# Simple Power Pack Protection for Block Crossings



## toddalin (Jan 4, 2008)

*Power Pack Protection for Block Crossings
*There are some who worry that if they run two or more power packs (whether it be a common rail system or not), that if a train crosses a “block” between two of these packs and they are set for opposite directions at elevated voltage, this could cause an overvoltage/overcurrent situation through the engine’s wiring leading to an internal meltdown of the wires in the trucks. I’ve devised a technique to avoid this potential situation combining “old school technology” with my Tortoise Bump Accident Sentinel System (Bump A.S.S.) track-gap system that uses nothing more than some track insulators, relays, and a wall wart.
*Youse want protection? Guido and Rocky say it’s gonna cost you. OK, so let’s keep this under “an arm and a leg.”*
What we need are two insulators and two cheap, low amperage, spst, 12 -24 volt relays (times the number of blocks -1), one 12 volt, dpdt, (or 3pdt, or 4pdt), relay that can handle the load (10 amps would be fine because we only need carrying capacity and not switching capacity), and a wall wart to power this relay.
*So, how is this to be wired?*
For simplicity, we will use the “common rail” method. This has been explained at length and I won’t go into it here. However, this system can use, or not use a common rail, as it makes no difference except that you end up buying 50% more insulators and more wire for no additional protection if you don’t use a common rail. For ease of discussion, we’ll call the other rail the “live rail.”
We will sandwich a small section of rail between two AristoCraft/LGB insulators just long enough to fill this space (“gap”) in the insulators. This section is placed between the live rails where the two blocks come together. We’ll call the block the train is coming from/already on the “rear” block and the block the train is approaching the “forward” block. A wire soldered to this gap is connected to two 12 - 24 volt relays. The other leg of one relay is connected to the “rear” block and the other leg of the other relay is connected to the “forward” block’s live rails just beyond the gap. These relays set the maximum voltage that could _only momentarily_ make its way through the truck wiring. So if you use 24 volt relays, they typically trip at ~18 volts and no more than this could make its way through the trucks in the event of a potential melt down. (This has nothing to do with how many volts you can actually send to your train engines for speed.) So if one power pack is set for +9 volts and the other for -9 volts, the relay trips. Similarly, if one pack is set at +20 volts and the other is less than +2 volts, the relay sees this differential and trips. A resistor can be used in series with the relay coil to adjust its sensitivity to the incoming voltage to get the desired/acceptable span.
So as the engine proceeds from one block to the next, it first hits the “gap” and voltage is sent to both relays. Because the “rear” relay is at the same potential as the engine, it does not fire. If the potential to the “forward” relay exceeds our acceptable span, it will trigger, and when this relay does trip, 12 volts from the wall wart routes through this relay and back to the “10 amp relay” breaking the power from one (dpdt relay) or both (3pdt relay) power packs to all of their block switches. The other pole of the “10 amp” relay is used to make the relay “self-latch” when activated. Removing the power from the wall wart after clearing the polarity/voltage problem will allow the “10 amp relay” self-latch to reset and no harm no foul.
*So why do we need a “rear” view, if it is always the same as the “gap?”*
If we run the trains in the opposite direction, the “rear” and “forward” switch places, and this takes care of that eventuality.


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## toddalin (Jan 4, 2008)

*Addendum - The Common Rail Rules*

With some thought, it occurred to me that while this will work with a common rail, or not, it will work much better with the common rail and would be easier to implement.

Consider that if the "gap" (trigger rail) is 1" long and we use a common rail, the engine will trigger the relay as soon as it touches the gap. But if we don't use a common rail, the other side trucks must cross over to the "forward" block before the current can flow from pack-to-pack, then to the relay.

So the system cannot activate until the other axle crosses its gap and now instead of having 1" of gap to work with, you only have <1/2" of gap (because the first 1/2" didn't do anything because the other side had not yet crossed over).

Also consider that if you don't use a common rail, the insulator on the "other side rail" must fall at/near the center of the gap so that this current transfer can occur. So instead of cutting a ~1" section out of one rail to accommodate the gap, you now have to cut 1/2" off of each of the rails to center the gap with the insulator on the other side.

Also consider that with a common rail, any metal wheel that strikes the gap can activate the system (e.g., backing a train during switching maneuvers). But if you don't use a common rail, it must be an engine or lighted car that can span both blocks at the insulator on the other side.


