network enabled home power monitor.

Hello,

I am new to the whole Arduino experience, and I want to construct a reliable home power monitoring system.
I've been researching on the web and practicing basic stuff with actual arduino.
The power monitoring system will be non-invasive, and it will measure 110V/50HZ/Single phase, 2 wire(United States). Also, I want it to be network enabled, so I can monitor the real-time power usage and history with my computer and phone.
I have no idea where to start except that I need to use current transformer with arduino.

Anyone has successfully completed a project like this?
any advice on safety with current transformer(i am new to this whole electrical engineering)?

thanks.

any advice on safety with current transformer(i am new to this whole electrical engineering)?

Don't.

I've seen projects where people have detected the flash of an LED on their meter that indicates an amount of energy has been used. I'm not sure that a current transformer is a good idea for a first project as I'm led to believe that they can pose dangers if used incorrectly.

I have no idea where to start

Start with posting a picture of your KWH meter ...

Are there moving parts to be seen that for example could reflect light (black/white disc), or a blinking led or ...

and it will measure 110V/50HZ/Single phase, 2 wire(United States).

Where, in the United States, are you finding 50Hz power?

As Grumpy_Mike says, don't.

sp. "Grumpy AWOL"

sp. "Grumpy AWOL"

Oops. Sorry about that. The advice sounded so much like Grumpy_Mike that I didn't scroll back to double check. It's still good advice if you have to ask how to do it.

If you do decide to proceed , here is a project like you describe using current transformers and a WiShield on the Asynclabs forum.
http://asynclabs.com/forums/viewtopic.php?f=18&t=78&sid=fd36d59fad1ebf0ad977579f6312e407

Hundreds of people were using GooglePowerMeter stuff.. the Google part is being retired as a project but there's lots of hardware out there.

See: http://www.google.com/powermeter/about/index.html

I'll post some hardware stuff when I find it...

The "sense your power meter without opening anything" approach is a good start.

But MANY people and projects are doing this, so calm down the Fear Factor. Just follow Universal Rule #1:

Don't Be Stupid!

Regards, Terry King
...In The Woods In Vermont
terry@yourduino.com

I have done exactly what you're describing and so have many others. Current transformers are extremely easy to install and safe, provided you simply turn off the power when you install them. They are low voltage so getting the wires out of the mains box is easy. And, then, this is almost the only place you deal with wall level power.

Personally, I put the current transformers in myself while the box was live (you don't have to disconnect anything) and it took about 15 minutes from walking up to the box to walking away with the wires already run inside the house where I put the electronics. I used a wishield, which isn't produced anymore and later switched it to an XBee and did the web interface on another Arduino inside my house. My mains box is on the side of the garage about 50 feet from the Arduino that interfaces with the web.

I used a wall wart to power the arduino and have another step down transformer to measure the mains voltage. I have the project posted and the code I am running to measure the power. There is also a link there to other folk that are doing similar things at an open energy project in Wales. They have created a library for the Arduino IDE that does most of the work for you. I don't currently use the library because it didn't exist when I started the project and why fix something that is working?

How easy it is to do depends on your skill level and interest. It took me a month or so to get the various parts and have a prototype running on my kitchen table. I split an extension cord and put the current transformers on it to test. I used a toaster (1500 watt) to create a load I could turn on and off for measuring power; comparing the various readings to a kill-a-watt I picked up at Home Depot.

So, what amperage drop do you have to your house? Mine is 400 watts, split in the box to two 200 watt feeds and I am only using one of them currently. It was the biggest drop I could get in a residential area and I didn't want to come back in a few years and have to upgrade. This number will determine which current transformer you need.

Of course, this got me started on handling devices around the house. Originally, I simply showed the power level on a web page. Then, I wanted to be able to see it any time so I made a display that would show the power and mounted it on a wall. Then I wanted to record it over time so I put in an interface to Pachube. Then I ........ Needless to say, I'm still working on it and incorporating lots of things around the house. I even went so far as to replace the heat pump thermostats in the house with arduinos and have full control of my heat and A/C over a web interface. Once I could measure the power and see what was actually going on, I installed a solar hot water heater for the house water, solar heater for the swimming pool, inside and outside temperature sensors.

