B15nac Posted September 18, 2018 Share Posted September 18, 2018 Hi I'm going to be wiring in my lamps On my layout soon an they each come with a resistors do I need to use a resistor on each lamp or would one on the live wire before the first lamp then wire them all together be OK? Kind regards Neil Link to post Share on other sites More sharing options...
RobertW Posted September 18, 2018 Share Posted September 18, 2018 (edited) Hi Neil, The answer is, it depends. Assuming that the lamps are LEDs, then if you wire all the positives together and all the negatives together (in parallel), then a resistor is required in the positive supply to each lamp. If you wire them positive to negative, then you need to be careful as to how many LEDs you connect between the positive and negative. Do you have a link to the product, as there are a couple of numbers in the specification that could make the difference. If you want a simple answer, then this site may give you a good answer, assuming all of the LEDs are the same colour and type. http://led.linear1.org/led.wiz Hope this helps, Rob - Edited to simplify the explanation Edited September 18, 2018 by RobertW Link to post Share on other sites More sharing options...
RMweb Gold Right Away Posted September 19, 2018 RMweb Gold Share Posted September 19, 2018 Resistors are relatively inexpensive. Providing a "bank" of them in order that every LED has its own dedicated one of the correct value negates the need for further calculation. It's also advantageous when fault finding. Link to post Share on other sites More sharing options...
DCB Posted September 19, 2018 Share Posted September 19, 2018 You don't say what you are powering the lamps with, or if they are LEDs. If it is an uncontrolled "12 volt" supply sold for model railway use it could be anywhere from 12 to 24 volts, maybe even more, and worse the voltage will decrease with every additional lamp. If we are talking a dozen or less lamps then its no problem, use one resistor per lamp as supplied, follow the makers instructions. The type of lamp makes a difference, Hornby / Scalextric Grain of wheat bulbs are fine on 12/16/20 volts. Most LEDs curl up and die on 5 volts (except old clears which need 5 volts to light) Modern clears, as in 2018, work on 3 volts. My clear LED string in the outside terminus came from Poundland and has about 20 LEDs powered by 2 X AA batteries with no sign of any resistors, so times they are changing. When you get into long strings of LEDs then it gets awkward and they get dimmer and dimmer as additional lamps are added, that's when folk start wiring in series to reduce the power required, series wiring can slash current by 75%. LEDs vary widely and reds light much brighter than greens and yellows from the same manufacturer. If you mix and match you need one resistor per LED so you can even out the brightness. I run LEDs in parallel from a dedicated 3 volt DC transformer using resistors to even out the brightness where required, mainly on signals to even out green and red. "3 volt" DC power supplies come with shavers, phones all sorts of kit, I have at least 12 in the loft from long dead tech stuff. To test a "3 volt" transformer's suitability take a spare LED (cost maybe 10p) and put it across the DC output. If it gets too hot to touch, glows brightly and then smokes and dies then it no good. If the LED lights and glows happily until you get bored and shut it off is probably OK, just put a 1/4 amp polyswitch in circuit. A couple of do's and don't. Do use a fuse, polyswitch what ever as an overload cut out to protect your wiring. Don't use rechargeable batteries without a fuse/ polyswitch. I did and a short melted the body on my class 47. There is a useful Motor Trade adage. "If all else fails read the instructions." Link to post Share on other sites More sharing options...
Junctionmad Posted September 19, 2018 Share Posted September 19, 2018 (edited) If you use LEDs on an unregulated power supply even with a low voltage , you WILL risk any LED that doesnt have current limiting , remember a LED is a DIODE, simply with a higher forward voltage drop , try putting a diode across a 0.75 v supply Leds can be used on any DC supply once the appropriate resistor is used , most modern LEDS, will operate on 1-2mA, you can 100 leds from Aliexpress.com for about 2-3 dollars Edited September 19, 2018 by Junctionmad Link to post Share on other sites More sharing options...
Junctionmad Posted September 19, 2018 Share Posted September 19, 2018 Hi I'm going to be wiring in my lamps On my layout soon an they each come with a resistors do I need to use a resistor on each lamp or would one on the live wire before the first lamp then wire them all together be OK? Kind regards Neil one resistor may be fine , is they are all the same , what type of lamps are they Link to post Share on other sites More sharing options...
Crosland Posted September 19, 2018 Share Posted September 19, 2018 To test a "3 volt" transformer's suitability take a spare LED (cost maybe 10p) and put it across the DC output. If it gets too hot to touch, glows brightly and then smokes and dies then it no good.Please, please, ignore this drivel. If the LED lights and glows happily until you get bored and shut it off is probably OK, just put a 1/4 amp polyswitch in circuit. A couple of do's and don't. Do use a fuse, polyswitch what ever as an overload cut out to protect your wiring. Do: Do it properly and use a simple resistor. Don't: ever take advice like the above about using LEDs 1 Link to post Share on other sites More sharing options...
