I have the blackbox wired to a VFD using the 1-10V terminal. I also use the onboard relay, configured as default, to send a signal to my automated dust collection system (home made, using meshed ESP8266s). I noticed that the relay does not close when the speed requested is below a certain RPM (did not test thoroughly, but under 16k to 18k). Is this because the signal sent to the relay tied to the VFD output and lower RPM means less voltage on the relay's coil? The documentation mentions that the relay configuration to respond to M3 commands should not be used in conjunction with the 0-10V output. Is this the reason why? Is there a way around that or should I use the coolant configuration instead?
Correct, PWM into a relay will make it chatter. ON/OFF (M3S0 vs M3S(max-value-of-$30) for relays Coolant output is the better way to deal with dust extractors
