Shorting on points.

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Tiddles
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Shorting on points.

Postby Tiddles » Tue Feb 06, 2018 4:25 pm

Why am I get a short here when a loco goes over it?

It is a insulated frog points. The fault is not with the point as I replaced it but got the same problem.
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Forfarian
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Re: Shorting on points.

Postby Forfarian » Tue Feb 06, 2018 5:41 pm

Hi Tiddles
Looking at your photo, I would suggest that your loco wheels are making contact with the track on the branch and both are positive (red wire supply)
It may be the width of your loco wheels or the insulated frog looks very small, which is allowing the short between the two positive tracks
Tim
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Bigmet
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Re: Shorting on points.

Postby Bigmet » Tue Feb 06, 2018 5:46 pm

Why? Because a metal tyre can bridge the two metal rails at the crossing. (Not just locos, any metal tyred wheel can do it.)

This design of point is basically incompatible with DCC in my opinion. It's a dated design that reflects the relatively high tolerance of DC systems for momentary shorts: there's typically a fair amount of resistance in series - and more of it the slower the loco is going when the duration of the short is thereby potentially more extended - and that limits the current. Not so with DCC where the short circuit current draw will be what the system supplies before the automatic trip is activated. Operate for some time and you will begin to see spark erosion of the metal.

One way around this is to rewire the point completely as a live crossing, with switching as the point moves. But really the thing to do is go all live crossing ('electrofrog' in Pecospeak).

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Dave
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Re: Shorting on points.

Postby Dave » Tue Feb 06, 2018 6:38 pm

Tiddles wrote:Why am I get a short here when a loco goes over it?


Are those metal rail joiners in the green circle :?:

Short.jpg


If so, look at the feeds that are just along the line Red & Blue, they meet at the frog... and that is the cause of your problem

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Bufferstop
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Re: Shorting on points.

Postby Bufferstop » Tue Feb 06, 2018 7:45 pm

That's the explanation, but what's to do about it? Treating it as an electrofrog point is probably the best bet. While you are considering your options, cut a piece of thin document tape (it's less messy than ordinary tape) and stick it over the frog, rub it down well over the edges and trim away any surplus. It will work for a while then wear away to remind you that you need a permanent solution.
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Mountain
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Re: Shorting on points.

Postby Mountain » Tue Feb 06, 2018 7:55 pm

Could the rail ends be slightly ground down and then filled with an insulating material to bring it back to rail height?

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Bufferstop
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Re: Shorting on points.

Postby Bufferstop » Tue Feb 06, 2018 8:29 pm

It could be done with a rotary tool and slitting disk, and a steady hand. Wouldn't need too much depth, but if you use something like plastic padding it would pay to fill in-between the two rails as well to give it something to key into.
It's a case of good intentions coming back to bite you. The original design had a larger plastic bit, but they reduced it to a minimum to help avoid stalling. Nobody was thinking about DCC at that time.
I've performed the reverse operation to grind out the plastic and slide in two new V rails to produce an electrofrog settrack point.
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RFS
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Re: Shorting on points.

Postby RFS » Tue Feb 06, 2018 9:11 pm

As these are Insulfrog points, the simple solution is to replace the metal rail joiners circled in green with insulated ones.

Brian Lambert has all the details on his website here

http://www.brian-lambert.co.uk/DCC.html#A
Robert Smith

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Tiddles
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Re: Shorting on points.

Postby Tiddles » Tue Feb 06, 2018 9:12 pm

If fit insulated fishplates would that solve the problem or would it give me a dead section of rail?
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RFS
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Re: Shorting on points.

Postby RFS » Tue Feb 06, 2018 9:48 pm

Tiddles wrote:If fit insulated fishplates would that solve the problem or would it give me a dead section of rail?


No, just follow Brian's diagram which involves adding a track feed downstream of the IRJ.
Robert Smith

MickleoverTestTrack
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Re: Shorting on points.

Postby MickleoverTestTrack » Wed Feb 07, 2018 12:37 am

Tiddles wrote:If fit insulated fishplates would that solve the problem or would it give me a dead section of rail?


Fitting insulated joiners (IRJs) at the V will mean that the current has to transfer from the stock rail through the blades of the point, so the rail up to the IRJ will only be live when the point is switched in that direction and the other rail of the V will be dead.

That does solve the shorting problem, however in the long term you can get problems if the contact area between the stock rail and the blade of the point becomes dirty.
As supplied, electrofrog points suffer in the exact same way and the solution - using a switch to change the polarity of the frog using a feed from the bus wires - is exactly the same, just that the way to do it is very slightly harder.

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Re: Shorting on points.

Postby Dad-1 » Wed Feb 07, 2018 8:01 pm

All the answers are given already - that's the trouble of not looking in so often
others have already done the work.

Wide tyres on the wheels bridges the small gap at the 'V'. Something often experienced
when reversing long trains where each wagon is trying to jack-knife forcing wheels to
the limit of sideways movement.

The true fix is IRJ's at both rails running off the 'V'. Poor contact between stock & switch
rail will sometimes cause a stall, but not a short. Using bonded rails, switched frogs and
IRJ's ideal

There is a tendency for Peco Streamline points to be more of a problem than Hornby due
to the gap between rails at the plastic frog of Hornby points being something like twice
as wide. Perhaps to accommodate wider tyres often found on Hornby locomotives.

Geoff T.
Remember ... I know nothing about railways.
viewtopic.php?f=22&t=32187 and Another on viewtopic.php?f=22&t=28436&start=60&st=0&sk=t&sd=a

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Bufferstop
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Re: Shorting on points.

Postby Bufferstop » Wed Feb 07, 2018 11:38 pm

You're spot on Geoff, it's Hornby loco wheels from the latter part of the Triang Hornby era through to Hornby shifting production to China. They are just wide enough that with everything conspiring to push the wheels laterally toward the frog they overlap onto the other rail. It might be worth checking B to B isn't too wide. It will be a particular problem if the point has been fitted with DCC continuity clips. As you say fitting IRJs, I'd go further and treat it as an electrofrog point. If it's not easy to lift for the IRJs attack it with the Dremel and glue in some plastic shims between the cut ends.
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Mike Parkes
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Re: Shorting on points.

Postby Mike Parkes » Thu Feb 08, 2018 6:29 pm

I have exactly the same problem with a Hornby T9 so its not just " loco wheels from the latter part of the Triang Hornby era through to Hornby shifting production to China". I originally resolved by wiring the point up as if it had a live frog but to resolve issues of locos stalling on the crossover formed by a pair of dead frog points have now replaced them with live frog points.

RFS
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Re: Shorting on points.

Postby RFS » Thu Feb 08, 2018 9:30 pm

Mike Parkes wrote:I have exactly the same problem with a Hornby T9 so its not just " loco wheels from the latter part of the Triang Hornby era through to Hornby shifting production to China". I originally resolved by wiring the point up as if it had a live frog but to resolve issues of locos stalling on the crossover formed by a pair of dead frog points have now replaced them with live frog points.


I agree. I started out with code 75 points, using Electrofrog but with a couple of Insulfrog diamond crossings. Just about everything would short on the diamond crossings if driven over slowly - T9, 9F etc. Had to replace with Electrofrog versions.

I also had problems with code 75 Electroflog slips with a couple of Hornby locos of early China manufacture where the back-to-back was to the then standard of 14.2mm instead of the now current 14.5mm. Kept shorting on the two closure rails adjacent to the frog tip as the insulation bit is very close indeed. Needed the offending locos to have their B2B corrected.
Robert Smith


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