tweetawatt/wattcher, different from (other) wattcher

[bartgrefte]

Hi

Every time I search with Google for an alternative for the not so cheap Wattcher, I run into the page of the Tweet-a-Watt which apparently at some time was called Wattcher as well, http://www.ladyada.net/make/wattcher/

Unfortunately the Tweet-a-Watt is not what I am looking for. I am looking for a way to get (more or less) realtime info about the current powerusage in watts, like the Wattcher does, measured with the help of the powermeter. A meter similar to this (the left) one:


This so that I can see what the whole house is using and so that I can see almost right away how much the powerusage increases/decreases when I turn something on or off. I can get the Wattcher though, but paying €99 ($130) for that seems a lot for what you get. I don't think it's much more than a sensor, transmitter, receiver, micro controller, display and some resistors and capacitors. I doubt that costs that much, or am I wrong?

Anyway, is there someone who knows an alternative? It does not necessarily have to be ready to use, a kit is okay too

[bartgrefte]

Huh? Got a email saying there's a reply, don't see any and it says "2 posts • Page 1 of 1 ", what's going on?!

[john444]

Hi Bart,

About the e-mail response when nothing shows up -

The forum gets a small amount of spam.
The staff is pretty good about deleting it but, it will result in the post count being off.

As for your Wattcher - I know nothing about it. Someone else will need to help with that.
The way these things generally work is to use a current-transformer (to measure current) and a voltage-transformer (to measure voltage)
convert both ac measurements to dc values and use the micro-controller to do the arithmetic for a Wattage value.
If high precision is not required, you might assume that the voltage does not change with variations in current (usually close enough).
With this assumption, you can just use the current measurement as an indication of wattage.

If remote readings are important, then you have the added complication of providing that feature.

Good Luck with your project, John

[richms]

Actually most of the commercial ones just seem to assume the voltage is constant so they end up not measuring the phase shift or even the true VA figure, and a shift of 10% on the line voltage will give a signifigant difference if you have mainly ohmic loads in the house.