I installed a circuit to automatically start a dust extractor when I turn on one of my woodworking machines.
I have one 230V circuit dedicated to powering the machines and another circuit powering the dust extractor. The live wire for the machine circuit goes through a current sensing relay, which then turns on a 40A solid state relay, which switches the extractor live on and off. The motor on the extractor is a single phase 1500W ac motor with a single capacitor.
I also wired in the motor thermal cutout, so that it switches off the 40A SS relay. Also a manual switch that I could use to switch off the 40A relay if I wanted/needed to.
My initial calcs were that the motor draws 6A at full load, so I thought that a 6 times starting current would be enough, hence the 40A solid state relay. Both circuits are protected by Type C 32A RCBOs (Residual current circuit breaker with Overcurrent Protection). I thought that the type C would cope with the starting surge better.
The setup ran fine for about 6 months, then stopped working. I checked the motor and thought that the starter winding was open circuit. I fitted a replacement motor, but the extractor wouldn't start via my circuit. I plugged the extractor directly into a normal supply and it started.
Further investigation showed that the solid state relay was not working - the input is still switching an indicator light on, but the output is staying open circuit.
I tried to start the extractor through the relay a few times while running diagnostics. The motor will now not start even when plugged into a simple mains circuit. It just hums loudly, which seems to indicate that the starter circuit is not functioning.
However, the single, 50uF capacitor tests OK on a multimeter; there is no short to ground (using a multimeter) on the coils or the thermal cutout; the thermal cut out is 0 ohms; and the resistance on the start and run coils are both 3.1 ohms. (Interestingly, the orginal motor tests with similar values - I was mistaken when I thought that the starter circuit was open circuit)
Any fundamental problems with my simple circuit? Should there be additional protection other than the RCBOs which have never tripped?
Both motors seems to test out OK, but won't start. Any ideas what to try next?
I think that the relay has burnt out because it is under size. Would a 60A chinese replacement be good enough or should I get a motor specific brand name one or a bigger one?
Am I correct to include the thermal cutout in my relay circuit?
Current Sensing Switch: https://www.amazon.co.uk/gp/product/B07RWCMWCK