I'm interested in monitoring power usage at the consumption level. i.e., inbetween the cord for my refrigerator and the outlet.
Everything I've seen here thus far is geared towards measuring it at the circuit level or higher.
Other than cost, is there a reason why measuring a single appliance is a challenge?
I have not been able to find any pass-thru measuring options for Arduino or Raspberry Pi, everything seems to rely upon CTs and if power consumption MUST be measure by a CT then I'm curious to know if a CT will work just as well external from the wall as it would internal, for example if I placed a CT on the refrigerator cord itself.
Note: Refigerator is just an example, I want to measure EVERY individual device in my house down to the device level.
Thanks,
Chad...
Re: Pass-Thru Monitor?
As you rightly say, the main obstacle is cost. There is no engineering reason at all why you cannot use a low-current c.t. to measure a single appliance. The reason c.t's are used is for safety. If you were to use a shunt, it would necessarily mean a metallic connection to a live conductor ("live" includes the neutral as far as the law regarding personal safety is concerned) and so everything must be double insulated or inside an earthed metal enclosure, and connections for debugging and testing become a major problem. Getting the data out via a display (as all the commercial units do) or by radio would be ok, any other way needs full isolation.
Obviously (because a lot of people fall for this one!) you pass only one conductor - line or neutral - of the cord through the c.t., and you can of course use the ring-type c.t. which will be somewhat cheaper and better for this application than the split-core type.
I've no experience of the MIcrochip PIC, I understand the programmer is quite expensive and the learning curve steep, however the devices are cheap and quite possibly more suited to what you want. It may be worth looking into.
Re: Pass-Thru Monitor?
Have a look on Google, wheres quite a few people who have taken an off the shelf single appliance monitor and added on a wireless chip to send the results somewhere else.
Starting with this sort of plug-in device..
http://www.maplin.co.uk/plug-in-mains-power-and-energy-monitor-38343
Re: Pass-Thru Monitor?
An option for using the EmonTx with an individual device is to purchase something like this:
http://www.amazon.com/Extech-480172-AC-Line-Splitter/dp/B0000YHN9W
These are designed for using clamp on multimeters and give you the option for 1X or 10X the current, so you can scale it up if you are measuring a lower current. You can also make one yourself using a single insulated extension cord that you carefully separate the conductors on, but I feel this is safer and gives you the 10X option.
Dan
Re: Pass-Thru Monitor?
Thanks for the feedback. The closest I've found for a consumption level power monitoring application is this: http://meterplug.com/
What I found absolutely astounding in it's short-sightedness is that this is a Bluetooth device.
It works great (I assume) if you're in range with Bluetooth, but why they went that route I have no earthly idea. If it were Wifi, or even RF w/ a hub, it could be easily logged to a server.
Still, the fact that they were able to do something like this with such a small form factor gives me hope that a wifi solution is possible.
Short of adding a picture of John Goodman holding a gun and asking this question.... Am I the only one around here that thinks using Bluetooth is idiotic?