DIY home energy monitor?

[Oval_Overload]

Has anyone here looked into creating a DIY home energy monitor? Prices for things like the T.E.D. are in the triple digits, and from my involvement in the EV space, I've learned magnetic current sensors can be had for $10.

For those of us who don't care about fancy internet connected features, How difficult would it be for the community to come up with a device that multiplies measured current by measured wall voltage to give a wattage value for the whole house?

~Jimbo

[Clev]

Are there any fairly accurate current sensors that could interface with something like an Arduino?

[dcb]

The tricky bit is getting a handle on the usage "on the cheap",
some electric meters come with a light that blinks every "x" watt hours, that would be relatively easy to monitor. The spinny disk kind might need some other setup, i.e. laser scanning or optical mouse type approach, to monitor the usage in real time.

Polling the system voltage (and current with a hall sensor) might be a more practical approach and easy to install.

but getting a handle on automatic monitoring of mechanical gauges has other uses, i.e. the gas meter and the water meter and ???

[Clev]

There's a cool system that has wireless sensors (a la Kill-a-Watt) that you plug in wherever you have appliances or devices. The base station tells you usage at each appliance, and also can turn off the attached appliances remotely. They have a web page, iPhone app, etc. However, to keep from using more energy at each unit than you save, you'd have to design them carefully to use as little energy as possible. Hence my question about Arduino-based sensors.

[Oval_Overload]

I think concentrating on a simple, instantaneous watt meter would be a good jumping off point. FOr the sake of intellectual curiosity, I'm going to go down in my basement and wrap a wire 'round a magnet to see if I can use it to get an readings off the mains.

[dcb]

ya know, that isn't a horrible idea. A couple wraps around the main (wait for a dry spell first) and a voltage divider might be all you need to get an arduino sized signal. I'll have to think about it a bit.

But yah, ipods are pretty low in the priority list

[Oval_Overload]

I wrapped laminated wire around a space heater cord, but it didn't seem to induce any readable voltage. This might actually require research *hides*

[thatguitarguy]

Try asking over at hackaday.com:
Search Results home watt meter Hack a Day
They play around with this kind of stuff, or over at the forums at endless-sphere.

[NiHaoMike]

Inductive pickups (without integration) are no longer accurate since many loads are nonlinear. The magnetic field produced by a current in a wire is proportional to the magnitude of the current, but the voltage induced in a coil of wire is proportional to the derivative (rate of change) of the magnetic field through the coil. That means that if the current is something besides a sine wave, integration must be done to undo the derivative distortion.

A better way is to use a Hall effect chip to sense the magnetic field. The output is directly proportional to the magnetic field (which is directly proportional to the current), which is exactly what we want.

[sc2dave]

Good postings