I am building a control panel with LED indicator lights. What is the best way to supply power for them? What voltage should I use?
Since no one seems to have an answer for you here in the forum yet, I would suggest you e-mail your question to railroadeditor@trains.com and mybe someone there can help you. Hope this helps.
Thanks for the tip
They run on filtered 3 to 5 volts DC unless they are made with a resistor or IC in them to work on other voltages or do special jobs. If you buy them from Radio Shack or other places the package lists this info. The best way to power them is with 2- 1.5 volt flashlight batteries in series. If you hook them up reverse polarity they burn up instantly BTW.
Didn’t see this post come up before now. Was there a delay somewhere?
Anyway, to answer your question - do NOT connect an LED directly to a power source unless it is the type that has a built in resistor, and most LEDs do not. It will burst forth in a blaze of glory and then shine no more - ever.
Do not run it from AC (the accessory terminals on your power pack) unless you put a standard silicon diode in series with the LED and a resistor to block the AC half cycle that works against (and can damage) the LED. Also note that when doing this, the cathode of the LED must connect to the anode of the silicon diode so that the current flows through both on every half AC cycle.
Always place a resistor in series with the LED. The resistor should be chosen so that its ohms value is (source voltage minus 2 volts) divided by desired current in amps; and it’s wattage rating equal or greater than the desired current in amps times desired current in amps (again) times ohms value. Or figure the wattage by (source voltage minus 2 volts) times (source voltage minus 2 volts) again divided by resistor ohms value, same thing. Or a third way for wattage which wil give the same answer - (source voltage minus 2 volts) times desired current in amps.
This desired current is generally 5 to 20 milliamps (which is the same as 5 to 20 thousandths of an amp), also expressed as .005 to .02 amps.
Example - we have a 12 volt DC power source. It can be the DC output from your power pack if you want the throttle knob to control the LED brightness (you probably don’t want this, but that’s what will happen).
Take 2 volts off the 12 to give 10 volts. Do this since the LED itself takes from 1.5 to 2.2 volts to operate, this voltage is not across the resistor itself so doesn’t come into the resistor calculation. We average the possible 1.5 to 2.2 volts into a nice easy to handle 2 volt average.
We want 10 milliamps or .01 amp to flow through the LED
An easier way to hook one to a power pack is with a 12 volt automotive dash light bulb and 5 silicon diodes. You use the 5-1n4001 diodes to set up a 3.5 volt voltage drop in series with the bulb and power the led from the voltage drop. Works like a constant voltage light circuit.
Thanks all.
Um, this may sound kind of dumb, but given all the math and stuff connected with LEDs for indicator lights on your control panel, might it not be easier to go with 12 volt bulbs for that application? You haven’t got the power source for the LEDs on hand yet, so theere’s nothiing invested in it yet. Radio Shack do a very nifty red and green bulb made for mounting in panels. They are bright, and mine have lasted for ages. Long life is probably why LEDs were mentioned to you in the first place. Just a thought [:D]
Most power packs have a constant DC output that can be used to power your LEDs. Just make sure you have the polarity right, and put a 1K Ohm, 1/2 Watt resistor in the line to each LED. If you are going to have enough LEDs you can wire all of them in series with an appropriate resistor. Each LED will drop approximately 1.2 volts, so if your power supply puts out 14V DC, you can power 12 LEDs in series. Something to watch out for is the initial power surge when the power pack is turned on, and the fact that most power packs put out more voltage than their rated output. Measure the output voltage with a meter to be on the safe side, and I would still use at least a 100 Ohm 2-Watt resistor to limit the initial current surge.
[:)]Sorry for the delay in response. I tried them. My kid keeps getting burned when switching.
TX
I am building a control panel with LED indicator lights. What is the best way to supply power for them? What voltage should I use?
Since no one seems to have an answer for you here in the forum yet, I would suggest you e-mail your question to railroadeditor@trains.com and mybe someone there can help you. Hope this helps.
Thanks for the tip
They run on filtered 3 to 5 volts DC unless they are made with a resistor or IC in them to work on other voltages or do special jobs. If you buy them from Radio Shack or other places the package lists this info. The best way to power them is with 2- 1.5 volt flashlight batteries in series. If you hook them up reverse polarity they burn up instantly BTW.
Didn’t see this post come up before now. Was there a delay somewhere?
Anyway, to answer your question - do NOT connect an LED directly to a power source unless it is the type that has a built in resistor, and most LEDs do not. It will burst forth in a blaze of glory and then shine no more - ever.
Do not run it from AC (the accessory terminals on your power pack) unless you put a standard silicon diode in series with the LED and a resistor to block the AC half cycle that works against (and can damage) the LED. Also note that when doing this, the cathode of the LED must connect to the anode of the silicon diode so that the current flows through both on every half AC cycle.
Always place a resistor in series with the LED. The resistor should be chosen so that its ohms value is (source voltage minus 2 volts) divided by desired current in amps; and it’s wattage rating equal or greater than the desired current in amps times desired current in amps (again) times ohms value. Or figure the wattage by (source voltage minus 2 volts) times (source voltage minus 2 volts) again divided by resistor ohms value, same thing. Or a third way for wattage which wil give the same answer - (source voltage minus 2 volts) times desired current in amps.
This desired current is generally 5 to 20 milliamps (which is the same as 5 to 20 thousandths of an amp), also expressed as .005 to .02 amps.
Example - we have a 12 volt DC power source. It can be the DC output from your power pack if you want the throttle knob to control the LED brightness (you probably don’t want this, but that’s what will happen).
Take 2 volts off the 12 to give 10 volts. Do this since the LED itself takes from 1.5 to 2.2 volts to operate, this voltage is not across the resistor itself so doesn’t come into the resistor calculation. We average the possible 1.5 to 2.2 volts into a nice easy to handle 2 volt average.
We want 10 milliamps or .01 amp to flow through the LED
An easier way to hook one to a power pack is with a 12 volt automotive dash light bulb and 5 silicon diodes. You use the 5-1n4001 diodes to set up a 3.5 volt voltage drop in series with the bulb and power the led from the voltage drop. Works like a constant voltage light circuit.
Thanks all.
Um, this may sound kind of dumb, but given all the math and stuff connected with LEDs for indicator lights on your control panel, might it not be easier to go with 12 volt bulbs for that application? You haven’t got the power source for the LEDs on hand yet, so theere’s nothiing invested in it yet. Radio Shack do a very nifty red and green bulb made for mounting in panels. They are bright, and mine have lasted for ages. Long life is probably why LEDs were mentioned to you in the first place. Just a thought [:D]
Most power packs have a constant DC output that can be used to power your LEDs. Just make sure you have the polarity right, and put a 1K Ohm, 1/2 Watt resistor in the line to each LED. If you are going to have enough LEDs you can wire all of them in series with an appropriate resistor. Each LED will drop approximately 1.2 volts, so if your power supply puts out 14V DC, you can power 12 LEDs in series. Something to watch out for is the initial power surge when the power pack is turned on, and the fact that most power packs put out more voltage than their rated output. Measure the output voltage with a meter to be on the safe side, and I would still use at least a 100 Ohm 2-Watt resistor to limit the initial current surge.
[:)]Sorry for the delay in response. I tried them. My kid keeps getting burned when switching.
TX