OK, I want to monitor my refrigerator. I have separate refrigerator and freezer appliances and when they kick on at the same time it creates a significant (at least to me) load. Additionally, they kick into defrost mode at times during my peak power period. The idea is that I want to control them such that:
1. No stinking defrost cycles during peak usage periods
2. Both compressors cannot kick on at the same time.
I can handle the code, but I want advice on hardware to do this little job. It would be perfect if I has a wall plug (120V power, US normal) that leads to a box that has a socket on the other side. This box would have an arduino-like device inside with other stuff to measure the current. Out the side of the box are controls to prevent the compressor from kicking on and maybe an input for a temperature sensor that would disable the controls if the temperature in the boxes got too high. Other suggestions welcome.
The box would also have an XBee inside that can grab the time and maybe other information off my in-home XBee network. so there's no clock to set and it could also broadcast the fridge temperature and status on the network so I can check on it. This last is mostly for fun, but it could be useful from time to time.
So, how would you approach this. I only want one plug to the wall so the power supply should be inside the box. The box should be small, I plan on using an Ardweeny (about the size of my little finger) as the cpu, so this should give you an idea of the size of stuff I'm talking about.
So, I need a little bitty transformer (for voltage measurement), another one for powering things, a CT to measure power, etc. I have a lead for a transformer: admin.powervolt.com/PVAdmin/Ensign_PrdImages/DataSheet///8_DataSheet_1225200973321DataSheet_AdmiralIP005%20DATA%20SHEET%20ensign.pdf This little guy is about an inch and a half or so, but maybe you folks have better suggestions.
Of course I'll document everything on my site so it can be reproduced. My other projects in this area are at draythomp.blogspot.com, so you can tell I'm serious about doing this.
Re: Project Advice, Refrigerator Monitor
Not sure what you need to do overall but it seems to me you will need to set both unit thermostats to lowest temp settings and monitor temps in both fridge and freezer from your unit. Then your unit will need to supply power alternately to fridge and freezer so temp in each is kept to the correct level.
This can probably be done quite easily with an arduino, a couple of relays or triacs and a handful of other components.
As to the defrost cycle I do not know how yours works. Are you saying it uses power to defrost them? If so how does this work?