Internal Fuses (PTC Resistors) on Window Motors
 

We are using a window motor on a clamp, and we notice that when we activate the clamp over and over it loses power as it heats up....eventually not opening at all.

It looks as though the motor has an internal thermal protection device....but not really a fuse, but some sort of Positive Temperature Coeficient Resistor that slowly "opens" up and lowers motor current.

Is this true.....are there specs on this motor that will describe this protection circuit?

Is there any to remove this feature? (I doubt it) :mad:

-Quentin

Off hand, I don't remember if it says so in this year's manual or not, but in years past, the manual worned that this motor has a PTC inside it. As far as I know, you are not allowed to remove them, as this is one of th emotors that you are not allowed to modify.

Definitely has a PTC
 

The motor definitely has a PTC.


The print I have says that it is a 15A breaker 6-8seconds.

In the past when we used the window motors to lock a gripper, we put a switch at the end of the travel to shut the motor off rather than stall it.

FYI, the keyang motors have a PTC also.

Joe J.

Re: Definitely has a PTC
 

We actually do stop the motor by detecting the stall by measuring the current increase. It works well, but in our debug session, we saw the motor "die a slow death" until it cooled.

I suspected the PTC, and you now confirm it.

Thanks,
-Quentin

Better to avoid a stall entirely if possible
 

If you have a choice, put a switch at the end of travel. Even though you detect the stall condition and take steps to stop it, you are still stalling the motors. To the extent that you stall them at all, you are lessening the time that the motors will be alive to do work you really need them to do.

Current literally adds up in the form a heat. The more you can keep from heating the PTC up, the longer they will take to trip when you don't want them to.

Joe J.

The tough part about the protection in this motor is that it is a thermal device and therfore subject to the heat buildup inside the motor. So it will trip off on friction built up in the transmission and bearings, high current or even heat from outside the motor and all of them will add together to raise the internal heat.
Good luck all

Seat, window, even the Van Doors used to have them
 

For the non engineers people ;)

In section 1.2.3 of "the robot", the mentioned that the seat motor have a Positive temperature coefficient (PTC) thermistor for over load protection. But actually, window motor and Van door have them too. The PTC device will reduce motor current and output torque as heat increases.

If you motors are heating up, try reducing side loads on the mechanism, use a bigger gear ratio to reduce the load on the motor, and reduce the internal friction of the device. Stalling out motors is one of the major ways to heat up motor. Competition usage and the temperature around the motor also add to that too.

You want to watch out for the windows motors, especially this year's because of their lower max power output. Do some calculation and see if these window motors satisfy how much torque your mechanism need while finishing the task with the speed you want.

If you find out that you demand a certain speed from these guys, and they are stalling out while doing the job... I suggest you get more powerful motors to do the job.