How to Design a Remote-Controlled AC Power Meter with 5V DC Supply?

[Pagedown]

Hi, I have forgo my previous idea of Tesla coil as my final year project and now moved on in doing an AC power meter monitoring, which monitors the kWh, voltage, current consumption of a device and remotely controlled switch to turn off/on the device.This power meter should be implemented like a wall socket point.

I am using an MCU in this case, thus I need +5V and maybe other ICs too. This power meter should be implemented like socket point, in my country is a 240V point.

1.How do I get +5V dc supplies from live wire with AC power in the simplest & most efficient way without causing much consumption or distortion in the socket point?

2.How do I control it wirelessly? RF module to a receiver connected via usb to a laptop?

 

[vk6kro]

You said it yourself. This is YOUR final year project.

So, you need to work out what you already know and what you have to find out.

I would not build it in a power plug. That is way too cramped.

You are going to need room for at least two transformers.
One, to provide a 5 volt power supply (and you can measure the voltage on the low voltage side of this as well).
And one to act as a current transformer.
So, you do all measurements at low voltage.

You haven't mentioned power factor, but if you have to allow for this, the device will get more complicated. Maybe that is a function for your micro.

Controlling it depends on what you want to control. Why not just have digital panel meters on it to show voltage and current? Or, do you want to monitor the consumption remotely?

 

[Pagedown]

Yea, but just need somoe guidelines to help me through it to make sure i don't get into a dead end =) Is there any way I don't need to use transformers? Ya, I want to measure power factor, what is the best way to do it. Ya it can be connected to a remote computer to monitor and switch on/off.

something like this :
http://courses.cit.cornell.edu/ee476/FinalProjects/s2008/cj72_xg37/cj72_xg37/index.html

 

[vk6kro]

Using transformers is not expensive and they don't have to be very big, but doing it that way could let you see 2012.
DISCLAIMER: AC POWER CAN BE EXTREMELY DANGEROUS UNLESS YOU KNOW WHAT YOU ARE DOING. PLEASE CONSULT A PROFESSIONAL AND REFER TO THE SAFETY SECTION FOR MORE INFORMATION.

Even if you do use transformers make sure your house has a safety switch (RCD) fitted.
http://en.wikipedia.org/wiki/Residual-current_device

I think you could detect when the voltage sinewave crosses the zero line and when the current sinewave does it and if there is a difference, work out how many degrees difference there is. Then work out the power factor from that.

Or you could do some rapid A to D conversions of both waveforms and integrate all the readings to see when they have the same polarity and when they don't.
You can assume that all sinewaves stay the same for short periods, so you can take readings on successive sinewaves. This gives you time to do some calculations.

This is a hard project. Any chance of doing something else?

 

[Pagedown]

It is up to me to propose but I can't think of anything else.. I'm not really into electronics, but more to electrical. Thus, not much samples for me to see on the internet, some are too expensive to work on. Any suggestions?

Thank you v6kro for your help in this, appreciate it =)

 

[vk6kro]

You might do best if you look around at home for something that would be useful for you or your parents.

Look for something that you really can do.

For example, if you wanted to grow plants you could make a box that kept the seeds or cuttings warm. The box from an old microwave oven or computer could be used.

How about an electric blanket for a dog which only turned on if the dog was in the bed? The dog's weight could operate a switch. This saves the planet and is kind to an animal, so it ticks some good boxes.

It is difficult to produce commercial products because they are probably already available but something that solves a specific problem in your house may not be available.

 

[Pagedown]

a lot other students are doing that already.

Anyway, I am doing it, I just got an approval signature from my supervisor for this project.
I like power engineering.
Which part is the hardest? I thought of doing an auto power factor correction also. =P