As this is my first post, welcome to all users.
At university I have to make an ammeter design on any microcontroller, I decided to use arduino. The task of this device will be to measure the quiescent current in the car with data storage on the SD card. The problem I am struggling with is what current sensor to use, a shunt? Measuring sensor ACS7XX? LEM sensors? The assumption is that after switching on the ignition in the car, the battery current sometimes increases up to 100A, and the quiescent current is calculated in milliamperes. The requirement that I have from the project leader is obtaining accuracy at the level of min. 5mA. The system will use a 16bit A / D converter to increase the measuring range.
Which measurement system (shunt, sensors) should be used that meets the above requirement, i.e. 100A flow capacity, 5mA measurement accuracy?
Any suggestions?
Your project depends a lot on which car your are using. Modern automobiles with many computers controlling systems already monitor the battery current by inserting a shunt or other device between the battery terminal and the automobile frame. Inserting another shunt will effect the existing sensor and may cause trouble for the car computer.
Paul
My father has been working as an electronics engineer on BMW for 20 years.
It gives me advice.
It is possible to safely measure the quiescent current
so as not to interfere with existing car systems.
I am looking for how to solve a measurement with high accuracy and a wide range
Szymon
Bibczok:
My father has been working as an electronics engineer on BMW for 20 years.
It gives me advice.
It is possible to safely measure the quiescent current
so as not to interfere with existing car systems.
I am looking for how to solve a measurement with high accuracy and a wide rangeSzymon
I guess your father is not willing to tell you how to measure the current with high accuracy and wide range.
BUT! How will you be able to determine if your accuracy is what you want to achieve?
Paul
I have access to a certified multimeter which I will be able to check accuracy 
Bibczok:
As this is my first post, welcome to all users.
At university I have to make an ammeter design on any microcontroller, I decided to use arduino. The task of this device will be to measure the quiescent current in the car with data storage on the SD card. The problem I am struggling with is what current sensor to use, a shunt? Measuring sensor ACS7XX? LEM sensors? The assumption is that after switching on the ignition in the car, the battery current sometimes increases up to 100A, and the quiescent current is calculated in milliamperes. The requirement that I have from the project leader is obtaining accuracy at the level of min. 5mA. The system will use a 16bit A / D converter to increase the measuring range.
Which measurement system (shunt, sensors) should be used that meets the above requirement, i.e. 100A flow capacity, 5mA measurement accuracy?
Any suggestions?
Firstly the starter motor circuit is separate with much thicker wires, if you want to just measure the rest of the consumption you might not need nearly so much.
Hall sensors will not have a big dynamic range or great accuracy - so it needs to be a shunt I think. One approach is to use a section of the battery positive wire as a shunt, sampling the voltage difference across it and amplifying it differentially. This will be somewhat inaccurate as temperature changes will change the resistance of the wiring, and it will self-heat at high current too.
Say the wiring is about 0.01 ohms (you'll have to measure and calibrate this of course), then 5mA produces 50µV, which will still need a high-spec opamp (CAZ style perhaps) to amplify accurately.
Try an 16-bit INA226.
Leo..
For wide dynamic range I would use a dual high current schottky diode as the shunt. One diode is the shunt, with a logarithmic output voltage, the other is used to (crudely) temperature-compensate the active one.
A power schottky might show 0.2V for 10mA and 0.4V for 10A, making measurements over a wide dynamic range possible, although with only moderate accuracy. The voltage drop is modest compared to 12V.
You can combine a resistor shunt with this too (parallel), so that at low currents the resistor takes over with nice linear response.