Question about lighting models.

[captain america]

Hi all.

I have a bit of a technical question for those of you who may have some experience in lighting model kits. I'm currently looking at a newly-purchased Bandai NCC-1701E Enterprise kit, and I had some questions about the small grain-of-wheat bulbs included.

Essentially, these look ( to me anyway) like scaled-down versions of regular lightbulbs, and as such, that most probably means that they'll burn out eventually. Problem is, once the model is properly built, there would be no way to open it back up to replace them. So in short, my question is twofold: what is the expected life of these grain of wheat/rice bulbs, and do they have any advantages at all over LEDs (particularly superbrights)?

Thanks in advance for anyone who could, um... Shed some "light" on my dimness

[Valkyrie]

Well, I've never lit any of my models, but I do know electronics.

Those 'grain of wheat' bulbs are indeed small lamps. So yes, they do have a limited life, though I have no idea how long that would be.

But I can see no real drawbacks to using white LEDs instead of those bulbs. LEDs will last damn near forever, as long as you throw a resistor into the circuit to limit its current to within the part's max current spec.

[captain america]

Hi Valkyrie.

Well, I took the plunge and replaced all the lamps in my Enterprise with superbright LEDs. In fact, I went even further, by adding 2 extra LEDs inside the saucer section to produce the "projection" effect onto the hull. The one on the top didn't come out as great as I would have liked, as it's hard to get a proper light patch onto a surface that's dipping away from the light source. I also added 5 LEDs into the black base which serve as spotlights to illuminate the lower hull... Not bad for a guy who sucks at wiring things!

Ok, now here's the thing. This kit now has 15 LEDs, which are powered by 3 AA batteries, and I'm guessing that since there are so many bulbs, that the batteries just can't produce the brightness that I seemed to get when testing the bulbs one at a time. Essentially, would there be a way to make the whole unit capable of using a wall outlet for power? Perhaps using some sort of off-the-shelf plug-in adapter unit?

I'd ask the guys at my local radio shack, but judging from the blank expression on their faces when I asked them about LEDs, I figured it would be safer to ask here

[Stamen0083]

John,

What size LED's did you use? What color? Are they super bright or ultra bright?

This is the specs sheet I'm looking at. Is it familiar to you?

http://www.alltronics.com/download/SE5084J.pdf

[captain america]

Hi Stamen.

The LEDs in question are superbrights, I guess. 5mm, 10mA

there are 6 "white", and 2 blue superbrights inside the ship, and two regular red LEDs (non-superbright) in the front of the nacelles to light the bussard collectors.

The 5 in the base are white superbrights also, all are 5mm size.

If it helps, the radio shack parts number for the white superbrights is 276-9083...2 per pack.

[Stamen0083]

Bleh. Forgot to ask. Are you wiring these LED's in parallel or series?

Anyways, I've determined that if you wired everything in parallel, you'll need a power supply that can supply at least 150 mA, which shouldn't be too hard to find. Typical supply can throw out more power than that.

Anyways, assuming your power supply can put out more than four Volts (anything less and the LED's won't light very well), just take that number, subtract 3.6, which is the turn on voltage of the LED, and then divide by .010, which is 10 mA. The result is the smallest resistor you'll need in that branch.

With my calculations, if you were to use a 12V, 150mA power supply, you'll need a 1K resistor for each LED.

Am I right, everyone else? My analog is very rusty. I'm much more comfortable with digital systems.

Edited August 27, 2004 by Stamen0083

[captain america]

Hi stamen.

Sorry, I'm just VERY new and dense with all this. Would I need a resisor for EACH LED in the kit, and if so, do I need to place it right on the LED itself? The ship itself has been glued shut, so I can't get inside it to access those LEDs anymore, but the base/battery box is still accessible. Inside this display base, there's essentially two main "poles": one positive, one negative, and these connect to the battery contacts. I simply soldered all the red wires from the LEDs to the positive pole, and all the blue ones to the negative. I was just hoping that there would be a way to replace the battery box (and batteries) with a wall outlet, and maybe a resistor of some sort in between them to keep from blowing the LEDs.

Alas, I'm an artist, not an electrician, so even the simplest of wiring jobs is a big step for me... Makes for a purdy model though

[Max Jenius]

Hi stamen.

Sorry, I'm just VERY new and dense with all this. Would I need a resisor for EACH LED in the kit, and if so, do I need to place it right on the LED itself? The ship itself has been glued shut, so I can't get inside it to access those LEDs anymore, but the base/battery box is still accessible. Inside this display base, there's essentially two main "poles": one positive, one negative, and these connect to the battery contacts. I simply soldered all the red wires from the LEDs to the positive pole, and all the blue ones to the negative. I was just hoping that there would be a way to replace the battery box (and batteries) with a wall outlet, and maybe a resistor of some sort in between them to keep from blowing the LEDs.

