Voltage Drop?

[mikeandnel]

I have a room 10' x 10' and have a double track circle all the way round in EM gauge.

Track is Scaleway one yard lengths with home made turnouts and all joints are soldered or looped with wire to ensure complete current continuity with section gaps as required.

However on certain sections the locos seem to slow down despite constant track cleaning

Can anyone suggest why this might be happening please?

Thank you

Michael dJS

[Crosland]

Nickel silver has poorer conductivity than copper, so the voltage drop will be worse than copper wire.

 

How is the track wired? Sections switched from a central panel? Do you rely on point blades to switch sections? Are the slow sections subject to a particularly tortuous wiring route?

 

I would run some extra wires in parallel with the track (bus wires in DCC parlance) where possible and not just rely on the track and loop connections. It shoould be easy to try on one of the slow sections.

 

Andrew

[SHMD]

Do these "slow sections" correspond with the curves?

Are the Turnout's rails gauged correctly?

 

 

Kev.

[mikeandnel]

Hello Andrew & Kev

All sections are fed from seperate connections with  each track adjacent to thedual  controller. All turnouts are controlled by Tortoise motors to change polarity where required. All connections have been tested and there are no breaks and no mis-feeds. One 'slow' section is on a very gentle curve (5' radius)

Is your suggestion that I run two parallel cables from the controller and link these wires to the track with uplinks?

Thanks

Michael dJS

[SHMD]

Do you have a multi-meter?

 

If so, keep the probes on the rails, of the slow section, and monitor the voltage as the train approaches.

What do you see?

 

All curves add additional friction so a motor, fed from an old analogue controller, will slow down.

Can you try using a feedback type controller?

 

Failing that, try running 2 "flying leads", to the slow section, and remove them just as the train reaches them.

Do you see any drop in speed then?

 

 

Kev.

[Fat Controller]

Hello Andrew & Kev

All sections are fed from seperate connections with  each track adjacent to thedual  controller. All turnouts are controlled by Tortoise motors to change polarity where required. All connections have been tested and there are no breaks and no mis-feeds. One 'slow' section is on a very gentle curve (5' radius)

Is your suggestion that I run two parallel cables from the controller and link these wires to the track with uplinks?

Thanks

Michael dJS

Is it feasible to use larger cross-section cable for the feeds from the transformer? The 10 mm sq. I used for a garden line is perhaps excessive, but something in the order of 2.5 mm sq. should reduce voltage loss considerably.

[SHMD]

Is it feasible to use larger cross-section cable for the feeds from the transformer? The 10 mm sq. I used for a garden line is perhaps excessive, but something in the order of 2.5 mm sq. should reduce voltage loss considerably.

Blimey - 10mm sq!

 

Don't let on where you live or the "metal fairy's" will be along!

(How authentic would that be!!)

 

 

Kev.

[Fat Controller]

Blimey - 10mm sq!

 

Don't let on where you live or the "metal fairy's" will be along!

(How authentic would that be!!)

 

 

Kev.

10 sq mm.. I looked to see if there's a right-hand numberpad shortcut that would give the small '2'', but couldn't find it. I think it's the size used for cooker cables. That line's long gone, and the cable's almost certainly been weighed in by now.

[Stringfingerling]

Nickel silver has poorer conductivity than copper, so the voltage drop will be worse than copper wire.

 

How is the track wired? Sections switched from a central panel? Do you rely on point blades to switch sections? Are the slow sections subject to a particularly tortuous wiring route?

 

I would run some extra wires in parallel with the track (bus wires in DCC parlance) where possible and not just rely on the track and loop connections. It shoould be easy to try on one of the slow sections.

 

Andrew

Agreed!  I always seem to have some old copper mains wire lying around from previous generations of DIY when the rules were less strict about who could tamper with house electrics.  Given that plug sockets have to deliver 13 amp currents, that would more than cover most people's trains.  I've used it on my "O" gauge layout, and the electrics have been 100% problem free over the 25' length i.e. no voltage drops etc.

