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Hi I m new to some of this . What ? iam trying to do ?is to dim leds down ?.I have tried several different types of resistors like 470, ?680 , ?750 and 1k ohms and can¡¯t ?dim them . ?I used resistor calculators online ?and still haven¡¯t gotten the hang of it ?at what point do they start ?to dim down what I have now is a color code of ?first line is brown ?black ?and yellow the last one is gold ?. ? What ohms would this be ? This dims it down to where I need to be. ?Sorry for making this a dumb question , I have never did any calculations for resistors. thanks?
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It's not a dumb question, but is highly relevant to LEDs. Stay away from anything below 1000 ohms. I use 5100-6800 ohms for headlights on steamers, and 22000-27000 for markers. It takes at least 3300 to see the difference with 1000. Between 20000 and 50000 you won't notice hardly any change.
If you like them really bright, like a diesel headlight, then 1000 might be OK. And I know a number of diesel people who use that, but it makes for extremely bright lights. Incidentally, brown black yellow is 100,000 ohms.
...Tom
On Mon, Sep 18, 2023 at 12:07?PM Dennis Beutler < mmartian74@...> wrote: Hi I m new to some of this . What ? iam trying to do ?is to dim leds down ?.I have tried several different types of resistors like 470, ?680 , ?750 and 1k ohms and can¡¯t ?dim them .? I used resistor calculators online ?and still haven¡¯t gotten the hang of it ?at what point do they start ?to dim down what I have now is a color code of ?first line is brown ?black ?and yellow the last one is gold ?. ? What ohms would this be ? This dims it down to where I need to be.? Sorry for making this a dumb question , I have never did any calculations for resistors. thanks?
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Two alternate ways of doing this:
1. Use a potentiometer instead of individual resistors. A 1 megohm pot should work well. Just connect the leads to one end and the wiper and adjust until you get the brightness you desire, then measure the value of the pot with an ohmmeter and pick the closest resistor value to put in your circuit.
2. Use a decade box. These are somewhat more costly than a pot.
Using the switches you select resistor values until you get the brightness you want. Multiple "ON" selections are added together within the box and you pick a resistor close to the sum of all resistors selected.
In either case remember to start with a high value and work down. Starting low you could blow the LED with too much current.
Rick Jones
If at first you don't succeed, skydiving is not for you.
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On 9/18/2023 1:57 PM, Dennis Beutler wrote: Hi I m new to some of this . What ? iam trying to do ?is to dim leds down ?.I have tried several different types of resistors like 470, ?680 , ?750 and 1k ohms and can¡¯t ?dim them . ?I used resistor calculators online ?and still haven¡¯t gotten the hang of it ?at what point do they start ?to dim down what I have now is a color code of ?first line is brown ?black ?and yellow the last one is gold ?. ? What ohms would this be ? This dims it down to where I need to be. ?Sorry for making this a dumb question , I have never did any calculations for resistors. thanks
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Dennis,
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I've added a chart I made to help determine resistor values to the photo section. Feel free to copy it.
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In my experience, you need to go much higher in your resistor values.? Try a 4K, and go up or down from there.
?
?
On 09/18/2023 12:57 PM MDT Dennis Beutler <mmartian74@...> wrote:
?
?
Hi I m new to some of this . What ? iam trying to do ?is to dim leds down ?.I have tried several different types of resistors like 470, ?680 , ?750 and 1k ohms and can¡¯t ?dim them . ?I used resistor calculators online ?and still haven¡¯t gotten the hang of it ?at what point do they start ?to dim down what I have now is a color code of ?first line is brown ?black ?and yellow the last one is gold ?. ? What ohms would this be ? This dims it down to where I need to be. ?Sorry for making this a dumb question , I have never did any calculations for resistors. thanks?
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Dennis,
In my experience the difference in brightness between 470 to 1k is to small for my eyes to pick up. Try 4k or even 10k.?
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Hi I m new to some of this . What ? iam trying to do ?is to dim leds down ?.I have tried several different types of resistors like 470, ?680 , ?750 and 1k ohms and can¡¯t ?dim them . ?I used resistor calculators online ?and still haven¡¯t gotten the hang of it
?at what point do they start ?to dim down what I have now is a color code of ?first line is brown ?black ?and yellow the last one is gold ?. ? What ohms would this be ? This dims it down to where I need to be. ?Sorry for making this a dumb question , I have
never did any calculations for resistors. thanks?
