Wiring a full wave rectifier a motor brake?

kalabdel

Member
Join Date
Feb 2015
Location
Ontario
Posts
1,108
Hello guys,

I had another one of those unique o_O experiences and wondering about the results.

A new machine just been installed and the brake on a 3HP motor would not fully disengage . The brake is rated at 200VDC +/- 6% and has a rectifier that states a max of 500VAC and doesn't specify the output but with 230VAC input I measured 110VDC with the brake connected and 135VDC with the brake disconnected from the rectifier. I figured that was the issue so the installer went out and picked up a full wave rectifier and wired it in. I haven't had a chance to measure the output of the rectifier and to my knowledge it will have a DC voltage with ripples peaking at 230VAC * 1.414 and the question is how likely is it for the brake to get damaged?

Thanks
Kal
 
I would never fiddle with the internals of a built-on brake. The coil is constructed so it won't get damaged by the voltage it gets from the included rectifier circuit. If you change the rectifier you're almost sure to get the coil damaged sooner or later. Better is to get a completely new brake adapted to the motor AND the brake force you need. The last part is almost always neglected, they mostly simply use the cheapest brake for the given motor. It's fairly complicated to get the right brake because you have to calculate the needed braking force for the motor and the attached load.
 
I have had many motor brakes apart for inspection and / or repair without an issue they are simple devices.

As for the voltage with a full wave rectifier the DC voltage out is a result for the AC voltage in
If your supply is 230VAC the coil voltage will be the 200VDC you are looking for. However on some systems they use a brake module. A brake module is used to reduce voltage supplied to the brake coil. This is called economizer. The brake doesn’t need as much current to hold in as it needs to pull it in. by reducing the voltage / current you reduce the heat generated and extend the life of the coil.

Keep in mind when you measure the voltage to a brake don’t forget with the brake coil disconnected the DC voltage will be higher and could read above the 230VDC supplied.

As for the brake not releasing correctly it sounds to me like the release springs are week and need to be replaced. A simple process, contact the manufacture. I have had to replace some over the years
Don’t forget to check the wear on the friction plate if the brake is not releasing correctly you most likely have warned out the friction plate as well. If I were to replace the springs I would replace the friction plate while I have it apart.
Sometimes very rarely it could be caused by residual magnetism it usually only happen when the brake is supplied from a pure DC supply. For that reason the brake is pulsed in reverse polarity when it is released.
 
Thanks gentlemen. The machines is brand new so I requested from the supplier to contact their motor supplier and ask them to replace the rectifiers.



Thanks
Kal
 
A 200vdc brake coil should be full-wave rectified from 230v, and half-wave rectified from 460v. (or hooked up to 1/2 winding -- 1 of 2 series windings)

Should be shown in the brakemotor manual.
 

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