Cheap and easy short protection for your DCC layout

n2BNSF Jul 18, 2017

  1. n2BNSF

    n2BNSF TrainBoard Member

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    Before you spend $$$ on circuit breakers and extra high-tech equipment, here is a very easy and inexpensive way of managing short circuits on your DCC equipped layout that protects your locomotives and your DCC system as well as confines shorts to one district without shutting down your entire layout. I have been using this method for 15 years and it has worked great. Check it out and give it a try.

     
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  2. Greg Elmassian

    Greg Elmassian TrainBoard Member

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    No offense, but people have been using auto bulbs since I can remember, which is the early 60's.

    It's slow, uncontrolled, and also can affect power to the locos resulting in inconsistent operations.

    It also limits the current but does not turn off power.

    I run G scale with many amps of current, so any light bulb that can lower the short to a manageable level (still not zero) adds significant resistance and loss to my trains. Not a solution there.

    I also run Z scale, and again, this solution does not work well, even a "little" short can damage the small gauge wire and pickups in Z scale.

    Yes, it's better than nothing, but there are more sophisticated means around to protect your expensive gear. I'd suggest fuses instead, or electronic breakers.

    I understand it is cheap, I get it, but it's not much protection. I'm sure you will be upset with this post, but this does NOT take the place of a system that completely interrupts the power, and I feel that people seeing this might believe that it is the same as a real circuit breaker.

    Also, I suggest you indicate how to size the bulb to the current draw, the draw of the bulb affects the short circuit current, and different scales can use different bulbs to at least limit the short circuit current. An amp meter from Harbor Freight is $5 so people could measure the current and size the bulbs themselves.

    I have found that the DCC circuit breakers, especially the one from DCC specialities are way cheaper than one loco, and a solid investment, even for multiple power districts.

    Greg
    www.elmassian.com

    let the flames begin!
     
  3. Hardcoaler

    Hardcoaler TrainBoard Member

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    Thank you for an interesting post Greg; I learned a lot reading it. Yes, this option has been around a while. I employed an automotive lamp for protection on an SCR throttle I built in the mid-70s.
     
  4. Greg Elmassian

    Greg Elmassian TrainBoard Member

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    There's actually some even finer points to doing this on DCC...

    Many people have marginal DCC signal, due to the way the rails are laid out, multiple feed points, etc, all of this can degrade the DCC signal.

    Now DCC is designed to be robust and decode a poor signal, especially in the last 5-7 years, but still signal integrity is important.

    The people at NCE are very smart guys, and the reliability and modularity and well, just their market acceptance tells you they know what they are doing.

    There's an important difference between the bulbs NCE uses, and the author's substitution, the NCE uses bulbs with a long straight filament, whereas car brake and stoplights use a coiled filament. Coils add an element called "inductance" to a circuit, and putting a coil in series with your DCC feed can actually harm the DCC signal.

    (too much inductance would "round off" the desired square wave of the DCC signal)

    In what cases will this affect the signal? How much? That would have to be measured, but prudence would indicate to not add any if possible unless the exact effect is known. Perhaps on some layouts with marginal DCC signal, this could be enough to cause an issue. Perhaps no effect.

    So I would recommend that if you really want to use a light bulb, and fully understand the limitations of this methodology, that you follow NCE's lead and at least use the same type of non-inductive bulb/filament. They are smart guys, even though the reasons behind which bulb might not be obvious or stated in their literature.

    Regards,

    Greg
     
  5. n2BNSF

    n2BNSF TrainBoard Member

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    Greg, I appreciate your opinion, and I would not suggest this or any other technique I demonstrate is the only war or is for everyone. I confess I have no G scale experience. What I do know is what has worked for me and others. I have used this technique on my N scale layouts under regular use for over 15 years and I have yet to experience a problem with DCC signal or cause damage to a single locomotive or my DCC system--the same one I have use for all of those 15 years. I learned about it initially from Joe Fugate who uses this method on his large HO layout with full success as well. I am aware of the theoretical problems with signal drop off, but I have yet to see this problem in practice on a layout. I am not saying it has never happened. I am saying that of all the people I know who have tried this method it worked efficiently.
     
  6. Greg Elmassian

    Greg Elmassian TrainBoard Member

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    Definitely do not want to start a war. I do wish to warn others of the information that (in my opinion) you left out: Your video suggests this is an alternative to a real system that interrupts the current flow.

    While it can provide protection, it needs to be clear that current still flows through the short circuit when the bulb lights. Since this is a 26.9 (lets call it 27) watt bulb at 12.8 volts then at through a dead short, you are passing 27/13 amps, or OVER 2 amps. So if you have a short circuit, up to 2 amps can still be going through the short.

    In small scales, this has melted plastic centered wheels, melted soldered connections, etc. It depends what the short is going through.

    I'm going to guess that you don't leave short circuits going very long. But for many people, they need to know that damage can still occur and there are many documented cases of damage.

    I believe you have had no issues, but it should be clear that a large amount of current STILL flows when the bulb is on. I run G scale and here is 10 amp damage:
    [​IMG]

    Yep, heated the trace, the short was through the wheels derailed in a switch.

    In HO, maybe many locos can handle a dead short through the wheels and pickups.

    In N scale, a lot more iffy.

    And in Z scale, the other scale I model, you have melted lumps of plastic.

    So all I want to convey is the "light bulb" method is NOT the same protection as a real device that interrupts the current in case of a short, this just limits the short circuit current to about 2 amps.

    You get what you pay for.

    Greg
     
  7. n2BNSF

    n2BNSF TrainBoard Member

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    I am not a warring guy, just having a healthy discussion. I said in the video that the bulb limits the currend, does not break it. As I said in the other forum, I have never seen a case of damage when an 1156 bulb is used with a modern DCC system in HO and N scale. Because something is theoretically possible does not necessarily make it a practical probability.

    Sent from my SM-G900V using Tapatalk
     
  8. Greg Elmassian

    Greg Elmassian TrainBoard Member

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    I've seen it, and 2 amps is a probability to me! So, you have had a good experience, I have seen melted locos.

    The warning has been issued, and all is calm, thanks for not taking it as a personal affront, it is appreciated.

    Now back to your regularly scheduled program...

    Greg
     
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  9. n2BNSF

    n2BNSF TrainBoard Member

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    Absolutely. I take being attacked personally, but I don't take a difference of opinion or a discussion about the merits of a technique as an attack. Some people are very thin skinned, but I am not. Thanks for contributing to a valuable discussion.

    Sent from my SM-G900V using Tapatalk
     

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