Lighting Moonbase HELP

[stargazer]

Hi Guys.. I need some help as I have never had so many lights to light together, before on a model.

I am finishing my build of my own kit, The Tyhco Moonbase.

http://www.planet3earth.co.uk/144%20sca ... 110017.jpg

It has some 85 lights on it, for which I am using small white LED's (each rated at 3.2 to 3.8 volts and 20 mA).

They will get wired together on the underside of the board the moonbase is attached to.

So, given that I might use batteries...or perhaps a plug in transformer.

What is the most 'useful' power efficient way to connect the LED's together. ????

I could I guess, wire them in all in series, or all in parallel.. but being the case, I understand that the power requirement would be problematic !

So perhaps a combination of sub groups of lights in parallel then all the groups wired in series.

what would be a good combination to wire this model...with the best voltage usage....

Hope the above makes sense....

Ian

Ps should have mentioned... I tried lighting one of the LED's using two AA batteries...It lit ok without a resistor.
I am not sure if these LED's I have 'need' resistors or not...If they do I guess that the rating of resistors I would need to buy, are dependent upon the wiring scheme ...

[EVApodman]

Great build for your kit Stargazer! I've been waiting to see it done since you first announced it.

Personally what I would do if I have to light several lights like the landing pad, would be to use fiber optics. But with a model like this that may be difficult unless it sits on top of a base. Or they may not provide the illumination you need.

If you need to use an LED for a light then you will have to bite the bullet and wire each one with it's own resistor to a power source. I know its slow and tedious but you knew this job was dangerous when you took it. You can use bus bars to connect each wire's power and return as you solder them.

As to the power source, unless you are familiar with electronics or know someone who is I recommend sticking with batteries since the voltages are low and safe. 115 VAC is dangerous unless you know how to work with it. A power line running from the model to a couple of "D" size batteries will provide sufficient power for your unit.

[EVApodman]

I have been doing some more thinking about your situation. You say the kit has 85 lights in it. Based on what is seen in the movie I can only count the landing pad lights and interiors of the spherical habitats as needing illumination.

Still you say you need 85 lights and that is a considerable amount in terms of current.

The average LED can handle a maximum of about 25 milliamps or .025 amps of forward current before it burns up. If we assume a resistance that gives 20 ma per LED we are looking at over 1.7 AMPS of current total for the model if each one is wired with its' own resistor. This is a significant amount of current whether battery or AC powered. The typical model has at most a dozen or so LEDs used for lighting.

One way to reduce this is to wire the LEDs in series. Since they all share the same current they will all light up equally. The bad news if one goes out they all go out like the old style christmas lights that all went out when one bulb burned up and they had to be checked individually. But LEDs are extremely reliable with long life times and under the right conditions could outlast you.

Theoretically you could wire all the LEDs in series and the current draw would be minimal.

Perhaps you could mix how the LEDs are wired in terms of how accessible they are to replacement if one burns out.

[Tracy White]

It would cost more but something like this could cut down on the number of LEDs depending on spacing of the lights.

[Zubie]

I would recommend that you understand your LEDs. These are diodes and really only want DC current. Diodes when passing current, which in LEDs is when they're lit, offer very, very little resistance. So, there will be math. Ohm's law dictates the relationship between the voltage and current in your circuit: V=I*R. If you can, run a little test rig with some batteries and an electric meter that checks resistance and voltages. Find what the resistance actually is for your LED, sb very, very high in one direction, and low in the other. The low is the lit R. Add one battery, apprx 1.5v, then another for approx 3v. See if it lights satisfactorily with the former (means you need less power).

Knowing R, and the test operating voltage you can work out what your circuit will pull. Remember your amperage limit. If you wire the system in series, one after the other, the total R is additive, but each will individually drop its percentage of the voltage. This means if you want 10 resistors to drop 3v in series, you need 30v on the line, but remember the amperage limit. For that 30 volt line, the amperage will be 30/Rtotal, which given a low total R may result in an unacceptably high current. That's why LEDs often need additional resistors.

Grouping them in parallel can help make handling the voltage easier since all parallel lines have the same drop, but parallel resistors offer LESS resistance than any individual element: 1/Rt=1/R1+1/R2+1/R3+...+1/Rn. That might be solved with a high resistor in series to the parallel circuit to limit overall current (although in a parallel circuit of equal resistors, each line carries an equal fraction of the current that adds up to the total)..

I think you can with some math come up with a circuit that won't kill batteries in nothing flat or short out a low voltage transformer. Remember, its the amperage that kills you.

[EVApodman]

Typically a diode when forward biased (current flowing) drops about .7 v across it. In reality it's usually around .6v.

