AB compactlogix measure pump elec load

[thehoneybadger]

Hey all. I have decided, for my own curiosity, that i want to know, and chart, exactly how much power my air conditioner actually consumes. And when.

This is for my home automation system. Running a Compactlogix 1769-L35E. I have 4 inputs available on my analog input module. I want to make use of it.

I have read many places that air conditioning accounts for the majority of a building's power consumption. How much exactly? And when does it actually consume so much?

This question will give me something to do on over the easter break. Practically speaking, it will help me better understand how useful a battery installation might be at my home to complement my solar panels.

A list of knowns:
V(in) = 240V

Likely need Current (I) as my unknown.

So i imagine i would need a handful of shunts, then measure the current passing through the shunts before and then after the pump. Difference between the current will give me the ability to calculate power.

I do not think my PLC would appreciate it very much if i sent the current directly into my analog module. So i figure i would need a device to convert the current reading into a 4-20mA signal, which i can send to the analog module. Then somehow do some fancy calculating in the program.

This is just my guess. Any suggestions, specially a "better" way of doing it would be appreciate. I am happy to purchase a piece of equipment that measures the power and sends a 4-20mA signal output. I do not want the piece of equipment to cost more than the air conditioner itself though.

Thanks all

 

[cardosocea]

I have a bunch of these in my plant:

https://uk.rs-online.com/web/p/current-transformers/0497209

4-20mA loop powered... the same brand, LEM, has a huge variety of devices available.

Edit: Just noticed the budget requirement... you can get stuff that meters this online if you search for Arduino Power meter or something like that. I've done one with an ESP8266 that spoke Modbus to Ignition (proof of concept, really) and it was ok.

 

[thehoneybadger]

Thank you cardo for your input. I would not mind paying that price. Much less than the air conditioner unit. My budget will alow for a few hundred USD on a device.

The input voltage is only 20-30V DC though.

I require 240V AC input

Any other ideas?

 

[parky]

Yes you need a current transformer to 4-20ma or 0-10v depending on your analogue card.
It should be easy to find the current consumption of any electrical equipment for example it should have a label telling you all power requirements, also an indication would be the size of the cable & the fuse feeding it (assuming it is on it's own circuit).
Or measure it with an amp meter.
It is unlikely unless designed for industrial or office purposes so i would expect it to be somewhere in the region of 3-4kw. depending on your voltage supply will determine the current drawn.
but probably not more than 20 to 40 amps I currently have a unit installed & the feed breaker is 20 amp at 240v so giving a nice margin a current transformer (or some other type of current measure) must be capable of at least 40 amps this gives a reasonable margin but pretty accurate results.

 

[thehoneybadger]

I think i am understanding this better.

This device loops around a cable. A 24V current is passed through the device. Some wizardry happens, and and induction is measured. The induction out put is a 4-20mA signal.

Am i on the correct path?

 

[cardosocea]

I'm a bit lost on what you meant by 20-30VDC... your analogue input card will output a voltage around 20-30Vdc which will "power" the device I linked and the device will give you a proportional 4-20mA current.

If you see the link you'll notice there's a little "clasp" of sorts in the device. This is so you can open it and clamp it around one of the conductors (conductors, not the whole cable).

It would look like this:

https://www.packetpower.com/hubfs/ct.png

So the 4-20mA will be proportional to 0-50A in that particular device.

 

[thehoneybadger]

Thank you. This makes a lot of sense. I will likely purchase this item.

 

[drbitboy]

Thinking outside the box, if the A/C unit is either on or off, and when it is on it runs at a more or less constant power, then if you know that power value, then to "measure" its consumption you would only need to time how long it is on.

I assume you have a watt-hour meter similar to what we have in the states:

​

If you turn every other circuit off at the breaker panel, and run just the A/C unit, you should be able to count revolutions over a fixed time, which will then give you an approximation of the (assumed) constant power usage.

Then a simple digital input that is 1 when the A/C unit is running, driving a retentive timer and a counter, which accumulations are stored once per day and then reset, or other logic if you want to know exactly when it is running (I read the OP), will give enough information to calculate you what you want to know.

 

[thehoneybadger]

Hey DBB. I do not think i will be wiring up this particular suggestion. But i thought i would respond to say hey .

My anemometer has been running like clockwork for months now.

 

[Tom Jenkins]

https://www.automationdirect.com/ad...0W-HPS&categoryId=0&TxnNumber=-1&searchqty=10

ADM100W-HPS

You may need to add a C/T or P/T

 

[parky]

you can buy CT with 4-20ma output see here there are many current ratings or to halve the current put the live side of the power cable through twice if enough space.

https://uk.rs-online.com/web/c/?searchTerm=current+transformer+wit+4-20ma+output
These will interface wth a PLC analogue input quite easy.

 

[thehoneybadger]

Thanks parky

 

[drbitboy]

Hey DBB. I do not think i will be wiring up this particular suggestion. But i thought i would respond to say hey .

My anemometer has been running like clockwork for months now.

Sweet!

 

[Saffa]

For this kind of application where you want to know kWh consumed over a period of time, but maybe also want to identify say, peak consumption periods, I prefer the code simplicity of a kWh meter with a pulse output.

Only needs one digital input.

If your air conditioning is on a dedicated circuit in your switchboard then a DIN rail mount direct connection option like below is easy to install within the board ( assuming you are a qualified and licensed electrician... )

Do a Google search for "DDS-1Y-18L" as an example.

However, if you're only able to get access to the outdoor units power conductors locally, then a clip on CT as suggested by others is easier and may be possible to install without breaking any local regulations.

The 240V supply is unfortunately, not constant and may vary several volts over the day as the grid is loaded up. Assuming it is constant is probably fine for your application though.

If you get higher than expected results for current draw, this can be due to harmonics or low power factor, both of which are a byproduct of modern inverter driven equipment.

I'm interested to see your results at the end of this, I've done a fair bit of power quality monitoring for industrial sites but not for the humble home air con unit!

(Have just finished putting individual power metering and harmonic mitigation on a 600kW DC drive... 0.5 power factor before correction... saving them around 150A of grid current by correcting harmonics and the subsequent poor power factor)