Transformerless Battery Charger Circuit

This post is a simple transformerless battery charger circuit which everyone can easily build within few minutes. Even a beginner in electronics circuit design and construction can have this circuit ready with a few minutes. This transformerless battery charger circuit requires very few components to construct it. You can even find these components in an electronic scraps box or bin. It can charge 6V – 9V Sealed Lead Acid Battery. This is a handy circuit not as bulky as you think in fact, you can have it closed in you palm.

For constructing this transformerless battery charger circuit, these are the components you need

  • 105J, 250V Polyester non polarized Capacitor (1)
  • 390 Kilo Ohms Resistor (1)
  • 330 Ohms Resistor (1)
  • 1N4007 Diode (4)
  • 3V Red Light Emitting Diode i.e. LED (1)
  • Switch (1)
  • 1A fuse
  • Optionally you can you may also need a VDC meter (DC Voltmeter)

Once you have the components you are good to go…

CAUTION: Always unplug the circuit completely from the AC source before connecting or removing the battery! Please note that, this is a transformerless circuit therefore, don’t have direct contact with the battery or the circuit entirely while is on the AC source! Charge ONLY Sealed Lead Acid Battery.

Below is the circuit diagram

Transformerless battery charger circuit

 

However, you can use a ready Bridge Rectifier Diode package in one component (IC) instead of using the four 1N4007 diodes. This is even more preferable as it eases soldering work and saves construction time. If you cannot find this IC, don’t worry; just use the four 1N4007 diodes in a bridge configuration mode as it is in the circuit diagram.

The below circuit is the same transformerless battery charger circuit, it uses a ready bridge rectifier diode packaged in one component that is; IC. Meanwhile not all bridge rectifier IC looks alike but however, they all have marks to indicate positive and negative output pins and the two AC input pins as marked on the one in this circuit.

transformerless battery charger circuit2

Components Values
  • C1=105J, 250V
  • F=1A
  • R1=390 Kilo Ohms
  • R2=33 Ohms
  • D1 – D4=1N4007
IMPLEMENTATION

After constructing this transformerless battery charger, do this:

  1. Don’t connect the Battery first
  2. Connect or plug in the circuit to the AC source of 100V to 250V, switch it ON
  3. The Light Emitting Diode (LED) should lit and the Voltmeter should also deflect a certain voltage. This shows that the circuit is OK
  4. Switch OFF and unplug the circuit from the AC source
  5. Connect the Battery minding also  the polarity across the DC Voltmeter, it should read the Electromotive Force (EMF) of the Battery
  6. Plug in the circuit back to the AC source and switch it ON. There will be an increase of voltmeter deflection compared to the step 5 above. Thus your battery is charging at this moment.
  7. Always unplug the circuit from the AC source before removing or connecting the Battery.
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