Here's my dilemma - I need to design controls for a robot with a tool changer that picks up 3 different end of arm tools, each tool has a different 24vdc motor on it with rated standstill currents of 4, 6.6, and 7a with a peak current of 18a for each. Our interface connectors on the changer use the same pinout for all 3 tools. I've thought about protecting each motor with their own fusing/MCB's, then switch power on to each when needed ie. when their tool is picked up. If the motors were AC then it would be easy but DC motors with this current I'm not so sure given the difference in switching characteristics of inductive DC loads. Many relays/contactors are rated for continuous current but on closer inspection their actual duty ratings (switching capacity) ie. DC-3, DC-5, etc. are really low. The expected frequency of switching between tools is ~80-100x per shift. So, here are some questions:
- since these loads are close in size, should I not bother with individually protecting and switching each on/off and just protect/switch for largest load?
- if I do that, I still need to switch at least the one line since I don't want to always have live pin at the tool change interface, also to safely switch off in case of e-stop situation
- what kind of switching component to use for DC inductive load(s) of this size that preferably is DIN rail mounted? SSR/power relay/contactor?
- if a SSR, what considerations do I need?
- Am I over thinking this? Should I just use contactor(s) and replace as needed if contacts weld? Thanks for reading and any input!
