Electrical brake for AC motors

When thread cutting on the lathe, it is easier if the motor can be braked automatically. This can be done simply by short-circuiting the windings by means of the counter electromotive force generated. For this purpose, the auxiliary switch of the contactor of the drive motor must have 2 free closing contacts. In the case of a single-phase motor, only one phase must be short-circuited via the make contacts of the contactors for both directions of rotation with the second phase via a 2-pole brake switch. With a 3-pole motor, the second phase must also be routed via the make contacts of the contactors, and the third phase is then connected to the short-circuited contacts of the brake switch. The wiring can be found in the wiring diagram. The required auxiliary contacts can be ordered from the contactor manufacturer. Since usually only 2-pole auxiliary switches are installed, these can simply be replaced with a 4-pole auxiliary switch with three make contacts and one break contact.

:hattip:


Attachment 44725

Prinzischaltpan der Motorbremse.
Attachment 44736

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The first switch is for the power supply, the second for baraking function

[video] https://www.dropbox.com/s/0lm75yl98t...hort-.mp4?dl=0

Hello,

now I want to show you how I installed the Aotostop at my CJM250 using shorting of the motor when threading. I made a little box with a limit switch, which can be slided over the lathe bed to adjust the sto point. The wiring is implementet to the regular stop switch of the lathe. it contains also two LED indicating the state of the motor. Green means the motor can be startet for threading, when the slide reaches the actuator of the switch it will stop the motor imdiately. The motor can be startet only in reverse direction again, to start a new turn for threading. t works exelent at a speed between 50 and 150 RPM. Do not forget to switch to autostop funktion bevore threading.

Attachment 44979Attachment 44980Attachment 44981

Excellent work. You just gave me an idea with the box with the LEDs on it. What about using a hall effect sensor instead of a mechanical switch?

I do not recomment a hall sensor underneaht a cutting tool, it may disturb your motor control system.

Attached the circuit diagram of my CJM250

New improved basic circuit diagram.

Attachment 45036

Right: Even I know (and own) hermetically sealed switches I'd like something-in-a-closed-box. Inductive switch or reed switch?

Hello uv8452
what you need is a contactor which can handle the load of your motor. My picture shows a toggle switch, which must be installed in a box.