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Please bear with me, I am new to electronics so my question may be stupid, but I want to make sure that the system is safe and won't catch fire.

I am trying to use an A4988 driver to power a stepper motor. The system is currently working pretty well, the stepper motor is rotating when I tell it to, but I have a safety concern over the use of a capacitor in the circuit.

This is the A4988 driver https://www.amazon.co.uk/gp/product/B0793K9KF8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I've been following tutorials such as this one https://www.makerguides.com/a4988-stepper-motor-driver-arduino-tutorial/ and they all mentioned the capacitor between VMOT and GND.

Here's a diagram enter image description here

The DC source in this picture is regular 12V adapter plugged into a wall socket.

The stepper motor and the A4988 driver are rarely used in the project and I am hoping to completely turn them off when I am not using them.

My questions are:

  1. If I am not using the motor, is it safe to have the capacitor there while electricity still flows through the wires? Won't it create a short circuit?
  2. When I am not using the motor, won't the capacitor draw power from the adapter? I'd like to minimize power consumption as much as possible. Especially since the motor will only be used 2-4 times a day tops. The answer provided here Is it acceptable to leave a capacitor across batteries even when turned off? makes me think that the capacitor will draw a little bit of power. I would like to eliminate this completely, if possible.
  3. Should I just add a relay to this to cut the flow of electricity completely when I don't need it? If so, does it matter if I put it before the VMOT and the capacitor(point A in the diagram), or after the capacitor and the GND of the A4988 (point B in the diagram)?
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1 Answer 1

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  1. Caps are not short-circuits once charged to the DC level of the circuit. It is safe though but caps can have an operational lifetime though it probably doesn't matter here.
  2. Yes, due to leakage always decreasing the cap voltage requiring it to charge up again. It is a small amount though.
  3. Yes because batteries. A factory would probably not go to this trouble though.

A or B technically don't matter in most cases but A is best since B is being used as the reference. It matters more for high voltage when everything is earthed to B so disconnecting B would make everything float and be unsafe.

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