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Confusion With DCC
Drew needs advice from readers and asks:
“I have a rather large HO layout – arranged in a L shape – 20 ft x 8 ft – which I am converting to DCC. Since DCC is supposedly AC power (or so I have been told), why are boosters needed since AC keeps a constant current regardless of the distance to the power supply (well, within reason…)? I have also purchased two (2) boosters for my layout. Since I now have three power supplies does it matter where I place the boosters on the “L”? Thanks VERY much for the answers!”
Add your comment or suggestion below this posting if you can help Drew.
31 Responses to Confusion With DCC
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Drew, As I understand it, the power booster does two things. Each locomotive or accessory draws a certain amount of current. The more locomotives, accessories, lights operating, the greater the current draw. At some point the current draw become too great and your locomotives won’t run well or you may pop a circuit breaker. The booster ensures that current stays at the same level. The second thing the booster does is keep the DCC signals at a steady level. Once again, this is due to current draw.
Drew..As far as I know DCC is not really AC but pulse modulated DC, hence the need for boosters.
The boosters can all go in the same place as long as your power supply to the track is 18 gauge or larger. You should place drops to that supply wire every 3 feet. This will eliminate places where your engine will show slower speeds. If your have a number of sidings you should also think about circuit breaker to help isolate shorts.
Yes, DCC is an AC voltage; however, your loco’s motors are still DC operated. That’s how many locos can operate on one track, while running at different speeds.
In a DCC decoder, there are components that change the AC voltage to a DC voltage for the motors. There is, also, a smoothing component that helps to prevent a jerky motion.
That’s about as simple as I can describe, without reverting to Electronics 101. Hope that helps.
DCC is NOT AC, it is pulse modulated DC. You can not run AC engines on it. It has about 14VDC with command pulses added to represent 1’s and 0’s.
Since DCC is good for about 50 ft in either direction from feed point, a booster shouldn’t be necessary if you don’t subdivide the layout. Just make certain that you cut the track circuit half way around the layout from the feed point. Ad a snubber circuit at both cut ends to corral run-away standing waves which can build a loco-killer spike.
Good point I knew that the bus wires should not form a complete loop. I completely missed the point that the track needed to be double gaped some place to prevent forming a complete loop in the DCC signal path.
What ia a snubber circuit?. Explain it in plain words please. English is not my father lenguage. Thanks. Guillermo, from the Patagonia Argentina
A snubber circuit is simply a non polarized capacitor and a resister in series across the track. The size for HO should be 100-15-ohm 1w (recommend 2w or 5w, keeps it cooler), capacitor .1 – .47uF.
I agree with James’ comment. Also, having more boosters allows you to isolate sections so that finding shorts is much easier rather than have the wholw layout shut down. Spreading them around the layout should allow continuous running no matter how many locos (within reason) that you are operating. Be aware that locos with sound draw more power.
Drew, you have been given some wrong information about AC. To put things simply:
1) Having more locos (etc) (all running at the same time) means taking more power from the track, so there must be more power put into it. Otherwise the voltage will drop and everything will slow down (or the overload will cut-out).
2) Whether a power supply is AC or DC, there is resistance in the supply wires and track, so it can help to have extra power inputs to the track on parts of the layout more distant from the main power input.
If only every railroad modeller would spend a little time studying the basics of electricity !
Also for your information, on a DCC system, the power supply is AC, and the DCC control signals consist of digital codes superimposed on the AC.
As already mentioned, the AC power is rectified to DC for the loco motors, and the digital codes tell the control system in the loco what speed is required.
The boosters are needed if you make use of the DCC capabilities to operate more then one or two trains on your layout independently.
Consider that one passenger train with loco and 6-8 lit up cars will take about 1,5 Amps -2 Amps to operate. If you then consider to operate a few Diesel engines in front of longer freight trains you may add 0,8 Amps per train. soon you will have exceeded the capacity of your standard DCC power supply which is around 4 Amps.
If you create separate power districts you can keep the amperage draw low as you most probably will operate your trains in the three districts that you could built with your equipment.
Be aware that if a operational mishap causes a short circuit and you have a power draw in the area of 4 Amps that may destroy the equipment involved in the short circuit. You are totally at the mercy of the speed of your DCC system short protection shut down.
