FET Current limiter 30A and overload detection
That won't work for multiple reasons.

1) You can't get JFETs that handle much more than 10 mA

2) If you current limit 30 A overload on a 12 V system, you'll dissipate 360 W of power and quickly fail your circuit

3) Most systems like this limit current for a short time (&lt; 1 ms), then turn off completely, and perhaps retry at intervals. If you turn off too quickly, the voltage spike from the inductance of the will will also damage your circuit.

Take a look at this - http://www.nxp.com/files/training/doc/dwf/DWF13_AMF_AUT_T1023.pdf and look for eXtreme Switches to see if any of those would work for you.