AC motor control - Forward-Stop-Reverse  - Page 1
Forum section: electronics / repair

author: rocmel
author_rank: Newbie
timestamp: December 27, 2022, 03:44:25 am
content: I have a garden chipper/shredder that the mechanical stop, between Fwd - Reverse is damaged.(fig1)it uses an induction motor with an external starting capacitorBrand "Wolf Garten SSD2200" 230v 2200WThe Forward switch is working fine, can't remember if reverse is workingThe original Switch is complicated using a relay with multi contacts, no longer availableLooking for ideas how to achieve the STOP in between Fw -R& discharge the starter capacitor 15uf in between switching.

author: abdulbadii
author_rank: Frequent Contributor
timestamp: December 28, 2022, 11:28:01 pm
content: isn't this better under repair forum section?just unscrew that part hopefully it's easy to find and fix the H bridge circuit; 1 mechanical/kinetic external switch action is to drive internal 2 ones, a stop switch will prevent any contact on internal switcheshttps://en.wikipedia.org/wiki/H-bridge#:~:text=A%20H%2Dbridge%20is%20an,to%20run%20forwards%20or%20backwards.

author: rocmel
author_rank: Newbie
timestamp: December 29, 2022, 01:17:46 am
content: My question wasLooking for ideas how to achieve the STOP in between Fw -R& discharge the starter capacitor 15uf in between switching.Thanks , your answer does not address the fact that is AC the capacitor placement determines the rotationor how to discharge the capacitor before changing direction of rotation.

author: abdulbadii
author_rank: Frequent Contributor
timestamp: December 29, 2022, 01:50:52 am
content: Forgot this' AC, sorryImho in AC instead of H it uses pole, throw or akin stuff configuration (but can't figure out yet as in big business else)

author: Vincent
author_rank: Regular Contributor
timestamp: January 01, 2023, 01:13:44 am
content: I remember this stuff being discussed back in trade school, but it's already been over a decade since then.If I remember right, you need to reverse the direction of the rotating magnetic field. With 3-phase motors it's a piece of cake, just interchange two of the phases.With single-phase motors things get a bit more complicated. You need to "flip" the phase angle between the start and run windings. With some types, like shaded-pole motors, it'd be rather difficult to do. Others use starting capacitors and these may be easier to hack to make them start in the other direction, maybe by designing a starting inductor, creating a phase angle opposite to that of the capacitor?On a related note, aren't there (single-phase) induction motors specifically designed to rotate in both directions?

author: IanB
author_rank: Super Contributor
timestamp: January 01, 2023, 01:35:00 am
content: Quote from: rocmel on December 29, 2022, 01:17:46 amYou have not given enough information in your question for an adequate answer to be provided. I cannot tell from what you have said whether the switch is defective, the relay is defective, or both.You apparently don't even know yourself:Quote from: rocmel on December 27, 2022, 03:44:25 amPlease don't post questions until you have at least got the basic facts in order. Otherwise it just wastes everyone's time.The short answer: reverse engineer the existing switch and wiring, then repair or replace with equivalents as needed.The long answer: do a detailed photo-by-photo disassembly, showing every detail of the construction, and post the photos here. Show where and why you think a part is defective. Explain where you have a problem getting a suitable replacement or substitute part. Remember the easiest way to repair something is to keep the wiring exactly the same as the original design. Redesigning a circuit to repair something needs much more expertise.Quote from: rocmel on December 27, 2022, 03:44:25 amA replacement for a relay is always available. It may have physically different shape, and maybe it is not the exact part originally installed, but relays are universal. You just need to find one of a similar size and rating and figure out how to fit it in the place occupied by the original.Additional information: single phase induction motors are reversed by swapping a single pair of wires. This requires either a DPDT switch, or a relay that performs the same function. The motor has to be stopped before trying to switch direction. If the motor is still turning when you try to change the direction, the chances are that it will keep going the same way.