I am running Miniatronic LED's Model # 12-310-05 in my HO PK1000 Erie Built using a Digitrax DH 123. I have been using the 470 resistor that came with the LED's. The LED's life span seems to be a lot shorter than I think it should be. I am getting between 40 to 60 hours run time before the LED goes out?
Should I go to a different ratting on the resistor? From what I have read LED's life is measured in years, not hours. You would think they would send you the right one in there package.
Thanks for the coming answers, Ken
I hate Rust
Ken:
I agree that 470 ohms is too small. I use 1K ohm resistors for my leds and they are plenty bright and I have never had one burn out. Some have been in my equipment for more than 5 years. I really don't know why they supply those smaller ohm resistors with the leds.
Joe
470 may be too small in your case but is okay for a lot of other installations.
Installers needs to check current and voltage ratings for their project to determine if the supplied resister is adequate.
I always use 1K Ohm for LEDs used with decoders and have never had any problems with them not being bright enough.
CNR378470 may be too small in your case but is okay for a lot of other installations. Installers needs to check current and voltage ratings for their project to determine if the supplied resister is adequate.
I agree. That's why I question their including the 470 ohm resistors. It gives one the impression of "one size fits all".
Thanks for the quick answers folks. I was thinking I had read 750 to 1000 resistors where used by most people here.
They are a 1/4 watt?
Ken
Miniatronics supplies the resistors with their LEDs for people to use on DC layouts. They are not packaged for the DCC segment of the hobby. If you wire an LED, resistor and motor in series then the 470 ohm is plenty for your little DC pack. Us guys running anywhere from 12 to 18 volts in DCC you need more resistance then you would for variable DC.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
Ken I use 1K 1/4 watt for all my LED installs. If you want to get fancy you can use one of the many on-line LED circuit resistor calculators and be more precise based in the requirements of the specific LED, but I find 1K is just fine in most all applications that I have come across.
Simon Modelling CB&Q and Wabash See my slowly evolving layout on my picturetrail site http://www.picturetrail.com/simontrains and our videos at http://www.youtube.com/user/MrCrispybake?feature=mhum
1K, 1/4 watt resistors here, too. I haven't lost a LED yet, and some of them are old enough for Kindergarten, at least.
It takes an iron man to play with a toy iron horse.
Interesting. I just installed an LED in a locomotive using a 1K ohm resistor and thought for this application it was to bright. So I added a 470 ohm resistor and it came out just right. Bottom line is not all LEDs are created equal. I usually use a 1K resistor.
1K 1/4 watt. Lather, rinse, repeat. An LED with the proper current level should outlast your grandkids. The 2780 ohm and 470 ohm resistors that come with the Miniatronics LEDs I just set aside in my parts box
Although for whatever reason in my Stewart AS16's a 1K results in a WAY too bright light, even though the circuit is exactly the same. I put the stock 470 ohm back in series with my replacement 1K. I think it has more to do with the high quality lens/light pipe than it does with too much LED current, 1K is 10ma or less on most common DCC systems and that's half of the LED's max rating. You CAN get too much resistance - in which case the current would be too lwo and the LED won't light. No harm.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I find using a 700 1/4 watt resistor to work best with the richmond golden white leds,very good lifespan yet still nice bright headlight.
locoi1saMiniatronics supplies the resistors with their LEDs for people to use on DC layouts.
Pete, that explains a lot to me and shows the short comings of my LHS. As much as I love K-10 Model Trains as far as pricing and stock the owner knows less than me when it comes to DCC.
Thanks for all your help folks.
Miniatronics SAYS the 470 is OK, but if you calculate it out it really isn't. Using LEDs on DC without some sort of constant lighting circuit is tricky, since the track voltage varies. Below the LED's voltage, it will never light regardless of what reistor is used - about 3.1 volts have to be across the LED for it to work. On old locos this was probbaly still before the motor turned, but on modern locos with better motors, you're probably going at a good clip beforee the light would even come on. Typical top voltage for DC is 12V< so if you base a reistor value on a 'safe' current level at 12V it may be too low a current at lower voltage, like half throttle at 6 volts, again resulting in the LED not lighting. SO you compromise and 'assume' people won't be running full throttle all the time.
