Adding a Pilot light to a 24vac circuit?

[slackdaddy1]

Compressor is in the shed 8' from the garage.
I interrupted the compressors control circuit (from the pressure switch to the mag starter coil) with a relay that has a 24vac coil. Added a 24vac transformer.

I ran a 18/2 direct burial wire to the shop where I have a switch that controls the relay in the shed.

NOW,, I want to add a pilot light by the switch.
My only option is to put some sort of pilot light in series with the switch.
Is there any sort of LED pilot light that has built in circuitry that will only pull off 5v of said series circuit,, and still allow the relay coil to work ??
In the end, I would have the relay coil and pilot light in series with a 24vac transformer,

Any Ideas?

 

[mike93lx]

Maybe a simple 12-24vdc marker light made for a trailer with a 24v rectifier?

https://www.etrailer.com/Trailer-Lights/Peterson/PET55PV.html

 

[N_Jay]

Does your 18/2 have a ground?

If so use it for pilots return.

 

[mm08822]

Go buy a 5volt pilot light and put in series. Maybe the 24v coil can pull in with only 19v or maybe not.

Or just re-pull a 18-3 or 18-4 using the 18-2 as a pull line through the earth. Yes, you need to expose the cable at both ends of the 8' to do so.

 

[Firebrick43]

They make 24 v switches that you can wire up so the switch itself lights up when you turn it on

There are 1000's of LED lights as well as industrial electrics use the metric **** ton out of 24 v

You could also just wire in another relay and light up what ever light you so desire.

What form factor of switch are you looking for?

This is why buried conduit is so advisable, it makes changes easy instead of hard in the future with only a few dollars added initially

Red 22MM maintained switch with LED 24v Automation Direct

ON / O?F Plate Automation Direct

 

[dave*99]

Could this work for you?

Put the 24V transformer, switch and pilot light in the garage.
Send 24V through the 18/2 to close the relay you added to the compressor in the shed.

Also - you could switch the 120V going into the transformer in the garage with a switch that has a built in 120V pilot light.

Like this:

Garage:

120VAC source
Switch with 120V pilot light
120/24V transformer

18/2 to shed carrying switched 24V

Shed:

Relay interrupting compressor control circuit receiving 24 VAC

 

[N_Jay]

Could this work for you?

Put the 24V transformer, switch and pilot light in the garage.
Send 24V through the 18/2 to close the relay you added to the compressor in the shed.

^^^^^^^^^^^^^^^^^^^
Good Idea!

 

[theoldwizard1]

This definitely works for 120VAC circuits. I think it will work for 24VAC.

The fact that it is a NEON bulb is KEY !

 

[dave*99]

This definitely works for 120VAC circuits. I think it will work for 24VAC.

The fact that it is a NEON bulb is KEY !

Neon indicator lamps typically fire at 90V.
But you could send 120V to the transformer through this type of switch.
If configured as described in post 6.

 

[mm08822]

He has 18-2 between buildings. Certainly conductor size and probably the voltage rating prevent using it on ac circuit.

 

[JSutter]

453

 

[Norcal]

Get a 24V, 22 MM (7/8") pilot light.

 

[larry_g]

Replace your switch with a dual pole switch. Add a wall wart and a light on the the second pole to indicate the switch is on. Now you have your old compressor control on one pole of the switch and a new circuit on the the second pole that is just the pilot light.

lg
no neat sig line

 

[slackdaddy1]

Thanks for all the responses!
The relay at the compressor has a 10-30vac coil at 55mA.
The 18/2 wire running to the switch in the garage does not have a ground.

everything is already set and drywall patched, so cant really change.

I was advised I could put a limiting resistor in series And a Led in parallel with that, and a diode.
I would end up with 3-5v across the LED and ~20vac across the relay coil.

