circuit.

Also, it uses one power to charge two batteries and it uses one small chip called IC 555 and other small things to ensure both battery get same charge.

Hence, if we want to use this device more then maybe this circuit will helpful.

What is a Dual Battery Charging Circuit:

People call a circuit that charges two batteries at the same time a “dual battery charging circuit,” and they use this type of circuit when they need to charge two batteries safely and separately.

Also, things like small electronic device, battery system and car stuff use this kind of circuit for many times.

Circuit Working:

Parts List:

Components	Values	Quantity
Resistors (All resistors are 1/4 watt unless specified)	33k	2
	8.2k	2
	22k	2
	15k	2
	100k	2
	470k	2
	10k	4
	Presets 10k	4
	Variable Resistors Rx and Ry (to be calculated)	1 each
Semiconductors	Transistor BC547	2
	Diode 1N4007	2
	Diode 15 Amp	2
	Zener Diode 14.4V	2
	IC 78L05	2
	IC 555	2
	Relay 12V	2
	SMPS charger for battery	1

The explanation below shows how the twin battery charger circuit works:

Here, the circuit uses IC 555 two times like two same parts and each part control when battery start charge and when stop one for low and other one for high voltage.

Also, SMPS give power to both IC 555 parts from same source and it also uses relays and diodes to send power to each battery.

Furthermore, diodes connect between the IC 555 and the SMPS and they stop power from mixing between the two parts.

Relay take care of charging which work like switch and when battery reach full level like high voltage then IC 555 tell relay stops charging.

Also, when battery go down to low voltage then relay connect again and charging to start.

Resistors Rx and Ry control how much current go to each battery and these resistors stop battery from overcharge or are not getting enough charge.

Here, the IC 555 controls each battery charging cycle and when the battery becomes full the relay cuts off the power, while the relay supplies power again when the battery becomes low.

Hence, to find correct value for Rx and Ry we can use Ohms Law and check battery AH (ampere hour); also resistors must be right to give safe and good charging.

Formulas and Calculations:

Formula for charging time show how long it take to full charge one battery using same current always:

Charging Time = Battery Ah / Charging Current

here:

• Charging time mean how many hours (h) will take to full charge battery.
• Battery Ah show how much power the battery can hold.
• Charging current is how much current in Amps A can charger give to battery.

How this formula work:

Battery capacity (Ah) shows how much electric power the battery can store, while charging current (A) shows how fast the battery charges.

Also, to find how many hours are for full charge it will just divide battery Ah by charger current.

Example:

If battery is 50Ah and charger gives 5A then:

Charging Time = 50Ah / 5A = 10 hours

So battery will take 10 hours to full charge.

How to Build:

To build a Dual Battery Charging Circuit follow the below connection steps:

• First, make simple drawing of twin battery charger circuit and then put all parts like in circuit diagram and how they connect together.
• After that, find pin numbers for relay, diode, IC 555 and other parts and look in datasheet to know correct pin layout.
• Then connect IC 555 same as shown in circuit diagram.
• Next, put resistors Rx, Ry, diodes and other wires for each timer part and connect SMPS to give power to both IC 555.
• Also, use diodes to send power to each IC 555 part.
• Here, the relay turns the power ON/OFF to the batteries, while Rx and Ry control the current to the battery..
• Then use diodes D1 and D2 in two different places and this will stop charging from mixing or disturb each other.
• Now connect the wires to the battery and be sure we connect the positive and negative sides correctly.
• Before put parts on PCB and test circuit first and fix problems now so there is no need fix later.
• Also, change IC 555 settings to correct battery charging level and only change resistor value if really needed.

Follow Safety Rules:

• Be safe and check wire direction, insulate wires and avoid short circuit.

Final Test:

• Also, after connecting to SMPS watch the charging and ensure both batteries charging good and with no overcharge.

Conclusion:

To conclude, when we make Dual Battery Charging Circuit then choose right parts for our battery type.

Furthermore, always follow safety steps from battery company to stop damage or danger and also this will help make charging safe and will work well.