The code, hardware and techniques are all documented on my blog at http://draythomp.blogspot.com/, the tabs at the top link to the various projects. It isn't hard, it isn't any more dangerous than any other project around the house and it's a heck of a lot of fun. Currently, I'm saving over U$100 bucks a month in power bills, but I use electricity for everything here in the desert.

Oh, every time you talk about touching the mains, it sets off an immediate reaction in folk. You start getting replies that tell you how horribly dangerous it is and how you'll kill yourself and void your home warranty or insurance. While you may kill yourself, it probably won't be from messing with the current transformers and when I checked with the home insurance folk, they said that it was a problem only if it didn't meet code. Since there is no code on low voltage wiring where I live, no problem. It's roughly the same thing as putting in a new doorbell transformer, except much safer since you never actually have to touch any of the wires.

And, the cardinal rule, if it scares you, turn off the breaker.

draythomp:
Oh, every time you talk about touching the mains, it sets off an immediate reaction in folk. You start getting replies that tell you how horribly dangerous it is and how you'll kill yourself and void your home warranty or insurance. While you may kill yourself, it probably won't be from messing with the current transformers and when I checked with the home insurance folk, they said that it was a problem only if it didn't meet code. Since there is no code on low voltage wiring where I live, no problem. It's roughly the same thing as putting in a new doorbell transformer, except much safer since you never actually have to touch any of the wires.

And, the cardinal rule, if it scares you, turn off the breaker.

Your entitled to your opinion. My policy is that anyone asking questions about working with or around AC power gets some version of "If you have to ask, then you shouldn't mess with it, get professional assistance".

Lefty

And, the cardinal rule, if it scares you, turn off the breaker.

There is no breaker from the utility supply here in the UK, just a fuse with a seal.

And you folks accuse me of evangelizing? First, in any legal mains installation in the US (where the OP said he was), there is a main cutoff between the meter and the house supply rails. Here is mine:

See the 200A breaker at the top and the house supply breakers underneath? Notice also that the circuit transformers wrap around the insulated wires from the main breaker to the house rails. They snap around the wires and nothing, absolutely nothing has to be disconnected. I had to put a couple of plastic ties on them so they wouldn't slide down the wires. Those wires are in excess of a half inch with about a sixteenth of kynar insulation on them. If you turn off the 200A breaker, there is no power down there to worry about. Electricians do this all day, every day, a reasonably intelligent person can be expected to do it once or twice. Other boxes have slightly different configurations, but this is the general idea.

So, no meter removal, no calling the power company, no need for a U$100 an hour electrician that will turn off the breaker for you. If one has concerns in this area, just look at it and use a little common sense. Maybe the OP needs to call an electrician in his particular instance, but I'm certainly not going to rant at him about how unsafe it is without seeing it. I've installed a large number of electric water heaters and they are exactly as unsafe as this situation. Turn the breaker off, do the job, turn it back on. Turn off the switch, change the light bulb, turn it on. The wires are bigger and scarier, but the voltage is the same, enough to kill you if you don't pay attention. I only know a few old ladies that call an electrician for a light bulb even a broken one.

As for my experience, how the heck can anyone determine that? Maybe, I am an electrician, maybe not. And, the reason I don't have a ton of bad experiences is simply because I take precautions and pay attention to what I'm doing.

And lastly, people do die of electrocution. But we can all look up the stats on that to see what the odds are. We can also look up the stats on every other way people die and compare them. McDonald's represents a more significant threat to people if we want to look at the stats.

But telling someone not to do it because you won't is just silly. Give them the information on what is going on and let them make an informed decision for themselves. They may come up with a new, better way that none of us thought of.

But telling someone not to do it because you won't is just silly

So is suggesting that you're in the US, and the supply is 50Hz.

You may not die from electric shock from wimpy US 110V, but the current is quite enough to give you severe flash burns (or worse) from your vapourising screwdriver or pliers.

Yawn...

People make simple typing mistakes every second or so, implying the OP did anything other than that when it came out "50Hz" is probably insulting to him (her, it). And you're right, 110V is somewhat less dangerous than 220 but notice that the CTs are around the incoming mains at 240V with 200A available; I'd venture to guess that's more than most of the people arguing with me. However, that's only a guess since I haven't seen their implementation. And at any rate, any voltage that will overcome skin resistance is dangerous. A 12V car battery will vaporize a screw driver and we don't worry much about it since 12V won't overcome skin resistance, but lots of people are burned working on them.