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From my understanding from 1k or 1000ohms ?resistors and under is drawing to ?much current ,which is could be problematic with decoder boards ?. I have several decoders that are using ?470 - 620 ?ohms ?. I was told these were average for esu ,soundtraxx older boards so I will change them to 1-3k ohms if this is correct. ?What I¡¯am doing now is attaching leds to my tortoises so I don¡¯t have to see what switch is thrown on the layout ?and look at the panel instead so what I have is a 100.000 ohm resistor which is a 10 k I think ?which works great. ?so I was going in the wrong direction ?with resistance ?. Thanks learned something new. Pease correct me if wrong.
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Dennis,
I have never heard what you mention about too much draw. I use 1/4 watt and have not had any issues.?
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From my understanding from 1k or 1000ohms ?resistors and under is drawing to ?much current ,which is could be problematic with decoder boards ?. I have several decoders that are using ?470 - 620 ?ohms ?. I was told these were average for esu ,soundtraxx
older boards so I will change them to 1-3k ohms if this is correct. ?What I¡¯am doing now is attaching leds to my tortoises so I don¡¯t have to see what switch is thrown on the layout ?and look at the panel instead so what I have is a 100.000 ohm resistor which
is a 10 k I think ?which works great. ?so I was going in the wrong direction ?with resistance ?. Thanks learned something new. Pease correct me if wrong.
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Hi guys going to try what rick said.I have a pot that will work,it may help ? This my first time doing this ?it¡¯s a new learning curve for me I have ordered ?100 k ?1/4 watt resistors .
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The problem with adjusting light intensity is that the light perception curve is not linear.
It is still simpler to refer to the LED technical sheet to have at least an idea of its brightness, but you still need to have the LED reference.
Between the two LED references, the intensity of the stronger one (OSXXXX3131A-1MA) must be reduced to 10% to have the same light perception as the weaker one at 100% (OSXXXX3164A-1MA).
This is why I only buy LEDs for which I have the reference.
/g/w4dccqa/album?id=289626
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Dennis,
Especially if you try the pot approach, be sure to put at least a 470 ohm resistor in series with it while you run your test.? This will prevent blowing the LED should you turn your pot all the way to zero ohms by accident.
Yes, when done, you should add the 470 to whatever you determine with your pot.? But especially if you end up with 10k or so, the 470 won't make a visible difference.? Also, you cannot buy a 10.47k resistor.
I see a few people recommended trying a 4k ohm resistor.? 4k is not a standard value.? You will not find a 4.k for sale at the typical hobbyist supplier. 3.9k and 4.3k are.? If you try either of these, you will not likely notice a difference if you had a 4k.? If you really want 4k, try 4 1k resistors in series.
Allan
Wiring for DCC.
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Decoder outputs usually are rated for 100 mA (1/10 Amp), so aren't likely to be hurt by smaller resistances. At 14V, any resistor of 140 Ohms or more will limit current to 100 mA or less. Check the function current rating of the decoder you are using to confirm the 100 mA rating, or learn its actual rating and adjust the minimum resistor size accordingly (double the resistance halves the current, and so on.)
The eye is a lousy sensor of light intensity. It's not able to distinguish two levels that are similar. So, you need to change resistances quite a bit to change observed LED brightness much. Your various resistances were all low, making the LEDs very bright, and changes hard to distinguish.
100,000 is the same as 100k. The k is scientific notation for 1,000 times.
If you use a pot to find the resistance you need for the brightness you want, then I strongly recommend putting a 1.0k resistor (1,000 Ohm) in series with the pot (in the line from the power source to the pot) to limit the minimum resistance and maximum current to safe values. If the pot is used alone, then turning it to one end will present a near short circuit, allowing excessive current flow that probably will destroy the LED and the decoder function output transistor, if using with a decoder. Measure the resistance from the power source end across the resistor and pot to the load (LED) end for the fixed resistance you need.
At or above 1.0k Ohms, on 14V, the power dissipated in the resistor as heat is 196 mW (196 milliWatts/0.196 Watts.) A 1/4 Watt resistor will get pretty hot at 196 mW, being nearly 80% of its power rating.?
Above 2.5k Ohms, even a 1/8 Watt resistor is fine, and smaller than the 1/4W. The body size depends on the amount of heat the resistor has to dissipate into the surrounding still air, and how hot the materials it's constructed of can be without damage. Some power resistors can be operated at much higher temperatures without damage, but are hazards to human flesh and other typical electronic components.
If brightness is OK at 100k Ohms, then you are operating those LEDs at about 12/100th of one milliAmp, which is tiny. The resistor won't even get noticeably warm, nor will the Tortoise power supply load be significantly increased.
