# Determine max current sensed using I2C current sensor

Hi

Im choosing some current sensors to see which is most suitable, INAxxx series seem be good
But when reading their datasheet, some say max current sensed, some not.

Example INA219's one, how we calculate the max current it measures base on details shown in the document ?

Thanks much

Max current depends on the resistance value of the shunt, and the PGA gain setting of the chip.
Common INA219 breakout boards have a 0.1 ohm shunt.
That gives a range of Â±3.2Amp with a PGA of /8 (Â±320mV).

If you lower the PGA (code), range will get Â±1.6A, Â±800mA, or Â±400mA. See datasheet, page 5.
Lower range also means higher resolution (more steps per mV).

If you replace the shunt with a 0.01 ohm external shunt, then range increases to Â±32Amp.
You can usually leave the board shunt in place, and just add the external shunt.
Leo..

Wawa:
Max current depends on the resistance value of the shunt, and the PGA gain setting of the chip.
Common INA219 breakout boards have a 0.1 ohm shunt.
That gives a range of Â±3.2Amp with a PGA of /8 (Â±320mV).

If you lower the PGA (code), range will get Â±1.6A, Â±800mA, or Â±400mA. See datasheet, page 5.
Lower range also means higher resolution (more steps per mV).

If you replace the shunt with a 0.01 ohm external shunt, then range increases to Â±32Amp.
You can usually leave the board shunt in place, and just add the external shunt.
Leo..

I dont find detail about shunt resistor , but you mean 0.1 shunt value in this page ?

If the board made with an 0.1R onboard, how we add another shunt resistor to ? , i supposed the new one added in parallel ?

Power dissipation of the shunt has to be checked. 10 milliohms at 10A dissipates 1W, 5 milliohms at 20A dissipates 2W for the same sense voltage of 100mV. To dissipate only 1W in a shunt for 20A takes a 3.3 milliohm for only 66mV voltage.

At high currents practical shunt values mean very low voltages have to be accurately sensed. It gets harder to measure high currents with a shunt due to this effect. Fortunately at higher currents Hall-effect sensing gets easier. For something like 50A a hall sensor chip might be a better choice.

m4u_hoahoctro:
If the board made with an 0.1R onboard, how we add another shunt resistor to ? , i supposed the new one added in parallel ?

Yes. Just buy a shunt, and connect the two current terminals of the INA module to the two small screws.
Leo..

Max current sensed is a maximum rating which should not be exceeded. I have measured well over 100 amps using a shunt. The temperature rise of the shunt depends on many factors but size being the biggest contributor. I am using shunts in the 4" range with a 1NA219. If you want to use these devices that come as arduino shields you can just place an external shunt across the on board shunt resistor or remove that resistor. You also need to determine what sensitive you need. Range is also a big factor as it directly impacts your A/D.This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil