The importance of the best possible power supply, calculating power needs, followed next page by wiring the DCC layout for best performance and what do in various special “trackwork wiring” circumstances.
We have no hesitation in saying that QUALITY WIRING on your layout and QUALITY ELECTRICAL PICKUP on your loco’s and stock are the single most important key to success in model railway operation… it can’t be skimped if the best result is wanted, as it is totally essential if reliable operation of DC or DCC layouts and smooth performance is wanted.
Of course there is more than ONE aspect to good electrical pickup:
Before we even get to the detail part where power goes from the transformer to the control system and on to the track… or gets from rail to the wheels to the loco or lights, we need to be sure that the source of the power is good… so just a few words here about that.
• Power Supply: A quality power supply is important. If budget is an issue use a no longer wanted Laptop computer power supply, not that gnarly old trainset transformer that never had enough grunt even when it was new…
• Don’t share a power supply between track needs and accessories: This is NEVER a good idea. When the load grows one wins and one loses, and you need BOTH to work at their best all of the time.
• Taking power from the system around the layout needs REAL wire: This is NO different whether it’s a DC or DCC layout. Stay away from light gauge wire for all power feeds. Use heavy wire for all main track “bus” or feeds – and try to standardize on something solid enough to carry a reasonable current.
We suggest even for a modest layout, no wire that carries power for more than 10 feet (3 metres) should be less than 16 gauge, and if the layout is mid sized or larger, 14 gauge would be great!
• Taking power from the main feed wires to the rails: We can be a little lighter here, and droppers can be relatively fine if they are kept to one foot / 300mmb or less, but DO use lots of “droppers” from rail to the main feed wires. One of the BEST phrases to keep in mind here is “every bit of track should be soldered to something”. We suggest that every yard/metre of track should have “droppers” from rail to the main feed wires for best results.
The simple and sensible approach to droppers is: Use the largest wire you can reliably solder TIDILY AND INVISIBLY to the rails.
• Droppers must always be adequate, but can be small if they are short: for droppers where it’s hard to get to, or in difficult places, use droppers as small as 22 gauge if they are short (150mm/6” or less). Standardise on 20 gauge for droppers in easier to get places. These can be as long as 16” / 400mm without much voltage drop. It’s OK to use solid wire if stranded is hard to use well… dropper wires have NO movement and its better to make a neat joint after all!
• Keeping things Clean: The rail tops should shine like the prototype and so should the tread of the wheels (wheel backs should be really clean too where there are pickups… ad pickups often need cleaning too—they accumulate lots of amazing stuff, fluff, hair, dust… all covered in black grunge most of the time!)
But… you can’t spend your whole modelling time just cleaning stuff, so do your best to keep the gunk off in the first place and try to establish a good routine for cleaning everything.
On this page we will cover why each set of devices used on your layout should have its own discrete wiring circuitry, how to work out what power is needed for each of them and how to choose the best power supply for the job.
The following pages will include Wire charts and recommendations as well as how to lay out the bus, add filters, connect droppers and go about handling any complex trackwork or wiring issues you may come across.
It is the nature of layouts and modellers that all are different, so if you cannot answer your questions by reviewing these pages, please do feel free to email us and we will do our very best to give you some “One on One” assistance with your wiring problems or questions
Just click here with your mouse to bring up an email window.
CHOOSING THE BEST POWER SUPPLY
There are many good power supplies out there, many more are at best inadequate but unfortunately there are few that are really great.
Modellers often have no trouble spending lots of money on lots of locomotives, but will often skimp on a power supply. How silly is that - spend a fortune on nice quality loco’s so they’ll run well and look great, then not providing the layout with the right power to let them perform at their best! Of course YOU aren’t one of those foolish modellers, are you?
While some “start sets: specify a DC power supply or provide one in their “starter pack”, the same isn’t often true of full power systems.
MOST of these are sold with everything except the power supply.
All of the higher power DCC systems that need a separate power supply are equally comfortable on either AC or DC, but many of those same brands sell AC power supplies only. Why do you think that is?
The answer is simply price!
You see they look better if the transformer is lower in price as then the whole system will look to be lower priced when an uneducated retailer sells it to an unaware modeller… They may talk of it in glowing terms in their catalog but its all hot air, as an AC power supply is an incredibly basic thing - nothing more than a pretty label or two, a box containing a transformer, a fuse or (rarely) a circuit breaker, a lead to plug it into house current plus some terminals to connect your control system to and a lot of air.
The PROBLEMS with AC supplies are either ignored or glossed over.
· AC transformers have no real voltage control. For example, a transformer that is stated to be 5 amps at 15 volts will be about 19 volts with a very low load or no load connected, 15 volts until it gets to about 80% of its current limit and then it will start to drop volts, passing 12 at its rated limit and from then on, its down to 10, 9, 8…..
· AC transformers have no spike or surge protection. They have no filtering to eliminate line interference from other appliances, and as a transformer is simply a ratio reduction device (ie, 240 volts to 15 volts is a 16: 1 voltage reduction) if the line voltage drops, so does the output, if it spikes… so does the output… and this can kill the electronics in a DCC system, via “brown out” when voltages drop, and by supplying over-voltage during peaks.
The answer is really simple: Spend very little more of your hobby budget on a high quality DC power supply.
· With a good quality supply, You will gain a totally stable output voltage, from no load to at least 10% above rated capacity
· You will gain a good degree of surge protection and if the voltage drops at the mains, it will still stay table at the power supply outputs so your DCC system is well fed 100% of the time.
· You will inevitably gain a more reactive overload protection as the power supply is packed with lots of electronics to protect itself and the outputs.
MOST importantly though, you will gain more pleasure from your hobby, as everything will simply perform at its best!
As a modeller I like to pass on good tips, and here is one that can save you some money on a mid powered DCC system power supply.
LAPTOP COMPUTERS regularly die, but the power supply that plugs into them is almost always still fit and healthy. Look for them at work, at friends, anywhere… they are usually free once the computer dies!
They DO vary. 15 to 18 volts, always DC, from 3 to 5 amps. MOST will be perfect, but look for 15 volts as the best choice for your DCC system. Just cut off the DC input plug at the end of the lead and hey presto –a high quality, really well regulated and presto power supply… NO CHARGE!
BUYING A GOOD QUALITY POWER SUPPLY:
If its transformer based, look for weight as well as a pretty case. For example, our own DCCconcepts power supply is nearly TWICE the weight of most of the power supplies we compared it with when testing. Heavy means a BIG transformer, and big transformers are stable as they do not saturate easily under heavy sudden load, so this combo of heavy + regulated DC makes for the perfect power supply.
The disadvantage of heavy is of course, expense in shipping so if you are NOT in the same country as us, it will not be economical—but this image will give you an idea of what a top quality purpose designed DCC system power supply might look like, and how its specification might read!
We are very enthusiastic about its quality and excellent performance!
THE DCCconcepts PS-5 DCC power supply:
14.5v DC regulated plus 15.5v AC– 100% stable at 5 amps +.
This power supply is tough and it’s performance is as good as it looks.
Guaranteed to give stable output at any power up to its full 5 amp rating, it has a smoothly regulated DC output that we like to use with all brands of DCC equipment plus a second set of AC terminals for accessory use or those very rare systems that do demand an AC input. (Very, very few of them do really - as the first component inside most DCC systems is a DC rectifier anyway!)
Of course, it also has excellent onboard short circuit protection and appropriate mains fuse protection too.
We are delighted to sell this power supply with nearly every DCC system we offer and can confidently say that as a result, we’ve never, ever had a customer with any form of layout control or power related operational problem.
Both power output and voltages are ideal… at the DCC systems default outputs it gives an almost Perfect track voltage of 13.4 volts with NCE and Digitrax and other main brands.... perfect for all HO, OO and On30 layouts!
We recently found one more BIG advantage we didn’t expect!
A friend and good client had a lightning strike on his home, and all of his electronics including computer, microwave, air conditioner, reticulation system control and dishwasher etc were well and truly toasted... but NOT his DCC system, which we were delighted to find had been protected by our PS-5!
Admittedly, the PS-5 itself needed attention but with a couple of minor parts replaced, it was soon back up and running like new…. and we rate that a small price to pay to protect a $1000 DCC system and a layout full of locomotives and electronics!
We can’t guarantee such protection but fortunately, it DID happen this time!
The PS-5 is designed to work perfectly with Australian 240 volt mains power. It complies with all Australian safety standards requirements.
To learn more about the power supplies we sell or to buy the DCCconcepts PS-5 as detailed above, please click here.
PLANNING THE POWER & DISTRIBUTION
This does not need to be expensive or complex, just well thought out!
As we said above, to get the best from everything from layout lighting through point/turnout control and to ensure the best performance for DCC system and locomotives, it is important that you plan ahead and do not share a power supply between track needs and accessories:
So… Why shouldn't you save some time & money by wiring to a common power source and share things like track power when you have such a high current DCC system?