Also no matter if you have DCC AC or DC operation with distance from the last power feed point you will loose Voltage. On our club layout we had DCC power Voltage drop of 2 V / 15 Meters. that will make LED lit cars shut down and sound to cut in and out.
One thing should remember about AC voltage the more distance and units you use pull down the whole system. The wire have restance and so do the tracks. And then if you add more the one power pull to the DCC each loco or item attached to that DCC unit shares with them all and you get less power per unit. One DCC would run your layout with little to no difficulty but more than one buster means that one DCC command unit don’t work as hard because it sharing the work. Long term you power units stay cooler and last longer plus it also eliminates possible dead spots in you track from bad joints or over switch’s so one bigger layouts the more power always good a good buss wire with multiple feeders save for lotscof head aches later.
if you check dcc is ac. the decoders change this back to dc for the motor this is why you haveto isolate the motor from track power and can,t use a com power point. the boosters are to keep currant balance , and brings it closer to points farr away from the main power without any voltage or curant loss , and you can splip it tino dist. you run the dist. on one booster at 5 amp.so that section of you layout has five amps on its own .if you get a short only that section of you layout will shut down .thats what the boosters does it almost like running two layout on one power supply and one central control.
The need for boosters is because the farther the engine gets from the energy source, the voltage drops, and with some engines being loaded with a lot of bells and whistles everything takes power. The boosters keep a constant flow of power. You will want each booster serving a certain amount of track so everything will run smooth.
Hi drew, my layout is same size as yours with 4 loops & a second level large terminus & sidings. I use a hornby dcc elite with 4amp psu. I use no boosters, all points dcc. I run 4-6 trains simultaneously & use no boosters. Sometimes I may run 2 sound locos (all with lights) approx dozen other locos with lights on too. Ive never noticed a problem. I don’t know how this compares with your system but would think as long a s psu ok & track clean you shouldn’t have any problems. Hope that helps & have fun
AC voltage drops over a line just like DC voltage. The amount of voltage drop is based on the current draw and the resistance of the conductor. Nickel silver rail has relatively high resistance compared to copper wire, so it is recommended to have feeder wires every few feet, that takes care of the voltage drop problem.
The other issue is that a DCC power pack can operate several trains simultaneously, as well as accessories, where a standard DC power pack normally only operates a single train. Hence, the boosters increase the current capacity of the layout because of anticipated increased load, not because of the increased distances.
The boosters should be placed so that during maximum loading (you have several friends/family operating during a session), the load is roughly evenly distributed between the three supplies. So, if you have 6 trains running, try to make it so that most of the time two are in each block as they travel around the layout.
My understanding is that boosters serve two purposes, firstly to isolate sections of your layout so that in the event of a short, only that section is shut down and the others will continue to operate, secondly your DCC unit outputs a certain amperage, and as the current draw nears that locos and accessories start acting up, electronics overheat and shut down occurs.
With only one controller and no additional boosters you might have 5 amps through the rails (or less depending on the type of rail and distance from the input source, and number of locos running. With three boosters you don’t have 3 x 5 = 15 amps, but 3 isolated sections each of 5 amps.
It is always a good idea to have the “Bus Wires” running around under the base board as big a diameter (wire gauge) as possible (stripped down house wiring is a good size), and ever piece of track should (ideally) have a dropper wire down to the bus wires. Hence the “every three foot” comment above.
Have fun
David
If you only run a few locos at any one time you will not require boosters. Try without them, and fit a booster if you find you have a problem. Most layouts only run 3 to 4 locos at once.
I can run 3-4 locos simultaneously on my 8′ x 11 ‘ layout, but I decided only to use the track power supply for locos and not for DCC equipment. My switch decoders for example run 12VDC from another power source. I have over 100 lit objects and 7 motorized devices that run from separate power. This makes for more wiring but it separates the loco power from all the rest. I use Digitrax throughout and use their 5A booster.
Ohm’s law applies to all circuits whether they are AC powered or DC. As stated Ohm’s law is E=IR where E = voltage, I = Current and R = Resistance. If you have a high load current (due to multiple engines or some other device) at some distance from your power pack, the resistance of the track will cause a voltage drop between your pack and the train. That is why it is important to, as has been stated, to run a buss line underneath the layout and connect the track at 3′ intervals. Boosters are used to increase the load capacity of your layout if it exceeds the capacity of your single power pack. The other advantage of boosters is they allow you to setup up districts so that a short in one area won’t impact the whole layout.
