Why is the indicator light always on?

I'm using 120volt neon indicator lights in my control panel. They are hooked up after the ssr to indicate when power is being supplied. For some reason they are always on. They do get brighter when the ssr closes, but are lit dimly before. What would cause this?

I don't think you can rig that up after the SSR and get the results you want. Something in how SSR's work their magic.

When I was testing my setup with a multimeter it always showed a constant 120v per lead, even the SSR lead (240v system), whether the built in SSR light was on or not, and whether or not the power should be flowing or not.

I wired my "element is on!" light to my switch that turns on the juice to the SSR, so while it doesn't truly show if the SSR is firing, it shows that it SHOULD be, and I can look at my element for bubbles.

Psych said:

I don't think you can rig that up after the SSR and get the results you want. Something in how SSR's work their magic.

When I was testing my setup with a multimeter it always showed a constant 120v per lead, even the SSR lead (240v system), whether the built in SSR light was on or not, and whether or not the power should be flowing or not.

I wired my "element is on!" light to my switch that turns on the juice to the SSR, so while it doesn't truly show if the SSR is firing, it shows that it SHOULD be, and I can look at my element for bubbles.

Click to expand...

+1. It's called leakage current. Basically even when a SSR is off some current can flow. It's not enough to turn the element on or heat up or anything, but the indicator lights are designed to take very little power and turn on. You wouldn't want an indicator light that draws as much power as the device. The leakage current is enough to turn the light on... hence it is always going to be on.

You really want to wire the indicator to the input/control current for the SSR and not the output.

I have a DPST contactor in line before my SSR that is energized by the element selector switch. Power is supplied to the SSR only if the element is actually selected for use. When the element is selected, the indicator light does have a dim glow when the SSR is in the Off portion of its cycle. I use that dim glow as a cue that the element is selected even though it may not be firing.
You may not be able to apply this information to your system but it is something to think about.

Thank you! I thought something was wrong with the way I had wired it. I feel much better now.

leakage current in SSRs always trips people up. I was measuring voltage at the output of my SSR, with no load attached to it, and was getting like 80V or something before I realized what was going on.

I also have an indicator light that REALLY behaves oddly. The light is a 240V neon one. One side of the light is fed from an un-switched 120V hot line. The other side is fed from the output of my SSR.

But... In front of the SSR, there is a contactor that is OFF, so there is no voltage available on one side of the SSR.

Basically, I have this circuit:

[120V line] ----- [neon light] ----- [SSR] ---- [nothing]

The light STILL lights up dimly.

Turns out... There is a capacitor network in the SSR. The cap inside the SSR is charging/discharging as the 120V line swings back and forth. The delay in the capacitor reaction is causing a tiny bit of voltage difference to be seen across the light.

That one REALLY boggled me for a while.