Hi Guys,
I'm wondering if anyone can help listing the considerations when looking to size a braking resistor for a VFD. It's typical for our clients to provide complete MCCs to interface with (we supply motor list, VFD/starter requirement, feedback if required and brake if required). I've found a manual from AB regarding sizing for a PF700 (Publication PFLEX-AT001J-EN-P – March 2007) which goes through quite a detailed process. It seems to me that one could quickly pick an oversized resistor to deal with the job and disregard the calculations involving load inertia (how is one to calculate these values?). Is this correct? If so - how is one to know what is adequate?
What is the typical protection type circuitry required for using an external resistor? I have seen different ideas on how this can be done, from using the DB thermal switch to open a contactor on the line power side of the VFD. Is it possible to rather simply wire the thermal switch direct into an input and configure it as an AUX Fault (fault action coast to stop)?
I'm wondering if anyone can help listing the considerations when looking to size a braking resistor for a VFD. It's typical for our clients to provide complete MCCs to interface with (we supply motor list, VFD/starter requirement, feedback if required and brake if required). I've found a manual from AB regarding sizing for a PF700 (Publication PFLEX-AT001J-EN-P – March 2007) which goes through quite a detailed process. It seems to me that one could quickly pick an oversized resistor to deal with the job and disregard the calculations involving load inertia (how is one to calculate these values?). Is this correct? If so - how is one to know what is adequate?
What is the typical protection type circuitry required for using an external resistor? I have seen different ideas on how this can be done, from using the DB thermal switch to open a contactor on the line power side of the VFD. Is it possible to rather simply wire the thermal switch direct into an input and configure it as an AUX Fault (fault action coast to stop)?