Short circuit protection for NCE Power Cab

[North Bridge]

Hello all,

 

I have a query about the short circuit protection for the NCE Power Cab that I am hoping that someone can help me answer.

 

I have tested the short circuit protection by placing a coin across the rails and the power cuts out as one would expect (i.e. there's a 'click' from the power panel and the display on the throttle unit 'flashes' and then re-sets itself). However, something 'strange' happens when a loco approcaches a point set for the wrong route. Clearly, when a loco reaches the crossing (set to the wrong polarity), one would expect a short circuit to result and the system to respond accordingly and shut off power. When this happens in practice, the loco does indeed stop. However, this is accompanied by a loud and quite alarming buzzing sound emanating from the NCE Power Panel. Also, there is no 'flash' on the display screen, which continues to show what was there prior to the short occurring.

 

Apart from the obvious 'panic' on the part of operator when this happens (usual gut reaction is to grab the loco before something awful happens to the chip - not really helpful on an exhibition layout!), I am wondering if this is what should happen?

 

My points are built from C&L components, with the crossing polarity being switched through a Tortoise motor.I asked someone using NCE Power cab about this at a show, and he said the power cut out on his system in the same way as when a coin was placed across the rails - he even kindly demonstrated this to show it was the case.

 

I am wondering if the above affect is something to do with the sensitivity of overload protection circuit on my system, and whether it is possible to adjust it? Can anyone offer any suggestions?

 

Also I am wondering whether an additional circiut breaker is recommended for the basic NCE Power Cab, or whether the in-built one is sufficient? My layout is only 7 feet long and just 2 boards. I know you can get circuit breakers to supply multiple power districts, but I'm happy with just the one supply given the small size of layout.

 

Hope someone can help/advise?

 

Many thanks

 

Karl Crowther

[Suzie]

It sounds like your wiring (possibly the wiring in the the loco) is a bit thin. If the resistance of the short circuit is too high to conduct the full current from the command station it will not shut down.

 

It will probably be best to beef up your wiring a bit, and check that the switch in the tortoise is switching properly otherwise you will really need to put in a lower current circuit breaker to prevent potential disaster of a melting loco.

[SHMD]

I agree with Suzie. The Loco-on-a-point short has too high a resistance to trip the Short Circuit Protection circuit.

 

But to pinpoint the single area of high resistance may be difficult.

There are many things I don't know about your layout:- size, complexity, wiring design, wiring application, decoders used, Loco wiring, etcetera.

 

Every joint from the output from the controller, the connection to the Bus, the DCC Bus, connections to the track, rail resistance, wheel contact resistance, pickups , internal wiring, electronics, motor windings – and then all the way back again – has a small and usually insignificant resistance.

 

With powerful controllers any short that draws less current than what the controller is capable of will be ignored by the protection circuit. The NCE Power CAB Pro can deliver 5Amps! That is a lot – believe me.

 

As the DCC Boosters get bigger then this problem will become more common.

If this short draws less than the maximum current rating of the controller then adding an external circuit breaker will also not trip!

 

Have you tried putting the 'coin short' on and around the point in question.

(You could also try the 'coin short' trick at the furthest extremity on your layout to see what happens.)

Do you have access to a multi-meter that can measure (accurately) down to 0.01Ohms?

 

 

Kev.

[BromsMods]

The NCE Power CAB Pro can deliver 5Amps!

 

Not the basic PowerCab, which the OP has - output from this is limited to 2 amps.

[North Bridge]

I agree with Suzie. The Loco-on-a-point short has too high a resistance to trip the Short Circuit Protection circuit.

 

But to pinpoint the single area of high resistance may be difficult.

There are many things I don't know about your layout:- size, complexity, wiring design, wiring application, decoders used, Loco wiring, etcetera.

 

Every joint from the output from the controller, the connection to the Bus, the DCC Bus, connections to the track, rail resistance, wheel contact resistance, pickups , internal wiring, electronics, motor windings – and then all the way back again – has a small and usually insignificant resistance.

 

With powerful controllers any short that draws less current than what the controller is capable of will be ignored by the protection circuit. The NCE Power CAB Pro can deliver 5Amps! That is a lot – believe me.

 

As the DCC Boosters get bigger then this problem will become more common.

