Output Leakage

I have Automation Direct D06 plc with transistor outputs. What size, (ohms/watt) resistor should I use to connect neon lights to output, (120vac)?

Do you possibly mean 'tirac' output? Transistor output is for DC only. Please list the exact part numbers of the module and the type of the neon light.

First off, neon lights are AC, so transistor outputs aren't going to work. If you meant triac outputs, read on.

Two ways to go about this: trial and error vs. measurement and calculation. Trial and error may very well be faster. But here is what you are trying to accomplish.

When the output is off, you have a certain amount of leakage current. You can try to find specs on it, but it may be faster to just measure it.
Next, you need to know what voltage it takes for the lamp to start glowing. Once again, you can try to find the spec, but guessing or measuring may be faster.

Once you know those two values, the calculation is:

E/I = R

Minimum volts to make the light glow / leakage current = resistance needed.

Next step, how many watts?

P = E*E/R

The voltage this time is voltage when the output is "ON".

OR....

You can buy a few sizes of resistor and experiment. The last step for checking the power rating still applies.

Also, WARNING! These resistors will get HOT.
Note: this design is for a resistor in parallel with the neon light.

Thanks

Bernie, Mellis,
Thanks, obviously you are both correct on the transistor/triac issue. Thanks for the info on the calculations. that will get me where I need to go!

Pete

Neon lights generally need some type of series resistor. Some may come with an appropriate series resistor as part of the package for a certain voltage (e.g. 120 vac). Check to make sure.

100K to 150K for 120V neons. 1/4 watt.
Link

as keithkyll says 150k for 120v neons .1/4 watt is the best option for you .