Layout lightposts ,and wiring??

Model Railroader General Discussion (Model Railroader)
1

I bought these lightposts off ebay ,and from what i can tell it wasnt that bad of a deal but,Do I need to add a diode or something to that effect? I know nothing about wiring anything so that is the problem. Earlier I was trying to add a wire to be able to extend the posts through the layout and for some reason when i would connect the wire via a connector or splice the light wouldnt work? Then after a bit of having the light on with just the wire twisted it started to smoke a bit?? well here is a pic of the post’s, there are only the two wires comming from the bulb from what I can tell.Any helpful info would be appreciated, dont really want to burn my House and layout down or kill my family cause I didnt ask.

Thanks

C.C.

2

You need to find out what the voltage rating of each lamp is. A typical accessory terminal on a typical power pack is going to put out anywhere from 12 to 16 volts AC. If you lights are rated for 1.5v each or thereabouts, you’ll need to add a resistor to each one before hooking them up to the power. Otherwise, POOF![oops]

Are they LED’s or incandescent bulbs?

Lee

3

Thanks Lee,

The voltage that was said to be( 6.5v,0.07A). And I believe they are bulbs, I havent took one apart yet tho.

C.C.

4

If they are 6.5V incandescent bulbs then you can run them at 50% or < power with a 12V power pack - without needing to add a resistor. I would wire them up “in parallel” vs. wiring them “in series”.

C.C., what size (gauge) wires were you adding to the light wires before they started smoking?

Tom

5

That sounds like a bulb. LED’s usually don’t go more than 3.5v in my experience (which is admittedly limited!)

Check the voltage of your power supply, and see what happens if you wire 2 or 3 lamps in a series.

Lee

6

I use a variable rheostst/resistor to get the brightness I want then measure the resistance to size the proper resistor. Start out with a higher resistance & drop it lower to get the lights brighter. Only as bright as needed will make bulbs/LEDs last longer.

7

If the bulb is rated for 6.5Vdc, DONT hook it up to the 12+Vdc terminals on any power pack! SUbjecting that bulb to 12+Vdc is placing the bulb in a 200%+ overload condition, and as mentioned before, POOF!

When dealing with non-solidstate components, aka bulbs, the voltage rating doesn’t really mean much, honestly. The 6.5Vdc in this case tells you that if you apply exactly 6.5 volts to this bulb, it will draw 0.07A or 70mA. This tells us:

I = E / R (ohms Law)

R = E / I (Solved for Resistance)

R = 6.5V / 0.07A Thus R = 92.85 (ish) ohms resistance.

If the bulb has 92 Ohms resistence, then applying 12V to it would yeild

I = 12V / 92Ohms = 0.13A, or 130mA… roughly double the rated current!

In order to limit the current down to <70mA, we need to at least double the resistance. So by adding a 100 Ohm resistor in series with the bulb and then hooking this up to 12Vdc, we get:

I = 12V / (92 + 100) Ohms = 0.0625 or 62.5mA, just under rated current.

Now the only reason why i posted this progression of equations is to you can calculate the additional resistance required for other voltage supplies also (9Vdc, 14.4Vdc, etc)

Hope this helps!!!

8

I use a trainset power pack to power all my lights. I make sure ALL of the lights are rated the same. I pull a common buss throughout the layout and solder one lead of the lights to this. Then, I wire several in groups that are controlled by switches (not all lights come on at the same time in the real world). I even wire structures that are next to each other in different groups so that I can turn on and off lights at different times).

9

thanks everyone for the input.When I was messing with it I was using a Model power hobby transformer(you know the old ones with the red lever on the side), And as for the wire it might have been 18 guage wire or so, not really thick wire but larger than the wires on the lamps?freaked me out when the lamp started to smokes thans why i asked.I have a few how to books but thy are vague when it comes to the little things.

Dave thanks for posting the stuff you did , I know it was extra trouble ,thanks alot

Thanks everyone.think later this week i am going to go buy some smaller wire closer to the guage on the lamps and try again?

chris

10

Cant tell by your post if you are thinking this:

“Wire gauge that was too big cause the lamp to smoke.”

If thats your mindset then please let me burst that bubble quickly. Think of gauge/thickness of a wire as lanes on the interstate, the more lanes you have, the more total volume of traffic you can safely push through. So, if the bulb has 22 guage wire on it and you use 18 gauge to get the power to the bulb’s wires… no worries!

What was making your bulb smoke was more than likely too high of a voltage pushing to much current through it. (See the 200% overload calc i posted for ya above)