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## kormsen (Oct 27, 2009)

not being an electricity expert, i think, i noted something about bump A.S.S.ing

1) it seems to me, that one can not use the common wire-rail for the switching operation circuit as well.
because any energy user, be it motor or interior lighting would short the bump A.S.S. circuit.


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## toddalin (Jan 4, 2008)

kormsen said:


> not being an electricity expert, i think, i noted something about bump A.S.S.ing
> 
> 1) it seems to me, that one can not use the common wire-rail for the switching operation circuit as well.
> because any energy user, be it motor or interior lighting would short the bump A.S.S. circuit.


Good feedback. You may or may not be correct.

When a "powered" axle "hits the gap," one would think that power can flow from the "approaching" live rail, through the relay, to the gap, then through the motor/light, to the common rail completing the circuit through this relay causing a trip.

But consider that at this same time one of the other axles is letting the power flow directly from the "approaching" live rail, through the motor/light, to the common rail without going through the relay. The relay has resistance and the current flow will take the path of least resistance which would be through the other powered axle rather than through the gap. 

If this were to prove to be a problem, it could be alleviated by using relays set at a slightly higher voltage than you intend to run the trains.

So if you used 24 volt relays (calibrated to ~24 volts with a resistor on the coil), and a power pack could not exceed say 22 volts, the only time you trigger a relay would be to have the two packs set at opposite polarities and you would never see more than 24 volts through the truck wiring.


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## kormsen (Oct 27, 2009)

your answer shows me, that i did not explain myself good enough.
and while making a drawing to show, what i meant, i saw, that the possible problems depend on the way one connects.

so, option one:
in the first pic, you see the bumpASS connected with one wire from pack to common, and from common to switch.
the other wire from pack to the short piece of rail, from there through the rail to the switch.

there i see one possible problem - depending of the polarity of the halfwave going through the bumpASS, there can be a short with the DC power in the rails for a quick moment, while a wheel bridges the gap.
the other question, that comes to mind: does not the part of the rail, that is in the pic below the arrow on the right side send its DC-power for the train as an continuous signal to the switch?












so, to me it seems, i would have to wire the bumpASS the other way round.

one wire from pack to common, from there to switch.
and the other wire from pack to the other rail and from the short piece of rail to the switch. (as shown in the second pic)

but, again depending of the polarities of the DC power and of the halfwave bumpASS-feeder - does not my "user" (lightbulb, motor, whatever) get then two different feedings of possible different polarity? (in the pic shown in the part above the arrow on the right)











do i have an error in my train of thoughts, or is it simply not possible to run the bumpASS over the common wire?


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## toddalin (Jan 4, 2008)

kormsen said:


> your answer shows me, that i did not explain myself good enough.
> and while making a drawing to show, what i meant, i saw, that the possible problems depend on the way one connects.
> 
> 
> do i have an error in my train of thoughts, or is it simply not possible to run the bumpASS over the common wire?


 

Thanks Korm, I see where you are coming from and will need to re-think this a bit.

Thanks for the input. It was much appreciated.


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## toddalin (Jan 4, 2008)

Thanks again Korm.

OK, a modified version of the gap takes care of the problem.

Instead of two insulators with a single short rail piece, we do a "modified gap" with three insulators with two short rail pieces. Of course to keep the span short, these need not be Aristocraft/LGB insulators.

This "modified gap" goes between the two power packs and replaces the insulator you show.

A 24 volt relay goes between the live "approach" rail, skips the adjacent portion of the modified gap rail and attaches to the far portion of the modified gap rail. Same thing in reverse with the "departure" rail.

The armature of each relay is connected in parallel and powers the 12-volt "breaker" relay.

Now if a lighted axle "approaches" and touches the "first" gap rail it pulls current through the "departure" relay. If this exceeds 24 volts, the relay triggers, triggering the breaker relay and shutting down the power.

As the axle moves on it hits the void space such that it actually touches both gap rails and pulls current through both relays. Again, as long as we don't exceed 24 volts, we're good.

As the axle moves on it hits the "second" gap rail and pulls current through the "approach" relay and if we keep it under 24 volts, we should be good.

Actually, if there are multiple axles receiving power, this approach relay to the second gap rail is by-passed because the power also goes directly through the axle wiring.

Same thing happens in the other direction.


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## kormsen (Oct 27, 2009)

hmmm, thanks.
but to be honest, you lost me.
i think, i'll have to set this up, to comprehend it.


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