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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Dennis,
?
I've added a chart I made to help determine resistor values to the photo section. Feel free to copy it.
?
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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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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Scott H. Haycock <shhaycock@...> added the photo album
Resistor Codes
: A chart to read resistor values
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Scott H. Haycock <shhaycock@...> added folder /Resistor Codes
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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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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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Re: Updated photo album Passenger car lighting for DCC and DC power
#photo-notice
I agree with what Don Weight said.
DonV
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Re: Updated photo album Passenger car lighting for DCC and DC power
#photo-notice
The circuit in the ad is only the rectifier and filter capacitor. There is no regulator, so the output depends on the input. I don't know why it's described as 6,12, or 24 V in and 12V out.. Clearly it isn't so. But, it should work fine on DCC, which has pretty consistent voltage to the track. You could always add a regulator circuit as Dan did in his homemade example. Really, on DCC, the capacitor could be much smaller, perhaps 33 or 47 or 100 uF instead of 1,000 uF.?
The bigger cap draws more of a surge for longer on power up, which might be a factor with multiple lighted cars plus multiple sound equipped locos. I still like the idea of a small resistance in the track side of the circuit to limit that surge current when powering up. The big cap will keep the lights from flickering if you have track power pickup issues.
-- Don Weigt Connecticut
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Updated photo album Passenger car lighting for DCC and DC power
#photo-notice
rrmaven <dan.shirleylee@...> updated the photo album
Passenger car lighting for DCC and DC power
: 2 photos of a homemade AC-to-DC bridge rectifier assembly powering an LED strip,
and one showing an inexpensive and ready-made assembly on eBay.
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Added photo album Passenger car lighting for DCC and DC power
#photo-notice
rrmaven <dan.shirleylee@...> added the photo album
Passenger car lighting for DCC and DC power
: Photos of ha homemade AC-to-DC bridge rectifier assembly powering an LED strip,
and a PDF showing an inexpensive and ready-made assembly on eBay.
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DCC Capacitors/diodes for passenger car lighting
Greg-
I am finally returned from my travels and can respond as per my note of Aug. 19.
Since I made my comments, I saw a ready-made AC-to-DC converter on eBay that I think will work for you
and costs $1.20 each plus $3.75 shipping.? At that price, you could buy a handful and not have to
do any soldering/assembly, and if they don't work the way you want, you've lost about $10.? The assembly looks
almost exactly like what I put together at more cost and time.? I am going to post several items in the "Photos"
section: (1) 2 pictures of my assembly and the assembly connected to a strip of
LEDs for my my passenger cars, and (2) a PDF of the current eBay ad showing the assembly and its wiring
diagram.? You will have to add a resistor between the DC output and your LED(s) to reduce the 12 volt output
to what is appropriate for your LEDs.? Look through the various posts to size the resistor.
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Re: LED and Resistor Sizing
Some decoders have dimming capabilities. That could, given people have the right software and programming capabilities, even be programmed to change with the time of day, for anyone who wants to go *really* over the top...
Wouter
I would add only that the brightness you want and need will depend on your room lighting. If it's bright, your LEDs will need to be brighter (use lower resistances and higher currents) for the same visibility than if your room is relatively dim. I find I need more light than when I was younger to see to rerail equipment and do other precision work. So, again, YMMV!????? :--)
Don W
--
Don Weigt
Connecticut
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Re: LED and Resistor Sizing
I would add only that the brightness you want and need will depend on your room lighting. If it's bright, your LEDs will need to be brighter (use lower resistances and higher currents) for the same visibility than if your room is relatively dim. I find I need more light than when I was younger to see to rerail equipment and do other precision work. So, again, YMMV!????? :--)
Don W
-- Don Weigt Connecticut
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Re: LED and Resistor Sizing
... just saying ...
w
? Although calculated resistor sizes are "correct" (you won't blow the LED) - most LEDs we use
are FAR too bright (to my eyes)?and so running them at reduced current/voltage is better
(in my book).? That means I use a resistor that is larger than the calculated value - because I
don't want full brightness.
? When deciding what resistor to use for an LED in an HO scale model running on DCC - I
start with a 3k, 1/4watt resistor and go UP from there to get the brightness that I want.? The
LED will often still be lighting up with a 20k resistor!? Dimming is not 'linear' so I experiment
using a resistor box until I get the desired brightness.? That sounds like a lot of "bother"?
and it is ... I usually just start with a 3k or 3.3k (can't tell the difference with the LEDs I
use which are 0406) and only do the resistor box stuff when that doesn't work out.
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?- Jim in the PNW
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Re: LED and Resistor Sizing
Tom's numbers look good to me, although I've not measured the voltage drop across white LEDs.?
If each LED gets 8 mA of current and the voltage across it is 3V, then 24 mW is used in each LED to produce the light. Two LEDs would then use 48 mW. (mA is milliAmps: 1/1000 of an Amp, mW is milliWatts: 1/1000 of a Watt, V is Volts.)
If the LEDs are in parallel, to get 8 mA in each requires 16 mA total. If the input voltage is 14 V, then the total circuit power will be 224 mW: nearly 1/4 Watt. And, since only 48 mW is actually used by the LEDs, the remaining 176 mW must be dissipated as heat by the resistor. The resistor would need to be about 680 Ohms, and rated for 1/4 W or more.
