LED flashing in proportion to AC power consumption

[minuslr]

Hi all - a newbie question.

Is it possible to create a circuit, using cheap components only, whereby a led would flash with a frequency in proportion to the power consumption of an AC power circuit?

I was thinking of this as a way to modify many extension sockets as a way of isolating and coupling to a single microcontroller which would count the pulses and calibrate to measure power usage in a house.

I've seen complex microcontroller circuits to measure current and voltage and multiply the two in circuit - just thought this way might be more cost efficient and more isolated than some ive seen.

Any ideas?

 

[schmitt trigger]

The power meters not only multiply the voltage and current, but also take into consideration the phase angle (power factor) to compute the real power (watts).
Better devices also multiply in real time the two waveforms such that any waveform distortion can be taken into consideration.

Unless you are only measuring incandescent loads with reasonably well regulated voltage (no more than +/- 5%), you really have to take into account all variables.

 

[misterT]

There are many ICs that does all that. Here is one: https://www.electro-tech-online.com/custompdfs/2010/05/22011a.pdf

The IC measures instantaneous voltage, current and power. It also has power to frequency output.
It costs only 2 dollars at DigiKey so probably you are not able to build your own circuit any cheaper.

 

[minuslr]

I get you - inductance and capacitance change the phase - thanks for that.

 

[minuslr]

Yes $2 is difficult to beat and I will probably go down this route thanks!

Out of interest I wonder how real power was measured before these wonderful chips came around - anyone know?

Just got to find a uk supplier now - ebay? .... ;-)

 

[crutschow]

Out of interest I wonder how real power was measured before these wonderful chips came around - anyone know?

There are Electrodynamic watt-meters with an analog meter type indicator that was designed in the latter part of the 19th century. The have both voltage and current coils that are configured to move the meter indicator in proportion to the multiplied value of the current and voltage, including the phase angle, so they measure true power.

 

[minuslr]

Thats a very interesting link and method. you have satisfied my curiosity - Thank you!

 

[RODALCO]

Watthour meters

The older style meters usually have a ferraris disc which drives a revolution counter via a worm and gear train which counts the kilowatt hours.
A certain amount of revolutions of the disc equates to 1 kWh.
this constant is stamped on the nameplate. e.g. 600 rev / kWh or Rr = 13 8/9 for US meters.

The newer meters are solid state and measure current with small current transformers or hall sensors which drive the metering IC as well as measure volts and power factor.
Often these have a LED (1000 imp / kWh) or LCD display.

You could scan your house meter with an opto isolator which counts the impulses from your house meter.

Have a look on my YouTube home page where you can see a variety of kWh meters ay work with internal parts exposed.

type in Landis & Gyr MF1tm kWh meter in the toolbar or rodalco2007
You will see some interesting meters on there.

Regards Raymond

 

[crutschow]

The older style meters usually have a ferraris disc which drives a revolution counter via a worm and gear train which counts the kilowatt hours.

You do realize that there is a difference between a watt-hour meter and a watt meter, which is what's being discussed here?

 

[minuslr]

checked out you youtube thanks. watt hours yes but theory must be similar.
[You could scan your house meter with an opto isolator which counts the impulses from your house meter]
yes this is where i got my idea from i want to create a similar system on an extension socket by socket basis! one per room.
IC metering is the way to go - but the analog system was based on a combined amps and voltage magnetic field (multiplying) although the eaxct configuration i havent managed to find.