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Discussion Starter · #1 ·
I have just been battling to fit a loco with a decoder and to get the lights (LED ) to work properly. This was on a thread on the DCC forum and assistance was given by others which helped. In the end the only workable option was to ditch the LED's and put in grain of wheat bulbs. I know LED's are supposed to last longer but what is their (if any) other advantages? What is the deal with resistors? I don't understand them and have read all sorts on here about them which has left me baffled. I know the answer will be on here somewhere and I think I have read it in Wiring for DCC but what does wiring in 'series' actually mean and how does that work if you have to hardwire a decoder into a PCB already fitted to the loco?

Sorry if these questions seem basic or could be answered by research on the forum but sometimes some of the items seem to presume that the reader has a level of knowledge beyond the basics.

Chris Wright
 

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Chris
one of the main advantages of LEDs is that they "run cold" unlike grain of wheat bulbs which can generate a lot of heat up to the point of melting some plastics if care is not taken. LEDs will last a lot longer than bulbs as well. As for the resister point an LED is sensitive to the amount of current that passes through it hence the need for the resister. The rating of the resister will depend on the supply voltage to the LED, the forward current of the LED and how many milliamps the LED uses. If you have a hunt around on the web you will find a number of sites that give you info for working this out, some have calculators on them to show what you need.
Mike
 

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Discussion Starter · #3 ·
QUOTE (mik @ 27 Apr 2007, 17:34) <{POST_SNAPBACK}>Chris
one of the main advantages of LEDs is that they "run cold" unlike grain of wheat bulbs which can generate a lot of heat up to the point of melting some plastics if care is not taken. LEDs will last a lot longer than bulbs as well. As for the resister point an LED is sensitive to the amount of current that passes through it hence the need for the resister. The rating of the resister will depend on the supply voltage to the LED, the forward current of the LED and how many milliamps the LED uses. If you have a hunt around on the web you will find a number of sites that give you info for working this out, some have calculators on them to show what you need.
Mike
Thanks for that Mike I have just been looking at http://www.siliconvalleylines.com which I think may have given me some of the answers. I want to try and put lights in some of my Bachmann locos without going to the expense of buying kits from say Express Models and think that it must be cheaper to buy the bits from Maplins or somewhere similiar and cobble up something myself. Anyone out there done it and is it simple (ish) and what is the cost?

Chris
 

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The other difference between LEDs and grain of wheat bulbs is that you have to connect LEDs the right way round. Current will only flow one way through an LED. A grain of wheat will light up no matter which way round you connect the terminals.

If you connect up an LED without a series resistor you will probably break it, never to light again. I killed two earlier this week whilst trying to build a circuit tester.

The method I used to calculate resistor size on my control panel was to start with the volts - 12, read the recommended forward current for the LED - say 7mA and then calculate the resistance from Ohm's law - V = IR so R = V/I which in my case is 12/0.007 = 1,714 ohms. The most readily available resistor size was 1,800 so I bought some of these. You need to select a power rating - power (watts) = IV, so for my circuit power was 0.007 * 12 = 0.084 watts so I bought 1/4 watt resistors which is way over the top, but they are so common I could only buy them in 50s.

David
 

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Chris
You may find that DIY on Bachmann loco for lights oftern hard due to the lack of space inside, have you looked at Express models site? they do a lot of very good kits to fit in tight spaces, this is what I use for Bachmann locos. When it comes to older Lima oners then I make up my own as there is lots of space inside the body.
Mike
 

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Discussion Starter · #6 ·
QUOTE (mik @ 27 Apr 2007, 19:39) <{POST_SNAPBACK}>Chris
You may find that DIY on Bachmann loco for lights oftern hard due to the lack of space inside, have you looked at Express models site? they do a lot of very good kits to fit in tight spaces, this is what I use for Bachmann locos. When it comes to older Lima oners then I make up my own as there is lots of space inside the body.
Mike
Hi Mike yes I have looked at the Express Models site and it is impressive. I just wondered if there was a viable alternative bearing in mind the problems of restricted space etc. I agree space is a problem as I have just fitted my pair of 20's with SWD sound decoders and there is no room left for anything but I bet someone has manages to squeeze both in!

