See the picture above, this is the simplest and easiest to understand. Originally, I wanted to use digital circuit, which is also very simple and reliable, but it is not easy to understand.

R2\C2\Q2 and R 1\C 1\Q 1 form two groups of RC charging delay circuits respectively, R2\C2\Q 1 is to disconnect the circuit between A and B, and the delay time can be adjusted by adjusting R2 (R is about1. R 1\C 1\Q 1 is the delayed turn-off of Q2, so adjust this time constant a little (larger than Q2 group 1-2 seconds).

Triode can be selected from commonly used 90 13. If the relay consumes a lot of power, the triode should be replaced with a bigger one.

In order to make the next startup delay accurate, a resistor with large resistance can be connected in parallel with C 1 and C2 to discharge C 1\C2 when the power supply is disconnected. If the back electromotive force generated when the relay is disconnected affects the safety of the device, a diode can be connected in parallel in the coil, and pay attention to the polarity.