[Crosland]

Even with mains cable you need to take heed of voltage drop. Knowing the current rating alone is not sufficient, you need to know the resistance per unit length. What's good enough for mains may not be good enough for low voltage.

 

The voltage drop is dependent on the current and resistance, and independent of the voltage in the circuit. A few volts dropped in a cable carrying 10A from a 240V supply are neither here nor there. Put 10A through the same cable in a 12V circuit and the same few volts can become troublesome.

 

Andrew

[Fat Controller]

Resistance per unit length is known as resistivity, I vaguely recollect from O-level physics; as a rule of thumb, the larger the cross-section of a conductor, the lower the resistance for a given length.

Wikipedia has this:- 

http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

which seems to fit with what I was taught.

[Silver Sidelines]

As an aside part of my layout is a circle 12 by 9ft. I have separate sections with a common return made from one conductor from 30amp cooker cable (240v). I am not aware of any voltage issues. In the past I have had problems which have turned out to be faulty section switches or occasionally poor contact across rail joiner (I don't use droppers to every length of rail - sections are typically two or three rail lengths.).

 

Regards

 

Ray

[Stringfingerling]

As an aside part of my layout is a circle 12 by 9ft. I have separate sections with a common return made from one conductor from 30amp cooker cable (240v). I am not aware of any voltage issues. In the past I have had problems which have turned out to be faulty section switches or occasionally poor contact across rail joiner (I don't use droppers to every length of rail - sections are typically two or three rail lengths.).

 

Regards

 

Ray

When I wired my layout I went for belt and braces - I used two droppers to the the copper cable on every piece of rail, including switch rails, knuckle rails etc.  It might be overkill, but, it has worked 100% free of electrical problems, so I've been able to stop thinking about electrics and get on with other bits.

[Silver Sidelines]

Hello

..belt and braces - I used two droppers to the the copper cable on every piece of rail, .

Nice idea but not practical on my layout with +100 points and 300 yards or more of track. With over a 100 individual track sections there is already enough wiring below board without connecting every length of rail. If you use quality rail joiners and check that they are gripping both rails there shouldn't be any need to wire every piece of rail.

 

Regards

 

Ray

[34theletterbetweenB&D]

The electrical conductivity side has been nicely covered. Bypassing the switched connections and powering the rail sections directly with heavy gauge flying leads from the controller terminals may help spot some resistance in circuit. It only needs a dry soldered joint on a switch or in the relay section of a point motor, and there's a significant voltage drop to the track once a motor is drawing current

 

Simple mechanical effects should also be considered.The layout could easily have a small gradient on it. Is the slow down effect seen in the same location in both directions of travel for example?

[martin_wynne]

10 sq mm.. I looked to see if there's a right-hand numberpad shortcut that would give the small '2'', but couldn't find it.

 

[martin_wynne]

If the layout is only 10ft x 10ft I think it is very unlikely that wire size is the problem.

 

It is probably a poor connection somewhere. Possibly a bad soldered joint, or a dirty contact in a plug/socket.

 

Another possibility for slow running is a partial short-circuit in the section. Metal filings mixed in hoovered-up re-used ballast? Copper-clad gapping with copper dust or fragments not cleaned out of the gaps?

 

Are you using the contacts in a Tortoise point motor to feed the section? There is a known issue with them and the design has been changed by the makers a couple of times. See:

 

 http://www.scalefour.org/forum/viewtopic.php?p=1919#p1919

 

For myself I wouldn't use such a wiper contact on a copper track to feed track power. They are too liable to get burnt in an occasional full short-circuit. They will then have a high resistance for the rest of their life. A relay is by far the most reliable way to switch crossing polarity.

 

regards,

 

Martin.

[Fat Controller]

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Thanks, Martin.

[mikeandnel]

Thanks for all the contributions and suggestions

There are no plugs or sockets in the wiring

Tortoise motors are only used to change the polarity of the frogs, and I have never had problems with them, so am reluctant to use relays instead as I would have to re-learn how to wire them.