 

[marinusdees]

Replace your switch with a dual pole switch. Add a wall wart and a light on the the second pole to indicate the switch is on. Now you have your old compressor control on one pole of the switch and a new circuit on the the second pole that is just the pilot light.

lg
no neat sig line

This is what I did. Use a two pole switch, feed both poles with the 24v, output, one line to relay (contactor) other feeding light 24 v bulb. You may have to come up with a ground for negative side of bulb. Use a little imagination, it can be done without running another wire to the shed. There are plenty of grounds near.

 

[mm08822]

When you're "locked in" to 2 wires, all of the other replies kinda mean nothing.

If the OP "must" keep the switch in the garage vs. changing to status light only, then his only chance is indicator light in series with coil and switch.

 

[dave*99]

When you're "locked in" to 2 wires, all of the other replies kinda mean nothing.

If the OP "must" keep the switch in the garage vs. changing to status light only, then his only chance is indicator light in series with coil and switch.

Not really. He can send 24v to the shed from the garage. And hang the pilot light off the send. Switch, transformer and pilot in garage.
The 24V can close the relay in the shed.
Given the relay spec of 10-30v he could send 12V.
But there is nothing wrong with the series light approach.

 

[mm08822]

Not really. He can send 24v to the shed from the garage. And hang the pilot light off the send. Switch, transformer and pilot in garage.
The 24V can close the relay in the shed.
Given the relay spec of 10-30v he could send 12V.
But there is nothing wrong with the series light approach.

True, but now it's another circuit involved. Not the end of the world.

 

[dave*99]

Thanks for all the responses!
The relay at the compressor has a 10-30vac coil at 55mA.
The 18/2 wire running to the switch in the garage does not have a ground.

everything is already set and drywall patched, so cant really change.

I was advised I could put a limiting resistor in series And a Led in parallel with that, and a diode.
I would end up with 3-5v across the LED and ~20vac across the relay coil.

You will need to know the coil current @ 20 V to calculate the sampling resistor used to develop the 4V voltage drop powering the LED. Might be around 40mA. So a 100 ohm resistor could work. 0.16W resistor dissipation. I’d use a 1W or half watt resistor. You need a current limiting resistor of the appropriate value in series with the LED.

https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-led-series-resistor

It will work without an additional diode if the LED can withstand the reverse voltage. If you use a series diode allow for the forward drop in your current limiting resistor calc.

I might design for a 5V drop if using a series diode for the LED.

 

[slackdaddy1]

When you're "locked in" to 2 wires, all of the other replies kinda mean nothing.

If the OP "must" keep the switch in the garage vs. changing to status light only, then his only chance is indicator light in series with coil and switch.

You are correct,
the 18/2 was buried, drywall opened, ran in the shop, mounted switch box,, done deal when I decided I wanted a "light"

Sounds like either a LED or even 6-9v bulb will work in series with the right resistor.

 

[slackdaddy1]

You will need to know the coil current @ 20 V to calculate the sampling resistor used to develop the 4V voltage drop powering the LED. Might be around 40mA. So a 100 ohm resistor could work. 0.16W resistor dissipation. I’d use a 1W or half watt resistor. You need a current limiting resistor of the appropriate value in series with the LED.

https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-led-series-resistor

It will work without an additional diode if the LED can withstand the reverse voltage. If you use a series diode allow for the forward drop in your current limiting resistor calc.

I might design for a 5V drop if using a series diode for the LED.

Thanks Dave, this helps me narrow it down.

 

[Citation]

Can you move the 24V transformer into the garage? If you can do that then you plug the transformer into an outlet in the garage, add a 24V pilot light to the transformer output in parallel with the line going to the relay in the shed. This is an example of such a light

Whoops, we couldn't find that.

<- I checked, the link to the Grainger part works even thought it shows an error

Of course if the 24V transformer is in the garage you could simply plug it into a switched outlet along with a desk lamp. If the lamp is on, so is the compressor.

 

[slackdaddy1]

Can you move the 24V transformer into the garage? If you can do that then you plug the transformer into an outlet in the garage, add a 24V pilot light to the transformer output in parallel with the line going to the relay in the shed. This is an example of such a light

Whoops, we couldn't find that.

