Vintage Electricity Meter

Vintage electricity meter gets new life with WiFi control.

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This project turns a vintage electric meter (build in 1958) into an industrial style decoration object. It can be accessed by WiFi and set the speed of the rotor according to a range of -15 kW to 15 kW. Additionally, it has some illumination.

The used electricity meter is essentially an induction motor, it needs alternating voltage.

The motor consists of a voltage coil, a current coil, a spinning disk and brake magnets.

In a Nutshell, an alternating current in the voltage coil induces an electric field in the non-magnetic, but conducting spinning disk. If a current flows through the current coil, a torque affects the spinning wheel. This torque is proportional to the product of voltage (over the voltage coil) and current (in the current coil). For a specific speed, a permanent magnet acts as an induction brake, it creates a negative torque proportional to velocity.

Usually, current and voltage are measured on the same line. The key modification for this project was to separate both coils. The voltage coil is powered by a transformed square voltage, the current coil by a 3.3V supply voltage with a 3.3 Ohm resistor in series. Additionally, the brake magnets were removed, thus the resulting damping is through friction of moving parts (spinning wheel and mechanical display) only. With this modification a spinning velocity of an equivalent energy consumption of -15 kW to 15 kW can be reached. The power consumption of the induction motor is at maximum 3.5 Watt.

Motor and lights are controlled by an ESP8266, which provides a WiFi interface. The electronics are fairly simple, a step down converter provides 3.3V for the micro controller and motor driver. As motor driver a MX1508 is used, a cheap chinese driver with two outputs. For the voltage coil a simple 50Hz transformer 230V to 2*6V is used in reverse, both 6V coils connected in parallel. A reflective object sensor reports each revolution.

It turns out, that 250Hz is ideal for the used transformer and motor. An upper bound is given by motor inertia, a lower bound by current saturation of transformer. For simplicity a square wave is used, but a PWM modulated sine wave should be possible too.

  • 1 × ESP8266 (ESP12E) Microcontroller with WiFi
  • 1 × Transformer 1.8VA, 50Hz, 230V to 2*6V
  • 1 × MX1508 Motor Driver
  • 1 × QRE1113 Sensors / Angle, Position
  • 1 × LM393 Amplifier and Linear ICs / Comparator ICs

  • Evaluate Control Parameters

    Karsten06/14/2020 at 14:45 0 comments

    The basic function work quite nice, for a given PWM value, the rotation speed of spinning disk convergates to an according value. However the transient response is quite long (about 6 minutes).

    The damping factor in cause of friction seems for a large range constant, only for slow velocities it seems higher.

    With a few more experiments and analytical consideration it should be possible to create a (open-loop or closed loop) control circuit which takes a specific speed as set point.

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