Re: Short detector

The way I understand it I think that the NCE power cab had something like this. I don't know anything about making one.

I'm with Ernest, is there a spell checker on this site?

-Ethan

Short Protection

The DCC system will shut itself down when it senses a short. You can also install electronic circuit breakers that will shut down smaller sections of your layout when there is a short. One such circuit board is available here: http://www.dccspecialties.com/

I think the light bulb technique was in an article in Model Railroader about a year ago or so.

The only catch is, if your wiring is not very good, and a short occurs very far away from power feeders to the rails, it's possible for there to not be enough current for the system to actually detect it as a short. In discussions like this, you will often hear of "the quarter test". Take a coin or small metal object and place it on the rails to deliberately short it out to test the circuit protection. Especially do this in places that are far away from the command station or power feeders. If the quarter test does not shut down the system, that area is not getting enough power to the rails.

light bulb

The light bulb is the brake light bulb for an automobile, no, 1156 as I remember.  Place it in series with the track feeder.  Works good--I've energized several on Master Fugate's layout.

"Quarter test" should be done as an "undetected" short can put a lot of energy where one doesn't want it and can cause a lot of damage, including the possibility of a fire although melted insulation requiring wire replacement is a lot more likely.  It's a simple test to insure voltage drops are not excessive in a blockand the trains run right.  Don't use a small piece of wire as it can get quite hot and burn fingers. 

Terry Roberts

Model Trains Video

The parent company of MRH, Model Trains Video, has Volume 3 of Joe's series that shows how to wire up the light bulb for short management.  The video is  model-trains-video.com/volume3.php

 You can check it out also in

You can check it out also in the MRH theatre presentation by Joe "DCC the good, the bad, and the ugly" (although I'm also a fan of Joe's DVDs - there's a lot of good info in them:

http://model-railroad-hobbyist.com/mrht_dcc-good-bad-ugly

- murf

More info at Wiring for DCC

Here's still more info on 1156 bulbs (and a great site in general):

Allan Gartner's " Wiringfordcc.com "

http://www.wiringfordcc.com/track.htm#a6

If you scroll down a ways, there are installation ideas.

info

Joe's video is great and is on sale for $14.95

Also, check out the free MRH Theatre for DCC the Good the bad the ugly, where Joe explains short management.

Thanks all

I watched the video, the good, bad and ugly DCC. It was very helpful. Where does all of these clinics take place? It seems I need to go next time.

Thanks

Ernest

Ernest do you mean something like this?

 Ernest,

Not sure if you have seen my version of a Short Management Device (SMD), that I am using on our HO layout?  But if this is it let me know, or if enough interest is shown I actually make a video or blog entry of how I went about building it.

Anyhow here are the two videos that contain my SMD.

Cheers,

Jas...

Clinics

You will find clinics at most bigger model railroad shows and at NMRA division meets, etc.

We were all new at this at one time.  I'm still new at it and I've been involved for awhile.  Things keep changing, I keep learning, seems like I'm always a noob in some way. [grin]

Regards,

Kevin

That's IT!!!

That is just what I was looking for. Great Videos. Thanks a ton.... or is it kilo??  lol

One question, you have to break your track into block and have several Light boxes for detection right? How do you get those blocks and still run a loco non stop from one to another....know what I mean?

Many many thanks,

Ernest

thanks Kevin

I am so lucky I stumbled onto this site, I can't tell you how many dumb questions I have posted and no one has yelled at me yet...... I have found this site to be the most helpful in many departments. Now if they only had spell checker I could look a little smarter.....

Many Thanks,

Ernest

Spelling & Dumb Questions...

Hi Ernest,

An editor window spell checker is coming I believe.  In the interim, the editor does have a spell checker of sorts.  If you look at the bottom of the field where you type your post you will see, "Switch to plain text editor".  If you click this, you will see your message in plain text.  Spelling errors are underlined in red.

Note you will also see some of the text formatting tags identified as mis-spelled words, just ignore them.

Once you are through tyoing your post, click to change to plain text to check spelling.  Once you are happy click save to post your message.

