Momentarily running A4988 drivers without a load?

It was bound to happen sooner or later... I accidentally tried to drive my 2 Z-motors through A4988 drivers, with the 2 Z motors disconnected from the board. I realized my error after about 15 seconds and immediately cut the power.

Now, with everything hooked up correctly again, the Z motors seem to be operating fine and can move the gantry up and down. However, I believe that running A4988 drivers without a load can destroy them.

Do you think I seriously shortened the service life of my A4988's by running them for about 15 seconds without a load?

You may have got away with it - what really screws them up is unplugging them while the motors are running, as the back-EMF from the motor coils can result in a massive voltage spike that blows the electronics.

I wouldn't have thought there would be a problem with no load. No power was drawn.

A4988s typically work or they don't. Not much of a halfway house with them, in my experience of them.

No harm was done. Obviously, unplugging the motor means there can be no back EMF. Any stepper driver will run quite happily while connected to a motor, or disconnected from a motor. In both cases the driver monitors its own output current, and regulates the output drive voltage to supply the requested current.

BUT...what actually happens is that if you disconnect a motor WHILE it is moving or holding, the driver may instantly try to provide more than maximum current, which may fry the driver. It really depends upon when the motor is disconnected, and is usually a matter of microseconds.

In summary, run your drivers either completely connected, or completely disconnected, from the motor. Do not disconnect the motor while the driver is trying to move it or hold it in position.

Edited 2 time(s). Last edit at 11/17/2021 06:46PM by rq3.