<- I checked, the link to the Grainger part works even thought it shows an error

Of course if the 24V transformer is in the garage you could simply plug it into a switched outlet along with a desk lamp. If the lamp is on, so is the compressor.

The "switch" in the garage is a 2hr wind up timer switch.
If the Lamp in series does not work,, I will have to go without a lamp or move the Xformer to the garage side.

I am **** about a clean, built in look. all my switches and outlets, etc are "built in, no surface mount.

 

[American Locomotive]

A typical basic indicator LED would only have a 10-20mA current limit. Not nearly enough to power your coil.

Your best bet would be to put a resistor in series to drop off about 3v across it (my math suggests about 65 ohms should do it based on 48mA coil current). Then off that resistor, you will need a diode and another current limiting resistor (which you have to determine later) and a red LED.

I really don't recommend doing this though, as I don't expect the coil to always operate reliably down around 20v, especially when the compressor starts and the voltage drops even further.

 

[Citation]

The "switch" in the garage is a 2hr wind up timer switch.
If the Lamp in series does not work,, I will have to go without a lamp or move the Xformer to the garage side.

I am **** about a clean, built in look. all my switches and outlets, etc are "built in, no surface mount.

Where is the transformer? Is it in the shed or the garage? If the transformer is in the garage (ie you are sending both legs of the 24VAC power from the garage) then it would be easy to do this. If it's in the shed (ie you are just cutting one leg that is routed from shed to garage and back to shed) then it's harder to do what you want. You might be able to get a light that indicates "off" if you can get a very low current light. Basically the light is parallel to the switch. When the switch is off, the 24VAC goes through the coil and across the light. The catch is the current though the light needs to be low enough to not activate the coil. That balancing game is why I like the idea of a 24V transformer in the garage. It lets you put an "on" light in parallel with the relay. Heck, you could put an on light in both the garage and the shed.

BTW, if you can get 120VAC into the wall box where the timer is and if the box is big enough you might be able to put the transformer (it may not literally be a transformer as a 24V DC converter should also work), switch and light, all into the existing wall location thus keeping a clean look.

 

[Shiftless]

If I understand all that correctly, I think 2 twelve volt bulbs wired in series and connected in parallel would do it. But maybe I’m wrong.

 

[Norcal]

If I understand all that correctly, I think 2 twelve volt bulbs wired in series and connected in parallel would do it. But maybe I’m wrong.

Why? 24V pilot lights are easy to find & not horribly expensive.

https://www.automationdirect.com/adc/shopping/catalog/pushbuttons_-z-_switches_-z-_indicators/indicating_lights#start=0

 

[Shiftless]

Why? 24V pilot lights are easy to find & not horribly expensive.

https://www.automationdirect.com/adc/shopping/catalog/pushbuttons_-z-_switches_-z-_indicators/indicating_lights#start=0

It would certainly be more craftsman like to use a single bulb. I was just throwing out an alternative for anybody who just wants to use something that is already in his spare parts bin.

 

[4x4Pete]

I used some amazon 12vdc leds for a similar compressor control circuit. My Compressor is located in the attached garage, I didn't want to relocate it when I built my shop. I used two start/stop switches out of some old starters, one in each building. I needed a way to see if the compressor was armed. The leds indicate that the start/stop circuit is energized, which "arms" the circuit, the compressor contactor is still energized by the pressure switch. The leds don't cycle with the pressure switch. I used a 240/24vac transformer, probably 50va, the two start/stop switches, a double pole relay, a contactor and two amazon 12vdc leds. The control circuit works perfectly, I had a problem since I only ran 18/3 to the detached shop (120' away)and my wiring schematic wouldn't work without the 4th wire. I ended up wiring the led from the circuit energized "on" to ground, no extra wire needed. It has worked for a few years now. Edit- There is fused protection on both the 240v and 24V sides the circuit that aren't shown.

