I have a 9 volt battery on my work bench for such purposes. I soldered a resistor to one leg of the LED and then make contact with the two terminals on the battery.
Rich
Alton Junction
Applying power is really the only way, but if you have good eyes, or a good magnifier, adn you are workign with an LED that has a clear case, if you hold it up to the light you will be able to see the little whisker wire coming from the smaller terminal to the top center of the larger - at the point of contact of that wire and the larger terminal is the diode junction. If that wire is broken, the LED won;t work. The only way for it to be broken after manufacturering though is if you sand away too much of the LED case and allow the lead to move. Not very likely though.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
mobilman44 THANK YOU !!! and only a test with a 9v and resistor will tell the story. Is that correct? Thanks again!
THANK YOU !!!
and only a test with a 9v and resistor will tell the story. Is that correct?
Thanks again!
Yes, I answered that a few minutes ago.
What amazes me is the people who read these messages and it never occurs to them to save the links and info to Favorites. I have also begun to find out, many have no idea what Favorites is about and just depend on the cookies stored in the PC to find the link again.
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.
mobilman44 As I understand, there is no obvious way to view an LED to determine if it is "no good", and only a test with a 9v and resistor will tell the story. Is that correct? Thanks again!
As I understand, there is no obvious way to view an LED to determine if it is "no good", and only a test with a 9v and resistor will tell the story. Is that correct?
Yep, a simple battery resistor is all you need. I like the tester in the link because I can test more than one LED at a time, so I can compare the brightness in case there is any miss-match. Plus I use a lot of LEDs and it is real convenient to just pop them in and press the button rather than fiddle with clips or wire attachment to the LED legs. Like Rich, I also forget, or at least don't trust my middle age memory and have marked the tester with a blue and yellow marks to remind me of the polarity and the DCC lead coloring.
BTW, it would be trivially easy to make such a tester, it is nothing more than an array of resistor wired to a socket and a 9V battery terminal.
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
Quite a few in the Yahoo SoundTraxx DCC group have purchased a similar LED tester straight from China, usually free shipping but your mileage may vary. Don't forget, just about all this stuff comes from China even if you buy it in the USA. Ever go to a gift shop somewhere in a little town in the USA and see a what looks like a local made gift? Look at the bottom of the item.
LED links.
http://www.nmra.org.au/Hints/SMDs/Using%20SMD%20LEDs.html
http://www.kpsec.freeuk.com/components/led.htm
http://www.theledlight.com/trains.html
http://www.modeltrainbuilder.com/LEDs.html
The only time I am concerned about the voltage for a LED is if too many in series for the voltage that is available but have not ever had that situation. The most I use in series are two for loco number boards. Two LED's in series with a 1k resistor. Both LED's draw about 9ma because they are in series.
Save all links to Favorites. Take your time reading about theem.
It never ceases to amaze me at the amount of knowledge available thru the kind folks on this forum!
ENJOY !
Mobilman44
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
Visual inspection may well not provide any hint as to if an LED is working or not, you really need to pass current through it to be sure. I find a cheap LED tester to be invaluable for this. The following link is an inexpensive one that I use all the time.
http://www.allelectronics.com/make-a-store/item/LT-100/LED-TESTER//1.html
I always check my LED's before installing them.
The leads are different lengths. The long one is the Anode, or +ve lead that goes to your blue decoder wire. The short is the Cathode or -ve which goes to the function output (White or Yellow) If you wire them the wrong way round they don't work.
You will almost always be needing a resistor when installing an LED. If you are simply replacing an LED on the Steward light board the resistor will already be in place. If you are using a decoder a 1K ohm will usually do the trick.
mobilman44 Hi! I'm in the process of replacing a couple LEDs in a Stewart Loco and am in need of some basic information on them (LEDs)............... - How can you visually tell if an LED is "broken"? - When you buy LEDs, do they all come with the same type/length of wire "feeds"? - What basic questions regarding LEDs have I not asked? Thanks all! While I know my bulbs, I realize I know beans about LEDs..............
Hi!
I'm in the process of replacing a couple LEDs in a Stewart Loco and am in need of some basic information on them (LEDs)...............
- How can you visually tell if an LED is "broken"?
- When you buy LEDs, do they all come with the same type/length of wire "feeds"?
- What basic questions regarding LEDs have I not asked?
Thanks all! While I know my bulbs, I realize I know beans about LEDs..............
Take a 9 volt battery and a 1,000 ohm resistor to test the LED. Put the resistor in series with one lead and one battery terminal. The other LED lead to the other battery terminal. If it does not light, reverse the leads to the battery terminal. LED's are polarity conscious. I nevver remember which lead is cathode or anode without looking at a diagram.
LED's come with different lengths and styles. There are SMD LEDs with no leads.
There are some being sold with the resistor.
Most LED's have a 20ma current max. A 1,000 ohm resistor with 12 volt DC will allow about 9ma current through a LED.
I have a few green 3mm LED's with a 2ma max current but are for battery operated projects I have built.
Go to the below link and do some reading.
http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm
LED's are current operated devices.
Bulbs are voltage operated devices.
Don't confuse the two.
Below are measurements I have made.
Measured with 12.2 VDC supply using 20 ma max current LED's. Values will vary a ittle depending on actual DC supply value.
Resistor Current
1000 ohm 9.0ma
750 ohm 12.45ma
680 ohm 13.12ma
510 ohm 16.25ma