Switching a motorbrake

Plc_User

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Our motors mostly have that are fed externally with 230V AC and a small recitifier at the brake makes DC voltage of it.
Up to now we have always been switching the the motor brake with a relay where one contact interrupted the 230V AC and one contact interrupted the DC voltage.
Is this common practice?
What if you only interrupt the 230V AC, I suppose in that case the relay would less suffer from the DC current interruption, but will the brake fall off as fast as when the DC was interrupted?
What configuration do you use to swith a motor brake? What relais do you use?
Thanks
 
In my limited experience, I do not use DC injection braking, I use ac breaks coming from 1 phase of the motor, so the brake is on until power is on the motor which releases the brake. Hope this helps. KEV
 
Test A Plug said:
In my limited experience, I do not use DC injection braking, I use ac breaks coming from 1 phase of the motor, so the brake is on until power is on the motor which releases the brake. Hope this helps. KEV
Click to expand...

He wasn't talking about dc injection but a dc brake on the motor rather than an ac brake
 
Sorry Dave, you are correct. Sorry to hijack this thread, what are the comparitive differences between ac and dc braking? Cheers KEV
 
All of the motor brakes I have seen on line-motors were directly connected to the motor windings. When the AC contactor energizes 3-phase to the motor windings, the brake rectifier at the motor was also energized to release the brake. Most of the ones I have worked with were SEW Eurodrive motors. We never saw any problems with this arrangement.

It sounds like your setup is using a separate relay to control the brake DC voltage.

Hope this helps.

Edit: the brakes would have mechanical problems due to wear. This occurred after 8-12 months of continuous duty. The motors were on a carriage that stopped and started several times per hour.
 
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Even mechanical brakes that are described as "AC powered" are, internally, almost always built with DC coils and a rectifier.

Breaking both the AC and DC circuits probably makes the brake operate faster. That may be an important aspect of your machine's operation. Also, be reminded that a DC coil kicks back with lots of voltage when it's supply is interrupted.

Sometimes, it is worth piloting the brake separately and adding some pickup and release timing to get the brake timing just right.

Finally, if a high cycle rate is causing high maintenance issues, it can be beneficial to change to DC injection braking to do the stopping and then using the mechanical brake to hold the stop stationary. Mechanical brakes used this way last a lot longer. And, DC injection is cheap and does not hurt the motor if properly applied.

Sorry for the random thoughts. Hope it helps.
 
DickDV said:
Even mechanical brakes that are described as "AC powered" are, internally, almost always built with DC coils and a rectifier.

Breaking both the AC and DC circuits probably makes the brake operate faster. That may be an important aspect of your machine's operation. Also, be reminded that a DC coil kicks back with lots of voltage when it's supply is interrupted.

Sometimes, it is worth piloting the brake separately and adding some pickup and release timing to get the brake timing just right.

Finally, if a high cycle rate is causing high maintenance issues, it can be beneficial to change to DC injection braking to do the stopping and then using the mechanical brake to hold the stop stationary. Mechanical brakes used this way last a lot longer. And, DC injection is cheap and does not hurt the motor if properly applied.

Sorry for the random thoughts. Hope it helps.
Click to expand...

I totally agree with Dick(except for `probably makes the brake operate faster', because it surely does) and hope this will help "Plc_User" and all the others readers since all the other answers are .... o_O
 
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I have seen 3 configurations on Eurodrive motors.
1. where the power for the brake comes internally from 1 phase and the motor star point (240/415v).
2. as above but the DC is switched externally.
3. Where the AC brake voltage is switched externally

In all the applications I have worked on where accurate positioning (Lifting, turning etc)is required the AC is switched externally.
 
We distribute AEG motors and they do both types of brake, i cant remember as we dont get asked often but there are two major differences between an AC and DC brake

1. Speed of operation
2. Holding Force of the brake (normally most important)

I'll look up the AEG data next week and let you know which one is better for what, too much red vino this week 🍻
 
I think it may be important to note that brakes also come in two flavors - those that apply brake when
power to motor is released ie brake is set by springs - used on cranes etc Brake is disengaged when power to motor is reapplied. Most common from my experience.

Those that are spring release and brake is set when power is applied to brake only (NOT MOTOR) Dont recall seeing one like this.

Dan Bentler
 
leitmotif said:
I think it may be important to note that brakes also come in two flavors - those that apply brake when
power to motor is released ie brake is set by springs - used on cranes etc Brake is disengaged when power to motor is reapplied. Most common from my experience.

Those that are spring release and brake is set when power is applied to brake only (NOT MOTOR) Dont recall seeing one like this.

Dan Bentler
Click to expand...

There are also braked motors that have no ac or dc brake and no springs

One of the hoist manufacturers use a tapered rotor, when the magentic field fails (power off) the rotor locks on the laminations (also tapered) and stops the rotor dead, very fail safe
 
a point on using one phase of the motor to operate the brake, it does work well, but if the motor is vfd driven, you will have a problem doing that
 
briancr said:
a point on using one phase of the motor to operate the brake, it does work well, but if the motor is vfd driven, you will have a problem doing that
Click to expand...

If its on an inverter you should have the brake on a separate supply not connected to the motor terminals
 
and i had in the past 3 phases motor 30 K.W. driving a 2 meters diameters cylinder which they had to wait 5 minutes until it stops by inertia , then i was asked to make a brake , i applied a dc voltage single phase 220dc for 25 sec, via a poerful rectefir with a suitable heat sink , it was impressing , nice application.
 

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