HM7000 locos and points with track packs

[TaffsTT]

Hello,

Upon my return to TT:120, I purchased track packs 2 to 5. However I have a power feed query:

DCC bluetooth. When I use the inside loop I lose power. I assume I need the clips but where do they fit on turnouts?

[Peachy]

Hi, they’re pretty easy, I show how & where to fit them in this video at approximately 9:06 Hope it helps.

NB as per most of my videos I talk way too much & don’t actually start showing how to install them until 11:07 🤣

[TaffsTT]

Thanks Peachy. I do subscribe and know your channel well so will check that out. Thanks for the info.

[ntpntpntp]

The point clips are ok but personally I'd add a second power feed to the inner oval, rather than use the point clips. With DCC you need to be sure the current carrying capacity is reasonable as you may have multiple locos and lit coaches etc. all drawing power.

[TaffsTT]

Thanks. I have purchased tbe 15V 4A pwr supply too.

[Rallymatt]

I would ignore point clips and solder in wire droppers. It is a more robust long term proposition. I know there will be a pile of opposite views but long term it will show its value 😁

[96RAF]

Point clips are meant to provide a carry thru’ of power to the odd siding or two a loop where 1 or 2 locos are involved, but they are just bent steel staples with little electrical load carrying capability. For serious running as stated use extra link wires or a proper power bus. Take a read of the track-mat and extension packs guide in the 00 section. The principles read across to any gauge.

[TaffsTT]

I have purchased the 15V 4A power supply and will do as advised with bus and droppers.

Also got the dcc clips to get me running and testing setup and configuration for now. What is nice is the clips come with instructions too.

[TaffsTT]

Hi, they’re pretty easy, I show how & where to fit them in this video at approximately 9:06 Hope it helps.

Chris,

Thanks and it did help. The packs now also come with instructions.

 

 

[Landyman130]

Rallymatt wrote - I would ignore point clips and solder in wire droppers. It is a more robust long term proposition.

Somewhere I saw a video, where they were soldering the metal fishplate joiners to reduce the track resistance. Has anyone done this in TT:120?

Sounds like a good idea on a permanant layout, but I'm a bit concerned about expansion in a hot summer causing the track to buckle. (I'm in the design stage of a new layout.)

[Fishmanoz]

The problem with track resistance is the fishplates as they work loose over time, tarnish and lead to higher resistance joins. So when you solder to the fishplates, you are soldering to the problem.

While soldering droppers to the fishplates is better than no droppers, much better to solder to the track and so remove the fishplates from the equation.

[Rallymatt]

Precisely what Fishy has said. Soldered fish plates don’t overcome the issue of poor conductivity in the rail/fishplate. They will develop galvanic corrosion which will also affect ‘point clips’ and why they are not a great permanent solution. In bad cases they have been know to get very hot due to excessive resistance.

[PeterM67]

There's been a few reports of issues with the turnout clips in the TT120 Facebook groups where the clips are used in conjunction with the 4 amp Hornby PSU with the end result being melted sleepers in the area around the clips.

What typically appears to happen is that a derailment occurs resulting in a short circuit. Where the short is on the wrong side of one or more of the clips the clips very quickly overheat. I suspect that the 4 amp PSU will happily supply 60Ws to the track (4A x 15V = 60W) and those 60Ws need to be dissipated somewhere with the weakest place being the clips.

Personally I would use droppers with this PSU for safety and reliability reasons or at a minimum ensure that each section that needs to be powered permanently has a direct feed. If you do need to use turnout clips maybe restrict yourself to the P9100 PSU as this is rated at 1 amp but is definitely good for 2 x HM7000 controlled locomotives in simultaneous use which is how I use it.

[Landyman130]

I previously wrote;-

"Somewhere I saw a video, where they were soldering the metal fishplate joiners to reduce the track resistance. Has anyone done this in TT:120?

Sounds like a good idea on a permanant layout, but I'm a bit concerned about expansion in a hot summer causing the track to buckle."

It appears that the following postings have only taken in my first paragraph. The second should have made clear what I was suggesting, so I’ll expand what I wrote.

When I wrote, “soldering the metal fishplate joiners to reduce the track resistance”, I should have said – soldering the metal fishplate joiners to the track rails. Thus, no resistance at joints in the track to cause overheating. The two sections of rail are soldered to each other and the fishplates. Not soldering a PSU feed to the fishplates. However, that could be a good place to power the track.

