Current Monitoring - How?



  • I've just bought a couple of these : http://www.ebay.com.au/itm/191286280578?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

    The plan is to create a smart switch which my washing machine and dryer will plug into, and using these sensors I am hoping to receive a notification through my Vera 3 to tell me that the appliance has finished. The problem is that even though I have read some stuff on here about current monitoring, there isn't a great deal of info detailing examples of sketches and the like.

    So I was wondering if anyone here has actually created a mysensor which does similar to what I am after?
    thanks
    dean



  • @Dean I don't know about this module but are you thinking of connect this one to the live 220V/110V/..V ? On the picture it looks like it have to small isolation distance for that.



  • Yes that was my plan. I might have to do a little more research, because from what I have read, it should work fine... Anyone else have any opinions regarding this sensor? Would also appreciate some sharing on how others have created current monitoring sensors πŸ™‚


  • Hero Member

    I'm I reading that correctly? 66mv/A ?? I've only ever used a non-invasive CT such as a SCT-013-000 and I think the highest output is 50mv @ 100 amps. Do you need to use a burden resister with these boards? I would assume not since it's hall effect.?



  • @Dean
    If I were you I would have a look at the datasheet for the used ACS712ELC-30A chip. This little device has (according to the specs) an 2.1 kVRMS minimum isolation voltage from pins 1-4 to pins 5-8. The use is to put it in series with one of the leads going towards your washing machine.

    So it's designed to be used with the 230 VAC / 110 VAC. If you take a look at the datasheet, you'll see that the IC is based on the hall-effect.

    Although it's safe to use with 230 VAC / 110 VAC, make sure you know what you're doing. If you don't trust yourself with this, then don't use them.

    as a starting point for your sketch I would start with the "BatterypoweredSensor" to be found in the Examples. The 66 mV/A will give you some decent voltage 660 mV or 0,66 Volts which for a starting point will work with an 1.1 V internal reference.

    Boozz



  • @boozz Thanks so much for your advice and guidance, very much appreciated! πŸ™‚

    I have two of these ordered, so while waiting for them I will do a little more research. Right now I am building a door bell which includes a mobile phone so I can use it as a video intercom πŸ™‚ Having some issues with Vera on UI7 so am downgrading right now back to UI5. But all that is a little off topic lol

    But thanks again for your help!


  • Mod

    @Dean I had an experience with this but it is AVR plain C (not arduino)

    this sensor produce oscillation across VCC/2, measurements bellow VCC/2 are corresponds to negative edge of the AC oscillation and measurement above VCC/2 corresponds to the positive edge. It means that your reading from analog input will be across 512 value while 512 itself will be equivalent to zero current. First of all you need to construct a formula to calculate the current based on this information, positive and negative, or absolute using ABS() function

    Second. Your load (like dryer) is reactive load. For a correct measurement you require to measure RMS current, this means that you need to measure a few points at each AC period (according to 50 or 60 Hz frequency). After measuring RMS you will need to calculate active power. that is it.

    Some theory is here http://www.analog.com/static/imported-files/recommended_reading/815002980PowerTheoryNew.pdf
    and here http://openenergymonitor.org/emon/buildingblocks/ac-power-introduction

    I have used interrupts for the analog input measurement because you need to measure at right timings.



  • Any updates on how this turned out?


 

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