Compact Logix 1769-OA16 Output Card

[whiteeagle32]

I am new to the PLC World. I have a 1769-OA16 Ouput card that I wired each ouput to a 120 Volt Relay. When I powered up the card all outputs turned on. Note: I have not programmed the card yet. When I checked my outputs with a meter I have 64 Volts between each output and neutral. Does this mean that my ouput card is bad or what? Please help. Thanks.

[Mickey]

Off state leakage of solid state output. See PDF below. OffStateLeakage.pdf

[BobLfoot]

Mickey has posted an excellent reference, but if youa re new to the PLC world and also new to electronics it might not help you. You state "All Outputs turned on". I must ask how you define or determined the output were on 1. Did your OA Card output LED's actually light up? 2. Did you "isolation relays" energize and you assume the ouputs were on when in fact the leds were off? If you witnessed case 1 then check the data table and make sure to turn the outputs off and see of the problem persists. If you witnessed case 2 then check the pull-in current for your relays I'm guessing it's 1 or 2 ma. You need something closer to 8 or 9 ma latch in / hold in value for your isloation relays.

[whiteeagle32]

I found out today that when I don't have a very large load on the ouputs then I have to have a 15K Ohms 2 Watt Resistor wired parrallel to my load. I have ordered the resistors and will find out tomorrow what happens. Thanks for the help.

[paulengr]

For next time... If you need output isolation, use an OWxx card (OW8 or OW16, depending on the specific backplane series). These have relay outputs on board the cards. If you don't need output isolation (the standard case), then use OA16. Preferably ditch your 120 VAC I/O and go to an OBxx series card or the diagnostic equivalent soon though. This gives you electronically fused protection with "fuse blown" indication (if a diagnostic card is available and you use it), outputs/inputs that are immune to crosstalk issues, much safer to work on (arc flash and shock hazards are a minor issue below 50 Volts), far less damage (usually none) even in the event of catastrophic damage such as a short circuit, and usually roughly 10 times the output/input speed. The places where 24 VDC falls down at is "high power" since you can't drive starter coils directly for instance and most 24 VDC hydraulic valve coils also have very high current demand.