I am expecting tomorrow the arrival of my first Peco flexi track, so I will measure the resistance of a yard (36 inches) of track. I would expect the resistance of the joint to be almost zero.

However, I will be building my layout in a loft and could expect the room it to get very hot in summer. So would continuous model track, a closer representation of modern day main-line track, buckle?

I am using the HM 7000 with BT, so no need for isolation at points.

[Daedalus]

What typically appears to happen is that a derailment occurs resulting in a short circuit. Where the short is on the wrong side of one or more of the clips the clips very quickly overheat. I suspect that the 4 amp PSU will happily supply 60Ws to the track (4A x 15V = 60W) and those 60Ws need to be dissipated somewhere with the weakest place being the clips.

I can not accept that! It implies all 15 V is being dropped across the clips which in turn implies an extremely high resistivity of the metal used for the clips compared to the ordinary rails. The only way that could happen is if the rails were super conductors at room temperatures and Hornby shareholders would be billionaires!

Also the clips would not perform their role in providing connectivity if they were high resistance.

The world of model railways seems to have become detatched from the Laws of Physics.

[LTSR_NSE]

@landyman - unless you intend to build your model railway in a room that is kept at an absolute constant temperature (a near impossibility) - it would be extremely inadvisable to solder up all track joints.

Expansion & contraction of rails will almost certainly occur (and if constrained by solder) result in buckling & deformation of the track. At the least this would lead to problematic/erratic running & more probably, sections of your track would be irreparably damaged & need replacing.

It would be perfectly acceptable/possible to solder some joints, whilst leaving others free to move. As modellers that construct modular layouts, usually solder the rails to special sleepers at the edges of the modules, specifically to prevent movement in these locations!

[96RAF]

Point 1 - your point clips are steel which is not a good conductor. Springy brass/phosphor bronze would have been a better choice. Properly linked but simply DC/DCC switchable points by the manufacturer would be even better.

Point 2 - in the real world rail is continuously welded but as it is laid each section is pre-tensioned to cope with a mean temperature-expansion range before "soldering', hence real rails do move during temperature extremes. That pre-tensioning would be difficult to do in our world. Real world rail is also laid on ballast to allow such movement whereas we pin or glue ours down to prevent movement, thus relying upon rail joiners to take up the slack.

[James-377653]

@Daedalus - And yet I have seen it with my own eyes more than once. White hot clips with a thin stream of smoke followed by total failure. Just like a fuse wire.

That was with the Hornby 4A PSU.

I replaced the links with soldered wires and fitted a 3A thermal switch, which solved the problem.

[96RAF]

Melted plastic due to hot point clips is well documented on the forum. The clips are meant to pass power across a point to enable a siding or two, not to power the rest` of the layout from a single source. Whether your clips glow or not depends upon the actual load on the downstream side of your power trail. You can power a whole layout if you only have 1 or 2 locos trundling around, but you try it with a dozen locos and watch for fireworks.

[Fishmanoz]

James, not sure why you needed the thermal switch given one of the features of all Hornby PSUs is good overload protection.

[96RAF]

The Hornby PSUs will attempt to maintain constant power by dropping voltage as current rises. Therefore as your clips get hotter the PSU will supply current until they fail.

[Daedalus]

@James-377653

I've metered the Hornby TT:120 rails and I get a value of 0.2 Ohms.mm^2/Metre. A reasonable value. I looked up non-corrosive spring steel and it has the same value or better if intended for electrical use. It would suggest there was greatly in excess of 4 A current.

[Fishmanoz]

Resistance of the material itself is no surprise. What would surprise me are:

• that numbers of people are running there layouts with non-compliant PSUs producing more than 4 Amps and are drawing that excessive current
• that a short piece of steel will get excessively hot with such currents

For me, using the S. Homes approach, that leaves loose fitting, tarnish etc at the joint between the clip and the point as the only remaining place where higher resistance might be present and heating occur. Resistance measurements with the clips in situ would confirm this.

[ateshci]

A reasonable protection for TT are self-resetting polyswitches, that can be bought from e.g. Amazon - here's one with a rating that will suffice even for banked trains , if your dividing a large layout into appropriate subdivisions:

https://www.amazon.com/Aexit-Resettable-Through-Cartridge-Polyswitch/dp/B07969KC7Z/ref=sr_1_6?crid=OBC2JD87BXYN&currency=GBP&keywords=polyswitch+resettable+fuse&qid=1705068076&sprefix=polyswitch%2Caps%2C176&sr=8-6

Unless you use the feeblest of wiring, a short won't do harm any longer.