Brake rectifier 2

[stuartfd54]

Hi

Over the last 2 weeks we have had to replace the brake rectifier 3 times on a 415v 3 phase motor with 415vac/205vdc rectifier. The complete motor and brake have also been changed along with contactor.
The rectifier is fed directly from the 415v from the motor so as the motor starts the brake releases. The operation that the motor drives requires start/stop 36 times/minute.
1st question - I presume there could be a slight delay in the motor start/ brake release but could this be causing the issue of destroying the rectifier?
2nd question - Should the rectifier be connected across U1/V1 or W1 incoming to the motor or U1 and copper bar for star connection?


Any other advise would be gratefully received.

Thank you
Stuart

 

[ScottyUK]

iop95, the contactor is at an MCC or similar, and it switches the motor windings. The brake coil is connected across the motor windings.

 

[itsmoked]

When wired across the motor (frequently) the brake release time is significantly increased.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

That's excellent Keith. Where did you find it?

 

[itsmoked]

Hi Scotty!

I just had to wrestle with a brake on a guy's bender. It wasn't disengaging correctly so of course the motor was -seriously unhappy- and the overload was getting cycled. I had to hunt down a data sheet on it and in the process stumbled over one that was a different model but pretty comprehensive. That data is out of a Lenze Brake Unit manual and I don't recall where I found it as it was a major battle since the USA site seems to ignore brakes altogether.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[iop95]

ScottyUK: sorry, I don't read careffuly.
At 36times/min (1.66s) operations, may arise in some moments high voltage across rectifier diode; add one more diode in series or a small resistor across brake coil connected when motor power is off.