deltanw12 Posted October 9, 2015 Share Posted October 9, 2015 Hi All Firstly I am an electrical non starter so any answers would be appreciated in the simplest form with illustrations if possible. I have recently purchased for the grand sum of 50 pence 2 Hornby R406 signals without bulbs. I have seen the price of bulbs, and would like to know if I could, and how, replace the bulbs with LED's. Regards Link to post Share on other sites More sharing options...
DCB Posted October 11, 2015 Share Posted October 11, 2015 This is not a beginners project. LEDs are difficult to solder and need some skill to get the right resistors to balance the light intensity between the red and green, which vary greatly with the same current. I find making my own signals from wiring connector casings and Christmas Tree LEDs easier than converting ready made versions. We had Christmas lights with Red Green Blue and Yellow sub miniature LEDs in clear plastic "Pea Pods" which failed and I rescued lots of LEDs from. The power supply needs to be a lot less than 16 volts the grain of wheats use, Red Green LEDs wont take much more than 3 volts before they start smoking and fail, so choose your resistors carefully, but I use inverse parallel wiring so I can reverse the polarity to change from red to green using a centre off DPDT toggle switch and only need two wires per signal (Christmas tree LED lamp wire). But really for a novice new grain of wheat bulbs look like the way to go Link to post Share on other sites More sharing options...
Gordon H Posted October 12, 2015 Share Posted October 12, 2015 Red Green LEDs wont take much more than 3 volts before they start smoking and fail... As has been said many times before, LEDs don't TAKE voltage, they drop it when current flows, and it is up to the user to limit that potentially smoke producing current with a suitable limiting device such as a resistor. Also, LEDs are no more difficult to solder than any other device. Link to post Share on other sites More sharing options...
michaelp Posted October 12, 2015 Share Posted October 12, 2015 Not being electronically minded this is interesting for me, I have always wondered about LED voltages and resistors, is it not possible to get the resistor for the job right first time? I thought that resistors could simply be measured with a multi-meter which would show what the voltage to the LED would be or is it all far more complicated than that? Michael Link to post Share on other sites More sharing options...
Brian Posted October 12, 2015 Share Posted October 12, 2015 Hi Try using this LED series resistor calculator web site. http://www.led.linear1.org/led.wiz As an example test it with... Suggest you state your Source voltage as 12v. The LED forward volts of 2.2v and you would like the LED to consume 0.02 Amp (20 milliamp) and you only have one LED in the circuit.. It should show 560R resistor is needed. Now decrease the current to say 10 milliamp (0.01A) and see what happen to the resistor value in Ohms.. It is possible to convert the Hornby signal but its not easy! I would suggest if you want to use the vastly over scale Hornby CL signal then fit replacement coloured filament lamps. If you want LEDs (low current consumption, runs cool and is more scale in size) then look at the Eckon or Berko range or TrainTech signals etc for reasonable priced signals. Link to post Share on other sites More sharing options...
DCB Posted October 12, 2015 Share Posted October 12, 2015 Calculating resistors is ok as long as all the LEDs are the same size colour/ spec/ size and if you know the supply voltage and know what forward voltage gives the brightness you require. Most power units sold as 12 volt are in my experience nearer 16 volt some are over 20 off load. From long experience the green LEDs in red / green signals needs more voltage to give the same number of lumens than the red, Which means different resistors for red and green which is why I use inverse parallel connections and reverse the polarity for red / green changes. What I do differently is in using an LED bus bar with only 2.5 volts. That is enough for Yellow Red Green LEDs but will not light clear ones which typically need around 4 volts to light as against circa 1.8 volts for Red. LEDs love melting when you solder them, especially the Christmas tree ones, unlike bulbs which will take lots of heat without damage. My advice remains stick to bulbs. Link to post Share on other sites More sharing options...
Brian Posted October 12, 2015 Share Posted October 12, 2015 I only ever use or recommend the use of a regulated power supply for DC applications. Typically 12v DC. The use of unregulated 'Train set' DC output power or general unregulated DC supplies is really outdated now for most DC illumination power needs, especially with low cost regulated PSUs available. As for colour matching on LED lit signal aspects, I personally don't and haven't ever seen any issues with colour light signal aspects? I have never colour matched or matched specs of red, green or single yellow LEDs used in MAS signalling. I'm sure Eckon, Berko or Train Tech etc don't bother? I have never noticed one colour being more dominant than another! Though if two aspects are incorrectly displayed e.g. Red and a green were light at the same time then one over the other may be more noticeable. But generally only one aspect is lit at any one time, except for a double yellow, then I use two LEDs for the same batch, with the same value Ohm resistor in each yellow! Multi LEDs wired in series may well cause illumination differences but this wouldn't apply to a MAS signal. Current limiting resistors should be used with any supply feeding an LED. This has been 'done to death' in other forum topics! Wire Lead style LEDs will benefit from a heat shunt being clipped onto their lead above the solder place - a Croc clip will do if needed. SMD LEDs offer different challenges when soldering leads to their pads! Edit to add... Wonder if two filament red/green Hornby lamps match... Think not :-) Link to post Share on other sites More sharing options...
Gordon H Posted October 13, 2015 Share Posted October 13, 2015 From long experience the green LEDs in red / green signals needs more voltage to give the same number of lumens than the red... Once more...they don't NEED more voltage as such, they DROP more voltage. Once you understand and apply this principle the whole matter of designing circuits for LEDs becomes much more straightforward. Clearly the available supply voltage has to be sufficiently high to allow current to flow, but beyond that any spare 'headroom' voltage is what the current limiting resistor works with to set the current that flows through the LED. Getting the green aspect the same intensity as the red is a rather moot point really because not only will only one of them be on at a time, the green will undoubtedly be the wrong shade for signals anyway. Cyan LEDs are much closer to 'Signal Green' if you can source them. Link to post Share on other sites More sharing options...
luckymucklebackit Posted October 13, 2015 Share Posted October 13, 2015 I did my own, using the Dapol Signal Gantry as a basis, found it quite easy if a little time consuming. See this and subsequent posts. Resistor values were calculated using the site mentioned before. http://www.rmweb.co.uk/community/index.php?/topic/26270-gateside-northbridge-honest-guv-im-no-longer-infected/?p=1266232 Jim Link to post Share on other sites More sharing options...
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