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Monitor AC current for Home automation
Monitor AC current for Home automation
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Old 13th June 2018, 07:47 PM   #1
randytsuch is online now randytsuch
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Default Monitor AC current for Home automation

I've been looking for a good/cheap way to monitor AC current to determine if things like washing machine/dryer running or done, pool pump on and spa pump on. There are a ton a google hits on the subject, and I've been looking at them.

Various reasons for this, washing machine and dryer are in the garage, so notification that wash is finished is the goal. My pool equipment is diy automated, controlled by ESP and relays, and for some reason they don't always turn on when they should, and sometimes they turn on when they shouldn't :/

Pool pump is variable speed, and normally runs at a real low speed, 600 rpm and draws less than 50w, some real small number. On the high side, washing machine is probably over 10a.

Don't really want to make a hard connection to AC, so likely a current clamp over the hot wire is what I'm looking at, unless I get a better answer.

Looked at Hall sensors, but they need to be connected to the AC. Same for a current transformers.

Because I'm cheap, I'd like to keep this as low cost as possible. I already have ESPs performing other tasks around these machines, so the plan would be to connect to an ESP IO pin, which will be broadcast to a Pi running Domiticz. I'll add a script to Domoticz to send me a text.
The ESPs have 5 and 3.3 VDC power supplies which I can use for this.

Since this is just a handful of devices, I have to advantage of being able to customize for each application, based on current draw and anything else that matters.

So wondering if anybody has any advice, other ideas, maybe worked on a similar project?

Thanks for reading
Randy
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Old 13th June 2018, 11:08 PM   #2
Speedskater is offline Speedskater  United States
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An engineer G.A.R. writes about using the TED system to monitor AC power.

BETATRONICS&reg, TED 1000 & 5000 Power Line Communication Data Structure, Electrical Measurement, Power, Voltage, Power Factor, Volt-Ampere, Problems, The Energy Detective
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Old 14th June 2018, 01:53 PM   #3
Elvee is offline Elvee  Belgium
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I built something of the kind, a long time ago: it was used to monitor an electric stove, in particular to make sure that all of the plates had been completely switched off.
Thus, it had to cope with a power ranging from several kW to a few tens of watt, when the smallest plate was used at its lowest setting.

As a sensor, I used a small 10mH or so drum core inductor, simply taped against the feeding cable.

The conditionning circuit consisted of a high gain, high Q 2nd order bandpass filter tuned to 50Hz.
I think I cascaded two of them, and the output was rectified to feed a threshold detector. A single LM324 was sufficient for all the functions, and the circuit worked spotlessly for ~20years.

I don't have the schematic anymore, but these indications should be sufficient to build something equivalent, since nothing was critical in the design
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Old 14th June 2018, 02:54 PM   #4
randytsuch is online now randytsuch
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Speedskater
Thanks for the link, but that looks more like a protocol, which I don't really need. I didn't see anything about how to actually measure current draw in there.

Elvee
Thanks for the input. I'm guessing with an inductor taped to the power wire, sensitivity wasn't great, so you needed a fair amount of gain to make up for that.

So, I could use a fairly cheap inductor, but would need to put more effort into making a conditioning circuit with enough gain, or spend a little more money and get a current transformer (non intrusive type). I can run the power wire through the transformer. This will give me more gain, so should be a much simpler conditioning circuit.

Randy
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Old 14th June 2018, 08:56 PM   #5
russc is offline russc  England
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Quote:
My pool equipment is diy automated, controlled by ESP
Extra Sensory Perception?
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Old 15th June 2018, 02:40 PM   #6
randytsuch is online now randytsuch
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Originally Posted by russc View Post
Extra Sensory Perception?
Yes, mind control

ESP8266 running espeasy. espeasy has a web interface to set it up. Allows you to fairly easily interface to a pi, or some other processor. I am using a Wemos mini D1 pro for the esp board, using the pro by the pool because it has a better antenna.

ESP's are pretty cool for the money, basically an arduino with wifi, but are somewhat limited in processing power. I have a few spread out around the house controlling relays, or monitoring sensors, and they all tie to a central pi running domoticz.

Randy
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Old 18th June 2018, 07:18 PM   #7
russc is offline russc  England
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Thanks for the explanation: behind the jokey comment was a genuine interest.
I will add it to my list of "to learn" things.

Found your blogspot but not the page you linked.
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Old 18th June 2018, 07:48 PM   #8
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Sounds like you need a "current transformer", which is typically a donut shaped device through which the current-carrying conductor passes. Some of them, often referred to as "split core", open on one side if you can't (or don't want to) break the current-carrying conductor. They are available in a variety of amperages and outputs: some produce a current proportional to the main current, others produce a proportional voltage. Look at "current transformer" on eBay as a good start to see what's available.


Where I work, we use a lot of these on panel boards and switchboards for industrial applications where customers want to measure load currents. Connected to sophisticated meters, they can also measure harmonics and other power quality parameters, as well as log data and communicate the data remotely via Ethernet.
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Old 18th June 2018, 08:54 PM   #9
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by randytsuch View Post
So, I could use a fairly cheap inductor, but would need to put more effort into making a conditioning circuit with enough gain, or spend a little more money and get a current transformer (non intrusive type). I can run the power wire through the transformer. This will give me more gain, so should be a much simpler conditioning circuit.
Yes, you could get away using a LM358 instead of a LM324, but even ~30years ago, I thought it was more sensible to use the costlier and more complex conditioning option, because it only required commodities and worked without disconnection or butchering of the existing cable: no need to pass through a tore or to clamp an individual wire.

50 or 60 years ago, I might have opted for a better sensor, because the cost of amplifying devices like tubes was high enough
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Old 19th June 2018, 03:26 PM   #10
Pano is offline Pano  United States
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Monitor AC current for Home automation
There are some good systems that install at the breaker box and sense current. They are network connected, of course. That allows them to sense and learn all the different loads in the house and track them - you can monitor them from your phone or computer.
Alas, they are not cheap. I haven't bought one because the possible savings in electricity would take a long, long time to pay it off.

I've also seen similar devices for your water mains. The question of course is, are there diy versions of this?
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