First post here, please excuse my electronic ignorance.
I am trying to design a 12V circuit to open and close the nitrous bottle on my race car. Here are the specifics of the design: It needs to
- open the bottle (CW motor) when the SPST switch is in the on position, stopping when it reaches a limit switch to prevent the motor from burning up.
- close the bottle (CCW motor) when switched to "off", again stopping on a limit switch.
The reason for the SPST switch is that the rest of the nitrous controls on the panel are the same type of switch and I don't want to have one oddball switch that doesn't match. I would prefer to use relays to prevent running the motor current through the switch(es), and have obtained 2 automotive grade SPDT relays for this purpose. I found circuits for a SPDT activation switch, and another for continuous automatic reversing, but I need it to stop when the bottle is open, and not reverse until the switch is turned off. I don't mind adding components as long as they are automotive-rated. The no-load current for the gear-driven motor is 230 mA.
Am I overbuilding it to use relays?
Best Answer
To get the reversing action you want, you need a DPDT switch somewhere, either on your panel or in a relay. I'd guess wiring is easier if it's a relay, and you have the advantage of your panel switches all being the same, as you desire.
Would this circuit suit your application?
Explanation: with switch S1 open, relay is unenergised, and with motor in mid-position limit switches S2 and S3 are closed. Thus current flows from +ve supply through relay contacts P1 through S2, through motor, P2 and GND: Motor turns counterclockwise and eventually hits limit switch S2 which breaks the circuit. When S1 is activated, relay moves to energised state and current flows from +ve supply through P1 to S3, bottom of motor, P2, then GND: motor turns clockwise until limit switch S3 is engaged.
Note that for inductive loads such as the relay and motor, you need to pay attention to whether you need flyback diodes and whether any sparking is entirely contained, as obviously sparks and your various car fuels are explosive. Modified race cars are definitely at your own risk!