Can anybody help me understand what I am doing wrong to get these inaccurate numbers.
Please (Any help gratefully received!!)
Problem: Using the basic Current_Only sketch and example hardware on a breadboard, my reading for IRMS is 3.94 for a 1500watt blow heater (US voltage of 120) so I tweaked the calibration number and burden resister values as shown below. But I am still not getting accurate IRMS numbers.
Details:
- I have the ‘out of the box’ Current Only Sketch.
- Changed double Irms = emon1.calcIrms(1480); to double Irms = emon1.calcIrms(1676);
- Changed Serial.print(Irms240.0) to be Serial.print(Irms123.0); // Apparent power
- Changed emon1.current(1, 111.1); to emon1.current(1, 350); gives better but still not accurate results (see below table)
My CT is a YHDC SCT013 100 Amp / 50mA device
My Arduino is an Adafruit M4 Airlift Lite
My Burden resister is 27 Ohm
Calculations to get to 27 Ohm:
• The voltage from M4 3.3v output on the M4 Airlift measures at 3.89 with my multimeter
• Primary peak-current = RMS current × √2 = 100 A × 1.414 = 141.4A
• Secondary Peak Current = Pri Peak Current / Num Turns : 141.4 / 2000 = 0.070711
• Burden resistance = (AREF / 2 ) / Secondary Peak Current so for me = (3.89/2) / 0.070711 which = 27.29
• My Voltage divider is 22k resisters (Voltage measured at divide = 1.99)
Table of tests (Attached file is prob easier to read)Power_testResults.csv (1.8 KB)
Serial Monitor Output (average of about 20 readings for each ‘test’)
Apparent IRMS Calibration
Power Number (in sketch)
1500 Watt Heater 485.72 3.94 111.1
90 Watt Heating pad 39.16 0.31 111.1
50 Wat Heating Pad 19.8 0.16 111.1
No load 8.77 0.07 111.1
1500 Watt Heater 1827 14.85 375
90 Watt Heating pad 132 1.07 375
50 Wat Heating Pad 68.3 0.55 375
No load 28.44 0.23 375
1500 Watt Heater 1515 12.32 360
90 Watt Heating pad 127 1.03 360
50 Wat Heating Pad 61.6 0.501 360
No load 26.97 0.21 360
1500 Watt Heater 1473 11.98 350
90 Watt Heating pad 123.3 1 350
50 Wat Heating Pad 59.34 0.48 350
No load 26.64 0.21 350
1500 Watt Heater 1269 10.31 300
90 Watt Heating pad 105 0.85 300
50 Wat Heating Pad 54 0.44 300
No load 23.58 0.19 300
Note: The values of each device are only what is printed on thee device, so not proven as accurate.