While it's true that there are differing local codes and that the codes have changed over the years, but I know for an absolute fact that every building code in the southwestern US requires a mains shutoff after the breaker and before the house wiring rails or the utility won't install the meter and the inspector won't approve the installation. True, there are some old places that have screw in fuses left over from the 50s that may present a problem, that's why I said to look at it and decide. And, yes waving a screwdriver around indiscriminately inside an electrical box is probably not a good idea. Did I suggest that at some point? Additionally, I don't remember saying, "just go for it".

And, it's true that all current transformers don't just snap around the wires. Don't buy those, buy the ones that snap on.....simple.

Lethality is something that can't be measured or predicted. If I told him to drive to the store and get a part, isn't that potentially lethal? Advising him to open the breaker box and take a look at what he's got could well be lethal, the door could come off and hit him on the head; especially if he has one of those boxes where the lid lifts up.

Just telling him not to do it because the wording of his post implies inexperience is, in my opinion, not the way to respond. I choose to respect the OP's intelligence and willingness to evaluate his own situation enough to offer guidance instead of alarm.

OK,OK, the OP DID ask for some advice, and he's getting it. Let's just discuss the subject and all learn something.

Anyone who looks at his service entrance panel and is not comfortable with how much they understand should find a friendly local Electrician to show them..

Most installations where I am (Vermont USA) have an outside-mounted meter and a main breaker right below the meter. That shuts off power to the entire building, including the input side of the service entrance. No notification to the power company needed... I was able to easily install a generator transfer switch ahead of my main service entrance panel using the wife-with-big-flashlight method.

Many/most service entrance panels have 3 or 4 inches of exposed Line1 and Line 2 conductors exposed at the top of the panel's main breaker and it's easy to add the clamp-around type current transformers on them. Yes, there ARE exposed 115/230V (USA) terminals just below. No conductive tools needed or wanted in that area while attaching current transformers and their low-voltage output wires.

I think the more interesting issue is putting current transformers on some branch circuits with significant power consumptions; that's where the energy-saving is likely. And you can turn off the regular main breaker to de-energize them...

Regards, Terry King
...In The Woods In Vermont
terry@yourduino.com

From what I've read, Current Transformers fall into that dangerous category of appearing to be lovely and safe as they are non invasive. They are just a transformer and come with dangers that come with that. draythomp - please do a google search for "current transformer open secondary"

Yep, current transformers can be somewhat dangerous on their own. They normally have a reverse ratio, one to many instead of the usual many to even less; that can lead to higher than expected voltages on the output limited by core saturation. This would be the case if we were using un-burdened current transformers and there is a distinct possibility of blowing out the pins on a little Arduino if the burden resistor opened, or we opened it by mistake. 21st century current transformers made for monitoring power don't have this particular problem, their open circuit voltage is around 10 volts for a lot of them and substantially less when we put our own burden resistor on them. That's why you test the thing on a mock up and don't go trying to build it directly on the power panel.

I have a couple of little current transformers on branch circuits to tell me when certain appliances are on. These are not for the faint of heart to install. You have to kill the power, disconnect the wire from the breaker, slip on the CT and put the wire back. I usually kill the main and pull the breaker out of the box to hook one of these up. My advice is different for these little things. There's not nearly enough room to mess around with power on, it's too easy to have a screw driver slip messing around and it requires you get in there with metal tools that you could forget about and grab an exposed something while standing on a damp lawn. Different thing entirely. My method of killing the main is probably safe enough.

Turns out though that once you have watched power for a while you can tell which things are on. My south air pump pulls around 4.6 KW and the north one pulls around 3.5, the pool pulls 2.8 on high speed and .25 on low. The dryer pulls 10KW when the heater is on and the oven is around the same but with different characteristics, etc. I thought the branch CTs would be useful, but I haven't looked at them in weeks. I may eventually figure out a use for them, but right now, they're just there because it's too much of a hassle to take them out.

Here is a commercial unit that works very well!

http://www.theenergydetective.com/store/ted-5000

As long as you don't touch any bare metal inside the panel you'll be fine, just be careful :slight_smile: ( perhaps wear rubber gloves )