Chris
 

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Discussion Starter · #8 ·
QUOTE (Gofer @ 27 Apr 2007, 20:21) <{POST_SNAPBACK}>Chris (and others), this site maybe of help in understanding LED's and how to calculate the value of the current limiting resistor.

http://www.kpsec.freeuk.com/components/led.htm

Steve B
Steve thanks for that I have just had a quick look and put it in my favourites to read later. This is where I find the forum really useful as someone always knows where to direct you for the right info. I trawl the net myself to look for stuff but this is always quicker I think and a huge help/

Chris
 

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I actually don't like LED's for lights. To me the colour of the light is all wrong and these super bright white LED's just look blue and mucking about with resistors is a pain. I prefer to use grain of rice bulbs usually from Minitronics in the US. These come in various sizes and ratings from 1.25V to 14V in the 20 to 50milliamp range. I generally use the 14V 30mA bulbs as they have a nice warm glow. I've used these bulbs in both RTR plastic, Brass and kit built locos. I usually combine the bulb with an MV lens of a suitable size.

Ozzie21

QUOTE (chriswright03 @ 28 Apr 2007, 02:03) <{POST_SNAPBACK}>I have just been battling to fit a loco with a decoder and to get the lights (LED ) to work properly. This was on a thread on the DCC forum and assistance was given by others which helped. In the end the only workable option was to ditch the LED's and put in grain of wheat bulbs. I know LED's are supposed to last longer but what is their (if any) other advantages? What is the deal with resistors? I don't understand them and have read all sorts on here about them which has left me baffled. I know the answer will be on here somewhere and I think I have read it in Wiring for DCC but what does wiring in 'series' actually mean and how does that work if you have to hardwire a decoder into a PCB already fitted to the loco?

Sorry if these questions seem basic or could be answered by research on the forum but sometimes some of the items seem to presume that the reader has a level of knowledge beyond the basics.

Chris Wright
 

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I used 3mm 12v LEDs from Maplins with built in resistors for my n gauge loco lights. Adding a 1N4002 diode on the short leg of the LED prevents burnouts. I found a good diagram on Kettlestack's project page at http://mysite.wanadoo-members.co.uk/genpics/
I find the Ohm's law calculations much too complicated for my simple mind and would much rather just be told which LED to buy.
 

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Discussion Starter · #11 ·
QUOTE (poliss @ 29 Apr 2007, 15:44) <{POST_SNAPBACK}>I used 3mm 12v LEDs from Maplins with built in resistors for my n gauge loco lights. Adding a 1N4002 diode on the short leg of the LED prevents burnouts. I found a good diagram on Kettlestack's project page at http://mysite.wanadoo-members.co.uk/genpics/
I find the Ohm's law calculations much too complicated for my simple mind and would much rather just be told which LED to buy.

Thanks for that. I too am baffled by this Ohm's law stuff far to techhie for me. I need it to be kept simlple as you say tell me what I need where I can get it that will do me. Good job there are people out there that do understand though otherwise we wouldn't have people to tell us this stuff. For which I am grateful. I am sure Express Models stuff is excellent value and very good kits but there has to be a cheaper way of doing it yourself once you know what you need. I think squeezing it all in will always be the main problem anyway.

Chris
 

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QUOTE Thanks for that. I too am baffled by this Ohm's law stuff far to techhie for me. I need it to be kept simple
Hi Its not so complicated as it first seems. There are a few bits of information needed before you can calculate the resistor needed.
These are... 1) The supply voltage. 2) The LEDs recommended forward current & 3) The LEDs recommended working voltage.
Item 1) can be obtained with a multimeter set on volts while 2) & 3) are normally supplied by the supplier of the LEDs in their write up for that LED. Typical LED info is shown here.... 2mm LEDS Look at the PDF data file and on page 2 it shows the IF values etc

Let's assume you have a supply voltage of 12v dc. The chosen LED is rated at a Max forward current (Shown as IF) of 20Ma and its working avearage voltage is 2.2v.
The sum is then supply V - LED v / forward current. Or 12v - 2.2 divided by 0.20. (12-2.2=9.8/0.02 = 490) Therefore a resistor of at least 490 ohms is required. Resistors aren't available in every value, so you select the nearest value ABOVE the calculation. Which is actually 560R (560 Ohms). If you want the LED to be a little less bright increase the value of the resistor to around a Max value of 1K 0r 1.2K (1000 or 1200 Ohms) Typical resistors are shown here.... Resistors

Remember, and as previously stated, LEDs are polarity sensitive and MUST be connected the correct way around if wrong they will blow immediately they are connected. I always check mine with a 1.5v AA type battery. This then ensures you have the positive leg of the LED correct - Positive battery to Positive LED leg = LED lights while Positive battery to Negative LED leg = No light and no damage so long as you don't leave the battery on for more than a second!
 

