Power districts how too

[Mark19]

Hi
I have an 8 x 4 layout with 3 tracks and one shunting areas although I know its not really needed on this size layout I would like each track circuit and the shunting area to have its own power district. I have looked into but it seems I would need a booster If I have read it correctly

I have a Digitrax EVOX Evolution Express Advanced 5A/8A Starter Set DCS210+ running at 5A, I was hoping I could use something like the Digitrax PM74 that allows for 4 power districts but I can only find wiring diagrams with a added booster.

IS it not possible to use my DCS210+ on its own by connecting it to the PM74 and then connecting my suggested power districts to this without a booster?

any advice would be great

Thanks
Mark

[Peterm]

The layout that I'm building now has seven 'zones'. I simply wire different parts, separated by isolating rail joiners. This means that if I have a short that stops everything, I just turn them all off, clear the short and then turn them on one at a time until the short re appears. Now I know where to look.

Having said that, I wouldn't bother with that size of layout.

[Mountain]

Why not wire for cab control but run DCC through it. That way fault finding is quick and easy. Just turn all section switches to "Off" and switch them on one at a time until the overload protection cuts in. The fault will be in that area that just tripped the overload cut out. One simply then goes straight to the line that the switch powers thus saving one a lot of time searching the wholw layout. No additional boosters needed. Just a few switches capable of handling 5 or more amps. I prefer cluncky toggle switches. Whilw I use DC these days, when I was using DCC, I was planning to wire this way due to the convenience of fault finding as one can trace shorts in seconds in some cases, as one goes directly to the area where there is a fault.

[RFS]

The purpose of multiple power districts is two-fold -

1. To ensure a short circuit in one district does not shut down the whole layout
2. If power requirements are large, there is the option for each power district to have its own booster

But you have a home layout where doubtless you are the only operator. If a short occurs, then I'm sure you won't be able to handle that as well as operate trains on the other parts. The need to keep the rest of the layout running, when one district suffers a short, really requires multiple operators and is most likely how a large club layout would be managed. I would also doubt your power requirements would require more than one booster.

Best solution is, as suggested above, to divide the layout into sections fully isolated from each other, ie both DCC feeds and IRJs on both rails. Feed each part via a switch and then it's easy to track down unexpected shorts to a particular section.

[RAF96]

The rule of thumb is if your layout fills both bays of a double garage then think about using power districts.
In practice if your controller is tripping out regularly due to overload or you need more sophisticated fault finding then look at how many power districts do you need to achieve that end.

[centenary]

Have to admit, I struggle with this sometimes! Numerous DCC manufacturers tell us starter systems with their 2 amp base units dont have enough power for 'large' layouts ie something in a typical UK single garage 5m x 2.6m. They tell us to buy their 5 amp or bigger power base upgrades and then to split the layout into numerous power districts for consistent running.

But my understanding is, where you have say a 5 amp power base, unless you fit a current limiter to each district, you'll be pumping 5 amp separately into each of those districts. And your 1.75 amp rated DCC sound chip will be lucky to survive intact if you get a short at that ampage. Even fitting 2 amp current limiters as suggested by Larry Puckett to overcome that possibility, seems to negate the very reason why you bought the 5 amp base unit upgrade in the first place!

What am I getting wrong?

[RFS]

But my understanding is, where you have say a 5 amp power base, unless you fit a current limiter to each district, you'll be pumping 5 amp separately into each of those districts. And your 1.75 amp rated DCC sound chip will be lucky to survive intact if you get a short at that amperage.

What am I getting wrong?

When you get a short circuit, it's exactly that - short. If a loco derails on a turnout the short goes directly through the pickups on the side causing the short, and will not be going via the decoder. A decoder can only get fried if you've wired it wrongly, for example, or it's not a make that has overload protection. Lenz and Zimo decoders have that protection which is one of the reasons I use them exclusively.

But any track short circuit should cause a circuit breaker (or command station if not using a CB) to trip immediately so the short only lasts a fraction of a second.

You also need to bear in mind that if you are supplying 5 amps to the track rather than 2-3 then your DCC wiring needs to be more substantial, so that when a short occurs it's detected immediately. If your wiring is too light, and a short goes undetected, it's the pickups and underside of the loco that will get seriously damaged by heat discharge rather than the chip.

