PeteN92 Posted January 25, 2021 Share Posted January 25, 2021 (edited) I'm following this diagram from Brian Lambert on how to wire up a 3 way point onto the frontier panel. I'm using blue LEDs with a DC forward current of 30mA DC forward voltage of 2.1 volts And am running them through a 12v power supply. The LEDs will not light however if I stick my test bulb before the resistors everything is changing correctly. Doing my resistor calculations it's says I should be using a 330 ohm resistor for 1 led. If my understanding is correct this circuit has 3 leds in parallel so I should be using a 110ohm resister before each led. When I add in what should be the correct resistor my test bulb will then light very dimly after the resister showing there is power flowing but the LEDs will still not work . I have even tried dropping the resistors down further to get the test bulb to be brighter but again nothing lighting on the LEDs . I have tested the LEDs with a button battery and confirm none of them have blown. Any ideas ? Cheers Pete Edited January 25, 2021 by PeteN92 Extra Link to post Share on other sites More sharing options...
cliff park Posted January 25, 2021 Share Posted January 25, 2021 The fact that the LEDs are in parallel makes no difference. Each LED is across the supply. The fact that there are others makes no difference. If the bulbs light, even dimly, this would suggest the LEDs are short circuit. Try an LED with resistor in series, say 1KΩ, straight across the 12V supply, it should light. If it doesn't reverse the LED connections. If it still doesn't it's dead. You surprise me with the 30mA figure, is this the LED spec. Link to post Share on other sites More sharing options...
smokebox Posted January 25, 2021 Share Posted January 25, 2021 (edited) 30ma is usually quoted as the maximum that LED can take but it is far better to run them at a lower current to prolong their life. 20ma or less would be better. A 1k resistor in series with the supply is a pretty "normal" value if the supply is 12volts. Edited January 25, 2021 by smokebox 1 Link to post Share on other sites More sharing options...
Nigelcliffe Posted January 25, 2021 Share Posted January 25, 2021 330ohm is the absolute minimum resistance for the quoted specifications. They'll be very bright with that value, and any less risks burning up the LED. As both posters above have said, use a higher value, of nearer 1000ohms. I can't see anything obviously wrong with the diagram. But, if LEDs don't light in simple circuits its usually because the LED is the wrong way round - so either turn the LEDs round, or reverse the positive and negative leads from the power supply. - Nigel Link to post Share on other sites More sharing options...
Michael Hodgson Posted January 25, 2021 Share Posted January 25, 2021 They aren't in parallel. They are on three separate circuits only one of which is live at any one time because of the action of the switches. 2 Link to post Share on other sites More sharing options...
PeteN92 Posted January 25, 2021 Author Share Posted January 25, 2021 Right so swapping the power leads round have got them to light up, however the sequence is now all back to front between the panel and the routes set. Swapping over the leads from the switches to the bottom of the LEDs in the panel seem to make no difference In curing this. Pete Link to post Share on other sites More sharing options...
Nigelcliffe Posted January 25, 2021 Share Posted January 25, 2021 Having got the LEDs the right way round (so they illuminate). Then, if the switches are wrong, its just a matter of working out which contacts on the switches are the "right" ones. There is a chance that a switch diagram is interpreted upside down. There are two approaches to getting the LEDs right: could swap the wires around. Or could just move the LEDs on the panel to the "correct" places - ie. see which LED lights for a particular route, and put it in that hole in the panel. If swapping wires, there are FOUR wires to consider, the three to the LEDs and the green (in diagram) from Switch 1 to Switch 2. To do it "from the bottom", start with Switch 1, and set the route to C. Identify which terminal on Switch 1 should illuminate LED for C. Connect LED C. Now connect green link from other terminal on Switch 1 to middle of Switch 2. With Switch 1 set so LED C does not light, identify which terminal on Switch 2 corresponds with route B. Connect LED B. And LED A is the remaining contact on Switch 2. Link to post Share on other sites More sharing options...
Michael Hodgson Posted January 25, 2021 Share Posted January 25, 2021 Glad you haven't burned them out. It sounds as though you are saying essentially that you have not actually wired them as per the circuit shown. Are you you perhaps being confused by looking at the switches upside down below the baseboard? I once wired up point motors wrongly on a 3-way point because I forgot the turnout to the left when viewed from above is of course to the right from below. Link to post Share on other sites More sharing options...
PeteN92 Posted January 26, 2021 Author Share Posted January 26, 2021 All working correctly now thanks for your help guys Cheers Pete 1 Link to post Share on other sites More sharing options...
Sol Posted January 26, 2021 Share Posted January 26, 2021 In fact as only one LED can be lit at any one time, only one resistor is needed in either leg of the power supply. 1 Link to post Share on other sites More sharing options...
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