Relay energizing indicator lamp not lighting triac PLC output

I hope I don't end up making a fool of myself here...(again) ...I connected three 110VAC relays to a SLC 500 triac output. The relays have some sort of indicator lamp on them (LED?) There are two different suppliers... releco and Dayton

Here's what is weird: the relays pull in normally and solidly, but the indicator lamps on the relays don't light. I spent a good bit of time checking things, thinking I had screwed something up... expecting to see the lights before I realized that the relays were in fact pulled in.

What could be the reason for that?

besides dumbness on my part.

I'll check things out more tomorrow, but could there be any kind of forward voltage drop on the triacs or something that could cause that?

Since you didn't post the part # of the relays for us to check. I'm go have to reluctantly ask,, are you sure they are 115v ac coil? Some of those relays are difficult read.

Are the coil spades running the same direction as the contact spades? I have one of each in front of me and that seems to be one of the differences (possibly a keying issue to keep someone from putting the wrong type of relay in a base).

thanks for responding... they are 8 pin relays... round pins

I'll have to look into this more tomorrow... I'm sure they are 110vac coils

the coils work well. the indicator lights on the relays don't illuminate.. I'm assuming they are LEDS

the PLC outputs are triacs.

I don't know exactly how things are hooked up in the relay, but it seems to me that disregarding the coil, the LED should conduct half of every cycle.

I think that triacs have a forward voltage drop... how much I don't know. I'm wondering if an LED with sufficient series resistance to refrain from evaporating on 110VAC would conduct because of that forward voltage drop of the triac.

It is always possible that the LEDs are defective (or maybe your relays and LEDs were made for 240 VAC or even 24 VAC or 24 VDC). The coils still might pull in.

You could quickly eliminate any supposition about your Triac outputs by simply hooking one relay coil to fused power-line 120 VAC. If the LED still does not light, then you have your answer.

Lancie1 said:

It is always possible that the LEDs are defective (or maybe your relays and LEDs were made for 240 VAC or even 24 VAC or 24 VDC). The coils still might pull in.

You could quickly eliminate any supposition about your Triac outputs by simply hooking one relay coil to fused power-line 120 VAC. If the LED still does not light, then you have your answer.

Click to expand...

Well, that's what I intended to do, but you're no fun... what's the point of trying to discuss theory and abstractions when you can just hook it up to what it's supposed to be connected to??

What if I connect it to 110vac and the lights light? I suspect they will.

What if I connect it to 110vac and the lights light? I suspect they will.

Click to expand...

If the relay power-on LEDs light with power-line 120 VAC, then that tells you the PLC output is affecting the LEDs somehow, and will it matter why? The bottom line will be that if you use this particular relay on these PLC outputs, you will not have an indicator LED.

You're no fun... what's the point of trying to discuss theory and abstractions, when you can just hook it up to what it's supposed to be connected to??

Click to expand...

Sorry, I didn't mean to short-circuit the conversation. I have seen too much to know there are probably some relay LED indicators that could be designed, selected, or wired so that they would NOT light up on some specific TRIAC (TRansIstor AC) output.

Hey I was just kidding... U didn't short circuit anything . I'm sorry if it sounded like I was griping at you. I didn't mean to I was trying to be funny. No offense intended and thanks for your reply I'm sure u are absolutely correct in ur assessment.

No problemo, carry on!

realolman said:

Well, that's what I intended to do, but you're no fun... what's the point of trying to discuss theory and abstractions when you can just hook it up to what it's supposed to be connected to??

Click to expand...

Almost the same disappointment when the ON OFF switch is put in the ON position

Dan Bentler

Ya know, a part number for the relays would be a big help.
Do they actually HAVE indicator lights?

Hi,
Sometimes these relay LED lamps are polarity sensitive. So. "A1" should be connected to the PLC output & "A2" goes to neutral.

The relay coil will operate either way, but the LED wont. The LED lamp must be forward biased or it won't work. The Triac will put out a small amount of current in the "OFF" state. Look at your owners manual for the particular specification. A pull down resistor will eliminate the leakage current if necesary.

BD