What is the best way to measure currents in the range of 50-60 amps?

Question

I’m working on a single phase inverter which drives a single phase AC motor. I want to measure the load current which I guess is in the range of 50 to 60 amps. which way do you suggest me to do ; shunt resistor, Hall effect transducer,current transformer or ... . price and accuracy is important . thanks

Answer 1

In case it is alternating current, I would suggest using a current step-down transformer, like this one. This particular device can transform 150A to 5A, with accuracy class 1 according to IEC 61869-1 (ratio error 1% at rated current). These devices are specifically made for current measurement in electrical installations.

Answer 2

How about two squares of copper foil, side-by-side so the temperatures are the same.

One square is 1" on a side, to handle the 50 amps. Use Kelvin sensing. The resistance, 0.0005 ohms, times I = 50, produces 25 milliVolts. Some ADCs have 1uV or 2uV (microvolt) quanta, and no amplification is needed; you will have 10,000 quanta resolution.

The other square is 1mm on a side, scaled by 100 squares; resistance will be 0.0005 ohms (500 microOhms) * 100, or 50 milliOhms. Run 1mA through the 1X100 foil resistor, and use the 0.050v to calibrate that 22bit ADC. Use the MCU to compute ratio of ONE_SQUARE to 100_SQUARES, with automatic temperature compensation of the copper foil's resistance: 0.4% per degree.

Ensure there is a plane UNDER the two resistors, so their temperatures are tracking.

Answer 3

I have had success using an ACS758 Hall Effect Sensor. It's no longer recommended for new designs but Allegro have an alternative. The ACS758 is sensitive enough to measure as little as 11ma (depending on sample speed). and up to 100A bi directionally, though you'll need quite a sensitive ADC to measure 11ma steps (0.275mV). There is an evaluation board design in the datasheet, a similar version of which is available online.

Futhermore there are some DIY versions around the web .

Be careful buying the chip online, except from reputable retailers. I have purchased a few from ebay and they've all been fakes. There was no issue with the ones I purchased from RS.

These hall effect sensors have ultra low power loss (100 μΩ resistance) and galvanically isolate your sensing from the circuit under measurement.

They are very simple to connect

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This Application Note discusses the use of Hall Effect Sensors in Inverters.