Created Date: March 13,2012

Created by: Adisharr

I am building a linear power supply for a DC servo application. The values are 105VDC at the 12000 uFd capacitor, 15A continuous.

The drives have enable pins. I also want to be able to cut the DC to the drives in an estop event. Simply cutting the power to a DC drive tends to fry them and I really don't want to open the transformer contactor or hammer the capacitor with a dumping resistor during an estop.

One method proposed to me is to have two capacitors with a contactor between them. In an estop event this contactor isolates the second (smaller) cap from the first and simultaneously dumps it to a power resistor. Any reflected load from the drives is absorbed by the resistor as well. The transformer, bridge, and first cap remain hot.

This method requires a contactor with at least one normally closed contact. Most safety relays ( McMaster 7230K871, for example) do not have adequate current ratings for this application.

Does anybody know of a force guided relay with at least one N.C. contact and sufficient size for what I propose.

Doug

Possibly use two standard contactors with auxiliary NC contact blocks. Most standard safety control modules will allow feedback from external devices.

Most of the time (hazard dependant) I'll forgo using a safety controller and simply monitor the output from the contactors against the outputs from each contact block to determine if the safety system is working correctly.

Created Date: March 13,2012

Created by: doug6949

I am building a linear power supply for a DC servo application. The values are 105VDC at the 12000 uFd capacitor, 15A continuous.

The drives have enable pins. I also want to be able to cut the DC to the drives in an estop event. Simply cutting the power to a DC drive tends to fry them and I really don't want to open the transformer contactor or hammer the capacitor with a dumping resistor during an estop.

One method proposed to me is to have two capacitors with a contactor between them. In an estop event this contactor isolates the second (smaller) cap from the first and simultaneously dumps it to a power resistor. Any reflected load from the drives is absorbed by the resistor as well. The transformer, bridge, and first cap remain hot.

This method requires a contactor with at least one normally closed contact. Most safety relays ( McMaster 7230K871, for example) do not have adequate current ratings for this application.

Does anybody know of a force guided relay with at least one N.C. contact and sufficient size for what I propose.

Doug

EDIT: As a half-answer to my own question I did find some lighting contactors that were N.C. Unfortunately, they were all contacts N.C. I could not find any with a combination of N.O. and N.C.