Battery source and lighting configuration

[blakeh1]

This will be my first attempt at setting up a model with lighting effects. (as well as my first time posting so forgive me if this has been covered ad nauseum....)

I want to start simple. I will be using the Battlestar Galactica Viper kit

The Plan...

4 LEDs
1 for each of the 3 engines, and the fourth to light up the cockpit instrument panel (mainly the display screen)


I have 4 white superbright LEDs

They are 5 mm
forward voltage is 3.3 volts
25ma (but it might be 20, I don't have the package handy)

assuming a 9 volt..

If I am correct then with a 9 volt I could set up 2 series of LEDs with 2 LEDs per series with a 100 ohm resistor on each series

+----|>|----|>|---/\/\/----+ R = 100 ohms
+----|>|----|>|---/\/\/----+ R = 100 ohms


From what I gather though, using AAA or AA is better from longetivity standpoint

Using those I would have to have 3 batteries with a 39 ohm resistor for each

+----|>|----|>|---/\/\/----+ R = 39 ohms
+----|>|----|>|---/\/\/----+ R = 39 ohms


I was hoping to have the whole thing self contained within the viper itself rather than wiring to the stand so I think the 9 volt will fit better

So my questions

1) Are the calculations for the resistors and circuit correct?


2) Assuming either 9 volt or AAA will fit, which is better, 1 9 volt or the 3 AAA?


3) Does it matter what guage wire I connect stuff with? I currently have 22 g wire

[tetsujin]

1) Are the calculations for the resistors and circuit correct?

For the 9V, seems like it's correct, yeah. For the AAA's - no. You said you were going to be using three cells, but you still show the LEDs being wired up in series... That would mean the LEDs wouldn't get enough voltage. (2 * 3.3V > 3 * 1.5V...)

You could hook up the LEDs to 3 AAA's by giving each LED its own resistor and hooking up each LED+resistor pair parallel to the others... (Maybe that's what you meant? Anyway, you'd need about a 50 Ohm resistor in that case...)

2) Assuming either 9 volt or AAA will fit, which is better, 1 9 volt or the 3 AAA?

With the 9V source you'd be wasting 2.4V * 25mA * 2 on the resistors. (voltage drop across the resistor times current through the resistor, times two because there's two of 'em...) - that's a little over a quarter of the whole output of the battery.

With a 4.5V source, and the four LEDs in parallel each on their own resistor, you'd be wasting 1.2V * 25mA * 4 ('cause there's four resistors now) - as it turns out, the waste in this configuration is exactly the same - 120mW.

If you wanted to be more power-efficient... You could use 5 1.5V cells (for 7V total) - then you could still use the two-LED series circuits but you'd only need to drop 0.6V from each one - cutting your total power waste down to 30mW. You could use AAA cells, in which case the battery would actually take a little less space than a 9V would. (A 9V battery is actually made of six AAA cells... So one option would be to buy a 9V battery, open it up, pull out a cell, and replace it with a piece of wire... But then again, what's the point? You've cut waste but at the cost of additional work - and you haven't saved any money...)

3) Does it matter what gauge wire I connect stuff with? I currently have 22 g wire

22 AWG is plenty for a job like this. Personally I wire most of my model projects with 30AWG stranded wire, which is less than 1mm in diameter including its insulation. You might want to consider something smaller - but if there's space in your model for the wire and you've got the stuff on hand and you're comfortable working with it, there may not be a compelling reason to get anything different.

If you were dealing with more extreme cases - like tiny wire or a lot of current going through it, then you might have to start worrying about the resistance of the wire, and how much heat it generates carrying the current. But for lighting a few LEDs on battery power it's not going to be an issue.

[brt]

As I understand it, AAs will last longer than AAAs

[robiwon]

Post your specs in here.

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

[blakeh1]

thanks for all the info!