| Electronics > Projects, Designs, and Technical Stuff |
| INA193 High side current sensing, ground problem? |
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| Atom:
hello! i'm working on a "power meter" that should be able to measure current and voltage of a dc power source, but i have a couple of problems 1- The ina193 and the load are connected to 2 isolated power supply, the DO NOT share a ground, if i try to measure the current its spot on. almost perfect, if i connect the grounds togheter the output voltage of the ina 193 is shifted by 20 to 30mV upwards, note that i'm using a switchmode power supply to supply the load so i thought it could be noise from the switchmode---it isn't, i've checked whit the oscilloscope and there wasn't any switching noise... that's STRANGE :-BROKE 2. i started measuring the current with an ads1115 and an arduino to serial monitor...everything good, so now i wanted to get the voltage on the load, so i added the resistive divider 39k and 3k for a maximum input voltage of 70v .... 70v in 5 out so the adc could read it. 3 the resistive divider shares a commoun ground with the load :-/O thats obvius, but if i want to measure voltage (from the divider) and current from the INA193 they HAVE TO share ground since i have only one adc :-/O 4now heres when the magic smoke escaped i connected the 2 ground togheter (1.5Kohm load ) and i started to increase the voltage from about to 5v to 40v and when i was almost at 40V the ina193 burned ...waited a few seconds and the 5V regulator started burning too (i'think it was burning because of the INA193 failed shorth circuited). :palm: 5 soldered new INA 193 and AMS1117 5.0v now whitout the 2 grounds connected i can measure current and voltage perfectly (with the multimeter not the adc). if i connect the 2 f*****g ground togheter the amps measurment goes up of about 500mv .... EXAMPLE SMPS SET TO CC 1A LOAD 4.7OHM (it is in CC mode so 4.7Vout from the SMPS) i attach the load and i can read 2V from the INA193 that's good 1A=2V because 0.1ohm(shunt)*1A*20(amp of INA193)= 2V i go to read the voltage from the divider ..everything good , THE GROUND ARE STILL NOT CONNECTED if i try to connect the 2 grounds the Voltage of the SMPS jumps to 5.5V ....now something is backfeeding voltage into the SMPS :palm: but i can see what it is, has anybody some solution? here's the schematics |
| Marco:
The polarity of Vcc is wrong? Hard to see how you're burning up the INA otherwise. |
| Atom:
nop, the polarity is good ... i've done further testing, When Vcc is lower than 5v so for example VCC = 3V if i connect the ground togheter i get an increased output voltage from the ina 193, and if a put an ammeter in series with the groun lead i see 500ma or even 1 amp flowing from ground of psu1 to ground of psu 2...WTF.. i'll do a video so its easier to understand. |
| Jeroen3:
Do you short the grounds at the supply or trough your board? Are the supplies properly floating? In any case, if you connect a floating supply on the shunt of the INA, it will fry itself. That would have been ~115 Vac common mode, not 80Vdc. |
| Atom:
--- Quote from: Jeroen3 on August 14, 2019, 06:30:47 pm ---Do you short the grounds at the supply or trough your board? Are the supplies properly floating? In any case, if you connect a floating supply on the shunt of the INA, it will fry itself. That would have been ~115 Vac common mode, not 80Vdc. --- End quote --- i short them by connecting them with a cable at the supply , i'll do a video. |
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