Introduction: 30 A. Clip-on Ammeter Circuit for Arduino

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I'm using a split core "clip on" style transformer to measure current used in my Heat Pump Water Heater. This will sync up with the three temp sensors. For the temp sensors I used DS18B20 and borrowed bits of code from Rui Sanchez at Random Nerds Tutorials to get the RTC going with an SD card to store the data. So, this ammeter will go into that board.

For my purposes I only need to know if the system is off (< 100 watts); heat pump only (400 watts) resistive element (4200 watts) or HP and RE (4600 watts). So I didn't put a lot of time into current calibration. This is the schematic only; no arduino code. I used two (single stage) OPA340 from TI. Here I use the arduino as a 5v power supply for the OpAmps.

Supplies

2) TI OPA 340

1) Arduino

1) IN4148

2) 100K resister (all resisters 1/8 ohm)

1) 10K Ω resister

1) 40K Ω resister

1) 1K Ω resister

1) 1 microfarad capacitor

1) Breadboard

*) 26 gauge solid hookup wires

1) SCT013-30 YHDC (aliexpress / amazon)

A pair of sharp cutting pliers will help form the wires.

Step 1: Wire It

make sure you have the IC orientation correct!

make sure you have grounded both Op Amps.

keep your work neat and it will turn out right the first time.

Attachments

Step 2: Test It

the coil voltage is AC

everything beyond the diode is DC

I validated the charging levels of the Tesla with a fluke clip on ammeter on the wire to the 50amp breaker.

The 100 Amp coil will work as well. Expect about 1 vac from the coil at 100 Amps and adjust R2/R1 accordingly

Step 3: Tune It

Gain = 1 + R2/R1. Substitue a pot to increase or decrease


Note that TP Coil is AC volts; everything beyond the diode is measured DC. The graph shows that the AC voltage is reduced after the first OPA and diode. The gain is in the second stage.

Step 4: Other Approaches

Another "new school" approach to doing this is using an ADC, such as this one (ADS1115 16-Bit ADC) from adafruit https://www.adafruit.com/product/1085

https://www.youtube.com/watch?v=TITtBkoaQ_s

I personally like futzing around with IC's and there is a little more flexibility in design.