Wiring Accessory Lights

[BestSnowman]

Last night on a whim I picked up some accessory lights to light up my passenger platform with these: http://store.modelpower.com/index.asp?PageAction=VIEWPROD&ProdID=2744

It came as a pack of three and all it says for powering it is 30 MA, 14V and wires to AC power pack. Now the AC output of the powerpack (bachmann dc pack) I am using is 16V. I'm a little clueless when it gets to this type of wiring, does anyone have any advice on wiring up these lights?

Thanks,

[Tylerf]

Wow 14v is pretty high for that, it'll get quite hot. Anyways, I preffer to use a seperate wall transformer rated very close to the bulbs and hook them up directly to that. I don't know about you but I find I have a ton of old transformers lying around that work great, I'm sure they can be found for cheap in used bins at your LHS or electronics store. Another thing you can find in a used bin is just   another power pack with ac connections for a similar price

[BestSnowman]

It is actually an extra power pack, I use an EZ-Command DCC pack to run my trains.

[lmackattack]

If you have an old tyco transformer they are great for controling bulb brightness

or simply hook up resistors to the bulb to reduce the voltage.

both methoids will extend the life of the bulbs

[Jim Banner]

To run your lights at 14 volts from your 16 volt supply, put a 68 ohm 1/2 watt resistor in series with each light.

Personally, I would run them at 12 volts.  Using your 16 volt supply, this would require a 120 ohm 1/2 watt resistor in series with each light.  This will cut down the brightness a little bit and extend the life a whole lot.

Incidentally, you can use either ac or dc to light your bulbs.  They don't care, one way or the other.

Side note to Tylerf:
How hot the lights will get depends on their power (voltage times current,) not just on their voltage.  A 1 watt, 1.5 volt bulb will produce the same amount of heat as a 1 watt, 120 volt bulb.  And if the two bulbs have the same physical configuration, they will both rise to the same temperature.  BestSnowman's 14 volt, .030 amp bulbs will produce only 1/2 watt at 16 volts.  The grain of wheat bulbs I use produce 50% more heat (12 volts .065 amps.)

I agree that there are lots of wall wart transformers and ac adapters out there, some of them free for the asking.  Many of these are internally protected, that is, they will blow an internal fuse or limit the current in some other way if the output is shorted.  They are usually marked as Type II transformers.  This link explains what that means in detail:  http://tinyurl.com/dhoxto

Unless you know your transformer or ac adapter is internally protected, you should add an inline fuse to be sure.  Model railroad power packs usually use self resetting circuit breakers for short circuit protection, which is something in their favour. 

_{Edit - added link concerning Type II transformers}  

Jim 

[BestSnowman]

To run your lights at 14 volts from your 16 volt supply, put a 68 ohm 1/2 watt resistor in series with each light.

Personally, I would run them at 12 volts.  Using your 16 volt supply, this would require a 120 ohm 1/2 watt resistor in series with each light.  This will cut down the brightness a little bit and extend the life a whole lot.

I thought about using a rheostat (not sure on spelling) but I figured with small inquisitive fingers I'd rather not go with that. I just want to make sure I'm understanding you correctly about wiring in series (I'm hopeless with this stuff).  I put a resister between the power and the first light, then the return wire goes to another resistor and the second light and so on and the final return wire going back to the power supply like this:

Power Supply (+)--Resister-Light--Resister-Light--Resistor-Light--Power Supply (-)

[Jim Banner]

That arrangement would put all the lights and all the resistors in series.  That would cut the voltage much too much.  What I meant was this:

Power supply (+)                                              Power supply (-)
                        | --- resistor #1 --- light #1 --- |
                        | --- resistor #2 --- light #2 --- |
                        | --- resistor #3 --- light #3 --- |

What I am trying to show is that one side of each resistor is connected to the power supply (+) terminal.  One side of each light is connected to the power supply (-)  terminal.  Then the free end of each resistors connects to the free end of its corresponding light.  An electrician might say that each light has a resistor in series with it and each resistor/light pair is in parallel with all the other resistor/light pairs.

In practice, those vertical dashes could be a pair of bus wires connected to your power source.  The resistor/light pairs could be tapped off the bus wires wherever is convenient.  One side of each resistor would still be connected to the power supply (+) terminal, except this time, the connection would be through the (+) bus wire.  Same for the lights.  They would all have one side connected to the power supply (-) terminal through the (-) bus wire.  This saves a lot of wire if you have a lot of lights but the bus wires need to be larger in size to carry the current.  For the one amp that a typical power pack puts out, 18 gauge lamp cord is big enough.

Jim 

[BestSnowman]

Ok, that makes a lot more sense than what I was thinking. I'm going to spend a little more time thinking about how I'm going to wire the bus and try to plan out what I'll be doing for lighting but at least now I am armed to start wiring up lights.

I greatly appreciate the help!

[BestSnowman]

Finally got the lights wired up and installed on my passenger platform so I thought I'd take a post a couple pictures:

http://www.flickr.com/photos/93301102@N00/3494858287/in/photostream/
http://www.flickr.com/photos/93301102@N00/3495673820/in/photostream/
http://www.flickr.com/photos/93301102@N00/3494854223/in/photostream/

Thanks again for the help!

[BestSnowman]

Decided to take a night snot before I hit the sack for tonight http://www.flickr.com/photos/93301102@N00/3495107649/in/photostream/