What voltage AC or Dc does one use to test an LED bulb to determine if it is burnt out?
Thanks
Read the manufacturer’s data that comes with the LED. Usually, most LED’s will handle no more than 3 volts…
Jim
Unfortunately I don’t have the mfr specs. The LED’s I am concerned about are in the Walthers crossing signals.
Assume 1.5 volts and move up from there…no way around it if you cant find out exactly what their ratings are.
David B
How about 4.5 volts with a 470 ohm resistor. Try in both directions. That should be enough voltage to forward bias the diode and enough resistance not to fry it once it turns on. Are you measuring right at the leads to the LED? I have seen some LEDs with internal resistors, but most do not have them. There may be resistors hiding in the signal too.
Jim
I clip a couple leads to the track and use low voltage from there. assuming a dc type power supply. so far so good.
The ‘correct’ way to match resistors to various LEDs is to use a meter in series to match the ‘specified Ma.’ current for illumination. Many LEDS Lilke 12,000 ohms. Some ‘Pros’ use higher yet values to get for longer life.
This is for RED/GREEN LEDs. Blue and White need more voltage to light. Contrary to popular opinion, LEDs DO BURN OUT- especially without an appropriate current limiting resistor.
1.5v Grain Of Rice bulbs work on both AC and DC, unlike LEDs.
danobie…Try looking here for led info, basic to advanced www.theledlight.com/technical.html Tons of information, ya might bookmark it…hope it helps…John
Thanks for that website John. It’ll really help me alot.
Paulie
That is correct, LEDs do not burnout. after many thousands of hours of operation so may stop working, but they are really long lasting. I have seen one explode though…
DC 2 Volts should do it. Be sure to use a resistor to limit the current!
All LED’s use “DC” voltage. While a Led will work on “AC” voltage you risk blowing it.
Leds are diodes and only let current flow in one direction. The exception is a bi-color led. This bi-color led can be turned on with AC. A Red / Green bi-color led will appear to be yellow when turned on with “AC” voltage because both leds are being turned on at the same time. Think of the Led as a water valve on a garden hose. Under normal conditions water only comes out of the hole. This is how a single color Led works, while testing if you have the polarity backwards the Leds will not turn on, reverse the polarity and the Led will light up if not burned out or blown.
For testing use 1.5 to 2 volts in most cases. If the Led does not light up with your test leads hooked up positive right lead, negative left lead. Reverse your test leads negative lead right positive lead left. If not bad the Led should light. If this does not work try increasing your voltage “SLOWLY” to a maximum of 12-volts “DC”. Do this in steps of one half volt or one volt. 1.5, 2, 2.5, 3, 3.5, 4 and so on to a “MAXIMUM” of 12-volts.
The solution is easy if all you want to do is simply see if it lights up at the workbench. Use a single AA battery as your power source and connect with a couple pieces of wire with an small alligator clip at one end of each to clip to the LED anode and cathode. Voila, a portable low-tech LED tester.