I plan to control a 12VDC motor that is rated at 250 mA under no load, using an Arduino Uno. I have a Grove 2-coil latching relay rated at 3 amps that will provide the forward/reverse selection, and then a STSP relay between the Grove and the motor to control on/off. This is new territory for me, and so I am hoping for some feedback on a few points:
I understand that using two zener diodes nose-to-nose (or back-to-back) in parallel with the STSP relay provides effective flyback protection while minimally degrading the relay contacts. I have had a great deal of difficulty finding a clear explanation for how to spec the diodes. I did find a post here that gave this rule-of-thumb: voltage rating roughly equal to that of the relay coil, and a current rating that is about 10% of the coil's draw. Does this sound right?
Do I need to similarly isolate the motor? I am assuming the Grove unit can handle it directly and so nothing is needed for it. Is that right? If I do need to isolate the motor, would the rule-of-thumb above apply here also?
I'm assuming I can use the Grove board without any additional buffering. Or should it too be isolated?
As you can see, I have only a marginal grasp on the principles at play here. Any advice would be greatly appreciated.