[TriEmbed] TriEmbed Digest, Vol 20, Issue 16

[Martin Brooke]

I never said anything about power only current.  The application was more
one of "is it on", and not much uses current when switched off.
Indeed for resistive loads like heaters you can just multiply by nominal
voltage to get power.
I think measuring voltage for power factor is sort of a challenge for
reliable low cost applications.  You tend to need to actually cut into the
wires which leads to trouble.
I had a Kill A Watt Electricity Usage Monitor in my basement till it
literally blew up and took a bunch of other stuff with it.  They tapped
into the power with a resistive divider that fried.
I have this idea that you can tell if a device is using a lot of reactive
power from the shape of the current waveform.  Or at least you can learn to
identify them and compensate based on the type of device.
For most home uses current is going to tell you what you need to know.

From: TriEmbed [mailto:triembed-bounces at triembed.org] On Behalf Of Mark
Sidell
Sent: Wednesday, January 14, 2015 10:35 PM
To: Triangle Embedded Devices
Subject: Re: [TriEmbed] TriEmbed Digest, Vol 20, Issue 11

If I'm not mistaken, the Arduino circuit described measures apparent power,
not true power, because it simply averages the current and doesn't take
into account the voltage to current phase shift caused by inductive loads.
Good enough to tell if your water heater is on, but it may not match what
your electric meter says.

On Wed, Jan 14, 2015 at 9:49 PM, Martin Brooke <martin.brooke at duke.edu>
wrote:
I used an audio jack breakout on an arduino proto shield with a simple RC
circuit to level shift the AC.

here is a.....
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20150116/2421e35d/attachment.htm>