 

[dave*99]

The "switch" in the garage is a 2hr wind up timer switch.

Please explain. If your switch is a 2 hr timer, what does the indicator light provide? Most folks adding an indicator do so so they remember to turn the compressor off. Yours goes off after 2 hours. Am I missing something?

 

[mm08822]

I used some amazon 12vdc leds for a similar compressor control circuit. My Compressor is located in the attached garage, I didn't want to relocate it when I built my shop. I used two start/stop switches out of some old starters, one in each building. I needed a way to see if the compressor was armed. The leds indicate that the start/stop circuit is energized, which "arms" the circuit, the compressor contactor is still energized by the pressure switch. The leds don't cycle with the pressure switch. I used a 240/24vac transformer, probably 50va, the two start/stop switches, a double pole relay, a contactor and two amazon 12vdc leds. The control circuit works perfectly, I had a problem since I only ran 18/3 to the detached shop (120' away)and my wiring schematic wouldn't work without the 4th wire. I ended up wiring the led from the circuit energized "on" to ground, no extra wire needed. It has worked for a few years now. Edit- There is fused protection on both the 240v and 24V sides the circuit that aren't shown.

Is this how it is wired?

Where are the motor overloads - manual reset or an overload relay in series with contactor?

 

[4x4Pete]

It has a manual reset overload. This was built from some old starters I had laying around. The overload is a bit light if you were to size it. I think it was rated at 20 amps and the motor was 23 fla. It is wired as my drawing. The detached shop is the lower start stop section of the drawing. Because I had only 3 wires run, the Led doesn't go to common, it goes to ground. The controls are all located in the attached garage at the compressor, the detached just has a start/stop and led.

 

[slackdaddy1]

A typical basic indicator LED would only have a 10-20mA current limit. Not nearly enough to power your coil.

Your best bet would be to put a resistor in series to drop off about 3v across it (my math suggests about 65 ohms should do it based on 48mA coil current). Then off that resistor, you will need a diode and another current limiting resistor (which you have to determine later) and a red LED.

I really don't recommend doing this though, as I don't expect the coil to always operate reliably down around 20v, especially when the compressor starts and the voltage drops even further.

The relay I am using has a coil rated at 10-24vac, This relay is not the mag starter contactor. It is a relay I am putting in series with the air pressure switch that operates the mag starter relay coil. That is a 120v circuit

 

[slackdaddy1]

Where is the transformer? Is it in the shed or the garage? If the transformer is in the garage (ie you are sending both legs of the 24VAC power from the garage) then it would be easy to do this. If it's in the shed (ie you are just cutting one leg that is routed from shed to garage and back to shed) then it's harder to do what you want. You might be able to get a light that indicates "off" if you can get a very low current light. Basically the light is parallel to the switch. When the switch is off, the 24VAC goes through the coil and across the light. The catch is the current though the light needs to be low enough to not activate the coil. That balancing game is why I like the idea of a 24V transformer in the garage. It lets you put an "on" light in parallel with the relay. Heck, you could put an on light in both the garage and the shed.

BTW, if you can get 120VAC into the wall box where the timer is and if the box is big enough you might be able to put the transformer (it may not literally be a transformer as a 24V DC converter should also work), switch and light, all into the existing wall location thus keeping a clean look.

The transformer is in the shed,,

 

[slackdaddy1]

Please explain. If your switch is a 2 hr timer, what does the indicator light provide? Most folks adding an indicator do so so they remember to turn the compressor off. Yours goes off after 2 hours. Am I missing something?

You are correct,, lets me know at a glance if the timer had run down, without walking across the shop.

 

[dave*99]

You are correct,, lets me know at a glance if the timer had run down, without walking across the shop.

Then put the indicator LED across the switch. It will tell you the timer ran out.

 

[slackdaddy1]

Then put the indicator LED across the switch. It will tell you the timer ran out.

Ya know,, that is brilliant!
Problem solved