4 ms·

Cheap Point of Use Electric Power Monitor

11 points by luu 12y ago

maguirre 12y ago
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.
Animats 12y ago
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-wattmeter http://electronicdesign.com/lighting/simple-digital-ac-wattm... 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 12y ago
  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 12y ago
    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.
pronoiac 12y ago
Huh. It's a rough sketch, from 2011. There's no follow-up I can see.
AdamJacobMuller 12y ago
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.

11 points by luu 12y ago

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.

Animats 12y ago

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-wattmeter http://electronicdesign.com/lighting/simple-digital-ac-wattm... 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 12y ago
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 12y ago
  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.

pronoiac 12y ago

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

AdamJacobMuller 12y ago

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.