Lets assume you have a 5v power supply capable of supplying 2 amps. To limit your forward current to 20 ma at 5v you will need a 250 ohm resistor. Common commercial values are 220 ohms (too low), so try to find a resistor that is 250 ohms or slightly higher. For the currents involved a standard 1/8 watt resistor will work fine and they are dirt cheap.

Now you have the choice on how to wire them. You can wire a resistor to each LED to limit the current. Which side, the anode or cathode is irrevelent but once you start with one way I would do them all the same. The bad news is that this creates a 20 ma current draw for each LED, creating a total of almost 1.7 amps for 85 LEDs.

Or you can wire some LEDs in series. The total current draw will stay at 20 ma for the circuit with the same 250 ohm resistor. But if one LED starts to go bad, increases it's forward resistance, this will dim them all. And when the LED finally opens, all the lights will go out.

The light bar LED is a good Idea but basically a variation on the use of fiber optics to create a light in the model.

To mimic what you see in the movie I'd want bright LEDs for the landing pad and walkway. I assume you want to light the interiors of the spherical habs too. This can be done with 1 LED per structure. If you want to be funky and also light the bulldozers, I would make them out of clear resin that can be illuminated by one LED per 'dozer and painted so the light only shows where you want it to.

Still this only comes to about 2 dozen LEDs or so, way below the 85 you call out for. What else are you illuminating? Even the Moon bus on the pad would add only 2 more.

How you will power this is another thing. To supply 1.7 amps from most available batteries, whether "C" or "D" sizes will require several and then you will only have so much use from them. in my work I test units that supply power to units from batteries at 4 amps and they are large batteries, only rated to supply this power for 30 minutes.

This leaves the AC power supply, which means finding a transformer rated for the wattage you need, a bridge rectifier, capacitors for filtering, also rated for the voltage and current you need and a 5v regulator, also rated for at least 2 amps. All of this is available commercially and I'm sure you can find a schematic to build it. Also you will need a circuit board to solder the components on and a box to keep them in. You will also need an AC power cord and I reccomend an in-line fuse in case of short circuits. A 1/8 amp fuse should be more than enough.

When I built the lighting kit for the classic Enterprise using the SFAM circuit board, I was able to use power supplies from Radio shack because my current needs were so low. Not so with this project.

[stargazer]

Hi Guys Thank you all for replying..

Firstly yes there are 81 Lights all over the moonbase you can see them all lit in the studio picture here.
http://www.planet3earth.co.uk/144%20sca ... 0MODEL.jpg
And yes, I have couple extra in each of the domes (I may light the moonbus too) so at least 85... This is why I need help, though I have used LED's in models before, there have only been a few... I don't know of any model needing 85 and want advice on just how to do it.

I found this on these threads...All good stuff guys. http://led.linear1.org/led.wiz So I punched in 3.3 V 20 mA and 85 lights with 12 volt supply...It gave three solutions. I lean toward what evapodman said about wiring some in series...and perhaps wiring these groups in parallel As in the 'First solution the calculator comes up with...What do you guys think of doing that, As I said I have no practical experience of wiring so many lights.

[EVApodman]

Ok, so there are over 80 lights in the movie, I forgot about the ones around the base.

That's a great site for the non-electronics person. I like the mix of serial and parallel circuits. You still have your work cut out for you though. Still, I'd try to see if I could cut down on the number of LEDs using fiber optics. The ultra-brights put out a lot of light.

Now I'd look at circuit boards to mount the resistors on. One wire from the LEDs will go to the board (anode), the other lines (cathode), will go to a return bus bar. If you want to be real hard core, offer a lighting kit to go with the model.

I'd recommend a power line going to an external power supply. A simple MIC type plug can be used to make it detachable.

[stargazer]

Thanks Again..

It was actually Solution 0 on the (wizard) calculator, not 1.
So do you think I should go get the resistors recommended and go for wiring
set up it gives??



The wizard says: In solution 0:•each 120 ohm resistor dissipates 48 mW
•the wizard says the color code for 120 is brown red brown
•the wizard thinks 1/4W resistors are fine for your application Help
•the 470 ohm resistor dissipates 188 mW
•the wizard says the color code for 470 is yellow violet brown
•the wizard thinks 1/2W resistors are needed for your application Help
•together, all resistors dissipate 1532 mW
•together, the diodes dissipate 5610 mW
•total power dissipated by the array is 7142 mW
•the array draws current of 580 mA from the source.

[Zubie]

(Second attempt...I thought I posted this reply already so if it doubles...apologies)

The complexity of your circuit is starting to look a lot like the Kirchhoffs Circuit Law problems I used to get in physics (which I also tended to screw up ). I wonder if one solution would be to not consider it as one big circuit, but a set of several individual ones like the circuits of model railroad set ups where you may have multiple loco's rolling on separate controllers in a wired rail network where each loco is on an isolated circuit (here model railroaders could probably help).

