Load Resistors

[marshjhm]

I have recently received a piece of equipment from an oem with an Allen Bradley Pico controller. I have pulled wires and set it up to run using a 1756-OW16 output card to drive three inputs from a supervisory Controllogix processor. The problem is the outputs have a small leak current that activates the inputs on the Pico controller even when the outputs are off. My quick fix was to put a small light bulb as load to bleed off the stay current and pull the voltage to zero. This has worked up to now, but this is not the best solution. What I think I need is a high resistance load resistor to pull down the leak current. Does anyone know what value/wattage I should use for this?

 

[kolyur]

OW16 is a relay output card so I don't see how you could be getting any leakage current. When the output is off, there is a mechanical break in the circuit. Is your control voltage 24VDC?

If I need to pull down an output or input, I typically use a 1/4W 10K resistor. The optoisolators on PLC inputs generally operate in the <10mA range, so this is more than sufficient.

 

[bernie_carlton]

Note the contact protection shown in the equivalent schematic. The table lists up to 1.5 ma leakage.

 

[Mickey]

Note the contact protection shown in the equivalent schematic. The table lists up to 1.5 ma leakage.

A little more on that

 

[marshjhm]

I should have stated the control voltage. I'm using 110V AC, so I think 10K would be a little small. Thanks for your help.

 

[danw]

Thanks for posting the details on relay contact outputs that leak current. That was news to me. Who'd a thought . . . .?

 

[Mickey]

Thanks for posting the details on relay contact outputs that leak current. That was news to me. Who'd a thought . . . .?

That got me with a flex relay output module once. Spent a couple hours troubleshooting before I got the manual out.
It ran fine for a few years with nothing but solenoid loads. We then connected an electronic strobe light, it worked fine when the relay was pulled in
but when the relay was open the light would blink about every 8 min. Something in the light was apparently charging up thru the leakage. I thought how could this be, its a "relay".