Putting the LEDs in series raises the circuit efficiency significantly. The total current then is only 8 mA, and total power only about 112 mW. The LEDs use the same 48 mW as before. That leaves about 64 mW to be dissipated in the series resistor: There will be about 6 V across the two LEDs. That leaves only about 8V across the resistor, which would need to be about 1k Ohm (1000 Ohms). A resistor rated at 1/8 W would be sufficient, and smaller than the 1/4 W or higher power resistor needed if the LEDs were in parallel.
Most small LEDs are rated for maximum currents of 20 mA. Most are bright enough for our uses at much lower currents. The "standard" 1k Ohm resistors used for many onboard LEDs produce more light than needed in many instances, leading to decoders needing brightness or dimmer adjustments. But, they are handy if using an IC that is 7 or 9 resistors of the same value, with a common connection. I use separate discrete resistors, and vary their values depending on the brightness I need.
As Tom said, you probably won't want your LEDs as bright as they will be if they are operating on 10 mA or more, perhaps on far less.
Also, resistor power ratings depend on heat having an exit path. Many power resistors rely on some of their heat being carried away through their leads, converting the circuit boards they are mounted on into heatsinks. Try to provide a way for air to flow past any resistors operating at half or more of their rated power level, or have them mounted where there is a circuit board or metal surface that can help carry away the heat.
Don W-- Don Weigt Connecticut
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Re: LED and Resistor Sizing
Puckdropper, using two LEDs in series is good. Use a 1/4 watt resistor as it has more surface area to keep its operating temperature down. Even though the LEDs are diodes, you should protect them from significant reverse voltage. use a bridge rectifier or a single diode in series (1/2 wave rectification from DCC track voltage) to further reduce resistor watts with almost no noticeable dimming of the LED.
If you are thinking about lighting passenger cars, you will need to add a Cary over capacitor to minimize blinking.
DonV
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Re: LED and Resistor Sizing
Use about 14 V for your starting voltage, and white LEDs drop about 3V each. So
14-6 = 8 V on the resistor. I = V/R = 8/1000 = .008 A = 8 mA. P = IV = .064 Watts.... Well below the rating of most resistors. So you can use a 1/8 W resistor. However, that means each LED will be functioning with 8 mA. This is plenty, as far as I'm concerned. In fact, I use LEDs with 1-2 mA going through them, all the time in my installations.? You can also do the LEDs in parallel.
...Tom
On Tuesday, September 5, 2023 at 08:00:47 PM EDT, PAUL HART via <psr436= [email protected]> wrote:
I have a program that I use and this is what it says to use. I hope this helps.?
On Tuesday, September 5, 2023 at 07:49:36 PM EDT, Puckdropper via <puckdropper= [email protected]> wrote:
I'm trying to avoid extra "stuff" because of space reasons, so I'm looking at putting two LEDs in series.? If I have two white LEDs* that operate on about 4V at 20 mA connected in series, using a 1 kOhm resistor at 12V, what rating does the resistor need to have?
Can I subtract the required voltage of the LEDS like this?
12V - 4V -4V = 4V
4V / 1000 ohm=.004A
.004A * 12V=.048W
Do I need to keep it in like this?
12V / 1000 ohm=.012A
.012A * 12V=.144W
*
Puckdropper
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Re: LED and Resistor Sizing
On Tuesday, September 5, 2023 at 08:00:47 PM EDT, PAUL HART via groups.io <psr436@...> wrote:
I have a program that I use and this is what it says to use. I hope this helps.?
On Tuesday, September 5, 2023 at 07:49:36 PM EDT, Puckdropper via groups.io <puckdropper@...> wrote:
I'm trying to avoid extra "stuff" because of space reasons, so I'm looking at putting two LEDs in series.? If I have two white LEDs* that operate on about 4V at 20 mA connected in series, using a 1 kOhm resistor at 12V, what rating does the resistor need to have?
Can I subtract the required voltage of the LEDS like this?
12V - 4V -4V = 4V
4V / 1000 ohm=.004A
.004A * 12V=.048W
Do I need to keep it in like this?
12V / 1000 ohm=.012A
.012A * 12V=.144W
*
Puckdropper
|
Re: LED and Resistor Sizing
I have a program that I use and this is what it says to use. I hope this helps.?
On Tuesday, September 5, 2023 at 07:49:36 PM EDT, Puckdropper via groups.io <puckdropper@...> wrote:
I'm trying to avoid extra "stuff" because of space reasons, so I'm looking at putting two LEDs in series.? If I have two white LEDs* that operate on about 4V at 20 mA connected in series, using a 1 kOhm resistor at 12V, what rating does the resistor need to have?
Can I subtract the required voltage of the LEDS like this?
12V - 4V -4V = 4V
4V / 1000 ohm=.004A
.004A * 12V=.048W
Do I need to keep it in like this?
12V / 1000 ohm=.012A
.012A * 12V=.144W
*
Puckdropper
|
Rick Jones
Jim Betz