• Battery Charger

    11/10/2020 at 13:19 0 comments

    Many years ago I purchased a battery charger from China in a local store. The charger is working well to this day.

    I am not sure exactly how it works. However, the charger must consist of two phases:

    1. Discharge phase

    2. Charging phase

    Those two phase especially essential for charging NiCad batteries that must be discharged before the next recharging phase of the battery charge and discharge cycle. However, the chances are that my cheap Chinese charger is only designed to charge the batteries and is not discharging them to almost zero before charging.

    This is why I designed my own circuit.

    Step 1: Design the Circuit

    I created a circuit with four BJT (Bipolar Junction Transistors) transistor inverters. I used BJT transistors instead of MOSFETs to reduce the costs. However, you can implement this circuit with MOSFET inverters. MOSFETs could be more appropriate for this circuit because you do not need linear characteristics of BJT transistors for this circuit.

    The switch is used to implement the initial battery charging state (1 V).

    The feed back look initiates the discharging phase when the battery is connected. When the voltage drops to about 0.7 V the discharging phase is OFF and the charger begins to charge the battery.

    Step 2: Simulations

    There was an issue with simulations. However, I believe that my circuit can still work well even thought I never build it.

  • Motor Power Converter

    08/27/2020 at 10:17 0 comments

    I made the following mechanical system with three driving DC motors and one generating DC motor:

    You can reverse the polarity of the input and the light bulb will still turn ON. I only specified the polarity of the input because the output capacitor is not bipolar and reversing polarity and motor direction will reverse the output current flow. I used three motors to drive the rotating shaft because the input is 9 V, not 3 V. However, the potential difference across each motor can exceed 3 V at certain shaft rotating cycle positions. A good solution to this problem is connecting a capacitor across the inputs of each of the 3 shaft driving motors. However, I did not bother with the time and the money.

    Videos

    You can see that the 1.5 V light bulb is blinking non stop without the capacitor:

    With output capacitor (wire terminals shorted) the blinking was not so sudden:

    USB Oscilloscope Readings

    The motor output is showing a lot of noise and is high frequency because the motor is rotating at fast speed:

    I tried zooming in on the acquired data:

    The readings show how the capacitor can filter the generated output signal: