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Wiring lights for a roundhouse?

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  • Member since
    April 2005
  • From: New Jersey, USA
  • 126 posts
Wiring lights for a roundhouse?
Posted by myowngod on Saturday, February 9, 2008 10:19 PM

I am wiring lights in the roundhouse for my Dad's layout.
See schematic below.


The bulbs being used are 1.5v 15mA, grain of rice style(YELLOW circles). I was thinking of having 5 rows, 1 for each timber frame between tracks, with each row having 4 bulbs. The wire leads (RED) would drop down below the structure located at the front door and rear wall locations. They would hook up to a set of "buss" wires (ORANGE) under the structure, and then those busses would hook up to a power supply under layout (GREEN). The power supply will probably be an old transformer, maybe 12v.

There is a total of 20 bulbs in the circuit. My question is, should I put a resistor on each leg of 5 bulb rows or one larger one at the point where the wires run to the transformer? Also any ideas how many Ohms they should be? Each row would total 6v, the whole building 30v. I would rather the bulbs be dimmer then brighter, since there's so many in the building. I'll put a few bulbs on the outside of the structure near the back service doors as well

Thanks

Keep the axels greased and the tender full, we're rollin' now.

Ron

My layout progress posting Named "PRR Schuylkill Division"

Link to my Youtube videos. http://www.youtube.com/user/myowngod2

  • Member since
    December 2004
  • From: Bedford, MA, USA
  • 19,814 posts
Posted by MisterBeasley on Saturday, February 9, 2008 10:29 PM

I lit up my Atlas 3-stall roundhouse, which I suspect is a bit shallower than yours.  Still, I found that 6 light bulbs were sufficient.  I put them over the tracks, 2 bulbs per stall.  I've also put a couple of exterior lights over the people-doors on the outside.

I used 12-volt bulbs, and I ran them at 10 volts.  I've used low-voltage bulbs with resistors before, and ended up burning most of them out pretty quickly.  With 12-volt bulbs, I can run simple parallel feeders to all of them, and not worry about resistors or which one burned out if I wire them them in series.  For simplicity of wiring alone, 12-volt bulbs are worth it.

It takes an iron man to play with a toy iron horse. 

  • Member since
    April 2005
  • From: New Jersey, USA
  • 126 posts
Posted by myowngod on Sunday, February 10, 2008 6:39 AM

I do want to light it to see inside but also make it look semi prototypical.  It seems like in all the photos the lights are in the areas between the tracks.  This would offer better light onto the engines where the work would be done, and also keep engines from hitting the lights.

I was considering 12v or 14v bulbs.  Maybe I should... Hmm?

I am going to add some interior detail and want to show it off a bit with the lights on.  The roof will be removable as well.  Below is a maintenance platform I want to scratch build.  I like the look of it... the roundhouse has seen better days thoughBig Smile [:D]

Keep the axels greased and the tender full, we're rollin' now.

Ron

My layout progress posting Named "PRR Schuylkill Division"

Link to my Youtube videos. http://www.youtube.com/user/myowngod2

  • Member since
    November 2003
  • From: Michigan
  • 227 posts
Posted by SteelMonsters on Sunday, February 10, 2008 9:45 AM
 myowngod wrote:


The bulbs being used are 1.5v 15mA, grain of rice style(YELLOW circles). I was thinking of having 5 rows, 1 for each timber frame between tracks, with each row having 4 bulbs....The power supply will probably be an old transformer, maybe 12v.

There is a total of 20 bulbs in the circuit. My question is, should I put a resistor on each leg of 5 bulb rows or one larger one at the point where the wires run to the transformer? Also any ideas how many Ohms they should be? Each row would total 6v, the whole building 30v. I would rather the bulbs be dimmer then brighter, since there's so many in the building. I'll put a few bulbs on the outside of the structure near the back service doors as well

Thanks

 

If the bulbs have a current of 15 mA at 1.5 volts steady state, then the resistance is 100 ohms.

With a supply of 12 volts with 5 bulbs in series, the voltage drop is 7.5 volts and the total resistance is 500 ohms if you allow 15 mA of current to flow through them. The voltage that the resistor needs to drop is 4.5 volts. To to this for 15 mA, it will need to be 300 ohms. 

