Per the Gargraves Uncoupling Section Instructions,
1)"Connect the two stripped leads to a 14 to 18 volt AC power source."
2)"Note: Do not apply power to this magnet for more tha a few seconds at a time
to avoid overheating the magnet."
If cars do not uncouple at maximum 18 volts AC, check the couplers, distance from uncoupler thumbtack/machined stem diecast trucks should be parallel to and inline with the center of the track and uncoupler, if no uncoupling, check the centering of the knuckle and coupler housing, broken springs plastic tang or spring, will prevent the knuckle from opening. I corrected a number of car couplers, they operate generally between 14 and 16 volts AC.