3Phase braking motor wiring

dbh6

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Join Date
Jan 2013
Location
Central, NJ
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552
Hello all,

First time having to work with a braking motor. i have attached the motor nameplate and schematic wiring. The motor is being replaced and i want to make sure i'am doing it correctly. The motor controls a sheet dispensers up/down movement. The motor is being controlled by two PLC outpus, one for up and one for down, wired into an allen bradley reversing starter typical setup,their is an AUX Normally open contact from both starters that is wired to another relay, lets call this the brake relay (relay that controls the on/off of the brake on the motor) that should energize/denergize the brake in the motor. The purpose of the Aux normally open contacts is when either of the starters pull in for up/down the normally open will be normally closed their by energizing the brake relay which which should inturn release the motors brake. The brake relay has 1 dry NO contact, and i want to know where to wire it in to the terminals of the braking motor to achieve what i have described.

I have the windings wired for low voltage, based on the schematic terminals A & B look like the supply for the brake. So if i wire leg 7 to terminal A then have a wire go to one end of the normally open contact of my brake relay then have the other end go to B i think i can achieve what i want, sounds simple, but i just want to be sure. Also if someone with knowledge of Bobine/coil can explain to me what that is i'd appreciate it, and yes i googled it, i didn't find anything credible.

photo.jpg 20140624_113449.jpg
 
If the A and B wires are hooked to terminal #1 and #2 then the "brake relay" contacts would be hooked to terminal #3 and #4 and the jumper wire would be removed. This is a rectifier to control the brake solenoid because it is a DC coil. The A and B wires are supplying power to the rectifier.
 
@ Mark, ok that makes sense, i thought that terminals 3&4 was a dry contact that closed when power is supplied from A&B to terminals 1&2. A rectifier would make sense, as i did not see any rectifier symbols on the schematic. So that contact 3&4 if it was "Not made" then is essentially the same thing as removing power to the Bobine coil, thanks mark.
 
The purpose of the Aux normally open contacts is when either of the starters pull in for up/down, the normally open will be normally closed there by energizing the brake relay, which which should inturn release the motors brake.
Not to be too picky, this statement struck me as not very logical. I don't think that a "normally-open" contact could ever be "normally closed". I think what you meant was that "...the normally-open starter contact will close, thus energizing the brake relay.
 
Just to make it clear, the rectifier can work without an external brake relay, only the reaction time when stopping will be slower.
So there must either be the jumper A in place, or an external braking relay.
That it is even possible to work with slow variant is because in some applications the brake does not have to activate quickly, and the expense for an extra cable is significant.
 
@ Jesper yes I'm using an external brake relay, and using the no contact in terminals 3&4 so when the external braking relay is denergized the brake on the motor will hold. Surprisingly we are replacing this motor because someone had wired up the windings for hi voltage 480vac when infact the line voltage was 240vac. The motor actually ran like that and can still run but it was overheating and would stop because they have overlad relays on the starters. I measured the ohms on the bad motor just to see if it is still ok to use if it's properly wired for 240 but the ohms were reading around 162 between two legs but With respect to one leg it was reading 16, so I don't think it's fine as that may produce imbalances.
 
Last edited:
Just to make it clear, the rectifier can work without an external brake relay, only the reaction time when stopping will be slower.
So there must either be the jumper A in place, or an external braking relay.
That it is even possible to work with slow variant is because in some applications the brake does not have to activate quickly, and the expense for an extra cable is significant.


Jesper is correct. If fast the brake needs fast a reaction time, an external brake relay should switch contacts 3 and 4.

In across-the-line wired motors, the brake rectifier supply is wired across two of the motor power phases; the brake releases when power is supplied to the motor.

When a motor is powered by a VFD, a relay or contactor switches AC power to the rectifier to activate the brake.

**This is important** The brake cannot be wired to the motor supply if the motor is VFD controlled.

That relay is controlled by an output on the VFD. That VFD-controlled relay could easily switch between pins 3 and 4 on the rectifier if you need the faster reaction time it affords, but in my experience, that's not usually necessary.


-rpoet
 

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