There is a 3 phase motor running by an inverter. motor specification is about 1.8KW power and 230/400V and 1.13A. I want to drive another DC motor synchronized with that AC motor so the DC motor goes ON and OFF with AC motor. there is no Neutral connection to motor so I can't use a relay or contactor, also inverter is connected to PLC through Modbus connection and I don't want to modify inverter or PLC.
What I have done and my questions:
I thought about using a current sensor (or hall effect sensor) to monitor AC current going to motor, and I found too many different kinds of it. I also tried 3 phase monitoring relay, when I connect it to main 3 phase supply it works correctly and a relay activated inside of it but when I connect it to motor/inverter it doesn't work in 6 different connection type I tried. why?
- Is it right to use current sensor for this application? for example allegro current sensor IC ACS758 is it the right choice for this application? as the inverter make different frequencies, doesn't it cause to make buzzing at sensor or op-amp outputs? should I connect 3 different sensor for each phases and SUM their output into an Op-amp?
- or is it better to use a non-invasive clamp current sensor (this) around all 3 phases wire? and/or one of the phases?
- why the phase control relay not works when I connect it to motor/inverter ?
my problem solved:
I use inverter discrete I/Os terminals to detect motor ON/OFF state.