Hi all,

Looking for a simple way to put a timer on a 12V DC circuit for an automotive application (so prob more like 13-14V). Currently I have a small 12V DC motor that opens and closes an exhaust valve. I have it wired to a DPDT illuminated 7 pin rocker switch that simply reverses polarity of the motor depending whether it's in the up or down position, like a winch control. When it's in the up position, The valve is open and a red LED is lit on the upper part of the switch, and when it's flipped down, the valve closes and a green LED illuminates the bottom part.

The problem is it only takes two to three seconds to open or close the valve, and then the motor is under constant load at failure trying to hold it open or closed (it doesn't need to). What I hope to accomplish is to be able to throw the switch (non-momentary) to change the position of the valve, and have it behave as a momentary switch for 5 seconds or so each time it is thrown, supplying power in the correct polarity to the motor long enough for the valve to open or close, and then cut power to the motor, but the switch stays in the same position and illuminated until it's flipped again. Make sense?

I have enough basic knowledge of circuitry to be able to see how I could accomplish this using an Arduino board, but that would require stepping down the input signal from 12V to 5V, then using the 5V output signal from the Arduino to activate a 12V relay to the motor for 5000 ms or whatever, but I'm hoping somebody else can see a much easier way (maybe transistors?). I do have most basic electronics tools at my disposal and am pretty good at following instructions (though my wife might disagree)...

Thanks!

 

You want a relay that can be activated by Arduino, you want a low signal relay. Low signal relays.

 

The problem is it only takes two to three seconds to open or close the valve, and then the motor is under constant load at failure trying to hold it open or closed (it doesn't need to).

Use a center OFF DPDT rocker switch like This.

 

You want a relay that can be activated by Arduino, you want a low signal relay. Low signal relays.

I have a low voltage relay and could go that route, but as I said in the OP, I was hoping for something simpler that could just use the existing 12V supply, like maybe some combination of transistors and/or capacitors.

 

I have a low voltage relay and could go that route, but as I said in the OP, I was hoping for something simpler that could just use the existing 12V supply, like maybe some combination of transistors and/or capacitors.

Circuit using a relay and mosfet transistor Q1.
The schematic inside the gray outline represents the DPDT switch wiring.
The circuit consist of two separate timing sections that close the relay contacts for appx 5 seconds to complete the motor connection.

 

Use a center OFF DPDT rocker switch like This.

Good thought, but that's not the functionality I want unfortunately, and I already have a custom switch with custom faceplate made for this application. Switch has to be a 2 position (ON-ON) and needs to stay in position with the proper LED illuminated. It wouldn't have the right look or feel I want if the switch is momentary or if you have to manually make it momentary (as the ON-OFF-ON would).

It works just as intended when wired as shown in the pic, but leaving the motor under constant load like that all the time can't be good for it. All I want is to power the motor for a few seconds in the proper direction each time the switch is flipped, but maintain the physical switch position and illumination to indicate the status of the valve.

 

You can insert a N-ch mosfets to your DPDT switch with RC timing circuit.

The 47uF * 100k gives you motor run time about 4.7sec.


This one is more reliable because the first capacitor discharge is not dependent on second capacitor charge (and vice versa):

 

Circuit using a relay and mosfet transistor Q1.
The schematic inside the gray outline represents the DPDT switch wiring.
The circuit consist of two separate timing sections that close the relay contacts for appx 5 seconds to complete the motor connection.
View attachment 342649

This looks like it might do it... So where would the leads to the motor be? Connected to RL1 (at +12V and Gnd in the schematic)? Thanks for this BTW!

Edit: Nvm, I see the motor in there now.

 

Edit: Nvm, I see the motor in there now.

How do you have the motor wired currently?

 

I see the connections like this:

 

Below is the LTspice sim of Michal Podmanický's circuit in Post #7 for the two positions of the SW1 DPDT switch:
The motor stays powered for about 5 seconds (bottom traces) when the switch changes position.