Problem with Bridge rectifiRr of Motor Brake

The pdf at this site may help:

http://www.weg.net/files/products/1-410.pdf

Have had similar problems. Ended up being caused by voltage drop. When utility voltage sagged due to consumption at peak periods, plant power dropped just enough that voltage delivered to the load, meaning the rectifier, was a little to low. We up sized the conductors feeding the rectifier and problem went away.

Thanks in interesting my problem.

1) Bridge rectifier reverse voltage is 600V.

2) There is no varister connected aspect a free wheeling diode. (Do I remove it now?)

3) The rating of Bridge rectifier is 10A.

4) The operation of motor is momentarily as it is for the sealing head of Signode bundle tying machine.

5) I tested the coil resistance at room temperature, did not test at high temperature.

The freewheel diode needs to be there if the brake coil current is switched on and off AFTER the bridge. However, the diode causes a long delay in the drop-off time of the brake, due to the inherently large time constant of such an iron-cored solenoid. Perhaps this will give you some more help, in addition to the excellent help given by others...

you have to connect varistors at the ac and at de dc side of the rectifier.

please use rectifier with reverse voltage equals 1000 or 1200 volt

1) 600V rating should be adequate, but

2) you must protect against high voltage spikes with a suitable varistor. I believe over-voltage spikes are the main reason for your bridge failure. A free-wheeling diode does not protect against positive voltage transients, only the negative inductive spike from the -Ldi/dt.

3) Current rating is very conservative and over-current damage is highly unlikely.

4) When properly configured/protected, frequent cycling should NOT cause premature failure.

5) With the new information, I believe coil damage is unlikely.

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Focus on getting varistor protection for the bridge.

Sorry for crude sketch...



On/Off control switch before bridge (1) allows bridge to act as its own freewheeling diode and extra freewheeling diode is unnecessary.

On/Off control switch after bridge (2) may NEED added freewheel diode to protect the SWITCH from inductive voltage spikes.

Varistor after bridge protects bridge from voltage transients.

AC side varistor should not be needed due to action of diode bridge.

Another detail that can damage the bridge, is if the pressure plate has restricted movement (cannot contact the coil armature due to dirt or binding) the impedance will rise as will current.

Sorry to contradict....this is a DC brake. No impedance. Current = V/R. Only the rise time of the current will be faster, since, time constant (L/R) with an open armature will be lower than when the armature is fully closed.

Correction ... This is DC current and not AC. Even though there is a ripple in the rectified current, the coil resistance remains the same (no reluctance here) except increase with temperature (small increase). the current remains the same....