Alas, I'm an artist, not an electrician, so even the simplest of wiring jobs is a big step for me... Makes for a purdy model though

MOAR PICS!

[Stamen0083]

Hmm... Everything glued shut makes this a little more complicated. Do you at least have access to the individual wires?

The point of the resistor is to provide a stable resistance for the electricity to flow through, since each LED's impedance (read: resistance) is not guaranteed to be the same through out.

You can use a resistor wired from the power supply to the big wire, but that can only guarantee that the voltage across the LED's are no more than they need, but there's no way to make sure that you'll have a stable current otherwise.

You know, I'm looking at my NiMH digital camera batteries, and they supply 2100 mAH, meaning that if a device is using 2100 mA, the single battery would be drained in one hour. If you were to use three AA batteries, you're looking at some 140 hours of illumination with these NiMH batteries.

If the problem is with brightness, you can add an extra battery. 3 X 1.2V = 3.6V, which is just barely enough voltage to light the LED's. One more, making it 4.8, would be pretty adequate, and you won't have to mess with power supplies.

Sorry to be so long winded, but that's the way I am, I suppose.

PS: MORE PICS!

The projected light looks incredible. Too bad it has to be a huge hole drilled into the hull that provides that light. I've been looking for ways to project lights on the NX-01, but I've no luck.

Edited August 27, 2004 by Stamen0083

[David Hingtgen]

When I lit up my Ent-B, I learned quite a bit from this:

http://members.misty.com/don/ledx.html I suggest "LED's 101" and "LED FAQ" for starters.

Seriously, just google "LED wiring" and you'll find lots of articles from people lighting up various Trek ships.

Only thing to be concerned about is wiring in parallel vs serial. Rules are different.

I'll go and see if I can find my wiring diagrams for my ship, I sure hope I didn't toss them, as I'll never be able to replicate from memory. (I copped out and used bulbs instead of LED's at the end, but it's all the same concepts, mini-bulbs just draw a lot more amperage)

Edited August 27, 2004 by David Hingtgen

[Opus]

It seems to me that since the job of an adapter is to convert alternating to direct current you could get one with the same rating as your batteries and wire your LEDs straight to it. Keep in mind I'm not an electrician but I do have what my friends call the "Mc.Guyver Touch".

[David Hingtgen]

Most people who go with LED's do get adapters. You can get SO many different adapters, you usually just wire up the system how you want, figure out what kind of power it requires, then buy whatever adapter you need. My Ent-B runs off a 9V 800mA one. Could just as easily used a 9-volt battery, but it'd be drained pretty quick. And since a starship needs a stand, might as well have the stand supply power from an adapter.

Batteries are useful in that you can pretty much create whatever voltage you want---NiMH are usually 1.2V, Alkaline are 1.5V.

[captain america]

Aight... Read the article on LEDs for dummies. Flawed article, because I'm more confused now than before I read it... Us simple-minded folk prefer diagrams; makes learning easier, so I included one of the wiring on my model.

The only thing that's wrong in the diagram is the position of the on/off switch; it should clearly be between ALL the LEDs and the battery contacts. Hopefully, this will provide a clearer indication of what I've done, and if it can be converted to a wall-outlet.

Edited August 28, 2004 by captain america

[captain america]

..And a few more awful pics of the finished model, which I can proudly say I assembled with NO painting whatsoever. I swear, these Bandai shake-n-bake models are like scaled-up versions of those little Kinder Egg toys... Makes me think it might not be such a bad idea to market them encased in a chocolate egg

[captain america]

Top of the saucer. The light projection onto the hull is courtesy of an LED which I held dangling over the model as I snapped the pic. Though there's a light shining from out of the base of the bridge decks, it barely projects onto the hull at all; the LED being too large to aim downward from inside the crowded confines of the kit's interior.

[captain america]

Shot of the nacelle strut illuminated by the white LEDs in the base.

[Stamen0083]

So, about my question... Can you get to the individual wires at all?

[captain america]

Hi Stamen. I can get access to the wires that are coming out of the ship, as well as the contacts to the power supply (batteries), but not the wires inside the vessel itself. In essence, based on my diagram above, everything "below the ship" is hands-on, but everything inside is not accessible. Am I screwed?

[Stamen0083]

Am I screwed?

Not necessarily. Let me do some thinking.

Is that diagram you have entirely accurate? It looks to me that if things were wired the way it's presented there, if you turn the switch to off, the LED's in the base that light the modelwould stay on.