With DCC the voltage is constant, and for typical HO settings, higher than 12 volts effective to the function outputs. So a resistor that just makes it as far as the current limit for 12 volts is going to go over it for higher voltages. And exceeding the current limit on the LED is the fastest way to kill it.
The below is from a post I made here a few weeks ago. I used a 12.2 vdc source and measured the current with a digital multimeter which I suggest you buy.
I believe 470 ohms is pushing the limit of the LED, most of which are 20ma max. I intentionally did not try this test with a 470 ohm resistor because of what I saw at 510 ohms resistance.
Using one LED and one resistor, measured with 12.2 VDC supply using 20 ma max current LED's. Values will vary some depending on actual DC supply value. Brightness will be a little different. Many use the 1000 ohm resistor.
Resistor Current
1000 ohm 9.0ma
750 ohm 12.45ma
680 ohm 13.12ma
510 ohm 16.25ma
You should NOT mess with DCC at the component level without some knowledge of basic electronics and without a multimeter. Many here and in other forums get into trouble without this knowledge and not asking questions first.
As a former electronics tech, I try to stay at 75 percent current of what a device is rated at. With used wall warts, never over 50 percent current of what it is rated at. Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
This is why I tell people with DCC to just use a 1K resistor. Forget the technical stuff that you don't understand, others have looked at it and 1K is great. 9ma is plenty, white LEDs are insanely bright, and with 9ma at 12V, you have enough headroom that if you accidently flip the voltage switch on the booster to 20V it won't blow out the LEDs.
Follow up to my earlier post. I installed an LED in a Genesis Santa Fe Freight F7 that had a Digitrax decoder in it. With that decoder I used a 1K and a 470 ohm resister to get the light output where I wanted it. Today I hooked up a Tsunami decoder to the same style LED in a SP 2-6-0 engine and I only needed a 1K resistor to get the lighting I wanted.
So I would say there are a couple of things going on. One depends on the decoder. 2nd depends on the lumens the LED was designed with. As has been said I think a 1K resistor is a good starting point when installing an LED.
I'm with the 1k crowd. Can it be brighter?, sure but if you look at one with the 1k resistor you'll find it's plenty bright enough. On top of that you might never have to change the LED again, which is an added bonus.
Springfield PA
I just installed an LED in a brass conversion to DCC and used a 1K ohm resistor. I thought it was going to be just right while testing but after getting it up and running it is still to bright to my eyes. So I think I'm going to tone it down some more and add a 220ohm resistor or maybe a 330 ohm resistor. Could be the LEDs I'm using that I need more resistance.
The only real exceptions are decoders that have a low voltage output designed to drive LED's directly. An example would be Tsunami drop in decoders for some Athearn loco's.
I finally got around to installing the LED with the 1000. I would like it a little brighter, do they make 900 or 800 or just go for the 750?
Here are the standard values available (you can multiply by 10, 100, or 1000 to get the bigger values - remember 1K ohms is 1000 ohms). http://www.elexp.com/t_eia.htm
Common cheap resistors are 10% tolerance, so that's the right hand column. 820 is the next step down from 1K in a 10% resistor. 750, 820, and 910 are available only in 5% or better.
ANother reason not to use the absolute smallest resistor value - if it's a 10% tolerance part the actual value could be lower then the nominal value, resulting in excessive current flow.
Thanks Randy, but it all so might just be the aim of the LED in the Erie Built. I just did a E-3 with the same LED and resistor and it is much brighter!
All so thank you for the link.
Or the clarity of the plastic "lens" that's in there. For example my P2K Geeps are MUCH brighter than my Walthers FA, same brand of LEDs, from the same pack, and same 1K resistors all around. The FA has a rather thick chunk of clear plastic for the lens, the P2K locos have a very clear light pipe