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Thread: EFWD Build

  1. #261
    Senior Member efwd's Avatar
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    Default Re: EFWD Build

    Very nice Paul, Thank You
    nothing to lose in wiring in the resistors and seeing if the light still illuminates in spite of the claim the light does not need resistor. If it doesn't illuminate then I would assume there is already a resistor inside and I can remove the one I installed.
    Eddie

  2. #262
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    Default Re: EFWD Build

    Sounds like a plan. When I get my LEDs then I'm just going to rig up a temporary circuit (as per the Rotax manual) on the workbench and see how the LEDs go. If I need the series resistors then I'll just tape them in until all is well and then I'll get out the soldering iron and heat shrink However, I'll start off without them because, as we've both said, the LEDs we've bought are made for the job, so why would you need additional series resistors?

  3. #263
    Senior Member Av8r_Sed's Avatar
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    Default Re: EFWD Build

    I'm not sure if this is going to help understanding on LED's, but here goes...

    LED's are basically current devices. If you take a run of the mill small red LED and pass 20 milliamps through it in the forward direction, you'll get a bright light with about 2 volts across the leads. Around that 20 mA point, a little more current makes it brighter and less dims it.

    The purpose of a series resistor is to limit the current going to the LED. So if you start with 12 V and subtract off the 2 across the diode it leaves 10 Volts. Using Ohm's law you can find the required resistance. So 10V / 0.020 Amps = 500 Ohms.

    The example shown has a 1K resistor in series so the required current for that LED at the brightness they decided was appropriate would be closer to 10 mA. Also, the voltage in an aircraft system is probably closer to 13 to 14 volts.

    The purpose of the 1.5K resistor is as described by Paul SS. It pulls down any leakage current from the driving device so the LED won't glow when it isn't supposed to.
    -- Paul S
    Model III SN910
    582 IVO Med

  4. #264
    Senior Member efwd's Avatar
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    Default Re: EFWD Build

    Thank You Paul. Is it not strange that your hooking up a resistor from the positive wire to the negative post? Thats what I really don't understand. I believe it was explained that having a greater resistor on that limb still has the flow of current through the bulb from Positive to negative. Do I understand that correctly?
    Eddie

  5. #265
    Senior Member Av8r_Sed's Avatar
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    Default Re: EFWD Build

    You've got it right, Eddie. It doesn't matter though.

    When the output is on, the second resistor to ground draws some extra current, but it doesn't affect the LED function as long as the output can source the extra current without dropping off in voltage. At these currents, it probably has minimal effect.

    What the 1.5K resistor does do though is drain off any leakage current from the output (in it's off state) to ensure the LED doesn't light up. This is the normal mode of operation unless you fly around with the Lane fault light on all the time.
    -- Paul S
    Model III SN910
    582 IVO Med

  6. #266
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    Default Re: EFWD Build

    The only thing I think is a little strange is the need for a series resistor if the LED bulbs we've got are designed for 12V use in the first place (although I do understand the fact that we'll get closer to 14V). I think most of us will buy an LED bulb from such sources as a car store, where you would think the bulb is already setup to glow at a reasonable level.

    It's not a huge snag. As I've said before I'll just experiment with a few resistors in series if they're required but I'd prefer to demonstrate as few times as possible my appalling soldering 'skills'

  7. #267
    Senior Member Av8r_Sed's Avatar
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    Default Re: EFWD Build

    Why solder? Just get a couple of clippy leads and a potentiometer. Dial that baby in until it glows how you like and then measure the resistance. We're all experimenters, aren't we?
    -- Paul S
    Model III SN910
    582 IVO Med

  8. #268
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    Default Re: EFWD Build

    Oh yes

    I can actually go one better than a potentiometer as I got on Ebay and have a very swanky benchtop variable power supply. I almost feel semi-professional in not having to bodge together another solution. I didn't get it just for the LEDs but I'll be using it for that. As you say, just clip some resistors in series until I get what I want and then get the soldering iron out. That's definitely Plan A because it involves a lot less swearing at molten metal

  9. #269
    Senior Member efwd's Avatar
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    Default Re: EFWD Build

    Anybody know where I can locate the information pertaining to the AWG size needed to wire into the HIC harness for the 912iS. Im looking through the manual from Rotax as well as the page provided by Kitfox. I see only colors suggested. Very few AWG size references in the manual and none that I see for all HIC connectors. If you look back a couple posts where the pic of the HIC wiring is provided you will see all the information that is provided. Nothing on wire gauge.
    Eddie

  10. #270
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    Default Re: EFWD Build

    this what you mean??

    r
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    Ross
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    Sold to Richard and Scott Taubman in OZ, 2019. Kitfox SS7,Rotax 912is Sport, Airmaster CSP 75" blades.
    Landcruiser and Cub off road camper (doesn't get any kudos on this forum!)

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