Do I need a power booster?

[RikkiGTR]

Hey guys and gals,

On running my layout, all trains will slow down when they go through my fiddle yard tracks. I have definitely soldered the power bus correctly to each track, and all wires are also connected properly. 
 

My layout is 8x10ft in 2mm scale, with quite a lot of track and many many droppers. I’m using a Gaugemaster Prodigy Advanced DCC control system. The power “begins” at the opposite side of the layout to my fiddle yard, although it is a complete circuit insofar as the main bus wire is concerned (which is 32/02 wire). 
 

If it were a single loco I’d simply look at that, but all locos suffer a noticeable drop off in speed when they reach the fiddle yard. Should I be adding a power booster, and if so which one? I don’t actually know anything about them. 

[Dungrange]

What is the current output from your command station and how many locomotives / accessories are you running when this power drop is occurring?

 

My first thought is that it's a problem with voltage drop due to too much resistance in the wiring.

[GrumpyPenguin]

Before you start adding boosters double check the integrity of your bus &/or wiring.

 

Easy enough to do using a simple multimeter/voltmeter & a "load" such as a 12v 21w indicator bulb.

 

Connect the bulb (rememberb that it will get hot) in parellel with the meter (set to, IIRC AC volts 25v + setting)**.

 

Check & note the voltage as close as you can to the output of your controller, keep taking readings round the layout - that will pinpoint any defective joints/connections. If all proves well, then look at the possibility of a heavier bus to the far side of the layout.

 

** Forget the "can't measure DCC voltage with a basic multimeter" guys, what you are looking for is consistant readings with a load (you can also forget the "short out the track with a coin" method too - the controller will probably trip before any dry joint heats up).

[RikkiGTR]

5 hours ago, Dungrange said:

What is the current output from your command station and how many locomotives / accessories are you running when this power drop is occurring?

 

My first thought is that it's a problem with voltage drop due to too much resistance in the wiring.

 

Power output to track is 3.5 amps, I'm running maximum 3 locos when this happens - I have 2 mainlines that can circulate (and go through the fiddle yards) whilst another train moves around the branch line and/or sidings. 

 

1 hour ago, GrumpyPenguin said:

Before you start adding boosters double check the integrity of your bus &/or wiring.

 

Easy enough to do using a simple multimeter/voltmeter & a "load" such as a 12v 21w indicator bulb.

 

Connect the bulb (rememberb that it will get hot) in parellel with the meter (set to, IIRC AC volts 25v + setting)**.

 

Check & note the voltage as close as you can to the output of your controller, keep taking readings round the layout - that will pinpoint any defective joints/connections. If all proves well, then look at the possibility of a heavier bus to the far side of the layout.

 

** Forget the "can't measure DCC voltage with a basic multimeter" guys, what you are looking for is consistant readings with a load (you can also forget the "short out the track with a coin" method too - the controller will probably trip before any dry joint heats up).

 

I don't understand... any of that. 

Well, it doesn't sound too complicated, truth be told. I don't have a multimeter/voltmeter so I obviously need to acquire one. Which would be best for the task at hand? 

[RFS]

I would definitely try the simple coin test as this can indicate the problem being under gauge wire. Where the problem occurs, place a coin across the track and make sure the command station trips immediately. If it doesn't, then it means that the wiring at that place needs to be improved.  

[Dungrange]

2 hours ago, RikkiGTR said:

Power output to track is 3.5 amps, I'm running maximum 3 locos when this happens - I have 2 mainlines that can circulate (and go through the fiddle yards) whilst another train moves around the branch line and/or sidings. 

 

As you're modelling in 2mm scale, I'd expect each of your locomotives to be drawing less than 0.5 Amps.  Three locomotives should be well within the capability of the DCC system without needing a booster (which will just provide extra Amps that I don't think you need).

 

The loss of speed is therefore most likely caused by a drop in voltage.  The drop in voltage is caused by high resistance, which is either wire with an inadequate cross section, or a poorly soldered / connected joint.  I suspect that it's probably the latter.  Whilst a multimeter is useful for identifying voltage drops, you've already highlighted that there is a notable drop in speed when entering the fiddle yard, so it's likely that any poor joint is in this area.  If you can identify which join the locomotive starts to slow at, then you can probably assume that the wiring is okay on the command station side of that join.  You then need to check the wires that connect into the fiddle yard from that point.  If the go slow section is quite short, then I'd hazard a guess that it's a dropper issue, but if it goes slow throughout the fiddle yard, then I'd be tempted to suggest it's the bus wire.  Is the fiddle yard a separate board, in which case it might be your cross baseboard connector?

