Introduction: Microwave Transformer As Battery Charger

About: My channel is interested in electronics and doing projects at home with recycled gadgets


Our project today is how to convert an old microwave transformer to a lead acid battery charger.

Step 1: The Tools

Here I will show you the components of the project :-

  1. plug
  2. Old microwave transformer, rolled 15 times with 2.5-millimetre wire
  3. bridge rectifier 50 amps
  4. 12-volt battery
  5. Lamp 200W

Step 2: Electrical Conductivity Method

  1. We connect one of the input AC plug terminals to the transformer, the other terminal separated by the lamp.
  2. the lamp is 200 watts connected in series for testing devices. One of the two wires connected to one of the plug terminals. The other wire is cutted by the lamp and attached to the other plug terminal. The third plug terminal is the ground and is attached to the body of the transformer. the positive terminal is different in status
  3. The negative wire from the bridge rectifier is connected to the negative terminal of the battery.

  4. The positive terminal of the bridge rectifier is connected to the positive terminal of the battery.

Step 3: Explanation of Work

    1. I removed the secondary coil and replaced it with another coil generating about 14.5 volts Suitable for charging lead acid batteries.
    2. I will wind 2.5 mm thick copper wire as a secondary coil with the largest possible number of winding.
    3. The output voltage is 14.8V, which is suitable for charging the car battery
    4. I connected the battery and measured the voltage and current, and after an hour I measured the voltage and the electrical current.
    5. While charging the battery, the voltage increases and the electrical current decreases.
    6. After half hour after cut off the main power, the battery voltage is 13.21
    7. The voltage is 12.3 volts after the bridge rectifier. Now how does the voltage rise up to 13.3 or 14.5 Volt after the battery connected? It's means the battery works as a capacitor
    8. One roll length is 28 cm, we multiply 28 cm by 15 turns, equal to 420 cm

    Step 4: Safety Warning

    1. : you are dealing with high current and high voltage, be careful

    2. Do not use a thin wire to feed electricity to the transformer

    3. You must use a thick wire because a high electrical current will pass through it

    4. Also, you should be aware of transformer's temperature and battery's temperature

    5. You should Monitors the charging process for an hour or two hours

    6. You should also measure the battery voltage during and after charge

    Step 5: Questions

    • important question is how much appropriate current to charge the battery ?

    The appropriate charging current for any battery is 10% to 15% of the battery capacity.

    If a battery is 100 AH, the appropriate electrical current for charging it is 10 amps or 15 amps.

    • What do you expect to happen in the circuit if you use a 100-watt or 60-watt bulb?

    The battery charging current can be controlled by the bulb used.

    If the lamp power is large, the charging current is large.

    Bulb resistance in the circuit is small.

    Notice I replaced the battery with another one, how much the charging current will be. If you change this bulb with a 60 watt bulb

    It has less power, so its less current , its resistance will be greater

    So the charging current will be less

    • A question was repeated in the previous video, why you did not use a capacitor?

    Here the battery work as capacitor, If we use a capacitor the voltage will rise up as Vrms which is danger charging voltage

    Step 6: Suggestions

    1. Some people suggested connecting a solar regulator
    2. Some people comment that the bridge rectifier is metal and should be placed on a heat sink
    3. Some people suggested that the bulb be connected in series
    4. Many people advised me to replace the plastic wire with a wire of varnish