4 Replies Latest reply on Apr 3, 2016 11:57 PM by jinzai

    Voltage and Current Sensors - Problem with High Power Loads

    tronJones

      Hello,

       

      I've built a solar metering/datalogging device with my Intel Galileo. I have input banana plug connectors that hook up to a solar panel (or any DC power supply), and output banana plugs that connect to a load - I've been testing it with DC light bulbs. My circuit is as such: I have a 470k/47k voltage divider connected to an analog input pin on my Galileio, and an ACS712-30A current sensor also connected to an analog input pin. This should yield a maximum of 5V on my analog inputs corresponding to maximum inputs of 52V/30A. I also have a common ground between by Galileo and power source. I have an LCD connected to an I2C port on a shield connected to the Galileo.

       

      I have been testing this with a small DC power supply that can output variable DC of up to 30V but 1A max, as well as a fixed 5V DC supply that can deliver up to 5A. These both work fine, and I was getting accurate readings at 30V/1A and 5V/5A.

       

      Today however, I tried hooking this up to an actual solar panel but I'm having trouble at higher wattage. The panel was delivering around 20V and to this I connected two 50W DC bulbs in series (with my solar meter in-line between the panel and load). I measured the amperage with a Fluke multimeter to be around just under 5A, but it's causing my LCD to freeze. Like I said, when I try connecting to <30W circuits, the LCD behaves normally, but there seems to be an issue with bigger loads.

       

      Any idea what could be causing this?

       

      -Tony

        • 1. Re: Voltage and Current Sensors - Problem with High Power Loads
          PabloM_Intel

          Hi tronJones,

           

          Several factors could be causing the issue, but based on your description I would suggest you to separate the digital part from the power circuit. You will reduce a lot of noise and possibly this will improve the performance of the digital part. Also, I believe it’s implied in your answer by I want to make sure, did the light bulbs worked when you connected them using the solar panel as power supply?

           

          Regards,

          Pablo

          • 2. Re: Voltage and Current Sensors - Problem with High Power Loads
            tronJones

            Thanks for your reply Pablo.

             

            The light bulbs do indeed work when connected to the power supply, regardless of whether or not I have my Galileo powered on/off and connected inline. The input/output ports in my enclosure are connected directly together, with just taps coming off them into my voltage divider and current sensors.

             

            Could you elaborate on what you mean by separating the digital from the power circuit? I assume you mean isolate the two, but I'm not sure how to accomplish that, as I was thinking they'd have to have a common ground. I have the negative of my power circuit connected to a ground pin on the ADC side of the galileo/arduino pins. My voltage divider is connected to A0 and my current sensor to A1.

             

            I have been doing some troubleshooting, and I can cause the LCD to freeze by simply unplugging the wire going into A1, regardless if there is a load connected. This is strange. With no load connected, I can unplug the voltage sensor from A0, and my reading simply goes to 0. However, when I unplug my current sensor from A1, the screen freezes. Strange.

             

            -Tony

            • 3. Re: Voltage and Current Sensors - Problem with High Power Loads
              PabloM_Intel

              Hi Tony,

               

              It would be necessary to provide different power sources to each specific part of the circuit, that way you eliminate the need of a common ground. Once you’ve done that I would suggest you to make the same test that you’re doing now, and see what happens if you unplug the wire going into A1. This won’t ensure that the circuit actually works, but you’ll need to test different scenarios to see which one is causing the issue.

               

              Regards,

              Pablo

              • 4. Re: Voltage and Current Sensors - Problem with High Power Loads
                jinzai

                So, you connected the solar panel directly to your analog input and the current sensor? I think -- you need to connect the measuring circuitry across a load -- it should not be the load. Its not a problem for the current sensor, but for the voltage divider -- it is the only path to ground for the potential you are measuring. Its the same reason why you should never measure unloaded house current with an oscilloscope.

                 

                I have a similar setup, although I am not measuring voltage. What I did was -- I went to Harbor Freight and bought a small solar panel and a charge controller. I connected the panel to the charge controller, a battery to the charge controller and took the load connection to my current sensor and a terminal block. I use that terminal block to power my Arduinos and the battery is actually a Schumacher Instant Power jump starting battery. Why? Because it has an AC charging system, as well. It also has an AC inverter....its a great setup, actually. It even has a built-in wattmeter. Galileo draws about 4 watts from that.

                 

                Anyway, I suggest that you load your solar panel and take the voltage from across that (parallel, not series) -- you are actually not interested in the open circuit voltage anyway -- that is just physics. You are, however -- interested in the voltage drop across a load -- that is what tells you the panel is working, right? (Which you can verify by your current reading.)

                 

                btw, you CAN measure the open circuit voltage with a voltmeter -- because it uses a very large value voltage divider and will not draw much current.