SciFi Model Action

Modelers Questions Board => Modelers Questions Board => Topic started by: GulKelan on August 26, 2018, 04:30:25 pm

Title: Trying to lightn up a galor class
Post by: GulKelan on August 26, 2018, 04:30:25 pm
Hi Mates!

Im new to the forum (Trekworks) and i try to light up a galor class from ertl. I origanally paint miniatures but this is my first model i try to light up.
The only problem where i find difficulties is the parralel lighting.

this is my list of leds which i want to install but i dont understand what kind of resistors i have to install... after many days of figuring out which resistors i have to install i finally have to ask in this forum.
Im totally confused by all the videos i watched.

can you tell me which resitors i will have to buy for a parallel circuit (i believe i have to make a resitor before every single led right?)

This is the list of lights i want to install with a 9 volt power suplly:

1x Led strip which i want to cut all 3 smds at lenght for the interior to get the windows light up.
In total i want to install 9 pieces which each has 3 smds on it:

1x the following red led for the Deflector in the front:!tab2

15x the following leds for the 3 Thrusters and the 4 Triangle things:

10x Leds for the very tiny Phaser arrays all over the ship:

4x at the back of the vessel in the tale section:

1x for the windows of the bridge saucer area. do you think the color white will be the same as of the led strip above? they write the strip should have a color temperature of about 6000k.

The goal is to run everything with 9v battery as power supply. how long will one 9v battery run with this kind of lighting setup if eveything is in parallel?

i hope somebody can help me cause im really stuck in this project...
Title: Re: Trying to lightn up a galor class
Post by: GulKelan on August 26, 2018, 05:13:55 pm
i tried to paint it as a scmeatic.

is this how it could be installed?
Title: Re: Trying to lightn up a galor class
Post by: Markeno on August 27, 2018, 07:40:34 pm
What resistor you need is based on several factors.  If you want to get the most basic..  It is based on your supply voltage and the Color and voltage rating of your LED.

Red, Yellow and Green LEDs typically have a around 1.9 or 2.0 Voltage spec at 20mA of current.

White and Blue are around 3.2 or 3.4 Voltage spec for 20mA of current.

That is for bare 3mm 5mm or even individual surface mount types. 

LEDs are rated at 20mA of current as their top end.  If you put more than that through them you greatly reduce their lifetime or burn them up nearly instantly if it is enough.

So for a 2Volt 20mA rated LED and a 9Volt power supply, you can do a simple calculation to figure out what Resistor "minimum" to use.

R = Voltage / Current

Now we need to take into account the Supply Voltage and the LED Voltage Drop.

R = (Supply Voltage - LED Voltage)/Current

The "Current" rating is in Amps not "milliAmps".  There are 1000mA in 1Amp, so we move the decimal over 4 places to the left.  So 20mA is .02Amps

R = (9Volts - 2Volts) / .02A

So take the labels off

R = (9-2)/.02
R = 7/.02

R = 350

So you are looking for at a 350 Ohm Resistor "minimum" for that 2Volt 20mA rated LED if supplying it with 9Volts.  So you would pick a resistor of 350 Ohms or higher.  Looking at what I happen to have in my stock, I have a 330 Ohm, but that means we will be driving it a bit too "hot", so the next step I have in my stock is a 390 Ohm Resistor, that would be ok to use.

In reality..... you don't "need" to drive them anywhere near 20mA.  You could drive it at 10mA and be plenty bright, many modern LEDs light up plenty bright at even half that.  Whites light even down in the 1mA and lower range..  You could use a 470 or 560 Ohm and likely have more than enough light for scale models.  You can light pretty much any standard LED just fine even with a 1k Ohm resistor when using a 9 Volt supply, although they are a good bit dimmer.  If you are trying to get your lighting to "scale", then sometimes you may want to use higher value resistors to dim them more.  Sometimes you want to try to get the apparent brightness of two colors of LEDs to be close, so you may use a higher value resistor on the Greens than the Reds or vice versa..

There is another rating on Resistors.  The Power rating or "Wattage".  You will see 1/8, 1/4, 1/2Watt etc.  The higher the Wattage the more power they dissipate before burning up.

W = V * A

W = (9-2)*.02

W = .140

Now convert that to 1/8 1/4 1/2 etc.  So 1/8th Watt resistors are .125Watts (then that isn't enough for this application).  You need a minimum of 1/4th Watt resistor which is .25Watts.  Always oversize the resistor if it is anywhere near close.  I would say often want around double what you need so say .28 is double what we expect to need, so that I would say should be ok for a 1/4th Watt resistor.


