Variable Voltage for colour-light signals

[Crepello]

I'd be grateful for recommendations on controllers on which the brightness of the signals can be adjusted. TIA.

[RAF96]

I use the speed controlled output from an old analogue controller to dim my led street lights.

Edited July 8, 2021 by RAF96

[AndyID]

1 hour ago, Crepello said:

I'd be grateful for recommendations on controllers on which the brightness of the signals can be adjusted. TIA.

 

Do you want to be able to dim them for night running or do you just want to adjust them and leave them at that output?

[kevinlms]

Use resistors in series. That way you can adjust each colour for your chosen brightness.

[DCB]

You can't control the brightness of heritage pre 2020 LED colour light signals by varying the voltage. The reds will be too bright and the greens too dim,  The reds need series resistors even if you get the greens brightness right.

You can use a Morley to power the greens if you really feel the need to spend £75 on one but I'd use a wall wart and a few resistors. Most folk use a 12 volt DC uncontrolled output  and waste 85% of the power in heating the resistors.  I start with 3 volts.

[kevinlms]

7 hours ago, DavidCBroad said:

You can't control the brightness of heritage pre 2020 LED colour light signals by varying the voltage. The reds will be too bright and the greens too dim,  The reds need series resistors even if you get the greens brightness right.

You can use a Morley to power the greens if you really feel the need to spend £75 on one but I'd use a wall wart and a few resistors. Most folk use a 12 volt DC uncontrolled output  and waste 85% of the power in heating the resistors.  I start with 3 volts.

Yes and using resistors is still a good idea, even if only 3 volts applied. If you pick the correct value resistors, they will never be heated up.

[Michael Hodgson]

Dimming colour light signals was possible in some places during WW2 as an air raid precaution - when there was an alert, the signalman operated a switch in the box.  These facilities remained in situ is some place (such as the Metropolitan/GCR Line) for many years after the war ended.  Other than that, I don't see a case for being able to dim your signals.

 

London Underground's tunnel signals did not need to be as bright as signals used out in the open, but that was just a question of the bulb rating and optical characteristics of the signal, they didn't vary the output.  They did have some Fog Repeater signals which were switched off unless visibility was poor because of the weather - it was more like the equivalent in semaphore areas of calling out men with detonators to do "fogging duties".

[SamThomas]

2 hours ago, Michael Hodgson said:

I don't see a case for being able to dim your signals.

 

If you want to be able to see what colour you signals are displaying on a layout during "daylight" ambient lighting & from an angle off what the "driver" would see they need to be brighter than they need to be during "nightime" ambient lighting.

[73c]

Some of these signal, buffer stop, platform/yard led's can be bright enough to cure cataract's, so I can understand the OP's desire to be able to dim them.

[Crepello]

21 hours ago, AndyID said:

 

Do you want to be able to dim them for night running or do you just want to adjust them and leave them at that output?

Just to get the right amount of brightness and leave it at that. I can live with a compromise.  Thanks to those who pointed out that reds will be bright--mine certainly are. My current set-up is powered by a Bachmann train-set controller, but it seems to fail regularly with all lights out, until I manage to re-set it, sometimes by changing direction with the slide switch or by switching off . I'm wondering if it's not really suitable for this application.

[Michael Hodgson]

37 minutes ago, Crepello said:

Just to get the right amount of brightness and leave it at that. I can live with a compromise.  Thanks to those who pointed out that reds will be bright--mine certainly are. My current set-up is powered by a Bachmann train-set controller, but it seems to fail regularly with all lights out, until I manage to re-set it, sometimes by changing direction with the slide switch or by switching off . I'm wondering if it's not really suitable for this application.

Use a separate resistor for each LED, not one on the Common return.  Resistors are dirt cheap anyway.

 

3 hours ago, 73c said:

Some of these signal, buffer stop, platform/yard led's can be bright enough to cure cataract's, so I can understand the OP's desire to be able to dim them.

If the light's too bright you need to use a bigger resistor a a lower voltage than you're applying. 

The brightness increases as the current increases, and the current is limited by the value of the resistor.

Too high a current and the LED will burn out.

[Brian]

Hi

 

Ditch the train set controller for powering lighting!   

Obtain a Regulated power supply like for example this one  Link to example in the 2.0Amp rating at 12volts. Also worth while obtain from the same supplier is the 2.1mm female DC barrel adaptor to make onward wiring easy.  Other suppliers are of course available.

 

You will then have a constant voltage being feed to all the lights.   I always fit one resistor per lit LED.  On a 12volt supply I start at 1K (1000 Ohms) and increase the resistance to reduce brightness as required. Going up to around 10K (10000 Ohm) or more if need be.   1K resistors are less than 2p each when purchased by the 100 Example... Link to resistors

[AndyID]

A USB phone charger might be the way to go. They all output regulated 5 volts.

[TheSignalEngineer]

10 hours ago, Michael Hodgson said:

Dimming colour light signals was possible in some places during WW2 as an air raid precaution - when there was an alert, the signalman operated a switch in the box.  These facilities remained in situ is some place (such as the Metropolitan/GCR Line) for many years after the war ended.  Other than that, I don't see a case for being able to dim your signals.

Dimming switches for ground signals were still being provided on the LMR in the 1960s. I think New Street PSB may have been one of the last places to get one.