[Colin_McLeod]

Rather than try to find the poor joint, I would suggest making a second, parallel  connection to the fiddle yard. Make the connection well past where the trains slow.  If that works, then problem solved.  The poor joint will still be there somewhere but that doesn't matter.

[Steven B]

As you don't have a multi-meter, try this:

Disconnect your DCC system from the layout and instead connect a 9V battery to the main track feed.

Using a 12V light bulb, connect it to the track (solder wire to the bulb, other end free wires touch the track) at various points. You'll probably find places where the bulb becomes duller. Somewhere along the feed to this section of track you'll find there's a poor solder joint or a broken wire.

 

 

Steven B

[PaulCheffus]

Hi

 

Have you connected your power feeds to each piece of track or are you partly relying on rail joiners?

 

I had a similar problem on my layout which is a similar size. It wasn’t the bus wires in my case as they were 24/0.2 wire but the fact I was relying on the rail joiners. Wired each piece of track to the bus and no issues since.

 

Cheers

 

Paul

[jamesed]

32/0.2mm wire is what we in Europe know as 1mm sq. and that is very small for using as bus wiring on what's quite a reasonable size N gauge layout. I'd suggest that high impedance issues are quite likely to be contributing to the issues you are experiencing. If your bus wiring has breaks and joins in it then that will compound the issue.   Although this may not be what you really want to hear, it may save you ongoing problems if you just bite the bullet and replace the bus with 2.5mm sq. / 14AWG wire. Ideally your track droppers will be 16/0.2 but 7/0.2 will probably be ok if they are kept short i.e. 8" or less. 

Edited May 3 by jamesed

[melmerby]

22 minutes ago, jamesed said:

32/0.2mm wire is what we in Europe know as 1mm sq. and that is very small for using as bus wiring

Europe includes the UK where 32/0.2 & 1mm are both used to describe the cable

 

The RS Pro cable has 17A rating, several other brands show 10A or more

Most DCC suppliers sell it for bus wiring and IMHO 10A is perfectly adequate.

[GrumpyPenguin]

19 hours ago, RFS said:

I would definitely try the simple coin test as this can indicate the problem being under gauge wire. Where the problem occurs, place a coin across the track and make sure the command station trips immediately. If it doesn't, then it means that the wiring at that place needs to be improved.  

The "coin test" proves nothing if the problem is a dry joint & you cannot be doing your controller any favours by shorting it out so many times.

[GrumpyPenguin]

5 hours ago, Steven B said:

As you don't have a multi-meter, try this:

Disconnect your DCC system from the layout and instead connect a 9V battery to the main track feed.

Using a 12V light bulb, connect it to the track (solder wire to the bulb, other end free wires touch the track) at various points. You'll probably find places where the bulb becomes duller. Somewhere along the feed to this section of track you'll find there's a poor solder joint or a broken wire.

 

 

Steven B

Not a bad method - I have done something similar using a 7aH SLA & a 55w headlamp bulb pausing at every stage to allow any dry joints to heat up.

[GrumpyPenguin]

20 hours ago, RikkiGTR said:

 

Power output to track is 3.5 amps, I'm running maximum 3 locos when this happens - I have 2 mainlines that can circulate (and go through the fiddle yards) whilst another train moves around the branch line and/or sidings. 

 

 

I don't understand... any of that. 

Well, it doesn't sound too complicated, truth be told. I don't have a multimeter/voltmeter so I obviously need to acquire one. Which would be best for the task at hand? 

One of those things easy to show, diffecult to describe.

 

A fairly cheap multimeter will do the job, absolute accuracy is not over important as long as you can see where any variations are.

[jamesed]

49 minutes ago, melmerby said:

Europe includes the UK where 32/0.2 & 1mm are both used to describe the cable

 

The RS Pro cable has 17A rating, several other brands show 10A or more

Most DCC suppliers sell it for bus wiring and IMHO 10A is perfectly adequate.