Drew,
Wire the Controller and all the boosters. Wiring is the most difficult so do it all at once and not
piecemeal. Each controller and booster acts as its own
circuit breaker so all of the transformers must be identical to maintain even power. Place the
controller unit in a central location and the boosters, if wiring permits, are best spread around
as having them all together creates excessive heat and you will need a computer fan to cool
them. Wiring to the individual blocks will determine placement. Blocks should be separated
by use and NOT by track length or size of run. ei- use the boosters for yard power as the number of loks and decoders can be extreme. Next would be an area with heavy siding use for industries. Last would be the mains. Buy a RRampMeter V1 from amhobby.com which gives accurate track voltage and amp readings and is something you will need to find shorts and dirty track as time passes.
I don’t know the gauge on your layout, but use cheaper zipcord wire for the main track buss wires from each unit. This is known generally as cheap speaker wire at the box store and use 12 AWG or in the EU 4 or 6. Zipcord has low inductance, but I suggest three twists per foot or 10 per meter.
It is not solid core so one will need to use a series of terminal buss strips or terminal strips to distribute power to track feeders, etc. as soldering is out. Using terminal strips makes it easier to repair track power and to track-down shorts and there is no soldering or suitcase attachments to remove. These buss wires are very large, lose less power over distances, but you must take a solid copper wire and insert/solder/shrink wrap it into the ends to make smaller wire size connections to the controllers, boosters, and feeder terminal strips. Track Buss Wiring is the backbone of the entire system. and you have the boosters to do it right.
Drew,
All is true. Don’t get tied up with AC power as you say. DCC is just DC with a constant power to the tracks and the control signals go out through the tracks with just a few volts higher than Standard DC. Like they said you only need boosters if you are running a lot of engines I have had 8 running on mine without boosters The constant power is to be able to send your signals to the engines and their chips at any time. There are some needs if wiring will go a long long way. and most of that is your throttle controller and the distance your cables for them go back to your DCC System to send the signal through your tracks. Any big distance in your track Buss Wires if there is power loss those long distance wires may need to be a heavier gauge like 16 or 14 gauge which will carry it farther. I have a 24 foot by 16 foot with wires to over 200 feet of track so far and I am only using 16 gauge trailer wire. My plan though is to link up some modules I had back in a club one time and they will be out in the second bay of the garage and I plan to feet that power with 14 gauge just in case. When I get my link bridge finished to connect the main layout to these module’s will give me a lot more layout when the guys come over for a lot more running room. Just think of DCC Power as DC with a twist. If it was really AC then I would not be able to try a DC engine on a DCC system to see how it would work , I don;t know about other systems but Digitrax will allow a DC engine be test run on the DCC system on a zero zero code even while running your DCC engines. (Caution though don’t run them to long under DCC and don’t let them sit on the track stopped under DCC as the voltage is still going to the engine even if it is stopped). It merely allows you to see how that engine might perform under DCC power. The Southern Pacific Cab forward running a test run in DCC. It was a very old DC engine but We did not leave it stopped on the track and we only took it around the layout a couple of times as with the extra few volts DCC has can overheat the motor of a standard DC engine if let sit on the track without a chip installed. Some MFG’s tell you on some of their engines that Not to run them at all on DCC without being converted to DCC. It could be the light circuit board or the wiring to the motor.But they will say that on the box. But most older engines can be tested on DCC as I just stated. I work with older engines and I test them to make sure it should perform well under DCC before I spend the money on the chip.
from Newman
Hi Drew
To understand how DCC works firstly you need to understand how a DC motor works. Briefly a DC motor or permanent magnet motor has one or two magnets acting as the field magnets around the outside of the motor the Armature is a series electro magnets that supply the magnet force to turn the armature the more voltage supplied to the armature the more magnetic power is generated to turn the armature faster. On DCC the main feed is AC power and the electronics that supply the motor with power to turn the armature of the DC motor convert the ac to dc in other words a small rectifier. the speed of the motor is supplied by increasing or decreasing that converted power through another or other part of that integrated circuit. now to control the variable power another part of the chip is fed via a digitally imposed signal on the ac power from the controller also this chip is programmable to an address that can be coded into the system so that it only picks up that signal that is intended for the operation of that particular loco or other device. To explain properly I would need to write a book. Now some do and can operate a DC loco on DCC but by not having the loco moving the spike voltage that is generated can and will burn out the DC motor over a period of time, this is why the motor has to be isolated from the ac and run via a decoder. Now all systems using power will incur a voltage drop depending on the distance from the controller, to over come this we use a booster pack placed at intervals around the layout to build this power back up to the optimum voltage again but the track has to be isolated from the first pack and so on. Usually three packs are sufficient for most medium layouts and the bigger the layout the more packs that will be supplied. you can also run a larger size track cable to offset this to a certain degree, However the more loco’s and other devices that you have running will drag more power or Amps from your system again increasing the voltage drop. In saying all that do not say I wont run DCC just because it sounds complicated learn as you go and I am sure you will never regret the decision and as with this or other system there is the added increase of costs. I converted from Dc to DCC a couple of years ago and have never regretted it.
Just want to put my 2 bobs worth in, if i may.
Please Please Please , If anyone wants to reply via this post then when discussing things (anything) then please try and explain things in a simpler way.
Some of you may have years of experience and knowledge re railway, dc , dcc etc etc, but,,,
many of us do not understand your lingo and become very frustrated re explanations.
Good point Charlie. The KISS principle should always apply, and I do TRY to remember I was once a novice. Back to my post about bus wires and droppers – I hope I made myself understood – bus wires under the baseboard, droppers from the rails to the bus wires from each piece of track. Drew, don’t allow yourself too much grief in the DC/DCC debate. Get your system and connect it up according to the manufacturer’s instructions and run some locos. For a small layout it might just be the mythical 2 wires.
DCC is not so hard to understand if you are starting from scratch – it is a bit harder for old fossils like me who sometime mix my whites with my coloureds as it were.
Whom is considered the better restoration shops in re-paint, can motors, LED lighting, lettering, etc?.
I have several late 40s-early 50s loco/tender I would like restore,,d to good running condition to give my grand kids when I check out. I wish them to enjoy the trains without having to piddle with the old AF reversing units and other finicky stuff like headlamp, drooping boiler fronts, etc.
Thank You,
Best to all,
David Woodruff
Sorry for you guys, BUT, DCC is neither DC nor AC voltage. DC power is like the 12V battery in your car; it’s a steady 12 V. with lots of Amp. plus DC has no frequency. AC power is like the juice in our household outlets; it’s a Sine wave curve which oscillates at 50 or 60 Hertz depending on the country you live in. So, what is DCC then ?? DCC (Digital Command Control) is a Pulse width modulated square wave. The wave looks like the ‘0’ bit or ‘1’ bit in a computer. Square wave means the top and the bottom of the wave are flat. In the DCC world, the ‘1’ bit is faster in frequency than the ‘0’ bit. Hence the term Pulse width modulation or PWM. Most DCC system will run into the ultrasound range so we can not hear them. Don’t forget here that the audible range for human beings goes from 20 Hertz to 20 kHz.
For example, my NCE DCC command station runs at 31.5 kHz which is really out of the AC 60 Hz range.
As a summary: DC= 0 Hertz, AC= 50 or 60 Hertz and DCC= 20 Khz and above.
Now do we need a booster? If your layout is wired with 10 amp. wire gauge and if all the metal joints are thight enough to keep the best conductivity (= zero resistance) between each section of trackl then the booster is useless. Unless your main line exceeds 30 meters long. Run your trains first before buying a booster. You will then find out. Good luck Drew with your findings.
Jean Alain
Hi Drew I run an oo scale layout which is in a u shape 17′ x 10′ x 17′ with a helix at both ends rising 15″ to another level of the same dimensions. The helix both run twin tracks. Altogether there is well over 300′ of track + a Walters 130 scaled foot powered dcc turntable with 7 twin engine sheds and I run 5 dmu s with lighted coaches and directional lights 4 diesel loco’s 3 steam engines and 1 shunter + take my building lights + signals from the same dcc unit which is an NEC powercab with 1 5amp booster. Never had a problem runs the whole layout from 2 power feeds.