Ensuring motor brake solenoids have energized.

Tharon

Member
Join Date
Jan 2007
Location
Other
Posts
1,430
I've seen many machines that have a small relay in series with a motor brake solenoid. This lets the machine know that the brake solenoid has been energized, no broken wires, etc.

Now I'm going to try to make a setup like this, but don't know where to begin in sizing the relay properly. Is it something that can be done with any sort of brake as long as you get the circuit math down right, or does it have to be a specially designed brake solenoid to do it?
 
Sounds like current sensing to me. In old days before solid state this was done with a current sensing relay whose windings were able to handle the current of the brake solenoid.

Another applicationn of this and maybe more common was a current sensing rely on shunt field of shunt motors loss of shunt field = no current and if motor not shut down will overspeed and possibly destruct.

I think get the brake and solendoid sized for the load so you know it will control the load.

Select the current sensing relay (or solid state sensor / relay) based on brake coil voltage and amperage.

Dan Bentler
 
I understand that it might seem easier to sense the brake solenoid, but that doesn't really tell you anything about the brake itself. I've seen many a time that the solenoid operated just fine, but the brake didn't release or set properly.

If you are looking for broken wires, etc look at safety I/O which uses pulse testing and feedback from the relay. You'll have better diagnostic coverage, but even that won't tell you what the brake is actually doing.
 
Last edited:
The only way to sense if the brake is set or released is to monitor its actual mechanical position with a micro switch. However that can cause other issues and increased maintenance especially in dirty conditioins

Dan Bentler
 
Current monitoring is the best method to monitor if the brake is energized or not.

Also depends on the brake setup and how you want to use it. Some brakes hold when energized and some hold when they are deenergized.

Are you looking to make sure the brake is holding before turning off a motor or something similar?

If you are using a encoder sometimes monotoring for movement is a good idea also.

There are also systems with redundant brakes for safety also.
 
If you are using a encoder sometimes monotoring for movement is a good idea also.

Reading between the lines, sensing that the brake solenoid has operated, is in my opinion, as much use as a chocolate teapot.

It's like saying that you're ok if you've put your foot on the brake pedal in your car... consider no pads, no hyd fluid, oil on discs, ice on road.

You should always close the whole loop, and PLC Kids's comment is the only way to go to inspire confidence.
 
All the automation in teh world will never be better than a competent and conscientious technician observe and take measurements of brake actuation. It is called Prevetitive Maintenance. Good stuff

Management hates it because of cost.
That is OK
the short term savings lead to breakdowns and job security.

Dan Bentler
 
All the automation in teh world will never be better than a competent and conscientious technician observe and take measurements of brake actuation. It is called Prevetitive Maintenance. Good stuff

Management hates it because of cost.
That is OK
the short term savings lead to breakdowns and job security.

Dan Bentler

I have to disagree, Dan.

In the UK, we have to have all our road vehicles tested annually to ensure they are safe and roadworthy. I guess you have similar.

We have a "competent and conscientious technician" test our cars, and are issued with a certificate (assuming it passes, of course), to say that it is safe and "roadworthy".

But, and here's the rub, it is only valid until we drive away from the test center !!

That is why modern vehicles are fitted with safety devices that monitor critical functions, like brake fluid level, brake lining wear, etc.
 
I have to disagree, Dan.

In the UK, we have to have all our road vehicles tested annually to ensure they are safe and roadworthy. I guess you have similar.

We have a "competent and conscientious technician" test our cars, and are issued with a certificate (assuming it passes, of course), to say that it is safe and "roadworthy".

But, and here's the rub, it is only valid until we drive away from the test center !!

That is why modern vehicles are fitted with safety devices that monitor critical functions, like brake fluid level, brake lining wear, etc.

Sigh
There just is no magic anwer - just because it was OK when looked at does not mean it will not break in future - and there is no guarantee when it is going to break.

Dan
 
If the brake is 230 volts and a current of 0.2 amps you could use a 12 volt relais in series also drawing this 0.2 amps. the voltage on the brake will be 218 but that is within limits.
The current is more important as the voltage.
You can also use a shunt resistor taking away most current to the brake and use a small relais.
This setup is also used in lights to check if they are on.
This apart from endswitches etc.
 
I'm not looking at making sure the brake is being held. I want to make sure the brake is released before I start to drive the motor. There is no position feedback (sensor or otherwise) on the brake actuator internal to the motor. There is a rectifier in the motor junction box, and it takes line voltage of the motor to release the brake. I'm putting the motor on a VFD, so I'm controlling the brake separate from 3 phase that drives the motor. I just remember a few of our German made CNC's monitored their brake circuits with relays wired in series to ensure the solenoid was getting power.

I didn't know about the current sensing relays. But looking back at the project, the motor is stationary and the cabling will not move, so I don't think I will have to worry about broken cables. I will just put an auxiliary contact on a thermal overload and contactor that will energize the brake to release. I think if the brake does manage to fail without me sensing it, at most I'll generate an overload fault on the VFD and shouldn't hurt anything.
 

Similar Topics

I hope to not sound unethical but I would like to know what you folks do to make sure you get paid, after a job? I did a side job about 4 years...
Replies
37
Views
11,154
Hello all, In my facility we have multiple 3HP 460V motors that are being controlled by VFDs which drive conveyor belts. The drives are randomly...
Replies
2
Views
173
Hi everyone, This is my first time posting, so please forgive any omissions or mistakes. I am attempting to control the velocity of a stepper...
Replies
18
Views
738
Kindly, has anyone tried to control Lenze servomotors with Siemens S120 drives ? Any special hints ? Have some concerns for the resolver and servo...
Replies
5
Views
177
Dear Members, Hello, we are working on a project and facing an issue with the plantpax 5 PMTR library, we have a bidirectional motor, which has 2...
Replies
6
Views
185
Back
Top Bottom