Question for all you LED pros. Would two in-series 460 ohm quarter watt resistors be adequate to properly resist surface mount LEDs? My power source is an 18 volt ac “accessories” power pack. I’ve tested this level if resistance on four or five SMDs and haven’t blown one of them. YET. I want to get maximized life out of my LEDs which is why I ask. Any direction, thoughts or advice would be appreciated. Thanks and happy modeling! PJ
You missed the Electrical DCC forum by the way.
Most LED’s are around 20 to 25 ma max if you do not have the specs. I go with 20 ma and usually limit the current to 15 ma. Remember, they are current operated, not voltage operated like light bulbs.
My NCE Power Cab uses a 1k resistor with a red LED to monitor the 14 VAC DCC signal to the track.
I have three of the below meterrs for some years.I never have to measure AC current as I only use DC power for any lighting.
Harbor Freght has a meter for a few dollars more that can measure AC current.
http://www.trainelectronics.com/Meter_Workshop/in
http://www.trainelectronics.com/Meter_Workshop/in
LED’s and light bulbs.
http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm
Rich
Should be OK, though you really shouldn;t run single LEDs right from an AC source, put two back to back. A pair of 460 ohm resistors is 920 ohms, which is fine for 18V on a typical white LED. Results in about 16ma.
–Randy
That would depend on the SMLED used. I put some in headlights run off a decoder and needed up to 3Kohm to get the decoder lighting functions to work with them. I originally used a 1/4 watt 1K resistor and the LED burnt out in a week. I then wired in a 2K resistor but could not get the dimming of the headlight until I added another 1K. I used these. http://www.traintekllc.com/Miniature-Wired-603-Surface-Mount-LED-Golden-White/productinfo/LED-603WG/
I put them in these. http://s1081.photobucket.com/user/locoi1sa/media/K5s%205698%20project/SAM_0562_zps82e1e836.jpg.html?sort=3&o=9
I still need to make a lens for the headlight out of a piece of acrylic rod.
Pete
Generally anyone who burns out an LED was not aware of the LED specs or or did not measure the current.
NCE Power Cab’s have a single LED with a 1k, 1/4 watt resistor which is standard for the controller and it is right across the DCC in the connection panel. I have traced out the circuit. At least six years with my Power Cab and the LED still works.
Rich
Thanks everyone. Very helpful. And Pete that’s a great looking engine.