As for dumb questions, there are no dumb questions, just dumb responses sometimes...like getting yelled at for asking! )

Regards,

Kevin

Effect of lightbulb on decoder.

The taillight bulb short circuit protection certainly has the appeal of simplicity.  But it's not perfect.  Consider what happens when you run a loco across a gap into a short, say at the frog of a turnout set against you.  The light comes on.  The decoder doesn't have full power, nor is it off.  It's got some percentage of full track voltage, since it's now in series with the bulb.  Exactly how much depends on the bulb, the internal resistance of the motor, and whatever else is in the loco.  This is not a happy place for a microprocessor to be, especially one which is at liberty to interpret some signals it may think it sees on the track in this weird intermediate power state as commands to change some CVs, etc.  Some decoders handle this well, others don't.  If you have trouble with decoders getting themselves into weird states and needing reprogramming, and you have used the taillight bulb approach, you may want to consider ripping out the taillights and putting in electronic ciruit breakers.

Note that you can also have a similar problem with an electronic breaker and a short that's not really solid, if you have the breaker configured to automatically try to reset itself periodically.  On a friends large layout we had frequent decoder problems until taillights were removed and all the breakers were reconfigured to stay off once tripped until you poke a reset button.

Ken.

Decoder brand?

Ken,

Do you happen to know the brand names of the decoders that were having issues with the tail light bulbs.

Your just a little off track

Your just a little off track so to speak. Without the light bulb circuit and you get a short your Decoder get the whole 5+ amps all at once and the results is Smoke and your out $20.00-$130.00 as your decoder has now burned out.

The Idea of the 12 volt light bulb is when you get a short the light bulb sees the increase in voltage and absorbs 80% of the Amps. Then at the same time you have your engine short you normally turn the power off at that shorted point on your tracks. It's like a safety valve on a steam engine and rather then Blowing the Boiler it blows the Valve.

Hopefully Joe will see this question and send you to the more technical answer.

Dan

Rerail

When a short accures and the bulb goes on, depending on the bulb size it apsorbes amps? or Volts? Also, if I run the bulbs like in the diagram I saw, with track breaks how does the loco run over those and stay running, or is it such a short "skip" that it does not bother it???

Thanks for all the replies.... it helps.

Ernest

Look at these... includes video

Try these threads from Joe's other sites.. the 1st has sample video from the DVD on 1156 short management.  If you like the segment wait til you buy the whole series!!!!

http://model-trains-video.com/e107_plugins/forum/forum_viewtopic.php?25 

Re: Decoder brand?

Kevin,  As I recall there were a couple brands that had trouble.  I think one of them was the older TCS decoders (I believe the newer ones didn't have the problem).  And I'm not confident enough that I remember the other one for sure so I don't want to name names and possibly be wrong.

Your just a little off track - right back at ya

It's not quite that simple.  Let's stick with the frog case - the short circuit current flows up from the frog, through the pickups on that side of let's call it the front truck on the loco, up into the loco wiring, back down through the SAME side of the rear truck, and into the rail.  So, what does the juice have to go through to get from point A to point B?  If the pickups from the trucks are wired together inside the loco, and the decoder is one of the generic ones with actual wires coming off it that you hook up to things, then the short current never gets to the decoder.

If on the other hand you've got one of the special decoders that replaces the light board in the loco it probably has bus traces down the length of it, one on each side to connect the pickups from the front truck to the pickups on the rear truck.  The electronics in the decoder never sees the short circuit current, but these traces do.

With the taillight bulb, you get a constant couple amps running through those traces.  They may get warm, but they'll be OK.  The electronics don't see any of it.  The fluctuating voltage powering the electronics may cause trouble though.

With an electronic breaker and good wiring, there will be a VERY brief high current spike, the breaker will trip, and nothing will get damaged or even warm.  And I'm not just spouting theory here, I have run my O scale SW8 & MP15 with HO decoders (older soundtraxx, zimo MX64) on my layout with an NCE 10 amp booster.  I have never fried a decoder.  The key is good solid wiring, so that when you get a short you DO get a real high current spike which kicks out the breaker.  With poor wiring there can be enough resistance when combined with a not-quite-perfect contact short to stay just under the trip threshold of the breaker but still pass enough current to fry stuff.

