Motor Turn Stall Detector

Motor Turn Stall Detector Circuit diagram. In single phase AC induction motors, often used in fridges and washing machines, a start winding is used during the starting phase. When the motor has reached a certain speed, this winding is turned off again. The start winding is slightly out of phase to the run winding. The motor will only start turning when the current through this winding is out of phase to that of the run winding. The phase difference is normally provided by placing a capacitor of several µF in series with the start winding. When the motor reaches a minimum speed, a centrifugal switch turns off the start winding. 

The schema diagram doesn’t show a centrifugal switch; instead it has a triac that is turned on during the staring phase. For clarity, the series capacitor isn’t shown in the diagram. Once the motor turns it will continue to do so as long as it isn’t loaded too much. When it has to drive too heavy a load it will almost certainly stall. A large current starts to flow (as the motor no longer generates a back EMF), which is limited only by the resistance of the winding. This causes the motor to overheat after a certain time and causes permanent damage. It is therefore important to find a way to detect when the motor turns, which happens to be surprisingly easy. When the motor is turning and the start winding is not used, the rotation induces a voltage in this winding.

Motor Turn Stall Detector Circuit diagram:

Motor Turn Stall Detector Circuit Diagram

This voltage will be out of phase since the winding is in a different position to the run winding. When the motor stops turning this voltage is no longer affected and will be in phase with the mains voltage. The graph shows some of the relevant waveforms. More information can be found in the application note for the AN2149 made by Motorola, which can be downloaded from their website at www.motorola.com. We think this contains some useful ideas, but keep in mind that the schema shown is only partially completed. As it stands, it certainly can’t be put straight to use. We should also draw your attention to the fact that mains voltages can be lethal, so take great care when the mains is connected!

Author: Karel Walraven - Copyright: Elektor July-August 2004

Rolling Shutter Motor Control Circuits Wiring diagram

An electrically operated rolling shutter usually has a standard control panel with a three-position switch: up, down and stop. If you would like to automate the opening and closing with a time controlled switch, a few additional wires will have to be connected. Typically, the controls are implemented as indicated in the schematic ‘Normal Situation’. If this is indeed the case, then you can see in ‘New Situation’ how the shutter can be automated with a timer. There is only one method to determine the actual schematic of your control schema, and that is to open the control box and using an ohmmeter, pencil and paper to check out and draw the schema. Make sure you turn the power off first though! Connect a 230-V relay (with both the contacts and the coil rated 230 VAC) to the timer.

 

The changeover switch between automatic and manual control needs to be rated 230 VAC as well and may not be a hazard for the user. The relay and switch are preferably fitted in a plastic mains adapter enclosure with built-in plug, which is plugged into the timer. It is a good idea to check first if this will actually fit. Because of the manual/automatic-switch, the operation is completely fail-safe and misunderstandings are out of the question. The switch prevents the issue of conflicting commands (with disastrous consequences) when, for example, the shutter is being automatically raised and manually lowered at the same time.

Source: http://streampowers.blogspot.com/2012/06/rolling-shutter-motor-control.html