-- Don Weigt Connecticut
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We ran into these issues on some of the latest control panels I built at the club. We switched to some high efficiency ultrabright LEDs for certain colors. With the 2.2K resistors we'd been using for standard LEDs for a while, they were much too bright. I had to use the pot trick I previously mentioned here to find a resistor value that made them look about the same brightness as normal LEDs on the panel. IIRC I wound up adding over 200 Kohms to the existing resistor to reduce the brightness sufficiently on those ultrabrights.
Rick Jones
Work harder. Millions on welfare depend on you.
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On 9/19/2023 2:55 AM, PaulXpress wrote: The problem with adjusting light intensity is that the light perception curve is not linear.
<>
It is still simpler to refer to the LED technical sheet to have at least an idea of its brightness, but you still need to have the LED reference.
Between the two LED references, the intensity of the stronger one (OSXXXX3131A-1MA) must be reduced to 10% to have the same light perception as the weaker one at 100% (OSXXXX3164A-1MA).
This is why I only buy LEDs for which I have the reference.
/g/w4dccqa/album?id=289626 </g/w4dccqa/album?id=289626>
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Guys (and I hope ladies),
? ? In the old days we used to use Resistor Substitution Boxes to figure out the necessary resistor. I bult my first in my first rear of high school and have built a few since as they wear out. They can be purchased for about $25, and they are available as kits. I double up when i build them and use both 1/4- and 1-amp resistors as 1/4-amp resistors carry very little current. The cheap way out is to use a breadboard and alligator clips.
????
Have fun JD
On Tuesday, September 19, 2023 at 10:41:17 AM EDT, Rick Jones <r.t.jones@...> wrote:
? ? We ran into these issues on some of the latest control panels I
built at the club. We switched to some high efficiency ultrabright LEDs
for certain colors. With the 2.2K resistors we'd been using for standard
LEDs for a while, they were much too bright. I had to use the pot trick
I previously mentioned here to find a resistor value that made them look
about the same brightness as normal LEDs on the panel. IIRC I wound up
adding over 200 Kohms to the existing resistor to reduce the brightness
sufficiently on those ultrabrights.
? ? ? ? ? ? ? ? ? Rick Jones
Work harder. Millions on welfare depend on you.
On 9/19/2023 2:55 AM, PaulXpress wrote: > The problem with adjusting light intensity is that the light perception > curve is not linear. > > <> > > It is still simpler to refer to the LED technical sheet to have at least > an idea of its brightness, but you still need to have the LED reference. > > Between the two LED references, the intensity of the stronger one > (OSXXXX3131A-1MA) must be reduced to 10% to have the same light > perception as the weaker one at 100% (OSXXXX3164A-1MA). > > This is why I only buy LEDs for which I have the reference. > > /g/w4dccqa/album?id=289626 > < /g/w4dccqa/album?id=289626>
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The politically incorrect mnemonic for resister values that I learned in school is:? "Bad Boys Rape Our Young Girls But Violet Gives Willingly" where Bad = Black, Boys = Brown, Rape = Red, Our = Orange, Young = Yellow, Girls = Green, But = Blue, Violet = Violet, Gives = Grey, and Willingly = White.? You use is as follows:? Black - 0, Brown - 1, Red - 2, Orange - 3, Yellow - 4, Green - 6, Blue - 6, Violet - 7, Grey - 8 and White - 9.? When reading a resister first 2 bands are numbers, 3rd band is number of zeros and 4th band is tolerance: Gold is 5% and Silver is 10%.? So if a resister is banded Brown-Black-Red-Silver it is 1,000 ohms 5% tolerance.? In the resister you used the bands are decoded 1, 0, 4 zeroes, and 5% or 100,000 ohms.
I installed hundreds of LEDs in locomotives over the years and have always used 1,000 ohm 1/4 watt resistors and have never had a failure.? If it too bright for your liking you use the decoder CV settings to lower the brightness.? If you use too high a resistance you are stuck with a dim headlight as you can't make it any brighter but you can always make it dimmer.
Good Luck, John Moonan
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Hi thanks for the information.when built this pot I did burn up a few leds then added a 470 resistor to it which solved the problem .This pot going to be used for testing leds for brightness.what I did find out was the100k worked fine for me . the problem I was having is using resistors from1k-220 ohms which were to bright and bought resistors trying to find out which way to go and went online found resistance calculators and i couldn¡¯t figure it¡¯s light level.nick showed some of brightness levels he was working on which I trying to achieve .then someone suggested a pot .
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Rick Jones