There are several reasons, all equally important:
(1) Retaining the ability to separately trace and maintain wiring:
As a layout grows, even though DCC itself requires relatively simple wiring and the total quantity of wires needed for track will remain relatively small, you will soon add wires for turnout / point motors, signals, lighting around the layout, and operating accessories etc.
Even though a single light may need only 2 wires, ten of them will need 20. A turnout motor may need only 3, but ten of them will need 30…. And it goes on. Before long you have looms of wires of various colours, and it becomes a blur.
How hard will it be to separate and work on them logically and systematically after a few months?
(2) Keeping the ability to troubleshoot problems
Its clear from this that if they are all added to the one main supply, then not only will loading increase, it will become nearly impossible to troubleshoot. Imagine if a fault in a simple light that you may not notice has failed creates a short circuit that will shut down the whole layout. How would you ever find it?
Therefore, you should do TWO things. Create a logical set of “Power districts” so you can turn off specific parts of the layout for troubleshooting and also make sure that accessories are powered by their own power supply….and via their own booster on a larger layout. Similarly lights should have their own power circuit, as should signalling and detection power as needed.
Allow each wiring circuit to do the job it should without unexpected interference or adding to current loading from other circuitry:
When different sorts of electrical devices share a common power source and wires, they will inevitably interact. This interaction is rarely without some form of negative effect on the performance of one or the other.
At its simplest it is one item draining current so there is no longer enough for the other to run reliably, but it can be much more complex.
For example, a DCC system puts out a clean square wave, and this is already influenced to some degree by the layout of the wiring or the distance it travels. IF YOU NOW ADD SOME OTHER devices, each will generate its own effect on the DCC signal even while static, and when it operates, it may generate a huge amount of “hash” or interference, causing locos to stop or run away, or preventing commands being received.
Good examples of this are solenoid point motors (Instantaneous current draw and a huge back EMF pulse when triggered) any form of motor connected to an accessory (constant interference with waveform, back EMF fed into track bus with negative possible effects). Even a simple light bulb can destroy control… I saw this recently where a bulb that had become intermittent really affected the smoothness of control of a DCC System, all because the tiny spring-like filament was intermittently losing contact as it vibrated.
In the following sections, I’ll explain step by step, from materials to the layout and configuration of the wiring.
POWER SUPPLY CHOICES
Achieving best practice without highest cost!
Power supply for the DCC System. We have shown you an excellent example above, and also shown you why a good supply is needed. The final choice is up to you, but make sure it matches the capabilities of your system in current draw.
DCC systems are rated at the level of current they are able to safely HANDLE internally and DELIVER to the track. Adding a power supply that has significantly higher power handling than the DCC system will NOT do anything to increase the ability of the DCC system to deliver power, but it MAY allow an excess of current to cause damage.
As a rule of thumb look for a 15 V AC supply equal or up to 20% higher in current rating than the DCC system, OR, ideally, a Regulated DC supply that matches the system properly.
Either choice will give you good stability at maximum current draw, and the regulated DC supply will always give the best stability under load..
Power Supply for Solenoid type turnout or point motors. Manufacturers may or may not provide guidance here, but one thing is dead certain - there is no way the average trainset controller power pack will give you enough power delivery for reliable operation of low impedance solenoids such as peco or Tenshodo/NJI types.
The simplest way to work out the ideal power supply for your chosen brand of solenoid motors is to use ohms law. This is expressed as E=I/R when used to calculate current need. (E = current draw, I = voltage, R = Resistance of coil
I have added some statements about How Ohms law is defined from the website “www.The12volt.com” and left all their hyperlinks in place as they will take you to a useful calculator for current draw etc. It is worth book-marking for future use.
They’ll open in a separate window so will not take you away from this website, so take a look and close the window when done and you will hopefully be back here!
Ohm's Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. One ohm is the resistance value through which one volt will maintain a current of one ampere.
OK… now how should you use ohms law to work out the power supply needs?
For a solenoid motor:
First, you will need to know the coil impedance. To measure it, set your multi-meter to “ohms”, put one probe on the centre or common terminals, the other on the left or right coil terminal.
Lets say you have a Peco PL-10 Point motor which will measure as approximately a 4 ohm coil. If your power supply is 15 volts, it will need to deliver 15v/4Ώ (ohms) which is 3.75 amps!
