Power Supply Issues

[Josef_G]

Hi,
I'm a new engineer working on a prototype with a circuit including the following components:
PLC (24V)
Servo Motor (separate channel, 5V)
Push Button ,fed by the same 24V and fed to the PLC.

I've written a very basic code, where I want the servo to perform a certain pattern of movement following the input from the button. The problem is that when I connect the grounds to each other, the channel that feeds the PLC spikes to nearly 50V. On the other, when the grounds aren't connected the input gate of the PLC always reads "HIGH", even if the wire connected to it isn't connected to any circuit at all!

Am I making a common mistake with a simple solution?

Oh and another bit of information, I've been burning through these servos like mad! I have no idea my the voltage/current are spiking like this.

Thanks to anyone who can give me any tips!

 

[VEBill]

You should sketch out a simple schematic, take a picture, and attach it to this thread - preferrably inline using the Image feature.

Schematic should focus on the power supply (or power supplies?) and wiring.

 

[IRstuff]

You have two separate questions; the latter may simply be due to an internal pullup function that pulls the inputs high to keep them from floating aimlessly. For many single-ended discretes, active low is the signal assertion, so it would possibly make sense that the PLC has all its inputs go high on a open circuit.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[Josef_G]

Thanks for your replies.
I definitely should have thought of uploading a schematic and will do so as soon as I can.

 

[jraef]

Are you trying to use PWM to run a 5VDC servo motor directly off of an output of the PLC that is also performing the logic? If so, that’s the problem. The servo motor is an inductive load, so it will produce a lot of noise on the circuit. That’s why servos have their own controllers (drivers) that run the motor but are isolated from the control system telling them what to do.


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