 

When choosing bus cable for a dcc system, ignore all the rules you've learnt about current rating for cables (which actually aren't as helpful as it may seem anyway even for general electrical use). DCC is a complex signal running at a much higher frequency than normal ac power. You need to allow a significant amount of headroom in cable size to protect the integrity of the signal. That's why, as a general rule, it is recommended to use a minimum size of 1.5mm sq for a small layout and 2.5mm sq, for medium and larger size layouts.  In theory you can go larger still but that's not necessary in most cases. The lower the overall impedance the better and more trouble free it will be. 

 

 

 

[melmerby]

2 hours ago, jamesed said:

DCC is a complex signal running at a much higher frequency than normal ac power.

It's just a square wave with a varying duty cycle, hardly complex.

This is mine using a 'scope with DCC capability

 

It's also very low in the frequency range (app 8kHz) where the effects of Inductance and capacitance do not have a huge effect

The biggest effect is resistance which will affect the speed of the loco if the voltage is dropping by any measurable amount

13/0.2 typically has a resistance of about 60 ohms per kilometer, that's 60 milli ohms per meter.

 

[RFS]

3 hours ago, GrumpyPenguin said:

The "coin test" proves nothing if the problem is a dry joint & you cannot be doing your controller any favours by shorting it out so many times.

 

The coin test is a important test for verifying the adequacy of your DCC wiring. With DC, the maximum track power is 12v at 1amp which equates to 12 watts. The OP's system is 3.5 amps at a likely 16v which makes this 56w. Not only is this nearly 5 times the DC load, it's also full power all the time. When a short occurs due to a derailment, that amount of power will flow through the loco's pickup wires until the command station detects the fault and cuts power. These wires are not designed to carry that much power other than for a fraction of a second. A couple of seconds would severely damage the loco (try putting 56w through a solenoid point motor for a couple of seconds, for example).

 

This why voltage drop can cause problems. If the Op's wiring means that the fiddle yard is only getting, say, 35-40w then a short will not necessarily get detected immediately if at all, and irreparable damage can be done. (Think how hot a 40w incandescent light bulb gets the moment you switch it on - its filament is white hot in an instant.) You're also not going to damage your command station by repeatably tripping its internal circuit breaker - that's what it's designed to do. However when checking your layout in this way, it's best to remove other locos from the track.

 

The Op says he has "many, many droppers" yet the problem is across the fiddle yard area. I would therefore doubt it's a sngle dry joint as that should only affect a small section of track. 

 

 

[GrumpyPenguin]

54 minutes ago, RFS said:

 

The coin test is a important test for verifying the adequacy of your DCC wiring. With DC, the maximum track power is 12v at 1amp which equates to 12 watts. The OP's system is 3.5 amps at a likely 16v which makes this 56w. Not only is this nearly 5 times the DC load, it's also full power all the time. When a short occurs due to a derailment, that amount of power will flow through the loco's pickup wires until the command station detects the fault and cuts power. These wires are not designed to carry that much power other than for a fraction of a second. A couple of seconds would severely damage the loco (try putting 56w through a solenoid point motor for a couple of seconds, for example).

 

This why voltage drop can cause problems. If the Op's wiring means that the fiddle yard is only getting, say, 35-40w then a short will not necessarily get detected immediately if at all, and irreparable damage can be done. (Think how hot a 40w incandescent light bulb gets the moment you switch it on - its filament is white hot in an instant.) You're also not going to damage your command station by repeatably tripping its internal circuit breaker - that's what it's designed to do. However when checking your layout in this way, it's best to remove other locos from the track.

 

The Op says he has "many, many droppers" yet the problem is across the fiddle yard area. I would therefore doubt it's a sngle dry joint as that should only affect a small section of track. 

 

 

"Coin test" will not put anything under load for long & when you think about it could actually be dangerous with a high powered system. It will never have time to allow a bad (dry) joint or other connection to increase it's resistance under load.

Continue abusing your system under short conditions by all means, it's your system after all.

As an electrical engineer I would never attempt to fault find using a dead short, not good electrical practice.

 

You do it your way & I'll continue to do it as a professional.

 

Have a nice weekend.

