Protecting small DC motor (power door lock actuator) from burning out due to stall

Question

This question of small DC motor burnout due to heat/stall has been asked in a few different ways/scenarios already, so I think I have a basic understanding of what the issue is -- I'm interested in understanding why the below is a problem in my case but seemingly not in another. Appreciate any insight anyone can share!

I am trying to use a 12VDC power door lock actuator in a specialized application, where it's connected to an on/off momentary push button switch that causes the actuator to push a lever to hold a door open when powered. Releasing the button to cut the power causes the door, lever, and actuator to retract simply because of gravity. My power source is an AC to 12VDC power supply rated at 8A. I want to be able to hold the button down to keep the door open for a "reasonable" amount of time -- perhaps 30s to 5mins, maybe.

My issue is that holding the button for a short time (approx 10-30s) seems to keep burning out the DC motor in the actuator. I understand it's likely because the actuator shaft causes the motor to stall once it reaches its max extension, which in turn causes the current draw and motor's heat to go up, which can burn out the motor.

So why don't these motors burn out when being used in their intended use case -- car door locks? These actuators have limited travel and the motors stall by design when they extend or contract fully. I know that in most cases, electronic door locks are probably just quick momentary ON states so the stall is very short...but as children in my car have proven, you can hold the lock/unlock button in a car and nothing burns out inside the door frame when you do. Why is that?

And I guess most importantly, is there any way I can use these actuators to hold open a door like I want without them burning out by adding something to the circuit or perhaps changing my power supply?

Thank you, thank you!

Equipment details:

Motor is this type: https://www.parts-express.com/High-Power-Door-Lock-Actuator-2-Wire-330-010 I've burnt through a few different manufacturers of this motor, but they're all more or less the same exact thing.

Power supply is this: https://www.amazon.com/gp/product/B07G5BQGYD/

Answer 1

I'm interested in understanding why the below is a problem in my case but seemingly not in another.

Look into how those things work in a car. Pull the door trim off, attach an oscilloscope, and activate the door locks via remote, and see how the car uses those things. You must drive them the same way.

So why don't these motors burn out when being used in their intended use case -- car door locks?

Because these motors must stay off. Being ON is an exceptional situation for them.

If you can count to three while the motor is turned on, it's on too long already!

Protecting small DC motor (power door lock actuator) from burning out due to stall

The things are meant to stall at the end of their motion. That's not the problem. The problem is that they cannot stay on for any length of time after that. You cannot just connect them to a button directly and expect them to survive. They were not designed to be used that way, and they won't take it.

In a car, the lock actuator is turned on for a fraction of a second to change the state of the lock. The driver circuit senses back-EMF to detect successful lock/unlock action. The body control module or the lock module can then reverse the operation if any of the motions fail. At least my Volvo does that: if you hold the door lock button "stuck in place" while locking the car, the doors will lock (except the one you're messing with), then they'll unlock. They'll only stay locked if all doors have successfully locked. Other cars also detect the stalls, but it's up to the vendor to use that information for something.

It seems that your design is just too simplistic. Those motors are only meant to be operated when changing the state of the lock: engaging it, or disengaging it. Intermittent operation for less than a second is what they are designed for.

To keep the motor happy, the system should be mechanically self-stopping: when the motor is off, nothing should be moving by itself. You then, at simplest, have two buttons: open and close. Each button activates a circuit that delivers a fixed duration pulse to the motor, of the correct polarity.

If you want to use a single button, then you'll need a circuit that detects the opening and closing of the button and activates two pulse generators as-if there were two buttons.

Answer 2

Automotive power window motors use current limiters to detect a stall.

Older types use passive PTC thermistors or magnetic current sensors with suitable cold resistance or current ratings.

Modern types might use active current limiters to stop or limit if held on. Many are automated. Some may use Hall current sensors.

Motor start/stop/stall currents are typically 10x max rated current and 100x no load current. The DC resistance of the motor limits the stall current.But without the back EMF that rises with RPM and the cooling effect of rotating air, motor windings will heat up as fast as the size allows.