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Thread: Am I calculating the resistance correctly? DR4088LN-CS with Push Button

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    Default Am I calculating the resistance correctly? DR4088LN-CS with Push Button

    There are a few different versions of the DR4088LN LocoNet Feedback Device, some which are designed to work with push buttons directly, but not the Current Sensing (CS) version. But the CS version can be used for block detection as it will detect the current draw of a locomotive on the block.

    But just because I like to make things complicated, I would like to use both block detection and push buttons with the same feedback device, the current sensing unit.

    So, I looked around online and did some math and I am hoping that someone can check my madness.

    Here is a link to a screenshot of the manual with the min/max current that will trigger the DR4088LN-CS. Based on this information, I took 2mA and 15v and using Ohm's Law came up with a resistance of 7500 Ohms.

    So, if I am thinking correctly, if I put a 7.5kOhm resister inline with the push button, I should get a 2mA current draw which will trigger the feedback device, but not set off the circuit breaker. Is this correct?

    My assumption, based on my science class from many decades ago, is that the resister works by dissipating the heat. Would this mean that if I kept the button depressed that the resister would eventually overheat and trip the breaker? Any idea how long it would take for this to occur? I am thinking about using this or similar resisters.

    Am I barking up the right tree, or am I heading to the river?

    Thanks
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    The math is correct. 15/.002 = 7500. I'm not familiar with the device you're referring to, so I can't speak to the triggering threshold.

    As for wattage, 15 volts x 2 mA = 30 milliwatts. There's practically no discernable heat dissipation by human feel there. Using a 1/4-watt rated resistor puts you well inside any chance of the resistor failing.

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    Thanks Paul. I am going to give it a try and see what happens. Thanks
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    Quote Originally Posted by Heath N Scale View Post
    Thanks Paul. I am going to give it a try and see what happens. Thanks
    Here's hoping there's no magic smoke!

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    Quote Originally Posted by Paul Schmidt View Post
    Here's hoping there's no magic smoke!
    I double checked the manual, and it does not say that smoke is included with this device, so I should be all good!!
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    It's not too well known a fact, but electronics do run on smoke. When it comes out, they cease to work

    I double-checked the manual, at what you are planning should work. I'd go for a slightly lower resistor value (like 4700Ohm, which is 4.7kOhm) to be on the safe side. Gives you about 3mA @ 15V which is 45mW, still negligible.

    Hope this helps,
    Heiko

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    So I finally got this all wired up and it did not work. I made a video of the process, thinking that I was going to post it as a how to video, but instead I am the one that needs help.

    If there is someone that is good with DCC or electronics I would appreciate if you can watch the video and tell me what I did wrong.
    https://youtu.be/-gOvJR_Vqf4

    Thanks
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