How to prevent power generate by a stepper motor, a fly back protection?

Other Hardware Motors, Mechanics, Power and CNC
1

Hi,

I made a slider with a stepper controlled by an Arduino Uno and a driver A4988. Everything works fine but if, for any reason, I have to move manually the dolly, I unplug the battery and the motor to make sure that the power generate by the moving motor won't "burn" my controller. If I use my slider very steeply inclined, if my battery runs off, the dolly could slide down on the track and my controller burned by the power generated by the stepper motor before I have a chance to stop it.
Would it be possible to add a diode somewhere in my circuit to avoid this problem ?

Thank you...

2

Best to fix the problem mechanically with a counter-weight really (reduces load on the motor too), but failing that, a beefy TVS or clamp circuit?

3

Should I put a diode on each stepper coil A and B ?

4

That would work, or across the driver supply (the freewheel diodes carry the current to the rails during back-driving).

5

I found this :

What do you think of it ?

Since my electronic knowledge is about zero, what should be the value of the different diodes and capacitor (for a nema 17 stepper powered by an arduino UNO, 12v power) of the third schematic ?

6

No, that would not work, because current must flow in both directions through the coils. You could disable the output of the A4988 by means of the enable input of the A4988. Then the stepper can be freely turned.

7

TVS diodes are unpolarized typically.

8

Something like a 20V TVS diode should be safe for 12V operation - they switch on over a range of voltage and you don't want them to conduct at all in normal operation.

9

The A4988 is a chopper current driver. If current flows through the coils, you must not unplug the coils. This can destroy the driver. TVS diodes may help in this case. If the driver is disabled by the EN Input of the A4988, you can freely turn your stepper, that's no problem.

10

I am not sure to free my motor is my main concern.
Because my problem append when my battery is off, so no current is flowing through the coils, it the manual movement , or the movement create by the fall of the dolly, that generate a fly back current in the controller that concern me.

I did understand that the current must flow in both directions between the driver and the motor, so if I can't control the sens of the current, I have to control it's level through a TVS diode.

Is that correct ?

11

No, it is a problem, that's the whole point of this thread - as the stepper spins it generates AC voltage, and this will be rectified by the free-wheel diodes in the driver to push up the supply rails, eventually this could burn out anything on those rails if the voltage goes high enough.
I speak as someone who's used at least half-a-dozen different stepper driver chips and even
built a discrete stepper driver circuit.

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