Allowing a little for possible voltage drop over wire length & through solder joints, you will need a power supply capable of 4 amps to reliably throw this point motor!
Because voltage drop will be at its max at the very moment it draws maximum current, please do consider a slightly bigger supply as lowered voltage really compromises efficiency… for example, look for between 15 and 20 volts at the terminals at 5 amps for a really solid point throw!
I promised you I’d try to keep costs down so there IS a low cost option here: It is a Laptop power supply that delivers 4 to 5 amps at 18 volts DC….
For a Stall type motor:
It is very similar really…. Measure the impedance of the motor (across the two motor brushes). This will give you the “R” part of your ohms law calculation.
(This is also handy for calculating current draw for DCC decoders by the way—it will give you the “stall current”)
For example, if the stall type turnout motor is very high in impedance it will need very low current to operate it at its rated voltage (usually between 6 and 12 volts with 9v about ideal. Pure DC is good for a stall type motor - lower voltage giving higher current… the advantage being slower changes which are still strong and reliable but have lower operating noise too!
A Cobalt motor will need no more than 30mA to operate, others will be similar and generally always less than 50mA.
Remember though that “stall” motors are always on and drawing power… so you should multiply current draw by the total quantity, ie: 12@30mA will be 360mA
Best power supply for these…. A regulated DC “wall wart” type, where the supply plugs directly into the mains socket - these are low cost and easy to find - you could for example happily power more than 15 Cobalt turnout motors safely with a no longer needed 500mA portable home phone battery charger!
For a Turnout motor with “end of throw” off switches:
Measure the motor as in the above example. A good example of this is the “Fulgurex” or “Lemaco” type. Please note that they have varied the motors they use over the years, however those I have here are about 40 ohm across the motor terminals, which would make them draw approximately 300mA at maximum.
This type draws power only when operating, so to choose a power supply for these, work out how many will ever be operating at once, the to be safe, add one more… (you never know what might happen in the future).
Best power supply for these…. Again it is probably regulated DC “wall wart” type, where the supply plugs directly into the mains socket - I would personally choose one that will let you choose the voltage, with a rating of approximately 1 to 1.5 amps to give you a bit of leeway for later changes in how many may be used at any one time.
For Signalling, Panel lights or layout lighting:
We can use a simple “rule of thumb” for calculating the power supply need for lighting of signal lamps, panel lamps or layout lighting (each of which ideally has its own supply of course). Simply use the figures below x the number which will be on at any one time, and you have a good guide to how big their power supply will need to be.
For normal low cost red, green or yellow LEDs, allow 5mA for every LED.
For standard super bright red, green or red LEDs, allow 20mA for every LED.
For white or Blue standard type LEDs allow 15mA for every LED
For standard super bright White or blue allow 30mA for every LED
This does NOT cover the LARGER sizes of LED, only up to 5mm. If you can, Check the actual LED specification sheets if your LED are anything but “normal types” for model railway use!
Incandescent bulbs: These vary quite a lot, however the figures below are pretty safe.
For normal grain of rice or wheat bulbs, allow 50mA
For small threaded base bulbs sold by most brands, allow 50mA
For any other lamp or light bulb, particularly automotive types, check before using—they will be a huge variety ratings, and can draw up to several amps each!
Best power supply for these…. LEDs should be run on DC, and incandescent bulbs will last longer on DC than AC too. Additionally, whilst LEDs are protected by the resistor you place in series with each of them, incandescent bulbs have no such protection.
For best life and to reduce the high heat output of any incandescent bulb of any size, run it at least 10% below its manufacturers ratings, and it will last a very, very long time!.
Yet again the best power supply is probably regulated DC “wall wart” type, where the supply plugs directly into the mains socket - I would personally choose one that will let you choose the voltage, with a rating to suit, but probably of approximately 1 to 1.5 amps to give you a bit of leeway for later changes in how many may be used at any one time.
TIME SAVING TIP:
“Wall wart” power supplies are low cost, so DO consider using several of them, distributed around under the layout. That way you will have several “local circuits” with perhaps just a couple of wires to the control panel - that will help you to reduce the number of long wires you need to run and keep tidy!
The next page includes Wire charts, wire size recommendations as well as how to lay out the bus, add filters to clean the waveform & suppress voltage spikes, connect droppers and go about handling any complex trackwork or wiring issues you may come across.
Do you still have questions? No problem – just click here to email us and ask, we’ll be happy to help!
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DCC INFORMATION & ADVICE # 8
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