12 V DC Motor control circuit


I am wondering if someone can help me with a circuit. Its for a set of retractable running boards that are installed on a vehicle. The running boards have to go down when the door switch grounds, and they have to go back up when the door switch goes open. But there is one catch. There are no limit switches. The polarity of the motor is easy enough to change, but without limit switches, the circuit will have to shut off and stay off when the amperage reaches about 15 amps. The circuit will have to turn on again when the door switch changes state again. In either case, the motor will have to stay off until the state changes again. I would suggest that the initial amperage may be higher, so a timer circuit may have to be used to keep it on for the initial amp ramp up of the motor.

Please let me know if you have a solution to this. Motor run at 2 amps when running boards are open, and about 4 amps to pull them back in.




A question about force feedback motors came up recently and @lukecyca suggested one of these modules:

Note that some of them come with current sense feedback, so if you are reasonably familiar with a microcontroller, you can use that to be read by an ADC pin (analogRead in Arduino parlance).

That way you can see when your motor spikes and cut it off.

Some of them also have the benefit of having a “brake” mode, which wasn’t described in your brief if there’s a latch or not.

That all said, if this is dangerous if extended, I’d recommend having a latching system and positional feedback so you can ensure that it is stowed during movement.

Good Luck!

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Have you tried searching for the electrical modules that perform that task in vehicles? I’ve seen that feature on some large american pick-up trucks.

Why is this better than building your own?

  • It’s already enclosed in a water-tight container or the board is conformal coated to protect against moisture
  • The electrical components will be automotive grade (higher temperature ranges than commercial grade)
  • It already has a power supply able to withstand the surges present in the power supply in a vehicle
  • The connectors are most likely water-proof.

I have looked around, all the aftermarket systems that I have seen all use serial Data, most use the OBD2 connector, some require tapping into the serial data system in other spots. If there was one, I would use it! The module sits inside the vehicle so there is no problem with water intrusion. The harness is already all in place. Someone has already adapted this vehicle and installed the running boards physically on it. However it is too old to have serial data. So now its just figuring out a system that works on the analog signal. If the running boards are stuck down, its ok, they are not really in the way. So this is much more about the “cool” feature of being retraceable.

I am emailing Pololu this morning to see if they can help me. Every other avenue has been dead. I have tried electronics repair guys, and they all refer me here.

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@Suprhonda, do you have any experience with microcontrollers (arudino etc), that might be a good place to start, as you need a little bit of control logic to handle this.

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No, I was hoping I could pay someone to do that type of thing for me. I think I may have found a solution to the problem though. After researching more, I found one of the companies does in fact have a door switch option for the really early trucks. I have ordered there controller and harness, and hope to be able to adapt it to my needs.

I will let you know if I have more problems. Thanks for all the help guys!

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Cool, if you end up wanting to learn how to do it, we are certainly the sort of community that could help you learn to build it. Cheers!

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