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Theoretical Question on Powering Frogs

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Theoretical Question on Powering Frogs
Posted by PennsyLou on Friday, September 30, 2022 11:27 AM

Theoretical question on the following scenario:

DCC Controlled layout, small industrial yard with powered-frog turnouts (specifically Tillig Elite 83), the yard will only have a single small industrial switcher (not multiple locomotives).

Is it possible to (1) electrically isolate the frogs (i.e. with insulating joiners), then supply ALL of the frogs (in parallel) through a single auto-reversing circuit (say a Digitrax AR-1), to effect the switching of the frog polarity?  Since the frog is a single rail switched either + or -, only a single output from the AR-1 is used.

My reasoning is that if a "wrong powered" frog (i.e. short) is detected, the AR-1 will toggle the power to all the frogs.  When the loco approaches the frog of the next switch, there is a 50/50 chance that it is the "right" polarity, and if it is not, the reverser will switch it.

Of course all the frogs still need to be wired, but only the single AR-1 is required vs. a polarity switch for each frog.

I am not an electrical engineer so apologies if this is a completely lame brained idea!

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Posted by AEP528 on Friday, September 30, 2022 12:06 PM

PennsyLou

Theoretical question on the following scenario:

DCC Controlled layout, small industrial yard with powered-frog turnouts (specifically Tillig Elite 83), the yard will only have a single small industrial switcher (not multiple locomotives).

Is it possible to (1) electrically isolate the frogs (i.e. with insulating joiners), then supply ALL of the frogs (in parallel) through a single auto-reversing circuit (say a Digitrax AR-1), to effect the switching of the frog polarity?  Since the frog is a single rail switched either + or -, only a single output from the AR-1 is used.

My reasoning is that if a "wrong powered" frog (i.e. short) is detected, the AR-1 will toggle the power to all the frogs.  When the loco approaches the frog of the next switch, there is a 50/50 chance that it is the "right" polarity, and if it is not, the reverser will switch it.

Of course all the frogs still need to be wired, but only the single AR-1 is required vs. a polarity switch for each frog.

I am not an electrical engineer so apologies if this is a completely lame brained idea!

 

 

Only if the locomotive could never touch two frogs at the same time that need to be opposite polarity. An example is a crossover, or any two turnouts near each other, where the two frogs are close together but on opposite rails. 

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Posted by fwright on Friday, September 30, 2022 12:17 PM

Your scenario works if and only if there is but one frog being shorted for wrong polarity at a given time.  In other words, rolling stock standing on any frog besides the one being approached could cause multiple short circuits simultaneously.  The standing stock has already flipped the polarity correctly, and now your moving stock wants to reverse it.

Your turnout frogs (all of them) must also be totally isolated so polarity of points does not change when frog polarity is changed without the turnout moving.

But the biggest problem is that the AR-1 does not throw the turnout, but simply reverses the frog polarity.  The most likely cause of the short circuit in the 1st place is approaching a turnout from the frog end that is thrown against the oncoming train.  The AR-1 changes the polarity of the frog, and the train shorts out again when it touches the closure/point rails.

On a small layout with a single train, having the frog polarity set correctly by throwing the points lets the circuit breaker shut the layout down if you try to run a turnout thrown against you.  Probably a desirable outcome.

On our club modular running multiple trains, shutting the whole layout down because somebody is running a turnout set against them is not a good thing.  So we require each module set to have it's own circuit breaker.  That way, only a few modules are shut down by a careless engineer.

Fred W

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Posted by gregc on Friday, September 30, 2022 12:26 PM

fwright
On a small layout with a single train, having the frog polarity set correctly by throwing the points lets the circuit breaker shut the layout down if you try to run a turnout thrown against you.  Probably a desirable outcome.

don't most auto-reverser act as a circuit breaker in this situation?

isn't it a commonly unavoidable problem running thru a mis-aligned turnout

greg - Philadelphia & Reading / Reading

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Posted by fwright on Saturday, October 1, 2022 9:01 PM

The autoreverser is essentially a very fast short circuit detector that attempts to end the short circuit by reversing polarity at the places it's wired to.

