24Vdc Tri-state LED

ranjana · Nov 10, 2002

We are building a mimic panel . we have a requirement for Tri-color LEDS.
namely RED-Forward, Green-Reverse , Yellow- faulted.
I want to switch on these leds from PLC. So i would naturally use 24Vdc.

But i could not find LEDS with 24Vdc. All i could find is LED for 2.4Vdc.

Is there any LED manufacturer who has tri color led(Red, green ,yellow)for 24VDC. Also LED size we are looking for is 8mm.

Can you please post their link.

Many thanks

Gerry · Nov 10, 2002

Two-colour LED's (red/green) give a yellow or amber light when both the red & green are on.

To make the LED's work on different voltages, use appropriate value current-limiting resistors. Run them on AC with diodes for reverse-bias protection.

Terry Woods · Nov 10, 2002

Yeah, yeah, yeah... so I had a little time on my hands...





            PLC        Amp Limiting       RED

 P/S     Output-1        Resistor         LED      P/S

24VDC+ -----\_/----------/\/\/\/\/--------|>|-----24VDC-

         Sourcing      ohms?? watts??     .7V

                                          40mA



            PLC        Amp Limiting       GRN

 P/S     Output-2        Resistor         LED      P/S

24VDC+ -----\_/----------/\/\/\/\/--------|>|-----24VDC-

          Sourcing     ohms?? watts??     .7V

                                          40mA

. <--- (Dummy Character to keep next line from running off-screen...Phil?)
Assuming Volt Drop across the PLC Output is 0-Volt when the output turns on... what resistor do you need to keep the LED from being destroyed?

Typical LED Characteristics (your milage may vary):

Voltage Drop = .7 Volt
Amperage = 40 mA
Power = approx 28 mW

Voltage Drop across Resistor:
VP/S - VLED = VR

24V - .7V = 23.3V

Resistor Value
VR / IR = RR

23.3V / 40mA = 582 ohms (use the next higher standard resistor value)

Resistor Power Value
VR * IR = PR

23.3V * 40mA = 932mW = 1-Watt

COLOR CONTROL

            RED        GREEN

STATUS    Output-1   Output-2   Color 

 none       OFF        OFF      No-Color

 Forward    OFF        ON       GREEN

 FAULT      ON         ON       YELLOW (RED + GREEN)

 Reverse    ON         OFF      RED

Charles1 · Mar 3, 2009

Back in the day when Radio Shack was worth a flip, they sold a two lead, tri-state, 5mm LED. Which would be green when forward biased, red when reversed and yellow when an AC current is applied. This is pretty clever as far as the packaging of the LED, but having to deal with a mix of 24V AC and DC would probably be an issue.

ATU · Mar 3, 2009

If you want to spend a little more, these are really nice and you don't need the resistors.

http://www.baneng.com/en-US/products/112/Indicator-Lights/710/Multi-function

Brijm · Mar 3, 2009

ATU said:
If you want to spend a little more, these are really nice and you don't need the resistors.

http://www.baneng.com/en-US/products/112/Indicator-Lights/710/Multi-function

I've been looking at those recently... Not a bad price, when compared to three pilot lights.... And not even close, if you bought three LED pilot lights or a stack light.

-MUR

ATU · Mar 3, 2009

I have used the 18mm prox type and also the larger 32mm dome. Both are more than bright enough.

I use HMI's on most all machines but sometimes when dealing with a manual operation , a simple light works best.
They are less expensive when you consider the cost of individual lights and labor to wire them.

I have not tried the stack lights yet.

Plastic · Mar 3, 2009

Off-The-Shelf

These are very effective visual indicators.

http://www.newark.com/78K9909/optoelectronics/product.us0?sku=BANNER-ENGINEERING-T30GRYPQ

Longhorn · Mar 4, 2009

Here in the uk we would probably use something like these:-

http://uk.rs-online.com/web/search/..._uk|1||new_uk|1&Nty=1&binCount=455#breadCrumb

Excuse the long link (just to save you searching)

8mm Panel Mounted LED's

Hope this is of use.

24Vdc Tri-state LED

ranjana

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Gerry

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Terry Woods

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Charles1

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ATU

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Brijm

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ATU

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Plastic

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Longhorn

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