There are two basic types of magnetic hall sensors. One is a switch type like what
you looked at, and the other is a linear type which puts out a voltage proportional
to the magnetic field strength.
The switch type have set switch points, and you have to have a signal and
core combination that can take advantage of the switch points.
The linear type have a continously variable output, so you can use an external
ic comparator to trip when needed, which makes it a bit easier to adjust.
The range of a device say for 1 amp to 60 amps could mean for one device
that it works within that range and doesnt work outside that range,
but for another device works within that range and blows out above that
range. It depends on the actual part being used. If you dont know, use
the 60 amps as an absolute max and dont go above that.
2 amps can be detected in a conductor using a magnetic core like you seem to
be considering. It's also possible to wind the wire around the core several
times (rather than just once through the center) to increase the apparent
current level because this increases the magnetic excitation and thus
produces a more intense magnetic field. The wire goes in one side, out the
other, and then back in the other side and out the other again, and this
constitutes two turns (instead of just one). The field increases and so
the hall detector will be able to detect the presence of current more
easily provided the core does not saturate. If you had a magnetomotive
force of 2 amps with 2 amps and one pass through the center, then
you end up with 4 amps with 2 amps and two passes through the center,
and 6 amps with 2 amps and three passes (three turns) through the
center, etc., so the more turns the more field as long as the core
doesnt saturate. With an air gap to fit the sensor it probably wont
saturate anyway, but if it does by then there should be enough field
to be detected by the hall device.
2 amps also isnt that high, and 12 gauge wire is an overkill. You could
for example wind the core with 16 gauge, then connect the 12 gauge to
the 16 gauge. In other words, you make a little inductor with an air
gap with several turns of 16 ga wire on it and then connect it to
the 12 ga circuit wire.
Experimentation depends on what device you you choose...HE switch or
HE linear. With the switch device you have to keep adding turns until
you get the device to switch with the desired dc current level.
With the linear, you have to get a decent change in output voltage
with the desired current level. In both cases you measure dc
current and adjust something until you get a switch transition to
occur.
You also have to consider your desired current level, is it really
2 amps or does it also have to work down to 1.5 amps?
With AC instead of DC, the output will be pulsing as someone mentioned,
so you'll have to use a detector of some sort like a peak detector
to average the output of the hall sensor or the comparator.
The permeability of the core affects the operation too, and usually the
higher the better, but sometimes even a small metal object like one
of those black paper clips (binder clips) with the wire run through
the opening and the hall effect device placed between the bind faces
of the clip. The metal of the clip amplifies the field and the
field is concentrated in the metal and follows the metal path, and
the hall sensor, being in the magnetic path, detects the field.
A small coil alone could work too. The hall sensor is placed
in the middle of the coils, as if to separate the coil into
two coils with the sensor in the center of the two. The more
turns the higher the magnetic field and the easier it is for
the sensor to pick this up.
Two steel nails, one inserted inside each coil, would help to
amplify the field also.
The hall sensor has to be oriented correctly however, with
the poles aligned with the axis of the coils.
For cutting the core in half, it is possible, but you probably need
a Dremel drill and a cut off wheel. A diamond wheel works best.
The cores are very hard. You can also wrap the core in a rag
and clamp it in a vice and turn the vice until it just cracks. You'll
get around 4 pieces that you can glue back together to make two
halves. This is a little messy but works. Using super glue the
gaps dont amount to very much once glued back together,
but then you'll be inserting the sensor anyway.
If you intend to experiment this way it's best to purchase
a few extra cores.
They do make very sensitive HE sensors too, but they may
not fit your budget. They might be sensitive enough to
simply tape to the wire and measure the output.