I'm building an Arduino circuit to detect/limit the maximum charging current to a camera flash.

I decided to use an INA219 breakaout board, which comes with a R100 resistor as a shunt so it should allow measurements of 3.2A maximum.

Before assembling the circuit with the Arduino, I decided to test the sensor to see if it would allow instant high currents to pass through it's VIN+ and VIN- terminals, without connecting any supply to it, nor SDA and SCL lines.

enter image description here

What happened is that it limited my bench power supply source to 300mA maximum. The flash charged, but slowly.

If I plugged my flash terminals directly to the power supply, it chaarges faster, with initial peak currents close to 3A, the way I need it.

enter image description here

I then tried connecting just the 5V VCC and GND to the INA219 breakout board, again without wiring SCL and SDA to an Arduino. Again only 300mA of current were drawn by my bench supply, and the charging of the flash was still slow.

Why is that happening? Do I need to fully connect it to an Arduino for the INA219 to allow more current to flow through its terminals?

Edit1: Inside the flash's 3V battery compartment I soldered a DC DC buck converter that converts the 8.2V to 3V, allowing 3A maximum current.

INA219 Datasheet

  • 1
    \$\begingroup\$ This has nothing to do with the INA219. The only thing your circuit will "see" is the shunt resistor. And with 0.1 \$\Omega\$ the voltage drop is only 300 mV. So it probably is something with your wiring or the Master Flash can not charge with a voltage below 8.1V. \$\endgroup\$
    – jusaca
    Mar 23, 2021 at 13:18
  • \$\begingroup\$ Do you have specs what the master flash is expecting as minimum input voltage? \$\endgroup\$
    – jusaca
    Mar 23, 2021 at 13:20
  • \$\begingroup\$ When you use an ohmmeter to read the resistance from Vin+ to - what do you see? You should see the value of the shunt resistor (.1 ohms) at most. \$\endgroup\$
    – BobT
    Mar 23, 2021 at 13:28
  • \$\begingroup\$ Is a solderless breadboard involved? These have huge contact resistance. \$\endgroup\$
    – bobflux
    Mar 23, 2021 at 13:40
  • \$\begingroup\$ @jusaca Will check the wiring, but I changed it in different ways and it always allows only 290 - 300mA max... The flash uses 3V, but I have a DC-DC converter inside it so I works normally converting the 8.1V to 3V. This converter allows 3A of current to flow. \$\endgroup\$
    – Rodrigo
    Mar 23, 2021 at 13:59

1 Answer 1


Solved. A cable I was using for testing was too thin to allow more current to pass. Changing cables make it work perfectly!


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