On the other hand looking at the picture shown from the top down angle you posted, it occurs to me that the light guide scheme might work better. I mean this, what about mounting the diorama on a light box using acrylic rods to pass the landing pad and marker lights. This would allow you to limit LEDs to special lights such as spots, vehicles, colored, etc. The light box itself is much simpler...basically a box with a commercial bulb or fluorescent tube, or even the kind of thing used for kitchen counter lighting and a translucent diffusing surface to evenly distribute the light. Even the domes could be lit with it if you give them open or transparent bottoms. Acrylic doesn't really bend much, but I figure a lot of those lights are really just beads on the surface. A shaped and lightly sanded rod should do the trick.

I realize you kind of already finished the set up with LEDs save the actual wiring, but it is just a thought.

[stargazer]

It is a brilliant Idea , And I wish I had thought of it and tried it...

I have gone to far to change the LED stuff now having already spent £ in it...
I do however have a 'Test' lunar surface I made first that I could try your Idea on.
and if id did work well...(as good as or better) at least I could recommend this to others doing my kit (when it hits the store)

[EVApodman]

The idea of a light box is a good idea with acrylic rods to pass light to the surface from below, this is just a big fiber optic. You can bend the rods with a dryer carefully into a bundle that is lit by a single LED. I would have each side of the landing pad and walkway bound together in their own bundle. This replaces over 40 LEDs with about 5, cutting you power requirements in half.

I don't know the size of your display and or what size lights you want to use, but I imagine that 1/16" rods would be fine for each one.

The biggest problem with fiber optics and LEDs is that that they are highly directional. The maximum brilliance is seen head on, they aren't omni_directional like incandescent lamps. A way around this is to put a small lens or clear ball on the ends to make the light more diffuse.

Also if you insist on the idea of a light box then I recommend fluorescent lamps due the heat generated by incandescent.

A 1/8w resistor will dissipate .125w. A 1/4w will dissipate .250w. Go with the higher wattage, the cost is minimal and it's good engineering practice to put in an additional load capacity beyond your calculated limits.

Even with an estimated 7 watts of power, since it is spread over a large area, the size of the display, the effect should be minimal.

[stargazer]

Well here it is lit.

https://www.flickr.com/photos/152476394 ... ed-public/

All the LED's came on first try Still need to light the Domes and moonbus. I tomorrow will take Pix of the wiring on the underside.
The power supply is a variable plug in 500 mA the LED,s work as low as 7.5 V.... the supply hardly got warm after leaving it all on for hours...

More later.

[EVApodman]

Awesome!

[stargazer]

Ok
So here is the back of the board.

It is wired in groups of three LEDs and a resistor,all in series and then all the groups linked in parallel

http://www.planet3earth.co.uk/WIRING%20 ... onbase.JPG

The drawing pins just hold the wire down. I did not have enough wire of the same colour to wire the whole thing
but generally positive is blueish wire and the negative brownish... and white links the groups of three led's and resistor'
Though the 'calculation' was done for 12 volts. It runs ok on 9 volts for daylight conditions and 7.5 V in a darker environment .

I used 3mm 3.2 V 20 mA Warm white LED's They are also 'frosted' and give a more general illumination than the 'clear' LED's which put out most light from the 'lens' and not the sides.

Here is the wiring plan http://www.planet3earth.co.uk/LED%20WIRING.jpg

While the diagram looks not much like the back of the board it is the same !!, The layout of the base dictated that though wired as above, for ease some connections have a 'common' solder join. The wiring groups are easier to see at the Btm. of the 'back' photo where the LED's have regular spacing around the landing pad.

[EVApodman]

I'm glad you were able to get all the LEDs lit and keep the current requirements down and still have a great model.

I assume that the kit was permanently mounted to the wood base first and you then drilled from the top down. Are there points on the kit for mounting lights?

The underside of the base gives you a good idea of the size of the kit. Next I'd like to hear about how you blended the resin moonscape with the non-resin one.

[stargazer]

I'm glad you were able to get all the LEDs lit and keep the current requirements down and still have a great model.

I assume that the kit was permanently mounted to the wood base first and you then drilled from the top down. Are there points on the kit for mounting lights?

The underside of the base gives you a good idea of the size of the kit. Next I'd like to hear about how you blended the resin moonscape with the non-resin one.

Thank you...
Yes fixed the resin slabs to the board first. All the stuff you mention (and more) are covered in the Instruction sheets supplied with the kit.
And yes the places to drill through the resin into and through the board are marked by 84... 1/8 dia tubes (which get destroyed by the drill bit.)

You can see the 1/8 dia marks on this picture (where the lights need to be placed)
http://www.planet3earth.co.uk/TYCHO%20M ... %20ART.jpg