[RAF96]

You could use a 50 amp supply and your locos and lights, etc will still only draw the power they need. The reason for upgrading your supply is to cater for the summed current used by all your connected devices, locos, points, lights, TT, etc. The reason for using power districts is to spread the total load, but that only works if you spread your locos around to match. Youcan have separate power districts but if 90% of your locos are in the yard then the rest of the power districts are under-utilised.

[jed10]

@RAF96 is absolutely right but let's try and unravel this a bit more to help explain things better.

Current is not 'pushed' into the circuit, rather the opposite. It's 'pulled' into the circuit as demand requires. That's quite a simplistic explanation but it is a way of thinking about how it works. If you have 4 locos running on the track, each drawing about 0.5A, then the current flowing through your system will be 2amps regardless of what it can potentially handle. If you have 4 sound fitted locos each drawing about 1A running on your track then that needs 4amps which is fine if you have a 5A system but if your system is only 3A you have a problem and it will probably trip out.

So, what you need to do is work out how much current is the maximum you may need to draw at any one time. That's including everything you intend to run from your dcc bus. For your locos, look up what current they draw as this is likely to be significantly less than the capacity of the decoder. For example, a N gauge non-sound loco with directional lighting is probably only going to draw about 250mA and certainly less than 500mA. Don't forget to include point motors if they are running from your dcc bus. Something like Cobalt IP Digitals use hardly any any current but other systems which include capacitor discharge units may use a lot more. However, you're unlikely to be simultaneously be changing more that three or four points at a time so make allowance for that. Also remember to include any signals etc. if they are powered by your dcc bus. Once you've added it all up, if the total of what is the maximum you may wish to run simultaneously is greater than the power capacity of your controller then you are going to need a booster. Then you can choose whether to use your booster to power two separate power districts or whether it would be better to use it to power a separate accessory bus. The second option is favoured by a lot of modellers where they have a lot of power hungry accessories, such as dcc controlled CDUs for points. Either way is fine so choose what works best for you. Two power districts is not uncommon but to need more is reserved mainly for very large layouts.

Now let's look at 'shorting' as this has been mentioned quite a lot. A short circuit is where the two poles join and there is no resistance or just minimal resistance across that join. When that happens the system will simlly trip out. If it didn't then things would start to catch fire so trip protection is pretty important. I would expect all dcc controllers to fulfil this task but the way they do it may vary. Some people choose to add a circuit breaker (like the PSX) to their bus but that's more to do with preventing trips through brief power overloads due to capacitor discharge. Most modellers will experience shorts from time to time but you should be working towards making this the exception rather than the rule. The most likely cause of a short is running a train into a set of points that isn't set to that fork. If that's something you are prone to doing it isn't difficult to create a track section power break immediately before the ponts which is switched by the activation of the point motor. Shorts may be caused by derailments so look into why your train has derailed and try to fix the problem. If you have a really big layout which requires multiple operators then maybe using power zones to isolate short circuits to a defined area is a good idea. On a home layout where it's just you operating then you're going to know where the problem has occurred and will be able to fix it and reset quite quickly.

Short circuits shouldn't damage your decoders. All decent or half decent decoders will cope fine with occassional shorts on track despite the scaremongering that is perpetrated by one particular manufacturer of dcc products. A brief short circuit which doesn't trip the system out may cause spikes which corrupt the dcc signal and cause your trains to do odd things. This is to be avoided if possible.

If you've chosen the right cable size for your dcc bus then it shouldn't matter whether you have a 3A, 5A or even a 7A power supply. Choosing the right cable is more about allowing sufficient capacity to cope with the dcc waveforms and harmonics than about the power capacity. If you've used 2.5mm sq cable it will be fine whatever power you run at. If you only have a small layout then 1.5mm sq cable will probably be fine too. If you've used anything smaller than that then you are likely to have far greater concerns to worry about than power rating. If you are starting from scratch then use 2.5mm sq stranded copper cable and you can't go wrong. Wiring your bus as a ring can also have advantages despite the misinformation which is often spread on this subject.

Try and avoid having switches on your dcc wiring unless it is for specific needs such as abc sections or safe zone cut outs on points approach which often aren't too bad if they are relay controlled. A switch, especially a manual switch, will create resistance and operation of a switch may cause spikes which will corrupt the dcc signal. Whilst the switching of track sections for isolation on DC layouts is commonplace and perfectly fine it's not a great thing on a DCC layout.

