street lights

[keitaro]

hey all,

so I have been thinking of buying some street lamps.

example http://cgi.ebay.com/10-x-N-Model-Lampposts-6V-street-lights-Resistors-111N-/400113971307?pt=Model_RR_Trains&hash=item5d28a6b06b

so my controller has a spare 16v ac and 1 12v dc acessories left.  both uncontrolled.

So my question is I know I need resistors so what accesory plug am I best to plug it into.

Also how is this best done ?

I was thinking the lights wire to ?? and then that wires to the a switch, which wires to the ac or dc plug in the controller.

anyone able to tell me what the ?? is. lol

I don't know what it's called but I think some form of box you can wire the led to and wire the resistor onto as well.

[KenS]

Note first that what you linked to uses bulbs, not LEDs (it says that on the page, and the 70mA current is a bit of a tip-off; there are LEDs that draw that much, but 30mA is much more common).

There's two issues there.  First, they're going to burn out and need to be replaced much sooner (although that's likely still years of real-world use), and second they're going to burn more power, so you'll get fewer per power supply.

To wire it up, I'd use the 12V supply since you'll waste less power in the resistors that way. The seller says he can provide 81 Ohm resistors (an odd size), although the more common 100 ohm (in 1/2 watt size) would likely work, at a slight cost in brightness and a slightly longer life for the bulb.

The way to wire it up is to run two wires from the 12V terminals. Then, for each light, connect one end to the + wire, and the other to the resistor, and the other end of the resistor to the negative wire.  You can add lamps like that (each connected to a resistor and the wires independent of the others) until you run out of power.  However, with 70mA per lamp, you're only going to get about 14 per Amp, and your supply may not even be one amp.

It's possible you could eliminate the resistor and run two lamps in sequence for each set (since they're 6V lamps and you have a 12V supply), which should double the number you can use (to 28 per Amp), but I've never tried that with bulbs.

With LEDs, you can typically fit 3 per string (with a small resistor) on 12V and run somewhere around 30-50 total per Amp of power (more in some cases, depending on the size and current of the LEDs).

If you want a switch, put it in line in one of the two bus wires (I'd put it on the +, but it should work on either), between the power supply and the first string of lamps.

If you don't want to solder, a terminal strip can be used to connect wires to each other and to the resistors.

[keiman]

On my tram layout I wired the 6v Lamps together and then connected them across the 12v bus bar I had wired under the board.
If they are bulbs you don't have a polarity problem
LEDs must have 12v DC with the correct resistor.

[stevenh]

If you do have LED lights, just use a calculator like:

http://ledcalculator.net/ or http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

and you'll be set :)

[keitaro]

Hi Keiman,

Thanks for info exactly what i wanted. btw i wasn't going to get those lights was just an example link.

To be hohnest i have not found what i am looking for.

I am after more telegrath pole ones like in japan.

However i can only find on hs and they look to be $35 each unless the description isn't stating the actual amount included

i will probably end up getting one of the cheaper ebay onese though

[keitaro]

ok so i got my street light leds with resistors and some 12v leds for buildings.

I suck at electrical so what i was wondering is what i need?

Will be running of a uncontrolled 1 amp 12v accessory output

I was thinking to wire to a switch then to some sort of box that will then provide multiple connections from the box to the led's if that exists?

was going to pop into my local jay car.

anyone able to tell me what i'd be best getting from here

also i figure anywire would be ok?

http://www.jaycar.com.au/index.asp


thanks for anyhelp / suggestions

[KenS]

If your LEDs are already wired with individual resistors or rated for 12V, then your planned arrangement (power-switch-splitter-parallelLEDs-splitter-power) will work, but I'd make one change: add an inline fuse holder and a fuse rated for 1 amp to protect the power supply from an accidental short, putting it inline between the + side of the power supply and the switch.

Fuse holder:
http://www.jaycar.com.au/productView.asp?ID=SZ2015&keywords=fuse+holder&form=KEYWORD

For the "splitter" Jaycar doesn't appear to carry what I'd use:

Barrier Strip:
http://www.radioshack.com/product/index.jsp?productId=2103229

Jumper:
http://www.radioshack.com/product/index.jsp?productId=2103227&clickid=prod_cs

What you do is get two of each, stick the jumper under the screws on one side of the strip, connect the wire from the switch to one screw, and the + end of the LEDs to the other screws.  Then you do the same thing with the second strip, the other end of the LED wires, and the - wire from the power supply (the switch goes between the + side of the power supply and the strip connected to the + ends).

You can fit a couple of wires per screw, so an 8-position strip could do about 31 LEDs.  If you need less, you can cut the jumper in half with some metal snips, and use one 8-position strip as if it were two 4-position ones, supporting up to 15 LEDs.