Check out my previous recommendations, and see what you think. I'll make another post (or, if no one's posted between now and then, I'll edit this post) if I figure out something useful.

[captain america]

Hi Stamen.

Yes, you're right, my diagram above was flawed. This one is accurate to the actual model, with the power switch clearly between all the LEDs and the power source.

I'll re-read the above comments again... Hopefully to understand them this time. I really appreciate all the help offered thus far

Edited August 28, 2004 by captain america

[Opus]

You guys might be over thinking this one. Have you read this?

http://www.starshipmodeler.com/tech/mh_led.htm

You should find the info you need to calculate the output of an adapter in this article. Resistors shouldn't be necissary with an adapter, that's the whole point of using one.

[Stamen0083]

Resistors shouldn't be necissary with an adapter, that's the whole point of using one.

Right. Use an adapter that puts out 800mA to pump juice through a device that cannot handle more than 10mA.

You still need a resistor to limit the current through an LED so that it doesn't burn out.

[Opus]

Resistors shouldn't be necissary with an adapter, that's the whole point of using one.

Right. Use an adapter that puts out 800mA to pump juice through a device that cannot handle more than 10mA.

You still need a resistor to limit the current through an LED so that it doesn't burn out.

From his diagram it looks like the whole thing is wired in paralell. According to the page I linked his 15 10mA LEDs would need a 150mA adapter. A 6v 300mA adapter would do the job just fine.

[Stamen0083]

From his diagram it looks like the whole thing is wired in paralell. According to the page I linked his 15 10mA LEDs would need a 150mA adapter. A 6v 300mA adapter would do the job just fine.

I know that. But wouldn't that mean a 150mA current source at most should be used?

[Opus]

I think it can be a bit over. You just can't put more LEDs than the adapter is rated for. There are probably lower rated adapters out there as well. I'm no expert, I just picked an easy to find adapter. Personally I would experiment with a mock up first. Radio Shack sells a sack of 20 LEDs for about $3. Having things blow up in your face is half of the fun of figuing out something new.

[Radd]

About the light you're trying to project over the top front of the saucer, if you were able to get into the kit again (I know, not possible, just a random idea that might help in future models) would there be room behind the LED to place a small mirror?

For the movie refit 1701 kit in another forum someone mentioned using something like that. An alternative I think they mentioned was putting electrical tape around the LED to direct the light.

[Radd]

This thread has got me thinking about that Polar Lights model of the 1701 refit again. I'd be willing to spend a couple years slowly putting that together with some LEDs in it.

[David Hingtgen]

Basically:

Voltage must match, Amperage merely needs to be "enough". Quick example:

2.6volt, 20milliamp LED. Give it 5 volts, it'll fry itself real fast. 1 volt, it won't light. Give it 2.6volts, with a small +/- margin.

However, it'll only draw as much power as it needs from an adapter. I mean look at the AA batteries the kit already supplies--probably several thousand milliamps together. But the LED's will never draw more than they need.

Resistors are for lowering voltage, not amperage. I managed to get my Ent-B down to just one resistor (though pretty significant wattage, had to order from Digikey)) inside the saucer.

[captain america]

Hi Radd.

The biggest problem with all that is reallya lack of space. I had actually wanted to try something with reflective mylar acting as a mirror to project the light more effectively, but the inside of the bridge is just so small, and the lighting "hole" must be so very small as well, that as soon as your light source is more than a mm away from the projection hole, the light beam becomes so narrow as to become useless.

David: if I understand you correctly, then I need an adapter in the range of 4.5 volts, which would be an identical replacement for the three 1.5 volt batteries that the kit uses as standard. Having said that, might you have a clue as to what my safe threshold of voltage is for 15 LEDs?

Also, since an adapter, as you said, regulates voltage, then I wouldn't really need a resistor...Or would I?

My biggest failing at this point is that I don't know the difference between volts, watts and amperage, but I do know that the milliamp rating on a battery determines the "duration" of power that it'll provide, and that if a device consumes 1200 ma/hr, and your battery provides 1200 ma/hr, then you'll only have an hour of battery life, and so on.

I may yet eventually get the hang of this

[David Hingtgen]

Smallest adapter voltage I can find in my list is 5 volts, sizes from 300 to 1500 milliamps. 5 is 1.11111 times that of 4.5, which is a little high, but not bad. Most stuff has a 10% tolerance or so.

Of course, then there's the issue of having the adapter plug into the stand. It's REAL fun trying to figure out whether you have a 2.0mm or 2.1mm plug...

[Valkyrie]

Basically:

Voltage must match, Amperage merely needs to be "enough". Quick example:

2.6volt, 20milliamp LED. Give it 5 volts, it'll fry itself real fast. 1 volt, it won't light. Give it 2.6volts, with a small +/- margin.