If this short draws less than the maximum current rating of the controller then adding an external circuit breaker will also not trip!

 

Have you tried putting the 'coin short' on and around the point in question.

(You could also try the 'coin short' trick at the furthest extremity on your layout to see what happens.)

Do you have access to a multi-meter that can measure (accurately) down to 0.01Ohms?

 

 

Kev.

Hi Kev, Susie,

 

Thanks for your suggestions. Funnily enough, after posting I did begin to wonder if it was a wiring issue. I've tested all sections of track on the layout and there are a couple of sections (not on points) where the DCC does not trip with a coin between the rails (I get the buzzing as previously described). This does not seem to correspond with distance from the input (so probably not a straightforward relationship with distance). Each board is 3'6" long and I think the main power bus was 3A multicore lighting wire, with 1A droppers from the rails. I don't know if the main bus could be simply 'doubled up' and more droppers run from point crossings and rails on sections of track that don't trip-out correctly at present (potentially also using both switches in the Tortoise). Or perhaps a complete re-wire using something like 13A cable for the main bus?

 

Thanks

 

Karl

[RedgateModels]

I would recommend a seperate cut-out module for use with a Powercab, it does not handle shorts gracefully and works far better if it is not subjected to shorts. I personally am using a prototype pcb from MERG that has not made it into production yet, but there are other proprietory modules available

[Suzie]

I know your layout is not large, but I would recommend using at least 1.5mm² wire (15A) and ideally 2.5mm² for the main track bus. The droppers and frog wiring should only be quite short and should not be a problem then - if there is a problem it will show up. There should be no need to double up any of the switch connections if all is well. 

 

If the coin test is failing in places it would indicate that your wiring is marginal and that areas of the layout have a circuit impedance of at least 6R - and it should be possible to measure that with a multimeter to isolate the specific problem area. One big problem with many systems (not sure about the Power cab because I have not seen one) is that the connectors are not quite big enough to get a reasonable sized wire in making getting a good connection to the track output rather difficult.

[North Bridge]

I know your layout is not large, but I would recommend using at least 1.5mm² wire (15A) and ideally 2.5mm² for the main track bus. The droppers and frog wiring should only be quite short and should not be a problem then - if there is a problem it will show up. There should be no need to double up any of the switch connections if all is well. 

 

If the coin test is failing in places it would indicate that your wiring is marginal and that areas of the layout have a circuit impedance of at least 6R - and it should be possible to measure that with a multimeter to isolate the specific problem area. One big problem with many systems (not sure about the Power cab because I have not seen one) is that the connectors are not quite big enough to get a reasonable sized wire in making getting a good connection to the track output rather difficult.

Hi, Thanks all for further advice. I was wondering if a separate cut-out device would help, something I will look into. I can also foresee an issue with length of wiring from point crossings to Tortoise switch needing to be as short as possible (i've used something like 16/0.2 wire for these connections and all droppers from rails).

 

Having done a bit more checking, I now find that all tracks on the second of the 2 boards produce 'buzzing' with the coin short test, rather than correct shut-down of the Power Cab. This is the 'second' board in that it's the other one that the Power Cab feeds into. Coincidentally, all points are on this second board. On the 'first' board, all tracks cut out correctly with the coin test. Potentially it therefore may be more of an issue of how the 2 boards are wired together (though I think I used the same cable as the main BUS). Best way to test will be to wire the 2 board bus wires together with another, temporary connection, as short as possible, and see if this cures the problem.

 

Thannks to you all

 

Karl

[Suzie]

16/02 will be fine for the droppers and frog connections. 

[North Bridge]

16/02 will be fine for the droppers and frog connections.

Evening all, Just connected power bus on both boards directly with lighting cable (by-passing D-connector and wiring loom connecting the two - wasn't excessively over-generous in length). Second board now cuts out with coin test on all sections of track (which didn't happen previously). When running 'wrong road' into a point crossing, there's now a very momentary buzz from the power panel and then it cuts out as it should (whereas previoulsy, the buzzing just continued). Don't know if the split second delay will be a problem, but intend to try a separate cut-out as suggested (I gather the PSX-1 is the one to use). That said, one point for some reason still fails to trip the cut-out. Need to turn baseboards over at some point and investigate more fully. Success of sorts and now hopefully have a way forward.

