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I'm designing an electrolysis machine controlled by an ESP8266 that also monitors the current and voltage of the electrodes with an INA226. There are two separates power supplies, 3.3 V, 1 A power supply for ESP8266 and 7.5 V, 70 A for the electrolysis machine. In order for the INA226 to measure the voltage of the electrodes it needs to share the same ground with the electrolysis machine.

schematic

simulate this circuit – Schematic created using CircuitLab

Will there be any issues sharing the same ground with the high current circuit? I understand that in theory it shouldn't be a problem but in a practical application will there be any negative effects such as leakage or noise cause by the high current? The ESP8266 is very sensitive and needs a stable power supply.

Also, will there be any difference in sharing the ground after or before the shunt? To measure the voltage of the electrodes ideally is to position the ground closer to the electrodes but that may cause a difference in the voltage between the two grounds.

PS: Both power supplies are SMPS that are powered by the same AC source.

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  • \$\begingroup\$ This is a good question. It can be tricky to get this right. Please note that the INA226 does not need to have its sense pin connected to GND. The examples in the datasheet show the shunt on the high side (which would be the 7.5V supply in your case). Also, the shunt will dissipate 2.5W at 70A. And running 70A on a PCB will require heavy copper indeed. \$\endgroup\$
    – user57037
    Commented May 16, 2020 at 18:53
  • \$\begingroup\$ @mkeith If not mistaken placing the shunt on the high side or low side won't make a significant difference in this case since the INA226 can measure either. For the 70A, the shunt is a high current shunt capable of handling 100A and the electrolysis machine is connected to the power supply directly through thick cables and not on a PCB. \$\endgroup\$
    – Max
    Commented May 16, 2020 at 19:09
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    \$\begingroup\$ In that case, there is very little problem. The high current path is completely outside the PCB. But don't just connect the shunt - side to PCB GND. Route the signal back to In- like an independent signal. This is called a "Kelvin Connection." Also, use two dedicated twisted pairs... one for 7.5V and one for the current sense shunt. As far as high side vs low side, it is your choice I guess. Just make sure there are no unexpected GND current pathways that allow current to flow around the shunt (for example protective earth GND schemes...) \$\endgroup\$
    – user57037
    Commented May 16, 2020 at 19:21

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