current sensing using ADC of microcontroller

[bishal]

I need a current sensor for MPPT based charge controller of max 10A current flowing.
Since the controller shouldn't be expensive, I don't want dedicated current sensors. So I have 2 alternatives:
1) Measuring voltage across Rsense using Op-amp.
2) Measuring voltage across Rsense by ADC of microcontroller.
I was wondered why no one is talking about using micro-controller for current sensing.
Upto now I plan to go for option 2. But please if there are certain things I must consider or if you have a better option, please suggest.

Bishal Paudel

[pebe]

Your proposed method should be OK provided you can afford the power loss from the current you are measuring. If you are using a micro like a PIC where you can input your choice of reference voltage, then 50mV would be about the lowest you could go, bearing in mind you would need to make Rsense to be 5milliohms, and it might be a bit difficult to make fairly accurately. It would still consume 0.5W at 10A.

You might like to consider using a Hall effect device, because it would draw no power from the current source you are measuring. A couple of turns of wire, possibly with a simple iron core, would give a magnetic field to operate the Hall device. You could use a switchable type or a linear output type, depending on whether you want to measure the current, or just switch at a given level.

[JoshMac]

Hi bishal,

I have also tried searching topics on the internet using a MPU to read current. I have tried several ways, using a shunt (essentially a resistor that has 1 or 0.1 ohm resistance to ensure it draws almost no power from the circuit) then read the voltage drop across it using an op-amp, that was ok for DC, but not very good for Ac, as the MPU dosent know what phase the AC voltage is at, at one point it could be 0amp, the next 5amps, the next 10mAh, it was pretty useless. After searching alot on the web I found a small component, called a ACS758 current sensor. Its in a very small package, and is commonly used in those energy meters you see around everywhere now. it runs off 5 volts, and gives a 3rd output proportional to the current draw, upto 50 amps. [url]http://www.ic-on-line.cn/download.php?id=1186014&pdfid=DAB05711DA59E308463E209367DE2A92&file=0117\acs752sca-050_1205582.pdf[/url] Check that address for the type that you want, remember for AC you will need a bidirectional sensor.

One of my future projects will involve putting one of these on every light or powerpoint in my house, to measure overall current of the house, also so I will be able to see how much a kids room is using, living room, etc and if all goes to plan, have central software controlling the house too, so if the motion sensor in the room dosent see motion for 10 minutes it switches off the light. Also so if a kid keeps leaving his light on, password protected software can disable his/her light.
But that is a future project, I hope to get around to it one day.

I hope this might point you in a helpful direction.
Thanks,
Josh