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Topic: Measuring Mains Voltage (Read 3 times) previous topic - next topic


Please don't assume that the whole world is the U.S.A. While the physics might be the same (much to the shagrin of the U.S.) the words are not.

Sorry, I wasn't thinking of the whole world picture that is the internet. I made an adjustment to the post.



cyclegadget, thanks for the link.

EmilyJane, I haven't made much progress on this yet.  I decided that I would get power from a disassembled wall wart; at U$3.00 or so I couldn't beat the price or ease of use.  I have a small CT I'm experimenting with that is actually working pretty well.  I suddenly realized that putting it around a wire in a box was not a big deal.  There were a number of problems making a hall effect current sensor work and those CTs are easily available and simple to work with.  I also realized that I didn't need much power from a transformer that was only going to be feeding a voltage divider for measuring the AC voltage.  So, a few milliamps would be fine, of course, that decision was AFTER I decided to use a repurposed wall wart for power.

Given the above, it's become a matter of having the time to slap it together, but it's summer and the yard is eating up my free time.

But, now you've got me intrigued with the Kill-a-watt all over again.  I didn't pay much attention when the wireless ones appeared since I had one of the wired ones and I was measuring power at the main for the entire house and didn't see any need.  However, I did (of course) take a kill-a-watt apart and was impressed by the fact that they simply measure the voltage across a wire to get the current level.  If you check really closely, they also use a voltage divider to sample the AC voltage.  With these two items the rest is just accumulation and calculation.

The problem is the $38 price tag for something that I will cut up and adapt.  I think a simple short extension cord with a box in the middle holding circuitry would do the job just fine and I could use my latest love, the ardweeney, to do the processing and tie the new device into my existing XBee network.

You're right, the form factor of the wireless Kill-a-watt sensor is really nice.  I could never match that cool little package.
Trying to keep my house under control http://www.desert-home.com/


Jul 25, 2011, 10:07 pm Last Edit: Jul 26, 2011, 01:31 am by EmilyJane Reason: 1

You're right, the form factor of the wireless Kill-a-watt sensor is really nice.  I could never match that cool little package.

Okay, I just wanted to point that out. I agree, the price is a little daunting. There are plastic enclosures available that have the plug incorporated anyway (ala DIY wall wart) that are pretty inexpensive that I'll probably end up using.

I'm going to start another thread because I want to look into hacking the protocol that the wireless sensor uses. They are priced pretty reasonably for my project budget and if I can use them, I want to.

Edit: The enclosure I settled on is from this series: http://www.polycase.com/ps-series

Some have a molded in place for a receptacle.

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