Replacement LEDs for Proto 2000 models

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#1
I am in the process of installing DCC and replacing the light bulbs in my Proto 2000 engines. I have and want to use my LED lights for this. I know I need to use resisters, but I don't know if the ones I have are good enough as I bought them on eBay to be used with 9V batteries. I am assuming that resisters for 9V won't do the job as the railroad may need more. Can anyone help me out please? Thanks.
 

Dave S

Tree Farmer
#2
I am in the process of installing DCC and replacing the light bulbs in my Proto 2000 engines. I have and want to use my LED lights for this. I know I need to use resisters, but I don't know if the ones I have are good enough as I bought them on eBay to be used with 9V batteries. I am assuming that resisters for 9V won't do the job as the railroad may need more. Can anyone help me out please? Thanks.
I believe it is track voltage minus LED working voltage (normally 2 volts) divided by .02 amps = resistor size in ohms.
 
#3
According to the printing on the power supply, the output to the DCC cab unit is listed as follows: 12VAC/18VAC, 65VA. I have no idea what any of this means so I really don't know what to do with the information you have me. I read on the instructions that the amps drawn by the lights needs to be 2 or fewer amps.

I can do the work, soldering, etc., I just don't know the ins and outs of figuring out which items to use, not to mention the terminology...
 
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trailrider

Well-Known Member
#4
According to the printing on the power supply, the output to the DCC cab unit is listed as follows: 12VAC/18VAC, 65VA. I have no idea what any of this means so I really don't know what to do with the information you have me. I read on the instructions that the amps drawn by the lights needs to be 2 or fewer amps.
Which "instructions" say the lights must draw 2 amps or less? If that is the decoder instructions, it means that the lights shouldn't draw 2 amps. That is a LOT of current draw. It probably would apply for an incandescent bulb, as LED's used in model railroading don't draw anywhere near that. (As Dave S posted, about 0.2 amp might be the draw of an LED.) The question is, what is the voltage output to the LED leads from the decoder at maximum voltage? You should buy a digital multimeter, which can measure volts, amps (current) and ohms (resistance). With the no LED attached to the light leads, check the voltage output at maximum voltage to the locomotive. This will probably be more than when the LED is attached, but that's alright. Guessing that the LED voltage is 2 volts, subtract 2 from whatever the reading is. Divide that by 0.02, and that will give you a first approximation. For example, if the volt meter reading at the leads is 16 volts, subtracting 2 = 14. Dividing 14 by 0.02 = 700 ohms. You probably won't find a 700 ohm resistor, but if you buy some 330 ohm, 270 ohm, etc., you can connect them in series to get close. If the light is too dim, you can change one of the larger resistors and see what happens. You might want to keep a few extra bulbs on hand, in case you guess wrong and burn an LED out. I'd buy 1/2 watt resistors, and be sure to mount them where the heat generated won't melt anything, or use some insulating material between the resistors and whatever they are near.

If my calculations are off, I'm sure somebody will jump in here.
 
#5
LEDs are not 2 volts. LEDs are usually 3 volts and up depending on color temperature with white ones typically being in the 3.5 volt range. Be careful to check the milliamp rating of the LED. You need to be above the threshold voltage, AND at or below the milliamp rating to light the LED and not blow it out.

Try using this calculator to figure out which resistor you need

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

The track voltage is the input voltage. You get that figure from measuring the track directly or reading what the default voltage is. The milliamp rating and threshold voltage comes from the packaging on the LED (except on Radio Shack ones.... they have no info at all)

If all else fails, you can buy an LED tester on eBay or Amazon for a couple bucks (hobby stores will sell the same thing for 10-20 bucks or more) which can show you the brightness of the LED at different currents.
 

Larry

Long Winded Old Fart
#6
I use 560 Ohm resistors on all my LED's for 12 volt max & I only run DC & I use the same resistors for all of my building lights. The headlites are real bright w/a 20 to 25% LED. The 20% LED is the best because it gives almost direct front lighting on the end of the bulb. I've been messing w/LED's for about 3 years now & I learn something new everytime someone brings up the subject.:D:rolleyes:
 

trailrider

Well-Known Member
#7
Although I didn't ask the question, and gave some wrong information, I greatly appreciate the input from both diburning and Larry. I bookmarked the calculator for future use! Thanks, guys!
 
#8
Ok, maybe someone can help me identify my resisters' value and whether they will be good enough. The resister's body is a light blue, with a red stripe on either end and three dark blue stripes in the middle. It is possible that the three stripes in the middle may be black. On the "baggy" they came in, someone had written 100 with symbol next to it that sort of looks like the pie symbol or a variant of the letter "r" in cursive or script hand writing style. I have several hundred of these and I would hate to see them go to waste. I also have some 1k Ohm, 1/4 watt 5% tolerane resister from another project. Can I use either for the LEDs for my Proto 2000 converstion?
 
#9
If you saw my earlier post I thought the package had 750 written on it. I was mistaken, the number was 100 with the symbol next to it. The 750 was the total number of resisters in the bag. Sorry.
 
#10
Ok. A blue resistor is a metal film resistor as opposed to the more common carbon resistors. I've seen some resistors where I couldn't tell whether the band was black, blue or purple because they all looked alike (hint: don't buy radio shack resistors if you're going to lose the packaging, because this will happen!)

The 5 band code stands for the following:

Band 1: first digit
Band 2: second digit
Band 3: third digit
Band 4: Multiplier (x10)
Band 5: Tolerance.

Since 266 and 277 ohm resistors are not standard sizes, I'll assume that your 3 middle bands are black.

So,

First band: Red - 2
Second band: Black - 0
Third band: Black - 0
Fourth band: Black - Multiplier is 0 (0 0s added to the end)
Fifth band: Red - 2% tolerance

So, you have a 200Ω resistor (Ω stands for ohms) with a 2% tolerance. Look closely at the resistor to make sure that both bands are red! If one is brown, then it's a 100Ω resistor as labeled on the bag! (or if both are brown, then it's a 100Ω resistor with 1% tolerance)

As for your LED conversion, if you are sure that your maximum output voltage is 12V, then a 470Ω resistor should be a safe bet for most applications. If you think the LED is too bright, you can increase the resistor to dim to LED, but 1KΩ would be about the upper limit.

Resistors are cheap. They're 99 cents for 5 at radio shack.
 
#11
Well, after taking a closer look at the resister and taking several photographs of the darned thing, it is difficult to say. It does not come out worth a darn using my Olympus camera or my iPhone camera, so I can't even post a photo of it. The outer bands could be both red, both brown, or one red and one brown. It is a very small resister. I am inclinded to believe that it is 100 (symbol) and not good enough for this project. Based on the information above, I will try the 1K resister I have before buying anything else. I am thinking that this will work just fine or I can get something in between the 560 and 1000 as listed by other folks who have responded. Thanks.
 
#13
To double check that you are reading the resistor value colors correctly use the Ohm scale of a DVM. Then you can be sure that its 100 or 200 Ohm.
I always have trouble reading the colors on the metal film resistors so use the DVM as a check.
 



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