Question on common ground causing component failures

Using Arduino Sensors
1

Currently developing a 12 volt marine/automotive system with volt meter and two different types of current monitors.

The Volt meter uses a 10M and 100M ohm voltage divider with Adriano analogRead. One of the current sensors uses Pololu ASC11EX -31A to +31A with analogRead. Code and circuit for these first two circuits are based on https://www.instructables.com/id/DIY-Amp-Hour-Meter-Arduino/ .

The second current sensor circuit utilizes a voltage difference shunt and 16 bit ADS. This third circuit code and circuit is based on Arduino Your Home & Environment: Reading a Current Shunt with an Arduino .

The voltage divider circuit was bench tested with the appropriate responses. Then the current sensor was bench tested with the appropriate responses.

However, when the voltage divider circuit and current sensors were tested together, numerous components failed (ASC chip fried and UNO failed to operate) when I attached the voltage divider ground wire to the common ground, See schematic.

I suspect the ADC senses the 12 volts from the shunt and somehow also senses the 12 V circuit voltage divider ground causing the overvoltage internal to the Ardunio and ADS. Also if was wondering ads.setGain(GAIN_SIXTEEN) could be responsible.

I researched common grounds but found no understandable info on this type of failure mode.

Thanks for any explanation provided to help me to resolve this problem.

Volt-current_fail.jpg
Volt-current_fail.jpg1644×979 205 KB

2

change "I suspect the ADC senses the 12 volts from the shunt "
to
"I suspect the ADS senses the 12 volts from the shunt "

3

Can't use a high-side shunt with the ADS1115.
Shunt voltages must be within the supply voltage of the ADS1115.

Currently the 12volt from the battery will flow through the input protection diodes of the ADS1115 to the power rails of the ADS1115, and destroy the ADS and/or the Arduino.
Leo..

4

You erroneously put the shunt for the ADC in the highside when it needed to be low side. You also didn't
protect the inputs to the ADC with series resistors which is always a wise precaution (unless the ADC requires
a low impedance drive).

I can't see any fuse in that circuit diagram - I hope there is one.

5

The ADS1115 also can't measure low-side if one of the shunt voltages drops below ground (negative).

There are chips that can measure voltage and current high-side, like the INA219.
But I don't think it could survive an automotive environment.
Leo..

6

Thanks for the input. Did some research on “high side” sensing and you were all correct that the ADS1115 with shunt sensor is not suitable for the high side.

I will start to look for an alternate circuit for the high side shunt. I did look into the INA chips but did not think I could work with just a plain chip and the chip installed on a breakout already had the shunt as part of the package.

I will also look into additional circuit protection (Ads115 series resistor protection and fuses).

Then again, I may just buy a marine quality battery/system monitor.

Thanks again

7

Wawa:
The ADS1115 also can't measure low-side if one of the shunt voltages drops below ground (negative).

Good point, the shared ground needs to be battery-side of the shunt. (Assuming only discharging).

There are chips that can measure voltage and current high-side, like the INA219.
But I don't think it could survivie an automotive environment.
Leo..

Yes, its 26V abs maximum, so some protection circuitry would be needed to prevent spikes getting through.