Hi everyone,
I have spend a large part of this afternoon browsing through the posts on this site. I am very impressed with the diversity of problems and solutions that arrive here. I have built circuits from plans and kits in the past, but I have only limited understanding of the operation of transistors and logic chips.
The reason for the post: I have a 12V motor with a lever connected to it so that it will turn a partial turn in one direction and stop when a limit switch opens. A single pole switch energizes a DPDT relay to cause it to turn clockwise. When the single pole switch is opened the relay is de-energized and the contacts reverse the polarity to the motor and it turns counterclockwise until stopped by a limit switch. The motor draws 1.4 A at 12 V when stalled, less when operating for a maximum of 0.2s.
The problem: I want to build a small delay circuit to prevent motor burnout if there is an obstruction that prevents the motor from completing its movement to actuate the limit switch.
My idea was a simple FET (or MOSFET or 1.5A transistor), a capacitor and a resistor that would allow current to flow from the time the relay closes or opens for only about 0.5 s (not a critical time) and then would turn off to prevent motor burnout. 0.2 s is sufficient time to allow the normal movement of the motor. I hope that there is an elegant 'one wire in one out' design that could be put in series with the limit switch. If a problem prevents the limit switch from turning off the power the circuit will.
I haven't found anything on this site or others specifically like this where the on signal (12V) starts the timer that then opens that circuit.
Thank you in advance for your help.
Dale
I have spend a large part of this afternoon browsing through the posts on this site. I am very impressed with the diversity of problems and solutions that arrive here. I have built circuits from plans and kits in the past, but I have only limited understanding of the operation of transistors and logic chips.
The reason for the post: I have a 12V motor with a lever connected to it so that it will turn a partial turn in one direction and stop when a limit switch opens. A single pole switch energizes a DPDT relay to cause it to turn clockwise. When the single pole switch is opened the relay is de-energized and the contacts reverse the polarity to the motor and it turns counterclockwise until stopped by a limit switch. The motor draws 1.4 A at 12 V when stalled, less when operating for a maximum of 0.2s.
The problem: I want to build a small delay circuit to prevent motor burnout if there is an obstruction that prevents the motor from completing its movement to actuate the limit switch.
My idea was a simple FET (or MOSFET or 1.5A transistor), a capacitor and a resistor that would allow current to flow from the time the relay closes or opens for only about 0.5 s (not a critical time) and then would turn off to prevent motor burnout. 0.2 s is sufficient time to allow the normal movement of the motor. I hope that there is an elegant 'one wire in one out' design that could be put in series with the limit switch. If a problem prevents the limit switch from turning off the power the circuit will.
I haven't found anything on this site or others specifically like this where the on signal (12V) starts the timer that then opens that circuit.
Thank you in advance for your help.
Dale