I am trying to replace the Life Like DC bulb headlight with LED. I have resistor protected LED attached to the pc board at the bulb sites, but LED does not light. I tested LED with track power at the rails, and it works fine. But not attached to the circutry of the loco. Do I use non-resistor protected LED, assuming output is not exceeding 1.5 v? Confunding to me. Thanks, Andy Chandler
The Life Like bulbs are 1.5 Volt; amperage rating unknown. An LED requires 1.5 Volts or slightly less, so the resistor value needed to limit the current through the LED will be very minimal -- probably in the range of 10 Ohms to no more than 100 Ohms.
I'm going to replace a Life Like bulb with an LED on Tuesday, October 29th, and will be using my Decade Resistance POT Box to determine the value of resistance needed with DCC. I'll post my results tomorrow.
Did you try? Reversing the leads at the decoder that you connected the LED leads to ?
Cheers,
Frank
I forgot,you said,DC, I would still try reversing the leads. Unless you already burnt out the LED, by having the wrong value resistor. You could have used a 12v,LED, with 1000k resistor
LED's are current driven devices. The voltage does not matter as long as you have the correct current limiting resistor.
On DCC the general voltage is between 14-18 volts. For DC is can range in max voltage from 12-16 volts. What is important though is how much current your LED can handle. Generally LED max out at 20-30 Milli amps (0.020-0.030 amps). A LED generally needs a minimum of 1.5-3 volts to light up depending on the color
To find the right resistor you can use Ohm's Law V=IR or rearranged as R= V/I where R= Resistance (in Ohm's, V= Voltage (volts), I= Current (Amps).
We know we need about 20 millamps (0.020 amps) as the max for the LED so that is our I. Our max input voltage is say 12 volts for DC at full speed which is our V so we get R= 12 volts/ 0.020 amps. This gives us a R (resistance) value of minimum value of 600 ohms. The nearest resistor manufactured is a 680 ohm resistor. I generally use 1000 ohm resistors for all my LED lighting.
The problem that you are most likely having is that you have a current limiting resistor in the circuit when you already have a current limited circuit as many locos have 1.5 volt headlights. Secondly, as previously mentioned check the polarity of your LED as well.
Colorado Front Range Railroad: http://www.coloradofrontrangerr.com/
Renegade1c LED's are current driven devices. The voltage does not matter as long as you have the correct current limiting resistor. On DCC the general voltage is between 14-18 volts. For DC is can range in max voltage from 12-16 volts. What is important though is how much current your LED can handle. Generally LED max out at 20-30 Milli amps (0.020-0.030 amps). A LED generally needs a minimum of 1.5-3 volts to light up depending on the color To find the right resistor you can use Ohm's Law V=IR or rearranged as R= V/I where R= Resistance (in Ohm's, V= Voltage (volts), I= Current (Amps). We know we need about 20 millamps (0.020 amps) as the max for the LED so that is our I. Our max input voltage is say 12 volts for DC at full speed which is our V so we get R= 12 volts/ 0.020 amps. This gives us a R (resistance) value of minimum value of 600 ohms. The nearest resistor manufactured is a 680 ohm resistor. I generally use 1000 ohm resistors for all my LED lighting. The problem that you are most likely having is that you have a current limiting resistor in the circuit when you already have a current limited circuit as many locos have 1.5 volt headlights. Secondly, as previously mentioned check the polarity of your LED as well.
The common resistor and LED series circuit works great on a fixed track voltage (DCC). However, with DC, track voltage usually varies anywhere from 3V to 12V (perhaps a little more under light loads). In the above example, if track voltage is reduced to 6V - normal running speed voltage for many locomotives - with a 1K resistor the LED is only getting 6ma of current. This may or may not be enough to light the LED. The LED probably will not illuminate on less than 6V with the 1K resistor, and will vary somewhat in brightness as the track voltage varies in the upper range.
The 1.5 volt light bulb that comes stock uses a series of diodes to create a constant 1.2V to 1.4V voltage drop in series with the motor. The 1.5V bulb is placed across the diode string to feed it a constant voltage, regardless of the voltage going to the motor. This gives constant bulb brightness on variable DC power. And because the diodes conduct before the motor turns, you can turn on the bulb without the locomotive moving by keeping the track voltage below where the motor turns but above 1.5V.
For DC, diode lighting with 1.5V bulbs is the simplest arrangement. For DCC, LED plus resistor is equally practical, takes less space, and creates less heat.
my thoughts, your choices
Fred W
An LED cannot be substituted directly for the Life Like bulb, with or without a resistor, because the Life Like bulb is a very low current device -- so low that there is not enough current for an LED.
