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Reading high currents on PCB: Hall effect sensor vs shunt resistor

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fourtytwo42:
Your problem is using a ratiometric sensor with an absolute ADC. Simple solution use the internal Arduino ratiometric ADC's that you dont like for the current sensors and use the absolute ADC for whatever you are currently using the internal Arduino ADC's for.

The supply voltage for the sensors and Arduino must be exactly the same, ie +5V from the same regulator for both and set the Arduino reference to Vcc.

As for the offset that simply means you have one bit less resolution than you thought you had. If you want to increase gain use a r-r i/o op-amp.

As someone else said you can easily take care of fixed offsets (that will also be present in the ADC) by a calibration period with no load.

Jeroen3:

--- Quote from: superKris on May 05, 2020, 03:46:45 pm ---For my application i dont mind a few % deviation on full scale, but i do need 0A to be displayed as 0A (or at least close to this)

--- End quote ---
Add deadband on the visualization. Those ACS sensors aren't that amazing. They're mostly easy.
You might get magnetic offset in the future not reading zero correctly again.

superKris:
So i think i now realized i can not use the differential input with the VCC. I really need the voltage divider you guys are talking about, and it needs to be adjustable by a adjustable resistor, or i can adjust in software, but there will be mostly theoretical gain error.

Or i need a different ACD. Can you guys suggest one that:
- Has a external reffrence
- Has at least 4 inputs
- At least 11 bits output
- 12C interface
- And a reasonable Arduino library


--- Quote from: Miyuki on May 06, 2020, 07:46:51 am ---
--- Quote from: superKris on May 05, 2020, 03:46:45 pm ---...
My main problem is with the bidirectional behavior of the ACS hall sensors. The zero current output of these is 0,5 * VCC.
...

--- End quote ---

They used to have unidirectional variants of them if you need to measure just to one polarity

--- End quote ---

It might indeed help, but these sensors are very widely available and that also makes them cheaper. There is also some advantage in them bering bidirectional, although i could easily do without.


--- Quote from: fourtytwo42 on May 06, 2020, 08:52:41 am ---Your problem is using a ratiometric sensor with an absolute ADC. Simple solution use the internal Arduino ratiometric ADC's that you dont like for the current sensors and use the absolute ADC for whatever you are currently using the internal Arduino ADC's for.

The supply voltage for the sensors and Arduino must be exactly the same, ie +5V from the same regulator for both and set the Arduino reference to Vcc.

As for the offset that simply means you have one bit less resolution than you thought you had. If you want to increase gain use a r-r i/o op-amp.

As someone else said you can easily take care of fixed offsets (that will also be present in the ADC) by a calibration period with no load.

--- End quote ---

Thanks for your input! the reason i dont like the Arduino ACD's is that these are only 10 bits, and in previous project i really did like their stability. 10 bit would be a resolution of 50 and 125mA with a less than stable LSB.


--- Quote from: Jeroen3 on May 06, 2020, 09:51:37 am ---
--- Quote from: superKris on May 05, 2020, 03:46:45 pm ---For my application i dont mind a few % deviation on full scale, but i do need 0A to be displayed as 0A (or at least close to this)

--- End quote ---
Add deadband on the visualization. Those ACS sensors aren't that amazing. They're mostly easy.
You might get magnetic offset in the future not reading zero correctly again.


--- End quote ---

For my application i do wanna it to show currents of 100mA. 50 or 25mA would be even better.

But you are right that these ACS sensors are far from perfect. The ACS758 inst that cheap either, so that is why i'm considering to take these out and switch to shunts with a INA219. I dont really know how to with with PCB shunt, and i can think of some disadvantages like i wrote in my first post.


So generally speaking: What method would you guys prefer for measuring currents up to 50A/12V on a PCB?
 

David Hess:

--- Quote from: fourtytwo42 on May 06, 2020, 08:52:41 am ---Your problem is using a ratiometric sensor with an absolute ADC. Simple solution use the internal Arduino ratiometric ADC's that you dont like for the current sensors and use the absolute ADC for whatever you are currently using the internal Arduino ADC's for.
--- End quote ---

The hall effect sensor he is using is not ratiometric; its gain is fixed.  What changes is its offset which is always 1/2 of the supply voltage.

fcb:
ACSxxx sensors aren't actually very good - you'll probably get within your few% though.  Zero drift will be your #1 problem to solve with anything hall based.

I'm assuming your application is DC and requires isolation - looking at your PNG then it looks like a a low voltage system (mention of accessories, chargers etc..) - in that case you could easily use current shunt shunt resistors and float the differential measurement?

Either way, I would defintley look at using shunt resistors rather than hall sensors if you want a reliable ZERO. Texas make some IC's worth looking at if your system is lower voltage DC: LMP8480, INA282 range.

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