To go off on a minor tangent, if you have two locos with metal chassis connected to one side of the pickups, and you have just installed metal KD couplers nicely lubbed up with KD greasem, and you happen to couple them up such that the chassis connected pickups are on opposite sides, the greasem lubed coupler springs will make a bright bluish white glow while the short current runs through them.  I don't know exactly how much current that was, but it wasn't 10 amps because the breaker didn't trip.

Anyway, the point is with a good electronic breaker with a reasonably fast trip time and good solid wiring, you stand a much better chance of not damaging or confusing anything than you do with a taillight bulb.

Ken.

Ken Rice watch this Video so you will understand

Click on the following URL

http://model-trains-video.com/assets/video/shortMgmt2_bbhi.swf

Tail light bulb $.69   Electronic Breaker $4.99  purpose Watch Video or to put it another way, one Video is worth 10,000 arguments.

Dan

It's true, light bulbs are slower

It's true - when there's a short it takes the light bulb about half a second to completely kick in.

This means on a 5 amp short, there will be a spike to 5 amps and then over half a second the current will drop to the 2.1 amps the light bulb lets flow.

Also, with a cicuit breaker, the current flow stops completely, so when power is restored you will get a huge current inrush on all your sound locos, which may cause your DCC system to decide there's another short and shut down again. You don't get that problem with the bulbs.

So it's true an electronic circuit breaker will be faster, but I've never had trouble with modern decoders and the light bulbs, and the bulbs neatly solve the sound loco current-inrush problem.

There's also the question of which is cheaper? Replace a few older decoders or replace all the inexpensive light bulbs with pricey circuit breakers on your entire layout?

Only you can decide.

I understand

Submitted by

on Sat, 2011-04-02 07:53.

Oh I understand all right.  It's a tradeoff.  Tail light bulbs are cheaper, but are not as good as electronic breakers.  Depending on the nature of the shorts you tend to get on your layout, the kind of decoders you have, etc. they may or may not be good enough.  I have a relatively small layout so the choice was easy for me.  Your millage may vary.

Ken.

Yes a trade off, as I have 45

Yes a trade off, as I have 45 light bulb circuits and My Decoder are all Tsunami Sound Decoders at $119.00-$125.00 each. So far I haven't had a short on my railroad.

If their is a major problem My Lenz DCC system has an internal circuit breaker.

Until I read Joe Fugates article on the light bulb safety circuits I just had a single circuit breaker which I paid $4.99 for. Had I decided to put these breakers on my whole RR it would have cost me about $225.00. The 1156 bulbs cost $4.49 for a box of 10 on sale and I bought 6 boxes so I'd have some extras for expansion, the $26.00 was the winning way.

I also looked at the fact that in close to 50 years of Model Railroading I have only Had 1 motor smoke on me caused by a frozen tender drive shaft and the engine was out of view behind a mountain. I could hear the Buzzing and it didn't register until I saw smoke rising above the mountain. Lucky for me it was a brass engine so no plastic to melt and it only required a new motor and drive shaft.

In the past 3 years of DCC use, I have not yet had a short on my current RR. It has 45 blocks

Except when I was testing the track and bulbs by placing a coin on the track to see that each bulb was doing what it was designed to do no bulb has ever lit up. Knock on Wood!!!

Ken yes if you have a smaller RR with just a few few blocks then the circuit breakers wouldn't put the cost up too high but considering I don't have electrical problems then I myself would use the bulbs as the only extra circuit safety feature on any RR I build.

I'm one of those people that checks the electrical system to death simply because I don't want problems. I hate building things twice do to my error so I'm a stickler for trouble shooting the system before I put an engine on the tracks. Cheers and Good Railroading to you and may you never smell Ozone on your layout.

Dan