SEW brake rectifier and brake issue

[whippee2]

Hello all,

I am new here and have been reading alot of topics on this forum and have learned quite alot. I work as an industrial service tech. Here is the issue I ran into on Friday.

Got called out to a job and there is a 5.5 kw sew motor with a brake assembly mounted on the rear of the motor. The brake wasnt releasing when the motor was driving. The motor is driven by a forward and reverse contactors supplying the 415 supply voltage to the motor. Inside the motor terminal box is a sew brake rectifier. It is a 5 terminal black rectifier. I has a phases from the motor terminals as the incoming voltage. the 3 coils are connected to terminals 1, 3, and 4. I measured the resistance of the coil windings and compared them to another brake on another motor and they tested the same. I also tested the outgoing Dc from the rectifier and had 140, and 159 volts dc to the brake. These reading were the same as the readings on another motor. So I concluded that the rectifier was working as it should.
We checked the brake and it wasnt mechanically jammed or anything. We changed the coil and brake assembly thinking that maybe the coil was breaking down under load. We then ran the motor again and it still wasnt releasing the brake was heating up again.
On terminals 4 and 5 of the rectifier there are control voltage cables connected as well. these cables are run from a normally open aux contact on the forward and reverse contactor. I checked the operation of these aux contacts and they are ok. when the contactors pull in the there is 150 Vac on these two cables. Would anyone be able to clarify what these connections are for? According to the SEW connection diagram you only need the 2 phases from the motor windings to operate the rectifier, so when the motor gets the voltage to drive the brake releases.
I also tried swapping a know good rectifer to test it out but the brake didnt release still.
So it seems like a simple brake setup, but I am confused as to what else can be wrong. Would anyone else be able to offer a bit of advice, or tests I can perform. Maybe I am just overlooking something simple.

Thanks for reading and any advice
whippee

 

[desertfox]

Hi whippee2

This might help but not 100% sure,but it gives setting gaps and torques for brake operation etc

http://www.sew-eurodrive.co.uk/download/pdf/16711211.pdf

desertfox

 

[itsmoked]

Sounds like you've hit all the points I would've.

If you're capable hook it up to power with the rear cover off and watch the mechanism operate.

If that doesn't help it's time to swap out or entirely replace the brake unit. It could also be mechanical - some sort of missing part or spacing issue that a replacement will help you identify.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

It may be that wear has increased the air gap to the point that the brake is no longer able to pull in.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[whippee2]

No worries, thanks for replies. I am sure I will get called out again for the same problem, probably tomorrow. I have printed out a pdf about these rectifiers and brakes and hopefully nut this one out. I am not quite sure what these control cables are for tho.
Ill ask a couple of gurus at work tomorrow.

thanks
whippee

 

[steve492]

Terminal 4&5 are switched by the contactor to give a rapid response of the brake. If there is 150v across these terminals there must be a break in the circuit to the auxillary contact.
Steve

 

[macmet]

I don't know a solution to your problem. However, I found the SEW sales rep I used was very knowledgeable and helpful for problems like this. Perhaps call your rep.