Good day.

After spending some time in the search section I didn't find any leads, so I ask for your help.

I have a simple circuit with lipo battery, motor and a microswitch.
I want to design a second, monostable circuit that will detect current in the main circuit and activate a 5v motor, and after the main circuit cuts off, run the 5v motor for 4 more seconds.
If the main circuit re-engeges during the 4 second period, the 5v motor should continue to run until main circuit disengages again, and again run for 4 more seconds.
The second circuit is powered by a 9v battery and a 7805 voltage regulator.
The main circuit has a very large inrush current, around 90A+, with variable voltage of between 11v and 15v.

I tried to make a one-shot 555 circuit with no luck, and have no idea how to tap into high current circuit.

So I ask for your advice, can anyone assist?

 

Start by posting a circuit diagram of what you have, what inrush current supply is it, to detect current you need a series resistor with op amp sensor, or transistor or current transformer.

 

Do you require electrical isolation between the two circuits? Does the first motor have a switch that's accessible as a trigger for the second motor?