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Suffolk Rob

Question on Peco code 55 n gauge points

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Firstly an apology as I may use the wrong terminology.

 

I have a small DCC layout and use a standard powercab. The layout consists of a point to 2 sidings with a kick- back from one of them. Essentially think exactly the same track plan as Neil's Shell Island.

 

The points are peco N code 55 elecrofrog and are used as supplied. Layout worked absolutely fine using seep motors with polarity switch for some time.Standard Gaugemaster accessory decoders were used.Due to small size of layout track and point motors fed from same Bus. Due to inconsistency with switching I disconnected the wires to frogs from point motor and fitted a Tam valley duel frog juicer. Worked fine for a couple of days then smoke emitted from both points within a couple of hours of each other where blades touch the outside running rails. Point motors and frog juicer continue to work but heat has disfigured tie bar rendering the points inoperable. Dug up and replaced one of the points and shortly afterwards, the same thing happened again.

 

As I understand it, a frog juicer recognises a short and switches polarity before running is affected (but the short still occurs if only momentarily) and the only explanation I can come up with is the short generated enough heat, possibly with help from a bit of stray static grass between blade and rail to disfigure the plastic in the tie bar and this occurs because in a code 55 electrofrog point, frog and switch blades are not isolated from each other. Never had this problem on DC but assume that' the heat is due to the different current/ voltage (or whatever) when now using DCC?

 

I've now ripped up all track to re-lay and wanted a bit of advice to avoid the same problem reoccurring.  I think I have the following options but wanted to check I've reached the correct conclusions.

 

Firstly, for one of the points I am now using a unifrog point. From what I can see the frog on these is entirely separate to the blades which are bonded to the running rails- as such the short where blades touch running rails cannot occur- do I have this right?

 

For reasons of space I cannot use a unifrog for the other point. I need to use a y point which is not available as unifrog. I think I have two options. I could, as read on other threads, cut the rails between frog and blades and solder a wire to bond blades to outside rails- frankly beyond my soldering capability. I think this only leaves me with option 2. revert to switching polarity using the seep motor which makes the changing of polarity mechanical rather than electronic and avoids the problem caused by the juicer needing a short to occur before it reacts?

 

I should also add that all rails leading from both frogs had isolating rail joiners fitted but would be grateful if anyone better informed than me could confirm my thinking and possible solutions.

 

Thanks

Rob

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The damage suggests a lot of current flowing, but not enough to cause things to shutdown.  

 

Question-1, what current are the Frog Juicers set to switch at ?  If its not set the lowest position (2Amps), that is part of the problem. 

 

 

A possible explanation is the blades were a tiny bit dirty at the contact point, creating a local resistance.  Enough to let say 0.5A to 1.5A flow, but not quite full contact to trip the "juicer" to switch.  That creates a local hot-spot (1A at 13volts nominal DCC output = 13Watts, or very small soldering iron!).  
But its only a possibility, not a certain explanation.   

 

 

Yes, the Unifrog ought to be better wired for this purpose, you don't ever get the blades and frog fighting each other.  Switching with the Unifrog+Juicer occurs via the pickups in a loco - as the driving wheels touch the frog, there is a path via the pickups between frog and fixed rails.  

 

In contrast, switching for the (unmodified) Electrofrog+Juicer ought to happen as blades close, but the high current melting at the tie-bar says this didn't happen, and instead there was resistance and heat.    

 

Can you stop this happening again with another Electrofrog and a Frog-Juicer ?  The answer is "no" if its a "dirty contact" failure due to high resistance, but not enough to trip the Juicer.    Other forms of switch are less likely to be "wrong" assuming the point motor movement is reliable.    Just using the points as Peco intended (ie. no external switching of frog) avoids the risk completely, but with the risk of poor blade-rail contact failure. 

 

 

 

- Nigel 

 

 

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Thank you Nigel.

 

I'm sure the juicer is only set to 2 amps looking at the instructions. If I'm intending to only use on 1 point I may well switch to a mono juicer I also have which I believe only has the 2 amp option.

 

Assuming I'm ballasting and painting rail sides then I think I'm pushing my luck on relying just on blade contact but also, if I understand correctly, using a unifrog means any dirt related issue leading to resistance can only occur at the frog. As this is a bigger, non moving part I assume this would not be terminal for the point but would it be damaging to the loco? I also assume I can mitigate by ensuring I clean the top of the frog before any and all running sessions

 

As I understand, what you are saying is that, if I rely on a mechanical switch for the electrofrog, I need to be sure the throw of the seep is clear enough to switch polarity and also that there is a paint free area where blade contacts rail as well as a further safeguard and only if I have an instance of inadequate throw of the point motor (as in switches point but not the polarity) and dirt related resistance should I have a repeat? I'm pretty sure part of my problem was caused by not understanding this last point thinking that the frog switching took care of this. Probably should have paid more attention in Physics!

 

Thank you again, I'm quickly learning that there is a lot more to this DCC malarkey than plugging in 2 wires! 

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Rob,

 

the Unifrog won't have issues with paint/ballast, apart from anything on the rail tops stopping the wheels picking up.  Juicer won't be a problem here.   All that might happen with too much paint is the train doesn't run (no pickup), there is no short circuit path, and no risk to the track.     ( You may see short circuits from using PVA as ballast glue;  its an acid, and conducts electricity.   Usually this goes away when it has fully dried.   ).  

 

Pickup problem usually occurs on top and inside corner of rails, which is a radius - use the ribbed side of a small bit of hardboard to clean track, its usually better than track rubbers.  A bit of solvent on the hardboard may help.  There are pages of internet stuff on "which solvent", so I'll skip that !   

 

 

 

If my theory on the tie-bar of the electrofrog is correct, then paint/ballast around the blades increases the risks.  Therefore I wouldn't use a Juicer on that combination because of the problem you saw.   A switch associated with the motor movement will be fine; that can be the switch on the Seep, or if that proves un-reliable there are lots of ways of attaching a micro-switch to turnout tie bar movement.  Small microswitches are very reliable if used correctly.   If the tiebar and electrical switch are in the same orientation, there cannot be a melting incident from poor contact of the blade.   If there is poor contact, the switch by-passes that contact, and if there is good contact, the switch is good.  

What must happen with any switch mechanism is either:  

a - single pole change over switch, must switch whilst blade is "mid-travel" (ie. not touching either rail). 

b - two on/off switches, must disconnect, have a "neither connected phase", then connect the second.  This must not contradict the blade positions.   

 

 

 

 

Nigel

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Thank you for explaining it all Nigel, I think I've got both cause and solution clear in my mind now thanks to you.

 

Cheers

 

Rob

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What's the current rating of the command station?  Have you done the "coin test" on all track sections?  

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