 If each rung of 5 bulbs has a resistor, each resistor will drop .0675 watts. A quarter watt resistor will do just fine. If you use a single resistor for all 4 rungs, then you will need at least a half watt resistor. What you could do on top of this is put in a 500 or so ohm pot and adjust it to dim the lights to whatever you want.

The above calculations where done easily with ohms and watts law.

Ohms law ( V = I * R )

Watts law ( P = V * I )

V is voltage in volts

I is current in amps (divide mA by 1,000 to get amps, so 15 mA = .015 amps)

R is resistance in ohms 

P is power in watts. 

 

The full wheel to get any 4 value from any combination of two others:

http://www.sengpielaudio.com/FormulaWheelElectronics.gif
-Marc
  • Member since
    March 2003
  • From: Scottsdale, AZ
  • 723 posts
Posted by BigRusty on Monday, February 11, 2008 6:11 PM

If you already have the 1.5 v bulbs you could put five in row, and 2 rows to a 12 volt supply. They would probably never burn out and you don't have to fool with resistors. Trouble is you have only five rows, so you could add 5 more lights on the back wall and have three 12 volt circuits.

When I have too much light, I just paint the bulbs. Yellow for an old round house, blue for modern diesel shops to simulate mercury vapor lghting,

You can also paint the upper half black to shine all of the light downward. It looks better that way from the outside.

Remember KISS!

Modeling the New Haven Railroad in the transition era
  • Member since
    April 2005
  • From: New Jersey, USA
  • 126 posts
Posted by myowngod on Monday, February 11, 2008 7:10 PM

Last night I hooked up 4 1.5v bulbs together with a 1000Ohm resistor.  The voltage from the powerpack was 18v AC.  The bulbs dimmed nicely.  I think I'm going to stick with this setup.  So know I have to make up 5 series circuits all parallleled together.  If 1 bulb goes out I only lose a string of 4, and not all 20.

I think this will do.

Thanks everyone

 

Keep the axels greased and the tender full, we're rollin' now.

Ron

My layout progress posting Named "PRR Schuylkill Division"

Link to my Youtube videos. http://www.youtube.com/user/myowngod2

  • Member since
    June 2005
  • From: Hot'lanta, Gawga
  • 1,279 posts
Posted by Rotorranch on Monday, February 11, 2008 7:45 PM

I think this might be better. You will still only need to drop 2 wires through the benchwork. In parallel if one bulb burns out, it won't take the whole string down. I hope the drawing makes sense.

Rotor

 Jake: How often does the train go by? Elwood: So often you won't even notice ...

  • Member since
    April 2005
  • From: New Jersey, USA
  • 126 posts
Posted by myowngod on Monday, February 11, 2008 8:17 PM

That picture makes alot of sense!Thumbs Up [tup]  I think I might try it that way. 

The question I have is, does each bulb recieve 18v from an18v transformer, or do they all add up together to make 30v(20 x 1.5v)?  If it's 18v each I need only 1 resistor at the beginning, I think?  But if that's the case, when 1 bulb  goes out does the voltage rise in all the others, possibly overloadding them?  Then they all blow in a chain reaction? Sigh [sigh] Sign - Oops [#oops] Banged Head [banghead] Dead [xx(]

Keep the axels greased and the tender full, we're rollin' now.

Ron

My layout progress posting Named "PRR Schuylkill Division"

Link to my Youtube videos. http://www.youtube.com/user/myowngod2

  • Member since
    June 2005
  • From: Hot'lanta, Gawga
  • 1,279 posts
Posted by Rotorranch on Monday, February 11, 2008 9:03 PM

The way my schematic is drawn, each bulb would get the 18 volts, or whatever voltage you are using. I wouldn't use 18v. The roundhouse would light up like you had the sun in  orbit inside the building. Cool [8D] About 6-9 volts should be sufficient.

If you used a voltage dropping resistor, you would only need one. But you would probably need a higher WATTAGE than the 1/4 to 1/2 watt used in LED circuits.

With the low current draw of the lamps, if 1 bulb died, there would not be a great increase in voltage. So the short answer is NO, it would not blow the rest of the bulbs.

You could use a toy train power pack to vary the voltage for different brightness. Radio Shack also has inexpensive transformers in different voltages, that work great for cheap lighting and accessory power supplies. You should mount them in a project box... but mine are screwed to the bottom of the layout. The way mine are mounted, it's probably not UL approved. Whistling [:-^]

Rotor

 Jake: How often does the train go by? Elwood: So often you won't even notice ...

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