LED Colour light signal wiring problem,

[ikcdab]

Hi there, I am trying to wire up a set of Eckon colour light signals. These are the standard heads but mounted on scratchbuilt posts and gantries. They are:

signal 1; platform 1 starter: a standalone 3 aspect signal

Signal 2: platform 2/3 starters - 2 x 3 aspect signals mounted on a gantry, wired via a 2 pole 5 way rotary switch such that when 1 signal head is showing green or yellow, then the other is showing red

signal 3: home signals - 2 x 2 aspect red/yellow mounted on a gantry wired via a 2 pole 3 way rotary switch such that when 1 head is showing yellow, the other can only show red. 

i have used a single 1k resistor as supplied by eckon. the power supply is a 12v 2 amp DC smoothed power supply from megapoints.

The diagram attached shows the wiring as i have it.

All the signals will show red concurrently quite happily.

when either of the three signals is connected on its own, all works OK. So i know the continuity is OK.

however, when all three signals are connected to the power supply and any signal is switched to yellow or green, although the reds on all the other heads stay lit OK, the yellow or green are so faint as to be virtually undetectable. 

I'm pretty sure i have enough power as all the five red LEDs light OK. however, to be sure i have tried alternative power supplies without any difference. so i am certain that the power supply is OK.

If i switch a signal to yellow or green (very faint) and then i unplug one of other signals then the faint yellow or green begin to glow and if i unplug the third signal, then the yellow/green spring into normal brightness.

so why are things not working OK? As the green and yellow LEDS are so faint, i assume i have some current leak somewhere. Do i need additional diodes or should i use individual resistors for each head? is a common return problem?

Grateful for all comments and help!

Ian

 

Edited January 21, 2020 by ikcdab
Clarified power supply details

[meil]

13 minutes ago, ikcdab said:

Hi there, I am trying to wire up a set of Eckon colour light signals. These are the standard heads but mounted on scratchbuilt posts and gantries. They are:

signal 1; platform 1 starter: a standalone 3 aspect signal

Signal 2: platform 2/3 starters - 2 x 3 aspect signals mounted on a gantry, wired via a 2 pole 5 way rotary switch such that when 1 signal head is showing green or yellow, then the other is showing red

signal 3: home signals - 2 x 2 aspect red/yellow mounted on a gantry wired via a 2 pole 3 way rotary switch such that when 1 head is showing yellow, the other can only show red. 

i have used a single 1k resistor as supplied by eckon. the power supply is a 12v 2 amp transformer supplied by megapoints.

The diagram attached shows the wiring as i have it.

All the signals will show red concurrently quite happily.

when either of the three signals is connected on its own, all works OK. So i know the continuity is OK.

however, when all three signals are connected to the power supply and any signal is switched to yellow or green, although the reds on all the other heads stay lit OK, the yellow or green are so faint as to be virtually undetectable. 

I'm pretty sure i have enough power as all the five red LEDs light OK. however, to be sure i have tried alternative power supplies without any difference. so i am certain that the power supply is OK.

If i switch a signal to yellow or green (very faint) and then i unplug one of other signals then the faint yellow or green begin to glow and if i unplug the third signal, then the yellow/green spring into normal brightness.

so why are things not working OK? As the green and yellow LEDS are so faint, i assume i have some current leak somewhere. Do i need additional diodes or should i use individual resistors for each head? is a common return problem?

Grateful for all comments and help!

Ian

 

It is not good to run LEDs from a transformer as they don't really like AC. You should run them from a DC source such as a switched mode power supply. Running the LEDs from a single resistor is also not good as different coloured LEDs require different currents, so your light intensity will vary greatly between LEDs.

[ikcdab]

Just now, meil said:

It is not good to run LEDs from a transformer as they don't really like AC. You should run them from a DC source such as a switched mode power supply. Running the LEDs from a single resistor is also not good as different coloured LEDs require different currents, so your light intensity will vary greatly between LEDs.

Sorry I was unclear. The transformer (power supply) outputs regulated 12v 2amp dc. It is the one supplied by megapoints.

As regards the resistors, I am using the 1k supplied by eckon.  I could easily use a different one for each aspect if that is what is required. But what values would I need?

