[TriEmbed] TriEmbed Digest, Vol 20, Issue 16

[Mark Sidell]

Martin,

I apologize for coming across as critical of your post. I just thought
people might be interested in the complications involved with measuring
true power. Or maybe I was just trying to justify to myself spending big
bucks on the WattNode devices. Fortunately, after twelve years, they
haven't fried yet!

Regards,
Mark

On Fri, Jan 16, 2015 at 4:29 PM, Martin Brooke <martin.brooke at duke.edu>
wrote:

> 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.....
>
>
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