 

Thanks to all, Karl

[SHMD]

Evening all, Just connected power bus on both boards directly with lighting cable (by-passing D-connector and wiring loom connecting the two - wasn't excessively over-generous in length). Second board now cuts out with coin test on all sections of track (which didn't happen previously). When running 'wrong road' into a point crossing, there's now a very momentary buzz from the power panel and then it cuts out as it should (whereas previoulsy, the buzzing just continued). Don't know if the split second delay will be a problem, but intend to try a separate cut-out as suggested (I gather the PSX-1 is the one to use). That said, one point for some reason still fails to trip the cut-out. Need to turn baseboards over at some point and investigate more fully. Success of sorts and now hopefully have a way forward.

 

Thanks to all, Karl

 

You never mentioned 'D connectors'!

 

I always, as a rule of thumb, allowed 0.1Ohms per connector in a circuit. (0.1 to 4 amp range, resistive load.)

Each change of wire/contact in the circuit – I refer you to my earlier list – would also add 0.1Ohms.

It all adds up, and what you are looking for is the “straw” that breaks the circuit breakers back!

 

'D' connectors may quote a 5Amp rating but this does not, in any way, make assurances for how the end application WILL be affected by inserting a male/female connector pair.

 

How many pins does your 'bus' use through the 'D' types. Try doubling up, or even, quadrupling up each side of the 'bus' through the 'D' connector.

 

Glad your making progress and to see the the NCE Power CAB is standing up to all the abuse!

 

 

Kev.

(Errr you havn't just twisted any wires together have you? No, thought not. Just remember Camels and straws!)

[North Bridge]

You never mentioned 'D connectors'!

 

I always, as a rule of thumb, allowed 0.1Ohms per connector in a circuit. (0.1 to 4 amp range, resistive load.)

Each change of wire/contact in the circuit – I refer you to my earlier list – would also add 0.1Ohms.

It all adds up, and what you are looking for is the “straw” that breaks the circuit breakers back!

 

'D' connectors may quote a 5Amp rating but this does not, in any way, make assurances for how the end application WILL be affected by inserting a male/female connector pair.

 

How many pins does your 'bus' use through the 'D' types. Try doubling up, or even, quadrupling up each side of the 'bus' through the 'D' connector.

 

Glad your making progress and to see the the NCE Power CAB is standing up to all the abuse!

 

 

Kev.

(Errr you havn't just twisted any wires together have you? No, thought not. Just remember Camels and straws!)

Hi Kev,

 

Just the one connection for each wire of the bus through D connector (all soldered connections!). I did wonder if doubling up might help, so that answers that question, thanks. In a way, this is what I did when I made an additional (temporary), direct connection of the bus wires across the 2 boards (which seemed to do the trick as mentioned in my most recent post).

 

I think I've identified two further issues with the point crossing/polarity wiring. After looking at my stock of wire, I may have used something like 8/0.2 and not 16/0.2, so perhaps this wire is inadequate. Also, two of the points are split across the baseboard join. This means that the wire from the switch takes quite a lengthy/circuitous route to the Tortoise - i.e. via the between board D connector and its associated wiring loom. Have ordered some 16/0.2 and need to look at ways I can minimise the length of these conenctions as much as possible.

 

Hopefully the PSX-1 that I've just ordered will help set things in order as well, and save my Power cab from further abuse!

 

A photo showing underside of Baseboard 1 is attached, if that's any help.However, note that this was taken before the wiring loom/D connector to the second board had been installed.

 

Thanks once again.

Karl

Edited April 10, 2013 by North Bridge

[Mallard60022]

This has been very helpful as I am no good a wiring and have been considering what I might do to 'protect' my now 5amp boosted Powercab set up. Just as an aside I have forked out on Hexjuicers on my own points that I built for my layout extension. The original three boards have conventional polarity switches and I suffer from 'forgetting to set the route thus loco sets off a short circuit syndrome' on these boards every so often. If I ever build a 'whole' layout I'd deffo have hexjuicers despite the cost.

Digitrains is my 'local' stockist and I shall be asking their advice as to which device to use for protecting when there is a SS.

Good luck and thanks for raising this issue.