However, it'll only draw as much power as it needs from an adapter. I mean look at the AA batteries the kit already supplies--probably several thousand milliamps together. But the LED's will never draw more than they need.

Resistors are for lowering voltage, not amperage.

Can't say I agree with all that....

First of all, resistors can indeed be used to lower a voltage, in certain configurations. But in simple circuits like the one we're talking about here, only current will be affected. The voltage will remain unchanged.

It's also not true that LEDs will just magically draw exactly the amount of current they need. They tend to draw MORE than they need (thus putting them over their max current spec), thus the need to add a current limiting resistor in the circuit.

What you said about going over the voltage limit may be true if you're not using the resistor. But as long as you're limiting the current to within its spec, you can usually get away with going over the max voltage a bit. Keeping the current in check is much more crucial.

Now, here's my take on John's situation:

He's got 15 LEDs wired in parallel, connected to a 6V supply.

Now, the LEDs will self-limit their current to a certain degree. But at 6 volts, they'll probably be drawing about 100mA each. That's gotta be way over spec. It also puts the total current load at about 1.5A. That's a lot.

Now, since he has most everything sealed up at this point, all he can do is add a single resistor at the power source to limit the overall current. And that overall current will be distributed evenly through every branch of the parallel circuit. For example, if a certain resistor value reduced the overall current to 450mA, then each LED would get 30mA. Which is probably right about where you want to be. (though I'm guessing, since I don't know the specs of your parts)

Also, if some of the LED are rated lower or higher than the rest of them, there's nothing you can do get them more or less power at this point. All of them will be getting the same thing.

[David Hingtgen]

I'll be the first to admit I'm REALLY rusty on wiring LED's...

Also I always design things so that either the voltage, amperage (or if I'm lucky both) are correct for what the powersupply can put out, to simplify things. Taking an already wired-up system with a lot of unknown specs is a lot harder to figure out what to do! I really should go get my Ent-B diagram/specs... (I tested that thing at EVERY soldering addition, and even pre and post-decaling just to be sure--I know it's wired right)

PS--I thought he was running off of 4.5volts, 3xAA. Also we need the LED specs, superbright whites, blue, and red are about as different as LED's get. Could easily fry a red trying to get a superbright white to go.

Edited August 29, 2004 by David Hingtgen

[neptunesurvey]

Go to the Starshipmodeler discussion forums. Those guys have lit so many different Star Trek kits they can help you.

[Valkyrie]

Oops, my bad. 4.5 volts it is. I was thinking 4 batteries for some reason.

[Stamen0083]

Basically:

Voltage must match, Amperage merely needs to be "enough". Quick example:

2.6volt, 20milliamp LED. Give it 5 volts, it'll fry itself real fast. 1 volt, it won't light. Give it 2.6volts, with a small +/- margin.

Sorry, David, but you're wrong on every count.

Current cannot exceed the item's limit. It's the current (amperage) that'll pump power through the LED's. The voltage merely determines how hard the current is being pumped through. So a superbright white LED, whose pushoff voltage is 3.6V, needs at least 3.6V to light, but it can handle anywhere above that. I've lit LED's at 5V before in my digital lab with no problems. Some have even lit them with 9V. However, the most current it can handle is 10mA. Put more than that through it and that thing will fry.

However, it'll only draw as much power as it needs from an adapter.  I mean look at the AA batteries the kit already supplies--probably several thousand milliamps together. But the LED's will never draw more than they need.

Actually, the reason is reversed. The batteries only put out what the LED's demand. If a component requires several thousand milliamperes, it will put out several thousand milliamperes. A power supply puts out several thousand milliamperes without being asked to.

Resistors are for lowering voltage, not amperage.

Resistors can reduce both. In a series circuit, resistors lower voltage. In a parallel circuit, resistors lower current.

By the way, there seems to be some misconceptions regarding voltage and current. Voltage is the potential between two points. Not potential energy, mind you, just potential. Current is how much charge (how many electrons) is flowing through the wire or component or whatever. Power is how much energy flowing in how much time. A simple way to think of all this is to imagine a waterfall, where voltage is how high the waterfall is, and current is how much water is flowing from the waterfall. Now, an LED needs to fall from a certain height, but too much water flowing with it will drown it.

I managed to get my Ent-B down to just one resistor (though pretty significant wattage, had to order from Digikey)) inside the saucer.

Yeah, you had to use one of a significant wattage to throw away most of the current the power supply is putting out. I'll bet that the total energy your Enterprise B is using is about 10% of what your supply can put out.