Large Scale Central

Q: using 3mm 12V LEDs on 18V?

Electronics Power and Sound
#1

Well, the subject says part of it: I’ve got some 12V rated, 3mm size LEDs. Probably around 25mA draw. (They never came marked for mA) I usually use 14.8V battery power, (no track power). LED’s have no resistor presently. I expect to occasionally run as high as 18V battery to my REVO board. So I’m thinking if I adopt a 480 ohm resister in the + lead of every LED, I ought to be safe up to my max. voltage. I need to use the small 3mm LEDs. (Have the larger LEDs in, “24V,” for other uses.)

I suspect I’ll lay the lamp leads down on the same REVO terminals as where the main battery comes in.

Am I missing anything?

Dennis

#2

That should work, although you might want to try a smaller resister. If you want to drop 6 volts at .025 amps, a 240 ohm resistor will do the job. Try it with your 480 ohm resistor. If the LED is too dim, try a 330 ohm instead.

#3

I suspect the 12 V LEDs already have a resistor inline? I agree with David, but another option would be to use a CL2N3 or similar so the current is maintained over a range of battery voltages.

#4

Hi Dennis, please tell us what brand LEDS you are using. For model trains I have not seen a raw 12V LED. The LED has a rating called FWD voltage drop between 3.1-3.8V. I use Dallee Electronics and Evans LEDS. Dallee gives you the specs of each LED and recommended dropping resistor. Evans offers a selection of LEDS with a resistor or voltage regulator inline so you can easily hookup to track/battery power.

Dallee instructions state: input voltage of 5.5v = 66 ohm, 15V = 390 ohm, 24V =1K ohm. For their brand of LEDS.

As Eric and others have stated you must use a dropping resistor for any LED or use a LED lighting driver called CL2N3.

When connecting LEDS to the lighting terminals of the REVO, AirWire, RCS, etc, you must have that resistor in place. If not the LED will blow and could short out the lighting transistor. I hate that when it happens.

Don

#5

Thanks, guys. First, my LEDs have no brand name… Specs on line I recall were similar to what you mention. I looked at Evan Designs and liked what I saw; bit more money, but probably no concerns with them. However, their resister seems soldered rather close to the LED and I need my leads, “slim,” a longer distance than that. So I got others knowing I could solder a resister farther down the wire. Dallee I’ve never heard of but will look.

Also I’ll search around to see who has this CL2N3. Constant brightness is always a desire. But I am stuck with the 3mm size.

#6

Dennis,

I have used the Evan Designs product on several jobs such as headlights for rail trucks, they work very well. I just moved the resistor farther down the line, quick and easy solder job.

Rick

#7

My default resistor is a 1K ohm resistor whenever doing LED installs. The calculators say I can use a lower resistance at 15 volts, but I don’t see any significant difference in brightness between the two, so I figure I’ll just go with what I know works and gives me enough headroom for voltages typical of large scale. That, and it’s an easy-to-remember number.

Later,

K

#8

I use the CL2N3 on all my installs. Works well with the Revolution.

#9

The CL2N3 wouldn’t restrict the physical size of the LED. It just goes in series with the LED (and resistor in your case) and limits current to 20 mA. If your batter voltage were to drop below 12 V or so, you’d be out of luck, but you probably have other issues at that point.

#10

Ah. Good info. So where are you all buying your CL2N3’s? And I understand if I use a CL2N3, I can skip using a resistor. The photo I see of the CL2N3 shows a simple 3-legged piece and wiring seems simple. Can hide it in a boiler, etc.

#11

I get all my stuff from mouser.com

https://www.mouser.com/ProductDetail/689-CL2N3-G

#12

Mouser has them available.

#13

OK. Good. I’ve actually purchased from Mouser before, I just can’t remember what. Martin, your link, (thank you), takes me right to the CL2N3 I think you all were talking about. Bingo on that one. I just looked for LEDs on their website, but they have SO much electronics it gets confusing. Can any of you that buy LEDs from Mouser tell me what part number or i.d. you use to get 3mm white?

I can see that buying, “bare,” LEDs with NO resistors or insulation, (just the LED and it’s, "legs), - then adding the CL2N3 farther down the lead where space is easily found, would give the greatest option for placing an LED in a restricted/tight space. That would be a good starting point. I have no trouble soldering small items.

For easy areas or applications, Evans’ ready-to-go stuff would be the pain-free option.

#14

OK. Good. I’ve actually purchased from Mouser before, I just can’t remember what. Martin, your link, (thank you), takes me right to the CL2N3 I think you all were talking about. Bingo on that one. I just looked for LEDs on their website, but they have SO much electronics it gets confusing. Can any of you that buy LEDs from Mouser tell me what part number or i.d. you use to get 3mm white?

I can see that buying, “bare,” LEDs with NO resistors or insulation, (just the LED and it’s, "legs), - then adding the CL2N3 farther down the lead where space is easily found, would give the greatest option for placing an LED in a restricted/tight space. That would be a good starting point. I have no trouble soldering small items.

For easy areas or applications, Evans’ ready-to-go stuff would be the pain-free option.

#15

Can any of you that buy LEDs from Mouser tell me what part number or i.d. you use to get 3mm white?

Bright white? (with the blue hue)

Warm white?

Cool white?

what kind of lens?

how bright?

That’s why there are so many part numbers. There are so many different variants.

#16

No blue tint.

All 3mm.

Some warm white. (reminiscent of incandescent filament lamp - loco headlight)

Some bright white.

“Top Hat,” envelope shape.

Forward projecting lens, (or maybe 30-degree spread or so)

Yes, I need to do some of my own homework, (grin).

#17

I have been using these for my headlights, and am very happy with the color temperature and brightness: https://www.amazon.com/gp/product/B01GDZW0HQ/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

For interior lights and number boards, I use these strawhats: https://www.amazon.com/gp/product/B006S2GBO8/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

#18

Always calculate the right resistor, get your ma rating. If you don’t know it, then select 3.6 volts drop for a white led and 20 ma for current for T3 and T5 types… remember smaller LEDs may have a much lower current rating.

Use a LED resistor calculator, or use the CL2 current regulating IC (assuming your LED will handle 20 ma)

https://elmassian.com/index.php?option=com_content&view=article&id=636:led-lighting&catid=19:trainelectronics&Itemid=844

calculator: http://ledcalc.com/

It’s not rocket science, but I cannot tell you how many people have burned up LEDs because a “friend” told them to use 470 ohm resistors always, and then they use an 18.6 volt pack… (35 milliamps).

At least check the calculations.

Greg

#19

I have 12 volt LEDS. They have a resistor built in and work just fine on 10 volts (this is what my decoder has for an internal power source).

Radio Shack did sell some of these but alas they are now gone.

I agree with Greg that one must size the resistor via current properly for an led to have a long life. I have yet to lose an led in my trains.

Note that even those dollar store lights have a current limiting resistor in them. If not needed they would not spend the $$ to buy and install them.

Wrong resistors on leds are like not stopping for a stop sign, soon or later one may pay the price!!