It is supposed to give impulse on relay for time determined by 555. On the other side of relay, I attach on one terminal + of 12V car battery (which I also use to supply the pcb), on the other terminal - ground. I use it to spot-weld nickel tape. It is a car relay, so it is a capable of driving high currents.
Everything is working fine when no load is applied to contact side of relay, For example relay contact closes for 0.5s. But as soon as I apply load (a very low resistance one), contact does not close for 0.5s, but it goes quickly on-off. Current does not flow through nickel tape for long enough and welding does not take place.
What might be the possible cause of this?
Because I connect power supply for welding pin by winding the copper cable around relay's contact terminal (on load side, those are also made of copper), I figured out that when high current goes through those copper wires and contact, it induces strong magnetic field (made by high current) that pushes back the contact inside of relay. Does it make any sense?