1.5 volt lights

[EWT123]

I am about to introduce 1.5v mini/micro lights to my layout. To date I have used inexpensive 12-16v lights mostly for the interiors of buildings. Also a couple of off the shelf lights/leds that came with an integrated resistor. These all work fine off of the 14v dc output from an old power pack for controlling the brightness. I have found numerous sources for these 1.5v lamps but I am real confused as to what resistor I need to place inline with each new light.  Or should I go the route of having a completely separate 1.5v circuit to power these lamps and thus eliminate the need for the resistors but would require an additional transformer for brightness...

[mlehman]

There are several issue with bulbs that complicate things. Once you've managed to get the circuit right, adding or losing any bulbs often changes the remaining bulbs' brightness enough to be noticeable. Calculating resistance values for bulbs is tricky and you'll often find you need a big 1/4 watt-rated resistor versus the smaller form factor of the 1/8 watt ones.

Yes, definitely provide a dedicated circuit for bulbs. You can take it off the current transformer, not really a need for a new one.

That said, I encourage you to look into doing structure lighting with LEDs. They're much easier to manage in terms of adding or substracting from the circuit. You can get them cheap min quantity by buying Xmas light strings and harvesting the LEDs from them. Yes, best to ngive each LED or small group of LEDs it's own resistance, but the small resistors easily handle the limited draw of LEDs.

Yes, there's a short learning curve if you haven't used them before, but once you start working with them it's so much easier than bulbs.

There's lots of info on how I added LED structure lighting in my Night Scene thread:

http://cs.trains.com/mrr/f/88/t/213765.aspx?page=1

[Mark R.]

Calculating the resistor value required for 1.5 volt bulbs is the same as calculating the resistor value for LEDs. Use this handy resistor calculator  ....

http://ledcalculator.net/

The voltage drop value will be 1.5 and you will need to know the current value of your bulbs as well. Most 1.5 volt bulbs are between 20ma and 40ma, but it should state that on the package. If it doesn't, you can connect one bulb to a AA battery and insert your meter in series with the bulb to read the current draw.

Mark.

[Train Modeler]

Consider using cheap LEDs from like Christmas lights with built in resistors?    I haven't done it, but many on this site say they work great.

Richard

[mlehman]

The results tend to speak for themselves. Another LED advantage is that LEDs are forever (almost). I don't worry if I  find it easier to install one in a place that will be sealed up or hard to reach. With a bulb, you know you'll end up replacing it.

Here's a pic of one of my bigger mills, the Sunnyside Mill in Eureka, with parts of the roof off showing the installed LEDs.

This is how the overall complex looks at night. The part of the mill above is on the right side of the pic.

The Durango roundhouse at night.

Looking inside the roundhouse.

I used magnet wire here, scrapping it clean to attach the LEDs, looks a little like knob and tube-ish wiring.

[richg1998]

To be on the safe side, I would use the 1.5 volt transformer sold my Miniatronics.

 

If you understand electronics, buld a voltage regulator. Two resistors, two caps and a LM317 voltage regulator. Select a resistor that will allow 1.4 volts from the regulator. A little safety margin for longer light bulb life. Will work of 12 ro 24 volt DC power supply.

Rich

 

[G Paine]

mlehman

I don't worry if I find it easier to install one in a place that will be sealed up or hard to reach. With a bulb, you know you'll end up replacing it.

A few years ago at Boothbay Railway Village we had donated to us an beautiful HO scale model of the Portland ME Union Station. The builder had passed away, and his family donated it to us. It was all styrene with a fully detailed interior and lighted with at least 3 kinds of incandescent bulbs. The problem is that the model is completely sealed up, and we will have to break into it when those bulbs start burning out. If LEDs had been used, we would have been much better off

http://www.railwayvillage.org/Portland.htm

[gregc]

richg1998

To be on the safe side, I would use the 1.5 volt transformer sold my Miniatronics.

If you understand electronics, buld a voltage regulator. Two resistors, two caps and a LM317 voltage regulator. Select a resistor that will allow 1.4 volts from the regulator. A little safety margin for longer light bulb life. Will work of 12 ro 24 volt DC power supply.

Actually using the LM317 as a current regulator may be better and easier.   

the limiting factor for LEDs is current, which expontially rises with voltage because they are a diode.    By using the LM317 as a current regulator you can string several LEDs in series (~7) with the LM317 using a 12V supply.   At some point, the total voltage drop across all the LEDs plus the drop across the LM317 will exceed the supply voltage.

[EWT123]

Thanks for the input. You, along with the others, have convinced me to go the LED route with a dedicated circuit for the structures, street lamps etc.. Fortunately the few structures that I have equipped conventional bulbs with have not been put in place yet so it will be easy to swap the bulbs for LEDS. I never would have thought of the Xmas light string option... Your 'Night Scene' is pretty impressive! I think I have seen it before.

[mlehman]

EWT,

Thanks, I appreciate your comments

Note that there are some ideas in there on power supplies. I run most of mine on power supplies built from parts. The link is in the Night Scene thread, but here it is for easy reference: http://www.spookshow.net/lowvcircuit.html

With it, your resistor values tend to be very low, as low as the ~5 ohm range and topping out around100 ohms, because of the low voltage.

One nice thing about the Xmas light string is that the brightness is pretty close for all of them. This is good when you need lots of lamps that appear identical, Also makes it easy to adjust them to be differfent be simply adjusting the resistance slightly.

[hon30critter]

EWT123:

eBay is also a good source for low cost LEDs. Not too long ago I got 500 - 3mm warm white LEDs for about $20.00 from Hi-Tech-LED-World Co Ltd, eBay ID: hitechledworld. They did not come with built in resistors but resistors are cheap. I get mine from Digi-Key http://www.digikey.com/us/en/digihome.html Just as an example, you can get 100 - 1/4watt 1K ohm resistors for about $2.00 and their shipping costs are very reasonable.

I do have to say that I still like the 1.5v micro bulbs for certain things like the exterior lamps on this engine shed where the bulbs can be clearly seen. I run them on about 1.2v so they will last a while albeit not as long as LEDs:

 

Dave