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Electrical Connections For LEDs
Bert used the ‘Ask a Question’ link to post this question:
“I purchased individual strands of battery powered (2AA) micro lights from a Christmas closeout. I intend to use a SPDT slide switch to control turnouts with one terminal lighting a red LED and the other terminal lighting a green LED. A wire from the switch arm will be used to throw the turnout. I plan to cut the strands into individual LED lights and solder them to the proper terminal such that when the turnout is changed, the correct LED is on. I’ve read that LEDs have long and short terminal legs but there is no way to identify them on the encased light strand. Any thoughts and comments regarding electrical connections would be greatly appreciated as I am an electrical novice. Thanks for your help in advance.”
Disclaimer: Obviously, readers are advised to seek proper technical advice from a registered electrician for any job that involves live wires that could result in injury caused by an electrical shock.
5 Responses to Electrical Connections For LEDs
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Bert, I have also used these micro LED’s by seperating them from the strand. by cutting the wires flush with one side. You must test them with a DC source of known polarity and determine the correct polarity. You can use a 9 volt battery as a known source. Caution, whatever the source you use you must use a series resister to limit the current draw. I use a 1000 ohm resister. 1/8 watt will do. Attach the source, if it lights you are OK. If it does not, reverse the polarity, it should light. Be aware that the wire in these strings is insulated and must be removed to solder. These work good as headlights, also use a series diode to protect the LED when running in reverse. Phil G.
LEDs are pretty tough. As diodes, they are fine with reversed voltage as long as it isn’t beyond the rated voltage. You can just connect the battery and if the LEDs don’t light up, reverse the connection.
Don’t go more than the 2 AA batteries since the LEDs are probably rated at 3 volts.
Philip/Dale: Thanks for your comments. I will heed your advice and proceed with due caution.
Apart from older Clear LEDs the vast majority of LEDs work on 3 volts. Clears needed 5 volts. If you use 12 or 9 volts on an LED it will burn very bright before emitting smoke and dying. The safe way to test LEDs is to put a pair of tired AA or AAA batteries which glow dimly in your flash light in a battery holder and connect the LED across them. They are marked + ve and -Ve and the max voltage will be less than the LEDs Vf anyway. If it doesn’t light turn it round.
Don’t use fully charged batteries especially rechargables as you can get impressive results if you short them out. I wouldn’t risk 9 volts or 12 volts or anything requiring resistors unless it was built into a test rig. Too easy to bypass the resistor and blow up the LEDs
David: Thanks for the insight. Once I get started and become familiar with what I am doing, the task should become easy. For now, it will be a learning process.