[RFS]

5 minutes ago, GrumpyPenguin said:

"Coin test" will not put anything under load for long & when you think about it could actually be dangerous with a high powered system. It will never have time to allow a bad (dry) joint or other connection to increase it's resistance under load.

Continue abusing your system under short conditions by all means, it's your system after all.

As an electrical engineer I would never attempt to fault find using a dead short, not good electrical practice.

 

You do it your way & I'll continue to do it as a professional.

 

Have a nice weekend.

 

Suggest you have a read of this article to get a better understanding of the purpose of doing the coin test for DCC systems.

[melmerby]

1 hour ago, RFS said:

 

Suggest you have a read of this article to get a better understanding of the purpose of doing the coin test for DCC systems.

IIRC Digitrax actually recommend this.

The McKinley Railway used this as it was being built to verify the wiring.

[melmerby]

1 hour ago, GrumpyPenguin said:

As an electrical engineer I would never attempt to fault find using a dead short, not good electrical practice.

But you are not a DCC engineer.

[Andymsa]

The poor op must be getting really confused by all the tech talk of specifications, re the coin test put simply it proves the bus wiring and droppers are not introducing to much resistance so when a command station or booster sees a short that track power will shut down, too much resistance and command station/booster won’t see a short, ie track power will stay on (not good for loco or track)

 

it would be a good idea for some sort of diagram from the op to show how the fiddle yard is wired and where isolation joints are, is the rail joiners soldered or just push fitted does each section of track if rail joiners are not soldered has a droppers to it. 
 

you really need to invest in a volt meter to trace the fault 

[peterm1]

For my two pennarth, I went to Bunnings (large hardware store in Oz) and bought a couple of extension leads. Stripped off the outer sheath and then used the blue and brown for the dcc bus, soldering dropper to every single piece of track, even a catch point. I've never had a problem with voltage drop on my layout which is about 8 metres x 2.7 metres  and has several sound loco's turned on at the same time.

 

I'd suggest as others have, that the op makes sure his bus wire is adequate and that every piece of track has droppers.

 

Ps: The earth wire serves as The common for all my Tortoise motors, so it's not an expensive thing to do properly.

[jamesed]

11 hours ago, melmerby said:

It's just a square wave with a varying duty cycle, hardly complex.

This is mine using a 'scope with DCC capability

 

It's also very low in the frequency range (app 8kHz) where the effects of Inductance and capacitance do not have a huge effect

The biggest effect is resistance which will affect the speed of the loco if the voltage is dropping by any measurable amount

13/0.2 typically has a resistance of about 60 ohms per kilometer, that's 60 milli ohms per meter.

 

 

When you start talking about the current capacity of cables that is always stated in relation to simple AC (alternating current) power which runs in a simple sin wave form at 50 cycles per second (or 60 in some countries). DCC is quite different, running at 8,000 cycles per second give or take a couple of thousand.  That's 16x faster. Also, unlike ac power where all we're really concerned with is the peak to peak measurement, DCC is a square wave where the time gap between the waves is critical to determine the signal being sent - each gap is effectively calibrated into 8 further time slots. The peak to peak in dcc typically stays the same because it's a constant voltage.  Now, you are right that in the world of data signals 8khz isn't huge but most higher frequency data signals (with a few exceptions such as poe) aren't carrying power as well as data.  Perhaps, when discussing cable size, the commonest analogy to make is loudspeaker cables. If you start to look at high end end professional loudspeaker wiring you'll see that they consistently use large size cables. It's normal to see 2.5mm sq and even 4mm sq. cables being used. That's not because those cables are carrying currents of up to 20A but because they are striving to achieve very low impedances to ensure to audio signal is not compressed and is reproduced at the highest quality. 

 

Sorry, this is all probably getting a bit too technical and maybe a turn off for many. You don't need to understand the technical background if you aren't interested in that, just look at the advice that is widely available. Everywhere you look you will see advice that a dcc bus should be at least 1.5mm sq cable for smaller layouts and 2.5mm sq. for larger layouts.  There are good reasons why this advice is so universally given.  

 

 

 

 

[Oldddudders]

A cheap digital multimeter, perfectly good enough for most modellers' purposes, is less than £10 on Amazon, probably cheaper on Aliexpress if you can wait a few days. A most useful diagnostic tool. I'm no amateur electrician - still less a 'professional', of course - but it serves me well.