The Life Like circuit board has a resistor/diode/transistor constant lighting circuit that allows the bulb to illuminate at minimal current and voltage, and holds that current and voltage at the lowest possible setting.
On the one I just worked on, the YELLOW wire is the NEGATIVE (function control) side and the BLACK wire is POSITIVE. With DCC track voltage, I received a reading of 1.6 Volts applied to the bulb, which is enough for an LED, but the current output is too low. So low, that an LED would not light even without a resistor.
Since I was working on an engine with a DCC decoder installed, I connected the LED directly to the decoder instead of going through the Life Like circuit board.
I was advised by Walthers that the pre-Walthers Life Like P2000 locos use 1.5v, 50 ma ≠ bulbs.
Dante
Do we know this is a P2K loco and not a Life Like 'train set' loco?
If it is one of the P2K locos with the circuit board with 6 diodes on it, it will need to be modified for LEDs. I always thought the bulbs were 3V, they appear to be wired across 4 diodes which would be about a 2.8V drop, the extra 2 diodes of the 6 provide directional lighting.
--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 use DC and took the board of 6 diodes out of the P2K locos. I used a 470 ohm resistor and the leds come on just before the loco moves. And I no longer have to turn the throttle up to almost the 40% mark to get the loco to move. The locos also MU nicely with my Katos and Atlas locos. Not sure what the actual voltage was to the old bulbs.
Jim
The OP should be thoroughly confused now - there is so much mis-information in this thread !
An LED requires 1.5 Volts or slightly less, so the resistor value needed to limit the current through the LED will be very minimal -- probably in the range of 10 Ohms to no more than 100 Ohms.
A yellow LED requires at least 2 volts and the more common white LEDs require 3.4 volts to function optimally.
You could have used a 12v,LED, with 1000k resistor
While 12 volt LEDs do exist, they are not very common.
Yes, LEDs are current driven semi-conductors, the proper voltage you drive them at is equally important.
Just about. The value used for V in Ohm's Law is V = Supply Voltage minus the voltage drop of the LED. If your supply voltage is 12V and the LED requires 3.4V, then the value for V in the equasion would be 8.6.
The Life Like bulb is rated at 50ma. The problem is not sufficient current, but insufficient voltage.
Again, the problem is not insufficient current. A white LED will not light on 1.6 volts no matter what your current is.
This is your best answer. Unless you have a habit of running your engines like race cars, a resistor value between 330 and 470 ohms wired directly to the track works the best. As an added bonus, since LEDs are polarity sensitive, you will automatically have directional lighting without having to use any additional components. For your headlight, wire the long lead (+) of the lead to the right hand rail. For your rear headlight, wire the long lead to the left hand rail.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Mark R. The OP should be thoroughly confused now - there is so much mis-information in this thread !
Hey, if you read it on the Internet, it must be true.
I just read this entire thread for the first time, and I was confused. No telling what reaction the OP had after reading through all of this. Thanks for clearing it up, Mark.
Hopefully, the OP will report back on what he ultimately does.
It would help to know which Life Like loco he was referring to when asking his question about the DC supplied bulb.
Rich
Alton Junction
Closure is a rare treat on the forums
Life Like P2K LED replacement success
To all who were kind enough to reply. I persevered and removed the printed circuit board, and made a central connector using copper clad phenolic board. I then seperated right and left side track pick ups, connected the motor leads to this board. Finally, soldered Evans Designs pre wired 1.8 LED with rectifier and capicitor attached. Wow! It is bright, maybe too bright, but then the headlight at night on the real thing is bright too. Thanks to all who took the time to write great ideas. My wife was impressed. Warm regards, Andy Chandler
I read this thread last night after it came up on a search about lighting model cars. Thanks for the info as I did a little research on the voltage regulation to keep lights from changing brightness. I looked at the "store bought" items and they seemed a bit pricey to me. Has anyone ever just set up a 3.3 volt DC regulator on a DC system to power LEDs?
It looks easy enough with a TO-92 regulator w/ 100 uF Elect input cap and a 4.7 uF Tant cap to get 3 or 3.3 volts DC output up to 100 mA. It looks doable for under $2.00 USD for the regulator. You could parllel white LEDs to get suffecient illumination as needed. (Ref: http://www.mouser.com/Search/Refine.aspx?Keyword=LP2950ACZ-3.0%2fNOPB , they sell to individuals.) Lights would come full on and stay at the same brightness at 3 volts supply.
Sorry, not trying to hijack a thread, just thought it was worth mentioning.