P @ 36E

[Gruffalo]

As I approach the point at which dreams become reality, I think I may start a topic entitled something like "Tortoises and Frogs for those with a non-reptilian disposition". I have almost finalised my track plan with 25 Peco Electro-frogs, 2 long crossings and 25 Tortoise motors. It seems Hex-Frog Juicers are the way to go but I want to get every bit of advice I can to avoid destroying my nice new NCE PowerCab. Unfortunately, Digitrains is about as far from me as was Bromsgrove Models, both of whom would have been great help, I'm sure.

[Nigelcliffe]

If you can attach a wire to the crossing (frog), and another wire from each of the running rails of a turnout, you have the three wires for controlling the polarity of turnout crossings. 

You can connect those three wires to the switch contacts provided on the Tortoise motor (there are two sets of contacts, which will cover most circumstances), or you can spend some money on a completely unnecessary Hex Frog Juicers, and wire the same three wires to the Hex Frog Juicer.

 

 

- Nigel

[Mallard60022]

Digis are great on the phone mate.

P

[Gruffalo]

Gentlemen, I am obliged for your advice and suggestions. £140-ish on HexFrogJuicers could be better spent on plenty of other stuff!

[Oldddudders]

If you have the opportunity to install a Tortoise, they are among the more reliable of model electrical components, so once properly adjusted they will switch frogs as Nigel says. The Hex Frog Juicer is a great way of avoiding shorts and embarrassment where a Tortoise isn't feasible. Other mechanical point & frog-polarity switching systems can be devised, and are regularly recommended by those who have succeeded with them. But they don't install so easily.

[Suzie]

Even if the frog juicer changes the frog polarity, it will not change the point which will remain set against the train and possibly derail it.

 

If you are likely to encounter this problem install circuit breakers to cut the power to the train without shutting down the whole layout until the point can be correctly set - a much more sensible investment.

[Gruffalo]

Thank you Ian and Suzie. Tortoises are at the top of the priority list for my build as I have been told by a few sources that they are the most reliable! I previously used unpowered frogs (1970 vintage) on code 100. This is to be all new code 75 so why spoil it with a ha'peth of tar as they say. My old solenoid motors will only be used to operate ancillaries. My NCE PowerCab power circuit will require at least two circuit breakers, possibly 5 if I really section it extensively. Do you have any recommendations?

 

I have (according to AnyRail) 50m of track to lay, I have plenty of 1.5mm new flexible cable of a style used for industrial process control and a good amount of 0.5mm stranded for the drops to lay the track bus. As for routing, I do have a couple of old plc's that I can link to a touch screen eventually but as a start, I will use diode matrices on veroboard. It is a long way off that yet!

[Suzie]

The NCE mini panel can be used for input buttons since you have an NCE system, and the NCE will allow you to set up routes in macros so there is no need for a diode matrix when you have a good system like the NCE. How many points do you have?

[Gruffalo]

The NCE mini panel can be used for input buttons since you have an NCE system, and the NCE will allow you to set up routes in macros so there is no need for a diode matrix when you have a good system like the NCE. How many points do you have?

25 points (none are three-way), no slips and 2 long crossings (which obviously do not require motors, just the frog polarity to be sorted). As with most layouts, the majority are concentrated around the station throat but there are a few for loco release on platform roads and the double track disappears into the distance where it forms a return loop around using a double crossing arrangement.

My power zoning would topographically be something like:

Station & Passenger platforms.

Loco servicing area and throat.

Freight and carriage sidings.

Out-and-back inner line.

Out-and-back outer line.

I will try and upload a track plan later today for your comments, thanks in advance!

[BromsMods]

You can set routes from within the PowerCab - this is standard functionaility using what are called macros.

 

As for circuit breakers I would recommend the PSX-1 from DCC Specialities (stocked by Digitrains) - not only does it work extremely quickly but can be set at a sufficiently low level to protect the PowerCab.

[Gruffalo]

You can set routes from within the PowerCab - this is standard functionaility using what are called macros.

 

As for circuit breakers I would recommend the PSX-1 from DCC Specialities (stocked by Digitrains) - not only does it work extremely quickly but can be set at a sufficiently low level to protect the PowerCab.

Thanks John. Hope the retirement is going well!

[Gruffalo]

Karl,

 

Apologies if I seem to have hijacked your thread but the expertise being added in my search for knowledge will probably be good for you too.

 

Regards,

 

Tony