Gel cell battery charger circuit

This is a Gel Cell battery charger circuit using LM317. It can charge any size of the Gel cell batteries with the charging current, 300mA, 650mA, and 1.3A.

It can extend the life of the Gel Cell battery. Because it is a lower voltage charging (adjust the voltage of 13.4V). Thus, no overheating.

While the circuit is running, the LED indicates charging. And the battery voltage rises and a full current as we setting. Then, the current-flow reduces to zero.  At the same time, the LED will go out.

What is a Gel Cell battery?

Some of you may still not know them. Let’s get to know it a little bit.

It is also acid-lead battery types. But is the maintenance Free Battery group. Inside there are Positive Element Plate and Negative Element Plate with Lead Calcium or Lead Silver (expensive).

We do not have to see inside. Just use it enough.

This type of battery The acid inside the battery has been gelled to reduce the problem of leakage of acid from the battery.

Cr: Photo from Amazon Mighty Max Battery

Gel cell battery charger circuit working

Gel cell battery charger circuit

In the circuit above, We use the LM317 as 1.5A Adjustable Positive Voltage Regulator. It converts the input DC voltage into the stable voltage to charge the battery. Which we adjust the 5K potentiometer-VR1 for 13.4V output.

We set the output current by the current sensing resistor( R3) in the ground or ( – ) terminal.

The R3 is current limiting. You can choose it to set the charging current.

  • 300mA = 2.2 ohms, 1 watts
  • 500mA = 1 ohms, 1 watts
  • 1,300mA = 0.47 ohms, 1 watts

When the current flow through R3. This results in a voltage across the base and emitter of transistor-Q1. It is forward-biased. Thus, Q1 conducts current to LED1 and adj of IC1.

The red LED1 will show a charging battery. When the battery voltage reaches, the current will drop to a few milliamps. And it makes the voltage across Q1 and LED1 to lower. When it current drops about 5%, the LED turns off and the current drops to almost zero.

See: Automatic battery charger circuit

The AC adapter

We use an AC adapter as a power source of this. As circuit above, the plug pack 500mA DC  for charging current of 300mA. But my son draws the circuit to mistake. We are sorry. The current of AC adapter should more than of 1500mA at 15V to 18V.

  • 300mA output requires the plug pack 500mA up.
  • 500mA  output requires the plug pack 650mA up.
  • 1,300mA output requires the plug pack 1,500mA up.

What is an AC adapter?

If you are a beginner sometime you may confuse the circuit inside it.
When you cannot buy the AC adapter use can build an unregulated power supply from your parts that you have. It saves than that.

Parts you will need
IC1 = IC1 = LM317_1.5A Adjustable Positive Voltage Regulator
C1,C2 = 0.1uF 50V_Ceramic capacitors
R1 = 470 ohms _ 0.25W Resistor
R2 = 2.2K _ 0.25W Resistor
VR1 = 5K _ potentiometer
R3 = 1 ohms 1 watts Resistor

Not only that I like to keep old circuit ideas. It maybe useful for your. See below:

Dry Cell Battery Charger circuit

This is the Dry Cell Battery Charger Circuit. This can use a charger battery to get that about 12 hours. When applying to the power supply 9 volts the equipment that fixes in the circuit used for size battery AA.

If using the size C or D should devalue of Resistor RX down be 68ohm and should not lead battery comes to serial while voltage in cell battery lower 1.6V.

Dry Cell Battery Charger using LM741 and IC4011

The Comparator Circuit with (IC741) control Gate output from Pulse Oscillator. We use the integrated circuit CMOS 4011 bias current to Transistor that does in front charger battery until voltage tall 1.6V.

The comparator Circuit makes LED Flasher alert know for protecting Charger battery full.

The next time is if friends have Dry Cell Battery that use to be finished already, don’t abandon, try to apply new again.

Keep reading:
5 Lead-acid battery charging circuits

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I always try to make Electronics Learning Easy.


  1. John al

    I am looking for a simple schematic for a 12volt 5Amp gel battery. I however, want to charge it all year around for emergency use with a possible low amp such as 0.2amp or lower is better. I will put it in my attic just for emergency alarm. It will support an alarm that it has only one SCR and one resister of 15k that I had already made.
    I need help of the 12volt low amp charger.

  2. Jose Aguilar

    I make the circuit , it charges the battery, le transistor limit the current of the circuit, so, the charger always work , but if the battery its very low limits the maximun current, it charger slowly, in general a practical circuit

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