[dhjgreen]

Eckon signals are quite happy with 1kohm for all colours. However you need to use all the resistors they have supplied, one for each head.  As the reds are lower voltage with your set up the reds steal most of the current.

[sharris]

I haven't gone through all the switch permutations but one thing is certain: you shouldn't have a situation where you can have LEDs in parallel (particularly if they are different colours) - the forward voltage at which an LED starts to conduct can vary slightly from LED to LED of the same type, and considerably for LEDs of different colours - when this happens the LED that has the lowest forward voltage will grab all, or at least, most, of the current and will be brightly lit, while the others will be dimly lit, or not lit at all. The way to prevent this is to give each LED its own series resistor (if I've counted right, that's 13 resistors) - the easiest place to put them might be to solder one end of each directly to the tabs on the rotary switches, and the other end to the wires leading to the signals (put a bit of sleeving over them to prevent anything shorting on the back of the switches). 

 

As for balancing the brightness with different resistor values, I can't suggest anything more than trial and error to get a brightness you are happy with - I'd temporarily use a set of resistors and pots in series, adjust them until I was happy and then measure the combined resistances for each colour - e.g. 

 

 

             1K             1K
+12V o-----/\/\/\/-------/\/\/\/
                            ^           ^^
                            |          //  RED
                            +---------|>|------o OV
              1K            1K
+12V o-----/\/\/\/-------/\/\/\/
                            ^           ^^
                            |          //  GREEN
                            +---------|>|------o OV
              1K            1K
+12V o-----/\/\/\/-------/\/\/\/
                            ^           ^^
                            |          //  YELLOW
                            +---------|>|------o OV

with the values shown, you'll be able to adjust the LED current between approximately 5-10mA (using the fact that you've been supplied with a 1K ohm resistor as a guide for the maximum current).

 

Edited January 21, 2020 by sharris

[steve W]

You need one resistor for each LED that is lit at any one time, so a minimum of five connected as shown below.

A better and neater option is one in each LED line with the 12V taken directly to the switch wipers, then if you reconfigure the signals at any time the LED's are protected. The double head signals in yr diagram share a common return line, so you can't fit the resistor in the black return line. 1KOhm .25W resistors are 99p for 20 on Ebay so extra ones are not a big cost issue. Increase resistor size if too bright.

 

 

Edited January 21, 2020 by steve W
removal of duplicated sketch /words added

[ikcdab]

5 hours ago, sharris said:

I haven't gone through all the switch permutations but one thing is certain: you shouldn't have a situation where you can have LEDs in parallel (particularly if they are different colours) - the forward voltage at which an LED starts to conduct can vary slightly from LED to LED of the same type, and considerably for LEDs of different colours - when this happens the LED that has the lowest forward voltage will grab all, or at least, most, of the current and will be brightly lit, while the others will be dimly lit, or not lit at all. The way to prevent this is to give each LED its own series resistor (if I've counted right, that's 13 resistors) - the easiest place to put them might be to solder one end of each directly to the tabs on the rotary switches, and the other end to the wires leading to the signals (put a bit of sleeving over them to prevent anything shorting on the back of the switches). 

 

As for balancing the brightness with different resistor values, I can't suggest anything more than trial and error to get a brightness you are happy with - I'd temporarily use a set of resistors and pots in series, adjust them until I was happy and then measure the combined resistances for each colour - e.g. 

 

 

             1K             1K
+12V o-----/\/\/\/-------/\/\/\/
                            ^           ^^
                            |          //  RED
                            +---------|>|------o OV
              1K            1K
+12V o-----/\/\/\/-------/\/\/\/
                            ^           ^^
                            |          //  GREEN
                            +---------|>|------o OV
              1K            1K
+12V o-----/\/\/\/-------/\/\/\/
                            ^           ^^
                            |          //  YELLOW
                            +---------|>|------o OV

with the values shown, you'll be able to adjust the LED current between approximately 5-10mA (using the fact that you've been supplied with a 1K ohm resistor as a guide for the maximum current).

 

 

4 hours ago, steve W said:

You need one resistor for each LED that is lit at any one time, so a minimum of five connected as shown below.