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Discussion Starter · #13 ·
QUOTE (Brian @ 30 Apr 2007, 09:46) <{POST_SNAPBACK}>Hi Its not so complicated as it first seems. There are a few bits of information needed before you can calculate the resistor needed.
These are... 1) The supply voltage. 2) The LEDs recommended forward current & 3) The LEDs recommended working voltage.
Item 1) can be obtained with a multimeter set on volts while 2) & 3) are normally supplied by the supplier of the LEDs in their write up for that LED. Typical LED info is shown here.... 2mm LEDS Look at the PDF data file and on page 2 it shows the IF values etc

Let's assume you have a supply voltage of 12v dc. The chosen LED is rated at a Max forward current (Shown as IF) of 20Ma and its working avearage voltage is 2.2v.
The sum is then supply V - LED v / forward current. Or 12v - 2.2 divided by 0.20. (12-2.2=9.8/0.02 = 490) Therefore a resistor of at least 490 ohms is required. Resistors aren't available in every value, so you select the nearest value ABOVE the calculation. Which is actually 560R (560 Ohms). If you want the LED to be a little less bright increase the value of the resistor to around a Max value of 1K 0r 1.2K (1000 or 1200 Ohms) Typical resistors are shown here.... Resistors

Remember, and as previously stated, LEDs are polarity sensitive and MUST be connected the correct way around if wrong they will blow immediately they are connected. I always check mine with a 1.5v AA type battery. This then ensures you have the positive leg of the LED correct - Positive battery to Positive LED leg = LED lights while Positive battery to Negative LED leg = No light and no damage so long as you don't leave the battery on for more than a second!

Thanks for that Brian and I will have a real of the two links and see what I can make of them. Have you fitted any yourself to loco's? If so how difficult is it as room is limited enough already in some of mine?

Cheers Chris (learning more all the time)
 

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QUOTE Thanks for that Brian and I will have a real of the two links and see what I can make of them. Have you fitted any yourself to loco's?
If so how difficult is it as room is limited enough already in some of mine?
Hi Chris. No, sorry I haven't. Main reason being is I'm virtually 99% steam outline, so head/rear lighting isn't an issue for me.

However, I do install LEDs into buildings and make street lights, plus welding simulators, traffic lights, Belisha beacon and lighthouse flashers etc. So LEDs to me are the ticket!
 

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Discussion Starter · #15 ·
Thanks Brian oh and I have visited your web site very helpful. So I could use LED's in the buffer stops in my terminus station then?

Chris
 

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QUOTE (chriswright03 @ 30 Apr 2007, 14:32) <{POST_SNAPBACK}>Have you fitted any yourself to loco's? If so how difficult is it as room is limited enough already in some of mine?

Cheers Chris (learning more all the time)

Hi Chris, I've fitted several of my Lima locos (Class 31, 37 and 47) and a couple of Hornby 56's. Below is a couple of pics of the Hornby Class 56 which was probably the most difficult due to the lack of space available.





Lima locos are much easier with regard to the fitting of the LEDs but a lot harder to stop the light bleed through the yellow coloured plastic from which the bodies are made.

The method I use is probably not the best as I prefer to insert the LEDs directly into the light lens hole rather than simply positioning the LED behind the lens. This does mean however that you'll need a small lathe or similar with which to turn the LED's to the correct diameter to fit the hole.

Couple more pics here of Lima locos:





The cost of the parts is probably about £1.50 per end which is for 1 x white LED, and 2 x yellow LEDs, 2 resistors, 1 diode and sundry bits and pieces (wire, solder etc).

