We use 10 kΩ resistors for mains powered monitors. Higher resistance lowers quiescent energy consumption. A value of 10 μF is suitable.Ĭhoosing a suitable value for resistors R1 & R2 Capacitor C1 has a low reactance - a few hundred ohms - and provides a path for the alternating current to bypass the resistor. Resistors R1 & R2 in the circuit diagram above are a voltage divider that provides the 2.5 V source (1.65 V for the emonTx). By connecting the CT lead we connected to ground, to a source at half the supply voltage instead, the CT output voltage will now swing above and below 2.5 V thus remaining positive. However, the Arduino analog inputs require a positive voltage. If you were to connect one of the CT wires to ground and measure the voltage of the second wire, relative to ground, the voltage would vary from positive to negative with respect to ground. Nor does it take into account component tolerances, so the burden resistor value should be decreased by a few (~5) percent allow some "headroom." There is more info about component tolerances at: ACAC Component tolerances.) Adding a DC Bias Saturation and distortion will occur if the maximum output is exceeded. ( Note: this tool does not take into account maximum CT power output. Tool for calculating burden resistor size, CT turns and max Irms (thanks to Tyler Adkisson for building and sharing this). The ideal burden resistance for the minimum voltage would therefore be: Ideal burden resistance = (AREF/2) / Secondary peak-current = 1.35V / 0.0707A = 19.1 Ωġ9 Ω is not a common value. If you're using a battery powered emonTx V2, AREF will start at 3.3 V and slowly decrease as the battery voltage drops to 2.7 V. The EmonPi has two CT channels both with 22Ω burden resistors. The standard emonTx V3 uses 22Ω burden resistors for CT 1, 2 and 3, and a 120Ω resistor for CT4, the high sensitivity channel. The emonTx V3 uses a 3.3V regulator, so it's V CC and therefore AREF, will always be 3.3V regardless of battery voltage. Here are the same calculations as above in a more compact form: Burden Resistor (ohms) = (AREF * CT TURNS) / (2√2 * max primary current)īurden resistor sizing for OpenEnergyMonitor energy monitoring hardware. The further from ideal the value is, the lower the accuracy will be.
Arduino program for single phase rectifier series#
In some cases, using 2 resistors in series will be closer to the ideal burden value. Always choose the smaller value, or the maximum load current will create a voltage higher than AREF. We recommend a 33 Ω ☑% burden. The nearest values either side of 35 Ω are 39 and 33 Ω. So the ideal burden resistance will be: Ideal burden resistance = (AREF/2) / Secondary peak-current = 2.5 V / 0.0707 A = 35.4 Ωģ5 Ω is not a common resistor value. If you're using an Arduino running at 5V: AREF / 2 will be 2.5 Volts. of turns = 141.4 A / 2000 = 0.0707Aĭ) To maximise measurement resolution, the voltage across the burden resistor at peak-current should be equal to one-half of the Arduino analog reference voltage. The YHDC SCT-013-000 CT has 2000 turns, so the secondary peak current will be: Secondary peak-current = Primary peak-current / no. Primary peak-current = RMS current × √2 = 100 A × 1.414 = 141.4AĬ) Divide the peak-current by the number of turns in the CT to give the peak-current in the secondary coil. For this example, let's choose 100 A as our maximum current.ī) Convert maximum RMS current to peak-current by multiplying by √2. The YHDC SCT-013-000 CT has a current range of 0 to 100 A.
If it is a voltage output CT you can skip this step and leave out the burden resistor, as the burden resistor is built into the CT.Ī) Choose the current range you want to measure If the CT sensor is a "current output" type such as the YHDC SCT-013-000, the current signal needs to be converted to a voltage signal with a burden resistor. This can be achieved with the following circuit which consists of two main parts:Ĭalculating a Suitable Burden Resistor Size Make sure you use the right supply voltage and bias voltage in your calculations that correspond to your setup.
Note: This page give the example of an Arduino board working at 5 V and of the EmonTx working at 3.3 V. a positive voltage between 0V and the ADC reference voltage.
To connect a CT sensor to an Arduino, the output signal from the CT sensor needs to be conditioned so it meets the input requirements of the Arduino analog inputs, i.e. Redirect: You have been redirected from Building Block Resources to our new documentation site Learn.
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