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    Monitoring homes power usage

    What would be the best way to get an Analog 0-5VDC of the current power usage of my entire home.

    I'm thinking either current clamp multimeter output on the main ground leg coming into the box. This would output MA relative to amps being used, but I'd need to covert this 0-200ma to 0 to 5V to tie to the SECU16.

    The other way would be an current transformer. I'm not sure what size I would need and what I would need to do to prep the output to get it into the 0-5V bounds.

    Any ideas? I'd love to see in Homeseer how many KW we're using at any giving time.


    Tim

    #2
    Tim,

    It would be better to just use a clamp on sensor. Take a look here: http://www.omni-components.co.uk/acsensor5.htm

    I know that it is UK based but I am sure you could find a suitable company in the US.

    As an example, the CTL-10-S50-30F-CL2 gives 4V out at a max current of 100A or 0.4V at 10 Amp etc. As you use 110V, 9 Amps current drawn approx equals 1KW so the clamp would give out 0.36V per KW.

    You would need to full wave rectify this clamp and place a smoothing capacitor across the DC output. I personally would then use a series resistor and a 5.1V zener to ground to prevent the output going above 5V. This could then be sent to the Ocelot input. A little bit of calibration on the Ocelot would be needed due to losses in the rectification process etc.

    I actually had the same idea but in a different context. In the UK, they have recently started to install electronic meters with a very bright LED that flashes for every 1000th of a KW used. As a test, I hooked up a photo diode which picked up these flashes and sent this to the Ocelot!

    Trouble is that I feel a little uneasy leaving a sensor on the meter as I am not sure what the power company would say when they read the meter!

    Jon
    Jon

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      #3
      Here is an American reseller of that same unit.

      http://www.urdamerica.com/Clamp%20on...e%20Sensor.htm

      Wouldn't you need two? One for each phase and then add up the results?

      Doug

      Comment


        #4
        Apparently I can't edit my previous post.

        If you place the clamp on the neutral, you won't get an accurate reading because some of the return power goes to the ground rods and water supply clamp that all tie to the neutral bar.

        The only way to truly measure is to take a reading from each phase and add the results.

        Doug

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          #5
          Any idea of the cost of the sensors?

          -Rupp
          ๐Ÿ’โ€โ™‚๏ธ Support & Customer Service ๐Ÿ™‹โ€โ™‚๏ธ Sales Questions ๐Ÿ›’ Shop HomeSeer Productsโ€‹

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            #6
            No idea. I'll email them for a quote and see what they say.

            Doug

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              #7
              I looked into current transducers from http://www.crmagnetics.com/4310_a.pdf

              They want $160 for a 100amp version and I'd need 2 to do both legs. This unit outputs 0-5vda so I wouldn't need anything else to connect it directly to the secu16... They also have a 4-20ma version that cost $220.

              I'm going to look into the prices for just current transformers instead of โ€œall in oneโ€ transducers. Then add a full bridge and 5.1 zenor diode. Has anyone done this before? I saw people that have used the transducers, but at $360 investment it would be extremely hard to justify to the wife why we need it.

              Thanks
              Tim

              Comment


                #8
                If you're willing to roll your own circuit. Check out http://www.crmagnetics.com/pdf/3110.pdf. These are current transformers, around $8, AC output. You can find circuit diagrams for opamp based precision rectifiers(ac/dc converter) on the web.

                Henry

                Comment


                  #9
                  http://www.crmagnetics.com/newprod/P...rodName=CR4260

                  It's a 2 element 0-50AMP, 4-20ma output current transducer. I'm thinking with the dual element I can use one transducer for both legs, since it supports two elements.

                  I know 50 amp rating is low, but it's the highest of it's class. I'm think I would rarely if ever use more than 50 amps per leg, since I have gas heat and all gas appliances.

                  My question is just is the 50 amp 2 element rating per element or is it total combined current of the 2 elements.

                  They want $129 for the unit, it's still pricey but it's a lot better than $320 for two 100amp units.


                  Tim

                  Comment


                    #10
                    Here's a link to a National Semiconductor application note describing precision ac-dc converters. http://www.national.com/ms/LB/LB-8.pdf. They're cheap and easy to make.

                    Henry

                    Comment


                      #11
                      Ok you talked me into it. I'm going for the low cost route. With 2 $12.95 clamp on type current transformers and a home built precision AC to DC converter.

                      I may try just a easy full bridge rectifier if that would out ok I'll keep that, if not then I'll put together the op-amp precision one. Basically I need a clean proportional DC output that doesnโ€™t exceed 5volts. I'm hoping I can get away with just a bridge and a cap, and I zenor(to limit). I shouldn't ever approach the 5v limit thou, I rarely use more than 25amps per leg. Then again I didn't run the pool pump or AC compressor when I took that reading.

                      Thanks
                      Tim

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                        #12
                        For your application, you can use 5% 1/4 watt resistors, and closest fit w/ standard sizes. The resulting error can be tweeked out via software. You should be able to buy all parts from your local Radio Shack. I'd use the TL08X part. Opamps normally use a split supply, +/. For your application, you can use a single supply, probably a 9VDC wall wart, and use one of the amplifiers in a package to generate a pseudo ground. Just tie a voltage divider between the + and ground of the wall wart, and the juction of the two goes to the input of a voltage follower. The ouput of the voltage follower can then be used as your ground. The TL08X are dual opamp packages are dual amplifiers, so 3 total at about 2 bucks apiece will do it.

                        Henry

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                          #13
                          low-key- warning - mixing low voltage stuff and 110/220 in the same Jbox is a technical code violation, I think. We don't want a fire and a reason for the insurance company to have an out.

                          Comment


                            #14
                            I was planning on just having the coils(current transformers) in the AC panel clamped to the legs. Then the outputs from these (2) coils wired via 4 conductor low voltage cable in flex conduit to a bread board in my basement then to the SECU16 also in my basement. Total distance from breaker panel to SECU16 is about 50 feet.

                            would this setup be "legal"? If not how do I legally get the coil outputs out of the panel and into a low voltage box?

                            Good point thou, thanks for reminding me about the liabilities of my tinkering.

                            Tim

                            Comment


                              #15
                              Stevech,

                              You are right to be concerned about codes and insurance loopholes.

                              I do not believe that there are any requirements for breaker box components, like a UL certification, but I think if any amount of contributory failure can be linked to your homemade product, you are in for a very expensive bill.

                              Doug

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