Steve
 

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Discussion Starter · #17 ·
QUOTE (Gofer @ 30 Apr 2007, 18:57) <{POST_SNAPBACK}>Hi Chris, I've fitted several of my Lima locos (Class 31, 37 and 47) and a couple of Hornby 56's. Below is a couple of pics of the Hornby Class 56 which was probably the most difficult due to the lack of space available.





Lima locos are much easier with regard to the fitting of the LEDs but a lot harder to stop the light bleed through the yellow coloured plastic from which the bodies are made.

The method I use is probably not the best as I prefer to insert the LEDs directly into the light lens hole rather than simply positioning the LED behind the lens. This does mean however that you'll need a small lathe or similar with which to turn the LED's to the correct diameter to fit the hole.

Couple more pics here of Lima locos:





The cost of the parts is probably about £1.50 per end which is for 1 x white LED, and 2 x yellow LEDs, 2 resistors, 1 diode and sundry bits and pieces (wire, solder etc).

SteveCheers for that Steve. I think it is time to buy a few bits and have a go. What is the diode for though?

Chris
 

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Chris, I'm not sure what you level of electrical / electronic knowledge is so forgive me if I'm trying to teach my Grandmother to suck eggs here. With conventional lighting a bulb will light regardless of the direction of the current flow through it. This means, when considering the locomotive scenario, that all the bulbs at both ends will illuminate regardless of which way the locomotive is selected to travel. To make sure that only the desired bulbs illuminate manufacturers fit diodes into the circuit to ensure current can only be passed to those bulbs. Now LED's are diodes in there own right and therefore do not technically require this diodes to decide which LED illuminates, they simply need to be wired correctly to ensure that only the LEDs required are forward biased. The problem is however that many LED's have a maximum reverse voltage tolerance (typically 5 volts) which is below the voltage that could appear on the track. I use a diode so wired that when a reverse voltage is applied to the circuit (to the rear headlight for example) this voltage is prevented from reaching the LED as the diode will block it. The diodes I tend to use are 1N4001 simply because they are a good general purpose diode rated at 1 amp and CHEAP (£4 plus vat per 100). As this diode has a maximum reverse voltage which is much higher than the maximum voltage which could appear on the track it won't be damaged. I'm not too good at explaining things so I hope you understood that lot. I'm not sure I do
 

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Discussion Starter · #19 ·
QUOTE (Gofer @ 30 Apr 2007, 21:21) <{POST_SNAPBACK}>Chris, I'm not sure what you level of electrical / electronic knowledge is so forgive me if I'm trying to teach my Grandmother to suck eggs here. With conventional lighting a bulb will light regardless of the direction of the current flow through it. This means, when considering the locomotive scenario, that all the bulbs at both ends will illuminate regardless of which way the locomotive is selected to travel. To make sure that only the desired bulbs illuminate manufacturers fit diodes into the circuit to ensure current can only be passed to those bulbs. Now LED's are diodes in there own right and therefore do not technically require this diodes to decide which LED illuminates, they simply need to be wired correctly to ensure that only the LEDs required are forward biased. The problem is however that many LED's have a maximum reverse voltage tolerance (typically 5 volts) which is below the voltage that could appear on the track. I use a diode so wired that when a reverse voltage is applied to the circuit (to the rear headlight for example) this voltage is prevented from reaching the LED as the diode will block it. The diodes I tend to use are 1N4001 simply because they are a good general purpose diode rated at 1 amp and CHEAP (£4 plus vat per 100). As this diode has a maximum reverse voltage which is much higher than the maximum voltage which could appear on the track it won't be damaged. I'm not too good at explaining things so I hope you understood that lot. I'm not sure I do

Steve my knowledge is VERY limted hence my questions here to try and improve it. So ANY help given will be gratefully received. So if I am fitting lights as you say and I use DCC which I do do I still need the diodes? Surely that is what the white and yellow wires from the decoder are for?

Chris
 

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Chris, now you've got me
I'm not a DCC man and I can't answer your question. Certainly from what I read the directional lighting is controlled by commands given to the on board decoder so I'm assuming that when any light isn't required the decoder will remove the feeds from them rather than relying on the LEDs being reversed biased. Thinking about it, this must be the case otherwise how would directional lighting on locos fitted with conventional bulbs work?. Yup, it's my considered opinion that the diodes we're talking about will not be required with DCC.

Steve
 
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