
Cheap Point of Use Electric Power Monitor - luu
http://josh.com/notes/cheap-point-of-use-electric-power-monitor/
======
Animats
From the article, last updated in 2011, it looks like he never built the
thing.

Here's the correct link for "Simple Digital AC Wattmeter".

[http://electronicdesign.com/lighting/simple-digital-ac-
wattm...](http://electronicdesign.com/lighting/simple-digital-ac-wattmeter)

That's a very neat circuit. It's a very good wattmeter. It measures
instantaneous voltage and current, multiplies them in an analog multiplier,
integrates the result, and produces a 5V digital pulse for each joule used. So
it will measure correct wattage for devices with non-standard power factors,
and work with power sources that are not pure sinusoids. Most such devices
just measure current and assume voltage.

This is the kind of wattmeter you need to measure power consumption of things
like the E-Cat cold fusion device, with its "proprietary waveform" that's
probably being mis-measured. That would be a useful bench instrument to have
around. For the application proposed, it's unusually complex, but not a bad
design. Bob Pease, who used to write an analog column for Electronic Design,
would have liked it.

The usual solution today is a Hall-effect current sensor, like this:
[https://www.sparkfun.com/products/8882](https://www.sparkfun.com/products/8882)
It only measures current, but it's easy to use and electrically isolated from
the high voltage supply. It doesn't require a high-current low-resistance
current-sensing resistor (0.002 ohm) in the high voltage side as the one above
does.

~~~
aceperry
I was looking at the correct link but it didn't have the part number for the
opto-isolator. This is a pretty clever circuit. I'm not sure how cheap the
finished product would be, especially if used for three phase high voltage
circuits.

~~~
Animats
This optoisolator might work:
[http://www.vishay.com/docs/83652/ild615.pdf](http://www.vishay.com/docs/83652/ild615.pdf)

It's intended for use in non-saturated mode, and is close to linear up to 10mA
at the LED. Frequency response is about 10KHz, so it's fast enough for AC line
stuff unless there are big spikes.

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AdamJacobMuller
I use a bunch of these:
[http://www.amazon.com/dp/B007UZH7B8/ref=cm_sw_su_dp](http://www.amazon.com/dp/B007UZH7B8/ref=cm_sw_su_dp)
to accomplish the same. They are a bit pricey for mass-deployment
unfortunately but have led to some very interesting insights about power
usage.

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maguirre
The article pointed by the link provides very little useful information. The
links are all broken and the general concept outlined offers little, if any,
useful information.

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pronoiac
Huh. It's a rough sketch, from 2011. There's no follow-up I can see.

