DIY home energy monitor?

[dcb]

good point about integration, but component wise it means basically a diode and a capacitor, I think, for the inexpensive-get you within a few %-version.

[Oval_Overload]

Researchin's highlighted my naïvety:

Basically a current transducer generates a current or voltage (depending on the type) that is proportional to the current passing through the center of the transducer. There is a slight complication however. You can't just clip one of these around a piece of romex wiring since it contains both legs of the circuit. Since the current going out on the hot wire is equal to the current returning on the neutral wire, they will cancel each other out and the transducer will read zero.

Ecomodding: I'm doin' it wrong.

Source: Circuit Monitoring

[dcb]

yah, the mains are usually separated though, but I wouldn't hang c-clamp bolt threads on them, they deserve a *little* more care than that.

Also dissecting an extension cord so you can get to a lead is possible, but the individual appliance thing has been done. I think we want whole house next.

you could shut off the main circuit breakers, and wrap the two legs (not neutral) of the mains in wire (do try not to kill yourself, get some inexpensive thick rubber gloves from the home improvement store, etc. <insert long list of caveats and precaution>, etc.) and see what the voltage reading looks like on those coils. Also you want to monitor system voltage on both legs.

[Oval_Overload]

I think I'm going to carry out the experiment on a hacked extension cord before I go futzing with the 200 amp service. However, I think there is plenty of room in the distribution box box to place a sensor.

~Jimbo

[NiHaoMike]

Originally Posted by dcb

good point about integration, but component wise it means basically a diode and a capacitor, I think, for the inexpensive-get you within a few %-version.

The basic integrator is an opamp and a few resistors and capacitors. Designing it to be accurate is not that easy. Hall effect is simply the superior way to sense current.

[dcb]

yes, a clamp on hall is simple, just a pain shopping for the "right" one to figure out the additional costs/sensitivity, as compared to the simplicity of x number of turns of small gauge y wire around diameter z mains wire. I don't think an opamp is even a requirement. Figure you can sample 4 readings (2 leg currents and 2 leg voltages) at 5khz with a atmega168 anyway, with or without a hall.

[dcb]

sanity check, wrapped a small jumper around a leg and hooked up a vom on AC. with 5 complete turns it was reading 1.2-2.5 mv, so not a whole lot of signal, with only 5 turns. no guess how many amps that represents nor what a usable minimum value for aref on the atmega is.

[morglum]

OpenEnergyMonitor ( i cant post links)

Arduino
+ Current clamps (for current sensing-- I'd get the CR3110 from digikey)
+ AC-AC transformer (for voltage sensing - -I'd try ebay?)
+ cheap stuff such as capacitors and resistors

= Energy Monitor

[Oval_Overload]

Home | OpenEnergyMonitor

[Ryland]

Black and decker makes an electrical monitor that clamps on to your electric meter on the outside of your house, it costs $75-100 depending on the store or ordering it online.

http://www.blackanddecker.com/energy/products.aspx
I realize this page was started for the do-it-yourself build, but why reinvent the wheel? this unit looks like it would work and be accurate.