If you want to measure current using an Arduino, there are several
sensors you can choose from. You will either want to measure
very high current for kW power devices (e.g a heater) or lower current
for battery charge testing etc.
There are really only two measurement methods:
The first method is suitable for low level currents as the voltage
drop will be insignificant compared to the supplied voltage whereas the
second method is suitable for very high currents (1A ~ ) ~50A ~ 200A.
You can get a fairly good reading at 1A but below this the inherent
hall noise won't let you see the data very well (see the tests in the
link below) - hence it is only very good for high current operation.
You could setup a simple low voltage system measuring the voltage
drop across a 0.1R resistor and amplifying this using a precision opamp
but it is more convenient to use the available devices (that do exactly
the same thing for less effort)...
The INA219 is a high side, voltage drop device that can measure up to 3.2A but can be configured for 10~15A (if you do some design work). On a breakout board it measures up to 3.2A within a 26V supply.
As a bonus it also measures the supply voltage a the high side of the circuit so you can calculate power usage easily.
You can select the voltage drop resistor but the standard fitted part
is 0.1R giving a resolution of 100uA which is not too shabby!
The great thing about this part is that it drops into virtually any
system providing an I2C interface for easy reading of the current
flowing in your circuit.
Click here to goto the INA219 page.
As with most hall effect devices the output of the ACS758 is
a voltage proportional to the magnetic field induced by the current, and
here the value is 40mV per Ampere. That means you need and ADC to read
the value output by this sensor.
This device can measure up to ±50A in the presence of 700Vrms.
Calculation show that it can measure ~8kW in a 240Vrms system (~35A - the
value is lower as the 50A is a peak value whereas the 35A is an RMS
value). Anyway 8kW is quite a good achievement!
From the image below you can see it is expecting some heavy current from the chunky connector tabs!
Click here to goto the ACS758 page.
The ACS712 is
similar to the ACS758 in that it is a hall effect device but it is
designed lower current operation; ±5A, ±20A, ±30A (depending on
the chip version used).
The advantage of using this device is that it is packaged in a tiny S08 case so its far smaller than the ACS758.
The reason you would use it in favour of the the INA219 is that the measurement path has a resistance of 1.2mOhms. If you use the standard INA219 you usually use the 0.1Ohm resistance for measurement.
It means the ACS712 does not drop any voltage (minuscule anyway)
while measuring current and that means there is no power dissipated in
the chip, so no heating - which could be important for encased designs
The only problem will be resolution and magnetic noise inherent in
hall effect devices. The theoretical smallest current measurement is
Click here to goto the ACS712 page.
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