RMweb Premium kevinlms Posted September 19, 2018 RMweb Premium Share Posted September 19, 2018 Please, please, ignore this drivel. Do: Do it properly and use a simple resistor. Don't: ever take advice like the above about using LEDs Agree totally. OP if your still reading, others have posted info on how cheap resistors are - much cheaper than ANY LED's, so why risk blowing any up? If you don't already have one, buy yourself a cheap digital multimeter and measure what the supply voltage of the power supply actually is. Don't just go by any label that may be on it. Once you know the output voltage, then there are any number of online resistor calculators. Remember the colour of the LED, WILL change the recommended resistance. Link to post Share on other sites More sharing options...
B15nac Posted September 19, 2018 Author Share Posted September 19, 2018 Here's two of the lamps in this photo. They are from layouts4u but I've also got a few lamps from express models. All suppose to have resister wire in I think I will use one resistor for each lamp so I don't cause damage. Thanks for all your advice an help Regards Neil Link to post Share on other sites More sharing options...
B15nac Posted September 19, 2018 Author Share Posted September 19, 2018 These are the other lamps I got from express models. Kind regards Neil Link to post Share on other sites More sharing options...
Junctionmad Posted September 20, 2018 Share Posted September 20, 2018 Once you know the output voltage, then there are any number of online resistor calculators. Remember the colour of the LED, WILL change the recommended resistance. [/quote ] These days even cheapie Chinese leds will run on 1-2 mA , I use 1K5 or 1k8 on 5 Volts and over double that for 12v In reality these days , you can use the same resistor for everything except white , it’s only if you need to balance brightness to the eye , where you need to adjust the value , electrically the same value is fine Link to post Share on other sites More sharing options...
B15nac Posted October 20, 2018 Author Share Posted October 20, 2018 I just wired up my 3 lamp that are wall mounted on my engine shed an put 12v to them an they all popped an smoked then game over. When I purchased them they state resistors fitted so where did I go wrong!? Kind regards Neil Link to post Share on other sites More sharing options...
RMweb Premium kevinlms Posted October 20, 2018 RMweb Premium Share Posted October 20, 2018 I just wired up my 3 lamp that are wall mounted on my engine shed an put 12v to them an they all popped an smoked then game over. When I purchased them they state resistors fitted so where did I go wrong!? Kind regards Neil Just goes to show that a resistor should be fitted FIRST as a trial. If too dim, then fit a lower value, until you get a suitable brightness. Is your 12 Volt supply, actually 12 volts. Many train controllers (such as a Duette), put out up to 20 volts, on low loads - which a few lamps is. Link to post Share on other sites More sharing options...
B15nac Posted October 21, 2018 Author Share Posted October 21, 2018 Been in contact with the company I bought them off and they were listed wrong on the website they need resistors fitting so there sending me out some new ones Monday Kind regards Neil 1 Link to post Share on other sites More sharing options...
DCB Posted October 25, 2018 Share Posted October 25, 2018 I just wired up my 3 lamp that are wall mounted on my engine shed an put 12v to them an they all popped an smoked then game over. When I purchased them they state resistors fitted so where did I go wrong!? Kind regards Neil By not checking the voltage you applied basically. Most model railway "12 volt" is 20 volt ish off load. Car 12 volt is 13.8 to 14.2 though some is 14.5, and Computer 12 volts is, wait for it, 12 volts. A 2X AA cell battery holder with non rechargeable batteries is a good test for Lamps, (Not old Clears though which are 5 volt) if they don't have "12 volt" resistors they will light on the 3 volts, so fit resistors ( use 20 volts as a starting point for calculations) if you want to use a "12 volt" supply. I run my LEDs off a 3 volt bus bar and haven't had one fail in 10 years or more. Link to post Share on other sites More sharing options...
Crosland Posted October 25, 2018 Share Posted October 25, 2018 By not checking the voltage you applied basically. No. The OP told us 4 days ago that the supplier admitted they were faulty. Link to post Share on other sites More sharing options...
RMweb Premium kevinlms Posted October 25, 2018 RMweb Premium Share Posted October 25, 2018 No. The OP told us 4 days ago that the supplier admitted they were faulty. Thinking about it, they were probably fine. Just incorrectly described, as being fitted with resistors for 12 volt when they weren't. Link to post Share on other sites More sharing options...
DCB Posted October 25, 2018 Share Posted October 25, 2018 No. The OP told us 4 days ago that the supplier admitted they were faulty. Should still have tested the lamps before installation. It would have saved a lot of work. Link to post Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now