I have a stepper motor controller which controls 4 fairly powerful steppers and has input pins for 3 proximity sensors. The controller requires 48v so I have the power supply for that. The 3 NPN proximity sensors I have operate at 10-30v and draw 150mA. I initially connected the out pins of the sensors to the controller and powered the sensors from a 12v psu I had lying around. I then connected ground from both power supplies. I was told this was incorrect because if one power supply failed it might wreck other parts of the circuit.
My problem then was how to get it all working correctly. I thought about a relay for each sensor but my preference was for powering all sensors from the 48v supply. I thought about stepping voltage down from 48v to 30v but it requires knowledge I don't have. I could use resistors to do it but I get the feeling that isn't a good idea. It would only draw a maximum of 450mA-500mA but steeping down from 48v to 30v would generate a lot of heat correct?
My other idea was to wire them in series but that's not working as planned. The voltage across sensor 1 is 22v, across sensor 2 is 15v and sensor 3 is 11v. Sensor 1 is operating correctly, when metal passes it the sensor triggers. Sensors 2 and 3 are always on which is confusing because they're clearly getting power but for some reason think they've been tripped when they haven't. When I read the voltage between the + of each sensor and its out pin I get whacky results. Sensor 1 is reading 0v which is correct. Sensor 2 and 3 read 8.33v and 25v respectively.
Since sensors 2 and 3 are trigger, I would've thought those readings would've been the voltage applied across them (15v and 11v) with slightly lower values due to resistance. But, seeing as they're triggered without anything near the sensor then it's strange they have a voltage across them at all.
Is there a way to get the 3 sensors working in series or should I tackle it another way? I'm wondering if there's something I can do to split the voltage into 3, thus delivering 16v into each sensor without any fancy electronics.