18v15 Motor Controller Short Circuit When Motor Reversed


I hope someone can help me.

I purchased a 18v15 Motor Controller and I am having some problems.

I’ve got the motor controller driving a Maxon DCX 35L (the 12V version) in signed magnitude PWM mode from a microcontroller.

The setup works well, I can set the speed with the PWM signal.

However, when I try and drive the motor in the opposite direction while it is going at 100% Duty Cycle, ie. toggle the DIR pin, the motor stops spinning and the Short Circuit flag is raised. Following that, if I reset the power, only then will it turn in the opposite direction.

I tested this further and determined if I brake the motor, then only change the direction bit, I can switch rotation. However, simply toggling the direction pin while the motor is driving full speed in one direction, always causes it to enter this fault mode. I’ve tested this with both a 6A Power Supply and a 3cell LIPO battery because the current limiting may be the issue.

Is this a limitation of the motor controller? Do I need to configure it in software to first brake if I want to change direction from full speed? Or is there something I am missing?

Thanks in advance,


We carry several products that have “18v15” in their name, including our Simple Motor Controller 18v15 and High-Power Motor Driver 18v15. It sounds like you are using the latter, but in the future, please try to be more clear by including a product number, exact product name, or link to the product.

When you switch direction from full-speed forward to full-speed reverse (or vice versa) with no braking or delays in between, the motor will briefly draw almost twice the stall current, which is likely more than the 18v15 can handle. (In general, your motor seems like it might be overpowered for the 18v15.) Please note that these motor drivers have no over-temperature protection, so using them with overpowered motors can permanently damage the driver if you aren’t careful.

As you pointed out, you can brake the motor and then change direction to avoid latching the fault condition. You could also modify your software to implement acceleration-limiting to help keep the inrush current down.

You might consider using our higher power 18v25, as it can handle higher current demands than the 18v15: