Wiring a relay into my 3 phase motor

[Bass_Player]

I have a Victor automatic bandsaw that's not too swift with bar location. It has the powered roller vise and the motor coasts to a stop when the limit switch cuts power to it. I want to install a brake such that the brake will be on until the motor is powered up, in which case a solenoid will release the brake. If it's practical to do so, I may directly wire the solenoid into the motor power supply, or more likely I'll put in a relay to handle the current for the solenoid.

What I need to know is can I safely put any such relay or solenoid in line with one leg of the three phase power to the feed motor? If so, what sort of relay or solenoid will I need to look for? What sort of specs would such a thing have, is it common, and where might I find it?

[murphy625]

Not a good idea to un-balance the legs to the motor itself..
Better to tap off the main line and create a start and stop braking circuit that is triggered by the motor starter.
If you have a combination line voltage starter, this is not going to be safe.. If your starter uses a control voltage to pull down a coil then wiring it should be easy..

My guess is that your going to have a harder time designing a brake that will work reliably than getting it to work electricaly.

Murphy

[Al_The_Man]

Why not use regenerative braking, I believe you can set up a 3ph bridge rectifier that is switched in when the main contactor is off and wired across the three motor lines self creating a DC field in the windings, I believe you can also inject DC into the motor to brake it.
Al.

[Bass_Player]

Thanks guys.

The mechanical part is no problem. The motor already has a small handwheel on the free end of the shaft for manually feeding stock for setup. Turning a handwheel to include a braking surface will be no problem, and something as simple as a bicycle brake caliper mounted on a bracket would provide plenty of braking power. It is the wiring that I'm more concerned about, since I don't know too much about it. Maybe just enough to get into trouble.

How can I identify the starter being used on this motor? It is a 1/4 HP 3 phase motor @ 60 Hz and 230 volts. Inside the main control panel of the saw there are contactors for everything including the feed motor. Would there be a way to wire a small relay in series with the limit switch? If the limit switch is a normally closed momentary switch, would it likely have enough current to it to activate a relay? Setting up the brake to either close or to open when current is applied would not be a problem.

The DC braking sounds like an elegant solution, but maybe too far over my head. One of the things I like about the mechanical brake idea is that I could push the brake out of the way when I want to advance the stock through the vise manually.

[murphy625]

Post a photo of your control panel guts...

I need to know how its setup..

Murphy

[Bass_Player]

The black contactor in the middle of the top pic feeds stock to the stop. The grey one next to it on the right feeds stock away from the stop.



Making a mechanical brake shold be no problem for this setup.

[murphy625]

Yes.. Electricaly it should not be a problem.....

It looks like your starters have coils and heaters (overloads) on them..

Making an electric brake should be easy...