A misaligned turnout is the most common cause of a short circuit - in both DC and DCC.  The autoreverser does NOT fix the problem of trying to run a turnout thrown against you UNLESS the autoreverser has the capability to throw the turnout.  Even if the autoreverser could throw the turnout to "fix" the short circuit, the throw takes too long for the circuit breaker not to trip and shut off power in the power district (or zone controlled by the circuit breaker).

The only function of the autoreverser in this situation is to serve as the polarity control of the frog after the fact, instead of mounting a contact on the turnout throw (which acts in concert with the throw).

The autoreverser used to control the frog polarity does NOTHING to solve short circuits from running a turnout thrown against you.  Therefore, IMO, the frog juicer or autoreverser is a very expensive frog contact replacement.  The frog contact works with DC or DCC, the juicer or autoreverser only works with DCC.

Running misaligned turnouts is an operational problem for both prototype (remember Casey Jones) and model railroads.  The prototype uses dispatchers, rule books, and interlocking to try to solve the problem.  On model railroads, short circuits aren't nearly as deadly, and eventually most people learn to check the alignment of the turnout before arrival.

Fred W

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Posted by dehusman on Sunday, October 2, 2022 12:49 PM

Casey Jones' problems really had nothing to do with a misaligned switch, he was speeding, short flagged and collided with the train ahead of him.

Dave H. Painted side goes up. My website : wnbranch.com

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Posted by cv_acr on Monday, October 3, 2022 9:59 AM

fwright

A misaligned turnout is the most common cause of a short circuit - in both DC and DCC. 

Only if the turnout is a "selectively power-routing" turnout. If you have a turnout that's built to always have both routes normally powered, you won't short out until the engine derails after running the switch and the derailed truck ends up bridging the rails for a short. In many cases the derailment won't cause any short, and sometimes the engine is heavy enough to push through any "springiness" in either the points or throw mechanism.

fwright

The only function of the autoreverser in this situation is to serve as the polarity control of the frog after the fact, instead of mounting a contact on the turnout throw (which acts in concert with the throw).

You're assuming the turnout throw has contacts...

Frog "juicers" or auto-reversers work with manually thrown turnouts as well.

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Posted by cv_acr on Monday, October 3, 2022 10:02 AM

Also this is a more economical solution than a full auto-reverser like an AR-1 which is specifically designed for powering frogs:

https://www.tamvalleydepot.com/products/dccfrogjuicers.html

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Posted by fwright on Tuesday, October 4, 2022 8:33 AM

cv_acr
Only if the turnout is a "selectively power-routing" turnout. If you have a turnout that's built to always have both routes normally powered, you won't short out until the engine derails after running the switch and the derailed truck ends up bridging the rails for a short. In many cases the derailment won't cause any short, and sometimes the engine is heavy enough to push through any "springiness" in either the points or throw mechanism.

All turnouts with a powered frog require some method to reverse the polarity of the frog.  Selective routing has nothing to with it.  Neither does the point wiring - whether point power comes from adjacent stock rail (preferred nowadays) or from frog.

You're assuming the turnout throw has contacts...Frog "juicers" or auto-reversers work with manually thrown turnouts as well.

Agreed, when using DCC.  There have been many articles in MR throughout the years on making contacts for turnout throws that don't have them.  But we're back to the same issue - having an insulated frog with no need for contacts or frog juicers, or having a powered frog, which does need a method to change polarity of the frog.  DCC users seem to need powered frogs more than DC users because a temporary loss of power is more detrimental to DCC than DC.

Even though I'm DCC at the club, and primarily DC at home, I prefer powered frogs (club requries them on all modules) because of my small steam motive power (tank switchers) which often start out with electrical pickup challenges.  There are many inexpensive ways to mount a contact to a manual throw - micro switches, magnetic reed switches, even screw heads and pieces of brass.

Fred W

....modeling foggy coastal Oregon in HO and HOn3, where it's always 1900...

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