OT: Brake Motor Help

I have a baldor brake motor VMB3546

http://www.baldor.com/products/detail.asp?1=1&catalog=VBM3546&product=AC+Motors&family=Brake%7Cvw%5FACMotors%5FBrakeMotor&winding=34WGX269&rating=40CMB%2DCONT

It seems we lose the brake coil on one of these every couple months and I can't figure out why and it is only on 1 machine. All the other machines have the same motor and no problems.

This brake is wired 120 ac and is controlled by the slc plc. We can't use it wired into the motor because the motor is on a drive and if the brake is powered from the windings it comes on when we don't want it to.

The motor shop converts these for us to bring the brake coil wires out to the terminal box but how is this possible? It is a 460/230 volt motor and the brake coil is 120 vac and from the factory it is connected to the motor windings? How does that work?

What could cause us to lose this coil so often? Every time I check the voltage it is 115 and the motor ansd brake are in a cool place.

Does anyone on else make a motor with brake like this that has external power to the brake that you can buy from factory without it being a special modification from the motor shop like we have? I have been looking but no joy so far.

Do you make sure that the brake is always de-energised when the motor is not running. If not then the brake is likely to burn out as the cooling fan is not turning. This is the most common reason for this type of fault that I see.

SEW Eurodrive motors/brakes can be either supplied externally, powered by the windings or powered by the windings with an external "Enable" signal (For faster operation). There are lots of voltage options.

The first thing I would do is to check the current going to the brake coil while the brake is released (coil energized) and compare it to some of the other brakes that aren't burning up. I'd suspect that it is higher. If that is the case, I would look at the mechanical gapping. Typically the gap is adjustable and has some spec to meet.

Like any electromagnet coil, it will pull high current when the object(the brake mechanism) it is attracting is far away. The current will drop as the object is closer. If the gap is too large when the brake is released, the coil will continue to pull higher than normal current and will tend to burn out sooner than others.

my 2 cents.

This brake is wired 120 ac and is controlled by the slc plc. We can't use it wired into the motor because the motor is on a drive and if the brake is powered from the windings it comes on when we don't want it to.

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I can see that if a brake is powered from the motor windings, then when a VFD runs a VFD at very low speed the brake coil could be deenergized due to low voltage. Typically, a motor brake is applied when power to the motor is cut off. The brake is applied by a spring when an electric coil is deenergized. Your PLC must have an input from the VFD to tell it when the drive is NOT in RUN mode. Otherwise the brake could be applied when the motor is turning. This specific PLC logic could be using the wrong input from the drive, such as a NO contact from an "At Speed" drive output, instead of a NC contact from a "Drive Enabled" or "Motor Running".

Lancie1 said:

I can see that if a brake is powered from the motor windings, then when a VFD runs a VFD at very low speed the brake coil could be deenergized due to low voltage. Typically, a motor brake is applied when power to the motor is cut off. The brake is applied by a spring when an electric coil is deenergized. Your PLC must have an input from the VFD to tell it when the drive is NOT in RUN mode. Otherwise the brake could be applied when the motor is turning. Thhis specific PLC logic could be using the wrong input from the drive, such as a NO contact from an "At Speed" drive output, instead of a NC contact from a "Drive Enabled" or "Motor Running".

Click to expand...

Yes, Methinks a wiring diagram is required!

Wire the brake up to a contactor and use the fault contacts on the vfd to energize the contactor when the vfd is faulted.

Many brake coils are actually DC coils, and require a rectifier to change the AC voltage to DC voltage. Either half-wave or full wave rectification can usually be selected, depending on the terminals used on the rectifier pack (my experience is with Sumitomo and SEW motors). Full wave rectification is to be used at 230v and half wave rectification is to be used at 480v. This gives roughly the same DC voltage at the coil.

Does your motor use a rectifier, either internally, or as an external rectifier module? Is it wired correctly? Did someone forget to install it (if it's necessary) at the rewind shop?

You mentioned that your brake coil is 115vac. Are you sure it wasn't inadvertently hooked up to 208/230v? That would cause it to heat up quick!


-rpoet