Required help with timed circuit breaker/timer circuit

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Thread Starter


Joined Jul 22, 2011

Im designing a circuit for electronic gear shifting in a car, using gear shift paddles behind the steering wheel. When the paddle is pulled by the driver, it closes a button behind it and this drives a relay to allow power through to the gear shifting solenoid. The circuit diagram can be seen here;

The problem is that if the driver holds down the button for too long then it will burn out the solenoid. The solenoid draws about 40-50A instantaneously when the button is pressed(paddle is pulled). I want to implement a timed circuit where the driver can hold down the button for as long as he/she wants but the circuit will open after a set time so the solenoid isnt damaged. Also as soon as the button is released the circuit resets to its original state ready for the next button push (gear change) - for example if I set the circuit to open after 1 second of the button being held, yet the driver only holds it for 0.5 seconds and then releases, then it will reset at 0.5 seconds. Yet if the driver holds it for 2 seconds, it will reset at the preset time of 1 second.

I have been dabbling with 555 ICs and looked at capacitor/transistor setups but havent found any tutorials that meet my needs. I have good amateur experience with electronics but have never had any experienced with timed circuits.

Any help would be much appreciated cheers.


Joined Apr 5, 2008

I am closing this thread as it violates AAC policy and/or safety issues.

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