There are no gradients on the track

The fault only seems to occur when travelling in one direction.

I have checked the connections at each end of the track where the loco slows and can see no obvious problem.

Track is Scaleway N/S flexible with plastic sleepers

Michael dJS

[SHMD]

...The fault only seems to occur when travelling in one direction...

 

I assume that you are not running a double track oval and that it does not matter which loco, or which way round it is to see the slow down?

 

Do you have access to a Meter?

What Controller are you using? (Feedback, DCC, Analogue, etc...)

 

 

Kev.

[mikeandnel]

Hello Kev

Layout is a double track circle with both tracks in a continuous circle. Circle is approx 4'6" radius

Controller is Dual Analogue with Simulators. I have tried an On-Track Walkabout but performance with that is not do good.

Slow down appears to happen regardless of direction loco is facing

I do have an Altai voltmeter

Michael dJS

[DCB]

It sounds like a dry joint/ dodgy fishplate or most likely faulty point blade.   Take careful note of exactly where the loco slows, I would use the OnTrack so you can control the loco while you follow it around. if it slows immediately after a non insulated rail joint put a bridge wire around it and if that cures it change the fishplate, likewise if it is after a point check where the point blade makes contact and or the polarity switch if it is the frog side.   As the fault is one way it would suggest the track or point blade is flexing, quite often this will mean the fault continues as the whole train runs over the fault, if the fault is a single fishplate this can mean the train slows in one direction and not the other.

 

if it is an insulated rail joint bridge it and if the fault goes away then it looks like the feed wire to that section has a dry joint, dodgy switch, etc.

 

What I have never found is any measurable voltage drop in a single conductor or length of track with sound fishplates, even on 40 foot lengths.  But I use DC at 2 amps max not  4 amps at 16 volts like DCC.

[SHMD]

Just a thought..

Get yourself a 9volt battery, you know, a bog standard PP3 LR6 or what ever.
A half used cheap and nasty Zinc-Carbon type would be best.

Set your train on the main line about 3 feet before the poor section starts and stop it there.
Switch off all the electrickery to the layout.
Now, turn the 9v battery up-side-down touch each running rail behind the train.
The train sets off. If in the wrong direction then just turn the battery around.
(For some reason, you always choose the wrong direction 9 times out of 10! So watch out!)

Watch the train as it enters the 'slow' section. Does it still slow down?
Repeat the above but with the battery placed on the rails at different places, including the 'slow' section itself.
What to you see?
 
If you are really ambidextrous, then you could try holding the meter leads, (set to read volts), on the battery as it is placed on the rails.
(Probably better off rigging some wires together for this as accurate readings here will point to the problem.)


Good luck.
Kev.

[Stringfingerling]

Hello

Nice idea but not practical on my layout with +100 points and 300 yards or more of track. With over a 100 individual track sections there is already enough wiring below board without connecting every length of rail. If you use quality rail joiners and check that they are gripping both rails there shouldn't be any need to wire every piece of rail.

 

Regards

 

Ray

 

I take your point about the +100 points etc (no pun intended).  I have to say though, that on my previous layout I had occasional trouble with the rail joiners that were used for electrical continuity - I think the temperature variations in the shed meant that the rails slid backwards and forward in them and they would stop conducting.  Your situation is probably different, and, if it works then, no problem.  The other reason I didn't go for rail joiners is that they are non-prototypical; as I had much less track than you, I was happy to fiddle around fitting cosmetic fishplates.

[Silver Sidelines]

Hello again

....- I think the temperature variations in the shed meant that the rails slid backwards and forward in them and they would stop conducting.  ...

Good point - not just sheds that suffer - loft layouts too.  I have just had to replace a section of Peco streamline sleepering on a curve on the non-scenic part of the layout where the track is only pinned and not ballasted.    The rails look to have expanded moving sideways and shearing some of the plastic chairs.

 

Regards

 

Ray