40034_Nick Posted March 7, 2019 Share Posted March 7, 2019 Hi Resistor experts. If i have a 15K resistor and want to use it on 3 lights. What will be the resistor outage or whatever you call it to each of the 3 lights in series and each of the 3 lights in parallel ? Also the same if i am using it for 2 lights?? Thanks guys Link to post Share on other sites More sharing options...
steviesparx Posted March 7, 2019 Share Posted March 7, 2019 Errrr, a little more information required please... Supply volts, lamp rating ( watts / volts ), filament lamps or are they LEDs...???? Link to post Share on other sites More sharing options...
40034_Nick Posted March 7, 2019 Author Share Posted March 7, 2019 NO idea... DCC loco lighting from a DCC chip. LEDs i think ???? Link to post Share on other sites More sharing options...
jpendle Posted March 7, 2019 Share Posted March 7, 2019 OK is this a DCC ready loco or are you hard wiring a DCC decoder? John P Link to post Share on other sites More sharing options...
40034_Nick Posted March 7, 2019 Author Share Posted March 7, 2019 some will be hard wired and some will be ready.. Basically its lighting my shunters, some old and some new.. Link to post Share on other sites More sharing options...
DCB Posted March 7, 2019 Share Posted March 7, 2019 We need more info. White LEDs need more voltage than yellow, mixing LEDS in parallel with LEDs in series is not going to end well. Measure the output voltage with Multimeter as a starting point. This applied to all electrics, DC / DCC etc as often "12 volt" model railway supplies turn out to be 21 or even more volts off load. Computer 12 volt is 12 vot and car 12 volt is usually 14volt just to make things easier. As LEDs are about 5p each and resistors even cheaper I tend to get a handful and take careful notes as I experiment to see what lights and what glows like a super nova smokes and dies. Link to post Share on other sites More sharing options...
40034_Nick Posted March 8, 2019 Author Share Posted March 8, 2019 Ok lets keep it simple.. Does series decrease or increase the brightness? Does parallel increase or decrease the brightness ? Sorry guys but i only want to know as i but 3 resistors for 3 lights in the one loco and it took to much room.. Lights work great but a really tight squeeze Link to post Share on other sites More sharing options...
Hroth Posted March 8, 2019 Share Posted March 8, 2019 (edited) 45 minutes ago, 40034_Nick said: Ok lets keep it simple.. Does series decrease or increase the brightness? Does parallel increase or decrease the brightness ? Sorry guys but i only want to know as i but 3 resistors for 3 lights in the one loco and it took to much room.. Lights work great but a really tight squeeze Resistors are there to reduce the current passing through the LED, preventing it from being overloaded and burning out. Series and parallel resistors both decrease the current depending on the value of the resistors. For series resistors the total resistance is R1+R2+R3... For parallel resistors, the total resistance is 1/R1+1/R2+1/R3... Each LED should have a resistor. Its not recommended to feed several LEDs via 1 resistor as its possible for the LEDs to be unmatched and one to draw more current than the others. Result? POW! You'll also need to ensure that the current draw on the lighting circuits is within the capabilities of your DCC chip, or that might say goodbye too. Edited March 8, 2019 by Hroth Link to post Share on other sites More sharing options...
40034_Nick Posted March 8, 2019 Author Share Posted March 8, 2019 thanks :-) Link to post Share on other sites More sharing options...
RMweb Gold The Johnster Posted March 8, 2019 RMweb Gold Share Posted March 8, 2019 To quote 7 of 9 (and I'll have to have a cold shower now I've thought of her), 'resistance is futile'. And with that highly valuable contribution to the debate, I will take my leave of it... 1 Link to post Share on other sites More sharing options...
jpendle Posted March 8, 2019 Share Posted March 8, 2019 13 hours ago, Hroth said: Resistors are there to reduce the current passing through the LED, preventing it from being overloaded and burning out. Series and parallel resistors both decrease the current depending on the value of the resistors. For series resistors the total resistance is R1+R2+R3... For parallel resistors, the total resistance is 1/R1+1/R2+1/R3... Each LED should have a resistor. Its not recommended to feed several LEDs via 1 resistor as its possible for the LEDs to be unmatched and one to draw more current than the others. Result? POW! You'll also need to ensure that the current draw on the lighting circuits is within the capabilities of your DCC chip, or that might say goodbye too. I'm sorry but this is factually inaccurate and misleading. A resistor in series with an LED will reduce the voltage drop across the LED, the current stays constant. A resistor in parallel with an LED will reduce the current flowing through the LED, the voltage drop will be constant. To calculate the resistance of resistors in parallel the formula is 1/(1/R1+1/R2+1/R3 ...). E.g 2 15k resistors in series gives 30k, 2 in parallel gives 7.5k, 3 in series is 45k, 3 in parallel is 5k. Regards, John P Link to post Share on other sites More sharing options...
Il Grifone Posted March 8, 2019 Share Posted March 8, 2019 The three LEDs should be connected in series with each other and with the resistor, though 15kΩ seems a bit high for a 12/15V supply. They will only get about 0.5mA each and LEDs usually need about 10mA (it depends on the particular type). Connecting the LEDs in parallel will probably work, but it is probable that they will vary in brightness through not sharing the current equally. In this case the LEDs will have nearly 1mA to share between them. A matched set will divide the current equally, but this is unlikely. A LED typically drops about 3 volts when lit, depending on colour. This drop varies little with current. Link to post Share on other sites More sharing options...
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