You can do something similar with these:

Screw Terminals:
http://www.jaycar.com.au/productView.asp?ID=HM3194&keywords=terminal&form=KEYWORD

using short wires on one side to link all the screw terminals together, but it's a bit more work.

And for wire, just about anything will do.  The current per LED is so low that for individual LEDs you can use wire smaller than anything that would be easy to work with (down to about metric 1 gauge, or 0.1mm dia, 40 AWG in open air, or metric 1.25, 0.125mm dia, 36 AWG in a tightly confined space). For the 1 Amp wire it's safest to use wire rated for 1 amp even if you don't have that many LEDs, meaning 29 AWG in open air or 21 AWG in a confined space; I don't have metric equivalents for those).

There's another approach than the splitter though.  Replace the + and - splitters each with a bare wire under the layout (or lengths of copper tape under scenery as noted in one of the other threads here somewhere) then connect each LED wire between the + wire and the - wire. The benefit of this is that the wires to the individual LEDs can be much shorter.

[keitaro]

thanks for the reply Kens i'll have a look at this and see what i can get from the local shop.

one thing though is that the street lights are 3v and i have the resistors so i would wire them in a seperate loop than the other LED's that are 12v.

Wth the resistor also on the + wire then - to the next resistor and + wire? i'm dumbat electronics.

[KenS]

Wth the resistor also on the + wire then - to the next resistor and + wire?

Nope, not in a line (serial) like this:

--resistor--3V LED--resistor--3V LED--

But parallel like this:

  --resistor--3V LED--
+--resistor--3V LED--+
  --resistor--3V LED--

Between the + and - splitters you can wire  either --12V LED--  or --resistor--3V LED--, and have as many of them in parallel as you have milliamps (if each LED in 20MA that's 50 strings with one LED each per Amp of power supply).

So:
--12V LED--
--12V LED--
--12V LED--
--resistor--3V LED--
--resistor--3V LED--
--12V LED--
--resistor--3V LED--
etc

Another important thing is that each LED that needs a resistor must have it's own, you can't do:

                 /--LED--
-- resistor--
                 \-- LED --

although you can do:

--resistor--LED-LED-LED--

if you are connecting 3V LEDs to a 12V supply.  You'd need a smaller resistor than in the 1:1 configuration.  The nice thing about this is that since the same 20MA flows through all three LEDs, you get three times as many LEDs per power supply (which seems counter-intuitive, untill you realize the smaller resistor is throwing away less power as heat).

[keitaro]

hey i just used this link i googled

http://led.linear1.org/led.wiz

for a basic diagram.

I guess i'll buy the bits and play about a bit and see how it goes.

[keitaro]

question what about solderless bread boards? are these anygood?

[rankodd]

They're good for prototyping - experimenting until you know how you want the circuit to go together. Almost invaluable, in fact. But no good for a permanent installation. You still have to get the soldering iron out for that :)

[KenS]

While you could use a solderless breadboard for a permanent circuit, it's an expensive approach and it could corrode and lose conductivity (or vibrate loose) over time, making something using a large number of them less reliable.  I'd also be a bit nervous about using one as the splitter; it should be able to carry a large fraction of an amp, but if your supply is large enough there could be issues since its conductors are enclosed, and that limits their heat dissipation and thus their maximum capacity.

You probably do need to solder, although one thing I've been thinking about for building lighting is conductive glue, which Amazon sells as Wire Glue, and there are probably other types, which should be suitable for the low currents used in individual LEDs.  Used in conjunction with adhesive copper tape, which is normally used for electrical shielding and circuit-board repair so even the adhesive is conductive, you should be able to glue components together, use the tape in confined spaces, and glue the + and - wires to the tape (or directly to components).

We've had a couple other threads on the tape: Inobu first mentioned it in January, and it also came up on a later thread with more info on suppliers.  I don't recally anyone discussing Wire Glue before, but there were a couple of threads on similar conductive paints and glues, including this post by Jeff. Lots of people sell Wire Glue, often at a large markup, so shop around if you're thinking of using it.

My own experiments with Wire Glue and copper tape haven't started yet, although I've picked up some of both to play with. I'm first going to try using them for car lighting circuitry, but eventually move on to building lighting. The tape has extremely low resistance (per the specs; I haven't tested it yet) so it should be good for normal lighting currents of a fraction of an amp.  I'm less sure of the glue, but it should work fine for tens of milliamps; I don't know how well it will work for hundreds, or how well it will stand up to use in a moving vehicle where it would be subject to vibration.  Inobu has mentioned using silver epoxy in a similar manner, but that's expensive stuff.  It may be more suitable for vehicle use, but I'd like to avoid it for car lighting since I have so many cars.