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  1. Drudge's Avatar
    Member Since
    Aug 2011
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    Jun 10, 2013, 8:00 PM - LED lighting.Am I figuring this right? #1

    HI

    I've been going through the numbers and I'm not sure if I'm on the right track with my assumption/theory and I'm sure I'm missing something important,but here goes.

    I'm trying to figure out how the aoshima 1/2000 enterprise D is configured for LED lighting.I will have one within a week or so.The model comes with 6 LR44 1.5v button cell batteries.From what I have been able to figure these batteries are likely to supply at least 108-110 mA per cell under real world conditions.I'm leaning towards 110 mA with this.They are an off Chinese brand I believe.

    The batteries from these photo's of the battery holders look like they would be connected in series.

    Attachment 196117

    Attachment 196118


    I've been trying to figure out how many LED's are being run in each section(saucer and hull) on each set of batteries and how many batteries for each section are being used.From the looks of the battery holders it looks like they would/could be holding 3 cells each.I know for a fact that the engine nacelles have 3 LED's each in them from a video I've seen with one of the halfs of the engine removed.I don't know how many more are being used in the rest of the body for illumination.From looking at sources on the net I would take a guess of at least 3 more being used to light the rest of the hull and deflector dish and possible another for the impulse drive.

    If I run the data through the LED wizard and assume that only 3 cells supplying 4.5v total are being used,and make the assumption that 9 LED's total are in use in the hull,the wizard says that they are wired in parallel and the current draw would be 180 mA. That's more than what the batteries can supply!

    Source voltage
    diode forward voltage
    diode forward current (mA)
    number of LEDs in your array

    Solution 0: 1 x 9 array uses 9 LEDs exactly
    +4.5V
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    The wizard says: In solution 0:
    • each 82 ohm resistor dissipates 32.8 mW
    • the wizard thinks 1/4W resistors are fine for your application
    • together, all resistors dissipate 295.2 mW
    • together, the diodes dissipate 540 mW
    • total power dissipated by the array is 835.2 mW
    • the array draws current of 180 mA from the source.



    Now I'm starting to think that the hull section is actually using 4 cells and the saucer 2. If I run the LED wizard using 6v what the added cell would make the total voltage,I get a series+parallel array configuration for the LED's from the wizard.This configuration results in a current draw of 100mA.That's just barely within limits if those batteries are in fact only supplying around 110 mA at the least.If they were configured in series the current draw would be 180 mA!

    I think the highest real world measure I've seen on LR44 cells is around 150 to 160 mA for name brand like duracell.


    Solution 0: 2 x 4 array, 1 extra LED

    +6V
    |-" height="35" width="35"> |-" height="35" width="35"> R = 1 ohms
    |-" height="35" width="35"> |-" height="35" width="35"> R = 1 ohms
    |-" height="35" width="35"> |-" height="35" width="35"> R = 1 ohms
    |-" height="35" width="35"> |-" height="35" width="35"> R = 1 ohms
    |-" height="35" width="35"> R = 150 ohms
    The wizard says: In solution 0:
    • each 1 ohm resistor dissipates 0.4 mW
    • the wizard thinks 1/4W resistors are fine for your application
    • the 150 ohm resistor dissipates 60 mW
    • the wizard thinks 1/4W resistors are fine for your application
    • together, all resistors dissipate 61.6 mW
    • together, the diodes dissipate 540 mW
    • total power dissipated by the array is 601.6 mW
    • the array draws current of 100 mA from the source.



    This result makes me pretty confident that the hull section would be wired in a series+parallel array configuration for the LED's running on 6v with 4 cells. This is of course based on my guess that the model only uses 9 LED's for the hull section.Even with 10 LED's entered in the wizard it still results in 100mA draw.

    If that's the case then the the saucer would be using 2 cells supplying 3v. If a take a guess and say it's using 6 LED's total then wizard tells me that they are wired in series and the total current draw would be 120mA.That's over the assumed minimum 110mA that the batteries are supplying.


    Source voltage
    diode forward voltage
    diode forward current (mA)
    number of LEDs in your array


    Solution 0: 1 x 6 array uses 6 LEDs exactly
    +4.5V
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    The wizard says: In solution 0:
    • each 82 ohm resistor dissipates 32.8 mW
    • the wizard thinks 1/4W resistors are fine for your application
    • together, all resistors dissipate 196.8 mW

    • together, the diodes dissipate 360 mW
    • total power dissipated by the array is 556.8 mW
    • the array draws current of 120 mA from the source.



    If I enter 5 for the LED amount I get 100mA draw.Which again is barely within the minimum mA that the assumed batteries can supply.



    +4.5V
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    |-" height="35" width="35"> R = 82 ohms
    The wizard says: In solution 0:
    • each 82 ohm resistor dissipates 32.8 mW
    • the wizard thinks 1/4W resistors are fine for your application
    • together, all resistors dissipate 164 mW
    • together, the diodes dissipate 300 mW
    • total power dissipated by the array is 464 mW
    • the array draws current of 100 mA from the source.



    Ok,here is what I'm getting at.If my assumptions actually pan out(I'll have to gently open up the model to inspect to know for sure how many LED's are inside) and I used higher quality LR44 cells that supplied around 150-160mA, would I be able to add an additional self contained flashing LED to each section with fiber optics attached(if they can be fitted) for nav lights and be able to still operate the model under battery power without issue?

    How close can the miliamp draw be to the milliamp supply from the batteries before there is an issue?

    The flashing LED's use 10mA vs. the steady state 20mA. I know that would draw more current,but it doesn't seem like it would be much of an issue unless this all results in the batteries draining very quickly or fire.




    Am I flawed in my assumptions? Please any input would be great!




    Thanks

    - - - Updated - - -

    The LED wizard wiring diagrams didn't copy properly to the post.I don't know why?
    Last edited by Drudge; Jun 10, 2013 at 8:11 PM.

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