[Mark19]

Hi

Thanks for all your reply they are very helpful

Mark

[centenary]

You could use a 50 amp supply and your locos and lights, etc will still only draw the power they need. The reason for upgrading your supply is to cater for the summed current used by all your connected devices, locos, points, lights, TT, etc. The reason for using power districts is to spread the total load, but that only works if you spread your locos around to match. Youcan have separate power districts but if 90% of your locos are in the yard then the rest of the power districts are under-utilised.

That's a good tip about loco's location. Thanks!

[centenary]

@RAF96 is absolutely right but let's try and unravel this a bit more to help explain things better.

Current is not 'pushed' into the circuit, rather the opposite. It's 'pulled' into the circuit as demand requires. That's quite a simplistic explanation but it is a way of thinking about how it works. If you have 4 locos running on the track, each drawing about 0.5A, then the current flowing through your system will be 2amps regardless of what it can potentially handle. If you have 4 sound fitted locos each drawing about 1A running on your track then that needs 4amps which is fine if you have a 5A system but if your system is only 3A you have a problem and it will probably trip out.

So, what you need to do is work out how much current is the maximum you may need to draw at any one time. That's including everything you intend to run from your dcc bus. For your locos, look up what current they draw as this is likely to be significantly less than the capacity of the decoder. For example, a N gauge non-sound loco with directional lighting is probably only going to draw about 250mA and certainly less than 500mA. Don't forget to include point motors if they are running from your dcc bus. Something like Cobalt IP Digitals use hardly any any current but other systems which include capacitor discharge units may use a lot more. However, you're unlikely to be simultaneously be changing more that three or four points at a time so make allowance for that. Also remember to include any signals etc. if they are powered by your dcc bus. Once you've added it all up, if the total of what is the maximum you may wish to run simultaneously is greater than the power capacity of your controller then you are going to need a booster. Then you can choose whether to use your booster to power two separate power districts or whether it would be better to use it to power a separate accessory bus. The second option is favoured by a lot of modellers where they have a lot of power hungry accessories, such as dcc controlled CDUs for points. Either way is fine so choose what works best for you. Two power districts is not uncommon but to need more is reserved mainly for very large layouts.

Now let's look at 'shorting' as this has been mentioned quite a lot. A short circuit is where the two poles join and there is no resistance or just minimal resistance across that join. When that happens the system will simlly trip out. If it didn't then things would start to catch fire so trip protection is pretty important. I would expect all dcc controllers to fulfil this task but the way they do it may vary. Some people choose to add a circuit breaker (like the PSX) to their bus but that's more to do with preventing trips through brief power overloads due to capacitor discharge. Most modellers will experience shorts from time to time but you should be working towards making this the exception rather than the rule. The most likely cause of a short is running a train into a set of points that isn't set to that fork. If that's something you are prone to doing it isn't difficult to create a track section power break immediately before the ponts which is switched by the activation of the point motor. Shorts may be caused by derailments so look into why your train has derailed and try to fix the problem. If you have a really big layout which requires multiple operators then maybe using power zones to isolate short circuits to a defined area is a good idea. On a home layout where it's just you operating then you're going to know where the problem has occurred and will be able to fix it and reset quite quickly.

Short circuits shouldn't damage your decoders. All decent or half decent decoders will cope fine with occassional shorts on track despite the scaremongering that is perpetrated by one particular manufacturer of dcc products. A brief short circuit which doesn't trip the system out may cause spikes which corrupt the dcc signal and cause your trains to do odd things. This is to be avoided if possible.

If you've chosen the right cable size for your dcc bus then it shouldn't matter whether you have a 3A, 5A or even a 7A power supply. Choosing the right cable is more about allowing sufficient capacity to cope with the dcc waveforms and harmonics than about the power capacity. If you've used 2.5mm sq cable it will be fine whatever power you run at. If you only have a small layout then 1.5mm sq cable will probably be fine too. If you've used anything smaller than that then you are likely to have far greater concerns to worry about than power rating. If you are starting from scratch then use 2.5mm sq stranded copper cable and you can't go wrong. Wiring your bus as a ring can also have advantages despite the misinformation which is often spread on this subject.

Try and avoid having switches on your dcc wiring unless it is for specific needs such as abc sections or safe zone cut outs on points approach which often aren't too bad if they are relay controlled. A switch, especially a manual switch, will create resistance and operation of a switch may cause spikes which will corrupt the dcc signal. Whilst the switching of track sections for isolation on DC layouts is commonplace and perfectly fine it's not a great thing on a DCC layout.

Thanks for this as well. I'll probably need to re read it a couple of times though!