A better and neater option is one in each LED line with the 12V taken directly to the switch wipers, then if you reconfigure the signals at any time the LED's are protected. The double head signals in yr diagram share a common return line, so you can't fit the resistor in the black return line. 1KOhm .25W resistors are 99p for 20 on Ebay so extra ones are not a big cost issue. Increase resistor size if too bright.

 

 

Thank you for these replies. I think you are both basically saying the same thing that each LED must have it's own resistor. It's just that the first solution has one resistor per LED and the other only has a resistor for the 'active' LED. whilst I am not short of resistors, I'll try the second solution and see what happens. Out with the soldering iron then!

Thanks again

[sharris]

5 minutes ago, ikcdab said:

 other only has a resistor for the 'active' LED. whilst I am not short of resistors,

 

As DJHGreen suggests 1k gives an appropriate brightness for each colour, that approach should be fine. 

 

 

[Brian]

22 minutes ago, ikcdab said:

 

Thank you for these replies. I think you are both basically saying the same thing that each LED must have it's own resistor. It's just that the first solution has one resistor per LED and the other only has a resistor for the 'active' LED. whilst I am not short of resistors, I'll try the second solution and see what happens. Out with the soldering iron then!

Thanks again

One resistor per signal head. Not per LED, though that option can be used if wished.

Steve W post above works correctly with Eckon signals with one resistor per signal head.

Edited January 21, 2020 by Brian

[ikcdab]

Many thanks. After a frustrating hour soldering upside down, I have now fitted the resistors as per Steve W and all seems now to work perfectly. 

Thanks again

[PSi]

I think Sharris has the right answer: one resistor for each LED.

 

True, you can manage with one resistor per head, but you cannot adjust the relative brightness of each LED that way. I think it would be a good plan to find out the correct (or suitable) resistor values like sharris suggests for each colour of a LED and this way match the brightness of the LEDs, and then (with power switched off) measure the common resistance over the combined 1k fixed and adujustable resistor for each LED colour, and use those values when purchasing the resistors for each colour of LEDs. Resistors are cheap.

 

I would also suggest taking the common wire of each signal mast or gantry through a rectifying diode. Any cheap small rectifying diode will do, like 1N4148 or 1N4001 or similar.

 

Why?

 

The diode would protect the LEDs aginst accidental polarity swap, as the LEDs will not generally tolerate reverse voltages in excess of 5 volts or so. If the supply voltage is accidentally reversed, the series resistors will not reduce the voltage seen by the LED, as no current will initially flow, thus the resistor will not create voltage drop.

 

 I'd put the resistors and the diode close to signal masts (gantries), right to the ends of the thin drop wires and cover the soldered joints with heat shrink tubing like sharris suggests. When the signal mast or gantry is removed for repair, painting or whatnot the resistors and the diode will come out with the signal mast (or gantry), and when checking the signal mast at the desk one will not accidentally apply full voltage directly to the LED. If one is fiddling with the wiring within the control panel or cables and connectors between the layout and panel, the accidental shorts or power reversals would not distroy the LEDs as the resistors and the diode are near the LEDs they are to protect.

 

I have once in my youth exploded a (then rather expensive) LED due to applying reverse 9 volts from a battery directly across LED terminals  -- good thing I had my glasses on.

 

pekka

 

Edited January 23, 2020 by PSi
typos again

[sharris]

@PSi

 

If the LEDs had significantly different brightness characteristics I would suggest my method, but as Dhjgreen, who posted a few seconds before me assures us they are close enough that they can all use 1k, Steve W's approach with less resistors and less soldering is suitable.

 

As for a protection diode, unless you're particularly clumsy with connecting things up, or don't use polarised connections, I wouldn't worry about that.

[Brian]

Eckon/Berko have Red, Yellow and Green LEDs that all have very close brightness when used with a single 1K0 resistor wired in the common return lead or the positive feed before switching is carried out.  If using a four aspect signal head the second yellow has its own dedicated 1K0 series resistor (2 resistors per 4 aspect head, one for R,Y,G the other for 2nd top Y) 

Adding single LED series resistor will IMO not improve their appearance. However, other makes of signals using LEDs may well benefit from this approach