Brake Rectifiers

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SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
I just had a heck of a time trying to source a half-wave brake rectifier module, suitable for 480VAC input. I had to have a brake coil on an induction motor rewound after it shorted and took out the rectifier pack. My motor re-wind shop wanted over $400 for a rectifier.

Amazon has lots for sale, all from dodgy third-party shippers which I'm sure totally aren't clone / knockoff parts - trust me, bro! I didn't feel like rolling the dice and trusting a maybe counterfeit part with 480VAC.

Practically no other websites like McMaster, Galco, or Zoro/Grainger sell them. I had to call my Mayr sales rep and order one direct from Mayr (they make electromagnetic brakes and clutches). Still overpriced, but not $400 overpriced.

It was honestly weird to have no trusted vendors sell a compatible part. It's not like I needed a particular model number either. Just a half wave rectifier with a 600VAC rating.


SceneryDriver
 
LarryFine said:
What current rating? Can you use two discrete diodes? What mounting?
Click to expand...
Less than 4A. Probably about 1A. It's a rewound coil that used to be wound for 105VDC, (fed from 208/230VAC) and is now wound for 230VDC (fed from 480VAC).

The coil actually survived almost a year wired for double its rated voltage before it let the smoke out and destroyed the rectifier. It was a roll bender that we rebuilt last year. The mechanics and hydraulics were in great shape, but the controls were a disaster. We scrapped the controls and completely refurb-ed the machine. The roller motor is a 4-pole or 6-pole 15HP motor, 230/480V, depending on how it's wired. It's almost 35 years old, and French so there's no documentation, even from the manufacturer, Lafert. The wiring diagram in the peckerhead showed absolutely no info regarding wiring the brake coil, so we connected it to 480VAC since we wired the motor for 480VAC.

Turns out the coil was wound and designed to be powered from half of the windings in series when the motor is wired for 480VAC. The half wave rectifier was supposed to turn the 230VAC into 105VDC. It actually rectified the 480VAC into about 230VDC, and the coil eventually failed short circuit. The old rectifier had a viking funeral, and rapidly disassembled itself with a bang.

I could've sourced a pair of 600V diodes that would've worked, but I liked the idea of some packaging and a terminal block for a component passing 480VDC. I was just supprised they're hard to source from reputable vendors.



ScenreryDriver
 
Back in the 1980's we had a chief electrician who was good with electronics and loved making or improving things. He came up with using a inexpensive 600 volt 30 amp cube rectifier that used the 480 volts from 2 to 5 HP motor normally closed contact from motor starters thru a fuse block and a timer. Would set the timer to energize the rectifier to provide a DC braking voltage to one set of motor windings for shortest amount of time to stop a motor. Usually set the timer for only a quarter of a second then slowly increased it. He also used a cube rectifier to supply 120 volt power to 100 HP Fan motors that were in very damp locations to keep them from building up moisture on windings and grounding out motor coils ( causing motor to burn up ). Cannot remember what he jury rigged to limit current flow. Was cheaper and did a much better job then placing a 5 KW Heater to blow on motors for halve a day to finally lower megger reading to safely start motors.
 
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