Once you know these calculations for the typical LEDs for 5 Volts, 9 Volts and 12 Volt supplies they don't change...  They only change if you change your supply voltages.   If you use the same 2Volt 20mA LED with a 12 Volt supply you need higher Ohms rated resistors and higher Wattage resistors, but if you stick to a 9Volt supply on all of your models, then you really don't need to recalculate.  Again Yellow Red and Green are basically identical, and White and Blue are rather close to one another.  There are some more exotic LED colors that are a bit different ratings.  Mostly it is the color of the LED, a 3mm a 5mm and a SMD LED of the same color typically have very nearly identical operating ratings.


If you make them a bit dimmer, you could find you have less issues with "light blocking" not working well for you.  You do need to "light block", which is painting the model plastic or some other method to stop the light from glowing through the model.  (Although the Raytheon lighting method is kind of the opposite or rather a creative use of light blocking, where you "don't" block the light in specific areas to get the effect that you want.)  Light blocking can be achieved by putting usually multiple coats of Black paint either on the exterior or interior of the model.  I prefer to paint the interior when I can, it won't risk getting too much paint buildup on the model.  A single coat of black paint is not enough, I have always needed at least two.  I then check the model with a bright White LED lighted around the 20mA rating holding it against the interior running it all over the inside surfaces of the model with the lights turned out in the room.  You can then see the light leaking through the thin areas of the paint.  When I am happy that the light is blocked properly, I then put a coat of Silver paint on the interior over the black to reflect the light better, others use White etc.  Then you have to concern yourself with the glue seams etc as you assemble.  I just rechecked some parts tonight, and found I have more work to do before I can start the final paint as I have alot of areas leaking even with two coats of paint on the interior.  Partly as some of that was done by brush, I use a dark nearly black spray primer more than the brush as it goes on more evenly, although I still have some areas that turned out to be a bit too light on that too.   Silver does not "block" the light, even several coats (although some types of silver that I haven't use myself may, typically I think it has suspended flakes in a clear paint meaning it can keep reflecting through it.)  There are other types of light blocking, using foil tape, or gluing in standard aluminum foil, building "light boxes" to keep light where you want it.  There are alot of different ways.
Title: Re: Trying to lightn up a galor class
Post by: Markeno on August 27, 2018, 08:12:24 pm
Btw. the "LED strip" that is a 12Volt Rated Strip.  So you don't need resistors for it.  If you supply it with 12Volts it will be "safe" in the 20mA area for each LED.  If you supply it with 9Volts it will be safer yet, and will be a bit dimmer but not much.  If you put a Resistor on with the Strip, you may make it too dim.

Two of those LEDs are 2-2.1 Volt as my example had.

Two are 3.2-3.4Volt

So you really only should need two types of resistors.  Ones for the 2 Volt rated LEDs and one for the 3.2-3.4 Volt rated LEDs, and none for the Strips.


For the strips, be sure you only cut them where they are marked to be cut.  They are actually 3 LEDs wired in series with a single resistor wired in Series already.  If it is helpful you can keep several "groups" together.  They don't have to be cut apart.  Each "section" is wired in parallel with each other with how the "strip" is designed.


You can get more complex in how you wired the LEDs up.  If you wired 2 Red LEDs in series with a single lower value resistor you will have less wiring and less resistors.  The calculations are the same, just taking into account you now have Two LEDs in the circuit.

R = (9V-2V-2V)/.02A

R =  5/.02

R = 250 Ohm

W = 5*.02

W = .1 Watts  (so here I would use a 1/4Watt resistor still, although it is "within spec" for a 1/8th Watt Resistor (.125W).  The reason being it will likely get quite warm..  It may melt your plastic model if it is touching it somewhere.)

If you want you can do Three Red LEDs in series with a single resistor..  Same thing R=(9-2-2-2)/.02..  So there is a 150 Ohm resistor, there you could use a 1/8th Watt resistor if you like as it is even lower Wattage.  You don't want to try 4 Reds though, as you will get the resistor value so low that the value of it gets rather critical, and that as your 9 Volt battery drops down to 8 or 7Volts as it drains the LEDs may quit working entirely.

When you use a combination of series and parallel to keep the number and Ohm rating of the resistors lower, you are actually saving power in the Battery and extending battery life.  Three Reds in series with a single resistor only uses 20mA of current, where the same three wired in parralel with individual resistors would be using 60mA of current.
Title: Re: Trying to lightn up a galor class
Post by: GulKelan on September 01, 2018, 10:48:25 am
Hi Markeno,
Thank you very much for these juseful informations!
I orderd the leds now and gonna show it off when its finished.

Again Thank You
much appriecated!
Title: Re: Trying to lightn up a galor class
Post by: Markeno on September 01, 2018, 01:31:41 pm
You are welcome.  If you have questions I may be able to assist with, just ask.  I randomly check the forum.