running stepper motor with capacitor - Page 1
Forum section: electronics / beginners

author: andy1942
author_rank: Newbie
timestamp: August 03, 2024, 04:51:47 pm
content: Hi,I have a nema 17 bipolar 12v 1.2a four wire stepper motor that I want to use as a continuous motor to drive a turntable, using a 5A power supply. I have watched vids on youtube using capacitors and for ease that would be perfect. I have tried various capacitors but with no luck. Can anyone help or tried this before and tell me the size of capacitors I need please.

author: Benta
author_rank: Super Contributor
timestamp: August 03, 2024, 04:55:05 pm
content: An audio turntable?But no, you can't drive a stepper motor with capacitors. You need a real controller.

author: CaptDon
author_rank: Super Contributor
timestamp: August 03, 2024, 11:33:33 pm
content: The best you could hope for is a stepper controller that allows PWM stepping and hope for several hundred steps per revolution. On top of that you would probably want belt drive to dampen the 'per step acceleration wobble' along with a hefty inertial weighted platter. Servo motors (two pole rotor / 3 pole stator) can be made to spin on A.C. with a capacitor phase shift. I am not sure a stepper motor would reliably start or run at a controlled speed with a capacitor. More of a novelty than a useful predictable outcome.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 04, 2024, 12:49:23 am
content: Contrary to what Benta wrote, this should work.The Ideal excitation for a 2-phase bipolar stepper motor are two sine waves with a 90 degree phase difference between them. This means you should use the biggest capacitor you can find to approximate this 90 degree phase difference. I'm thinking about a bipolar electrolytic of a few thousand uF. You can also put two "regular" electrolytic capacitors back to back to prevent AC leakage, but I don't know how long that will hold.As you don't have a real controller in this case, you will have to limit the voltage to the motor to prevent overcurrent and over heating.Most common are the 200 steps/revolution motors, which would result in 1 revolution per second with a 50Hz input signal.I wonder why it does not work for you. Do you have a schematic? What sort of capacitors did you use? Which youtube video's did you see?

author: BennoG
author_rank: Frequent Contributor
timestamp: August 04, 2024, 11:16:30 am
content: Quote from: Doctorandus_P on August 04, 2024, 12:49:23 amBecause he is using a DC power supply.What you suggest us only work on AC.

author: wraper
author_rank: Unknown
timestamp: August 04, 2024, 11:19:57 am
content: First of all you need a stepper driver that will be switching the windings. Secondly, just don't, it's the most unsuitable type of motor you can think of to run a turntable (unless you want hearing its steps from the motor itself and in the sound).

author: tooki
author_rank: Super Contributor
timestamp: August 04, 2024, 12:55:49 pm
content: Quote from: BennoG on August 04, 2024, 11:16:30 amA DC power supply isn’t specified; OP only gave a uselessly vague description of having a “5A power supply” with neither voltage nor AC/DC specified.

author: tooki
author_rank: Super Contributor
timestamp: August 04, 2024, 12:57:37 pm
content: Quote from: wraper on August 04, 2024, 11:19:57 amIndeed, one could not choose a more ill-suited rotary motor type for this application.