Pekka asked me to start a thread about hall effect sensors and their use on measuring current.
Well, these sensors can be used to measure current. Actually they do not measure electrical current but the magnetic field that the current creates.
If You pass current through a wire there is a magnetic field created around the wire in 90 degree angle to the direction of the current. If it is a wire then the magnetic field takes a cylinder form around the wire.
In order to measure this magnetic field the sensor has to be in 90 degree angle with the magnetic field to be measure so that the magnetic field goes through the sensor.
Luckily the hall effect sensors are quite small so placing those nearby the wire might give acceptable result.
However, the magnetic field is rather weak as compared to the sensitivity of the sensor. To overcome this issue a concentrator can be used. Basically it is tube made of some ferromagnetic materiall having a slot on one side. The sensor is then placed in that slot.
I have made a solar panel current sensing equipment for 12 solar panels where the current of each panel was measured separately. Ended up using hall effect sensors with concentrators made from mild steel tube. These sensors were then equipped with microcontrollers and finally all of the communicated with a master device using I2C.
Sensor data sheet