Help with power supplies

[Porkster]

Apart from the track supply, should I have one power supply for all of the accessories including point motors, lighting and signals etc or should I split these items into two And also, what current rating should be used. Your comments would be helpful, thank you 

[Chrissaf]

It depends........

.

Put 10 people in a room and ask them your question and you will get 10 different answers. It depends upon the size of layout, the complexity of the accessories you want to power, how many individual items and personal preference.

.

You mention point motors, so I am assuming that you will not be intending to power and control them via DCC Accessory Decoders.

.

Different accessories have, in an ideal world, different optimum power requirements. Yes, you could power everything from one single source, but then most things will end up being a compromise. Plus the amount of current needed from a 'one size fits all' approach starts to add up.

.

My personal choice, but I separate my points operation from my general power distribution. For points, I use a 16 volt AC supply fed into a powerful CDU.

.

For accessories (non points) and LED lighting I use a recycled PC ATX power supply. The ATX power supplies are really cheap and give very high current capabilities. My ATX has a total aggregate current rating of 22 amps split dynamically across the 12 volt DC and 5 volt DC rails. There are loads of YouTube videos on converting ATX power supplies for generic use. The main key things to note when converting an ATX are:

.

1. The 'Green' wire needs to be connected to a 'Black 0 volt ground wire' to switch the ATX output 'ON'.
2. Although the mass of output wires give multiple outputs of the different voltages. For each voltage value, the wires are 'commoned' within the ATX. This means for example, once you have identified the voltages you want to use then the excess duplicate wires with the same voltage (wire colours) on them can be cut away.
3. All the 'Black 0 volt wires' are also commoned within the ATX. Thus all you need to retain is a 12 volt wire (typically Yellow) an optional 5 volt wire (typically Red) two Black 0 volt return wires and the Green wire connected to a Black wire. Everyting else, output wire wise, can be cut away and discarded.

.

The 12 volt output I use for trackside signals and any shop bought accessory designed for 12 volt use. The 5 volt output I use for general layout LED lighting. I run the 5 volts through a switch, so that I can switch the layout lighting off if I want to.

.

I work on the basis of 10 mA max (but prefer 5 mA) per individual LED, and choose my current limiting resistor accordingly. Typically a 'white' or 'warm white' LED has a forward bias voltage of 3 volts. Therefore on a 5 volt supply one needs to drop 2 volts across the current limiting resistor. Resistance = Voltage / Current. Therefore, to drop 2 volts on a 5 volt supply drawing 5 mA the resistor value needed is R = 2 / 0.005 = 400 ohms.........thus a standard resistor value of 470 ohms is more than adequate (or 1,800 ohms on a 12 volts power supply).

.

The one thing I actively avoid, is using the aux output of any controller for accessories. I much prefer using a dedicated separate power supply that is 'fit for purpose'.

[Chrissaf]

PS to above. Some of the YouTube ATX conversion videos mention the need to fit a dummy load resistor. I have converted more than one ATX for generic use and not found it necessary to fit a dummy load. More modern ATX supplies don't appear to need them.

[Porkster]

Hi Chris thank you so much for the time and effort you have put in to helping me with this decision. i understand exactly what you are advising and I can see how one supply would not be be the ultimate way to go. I didn't quite appreciate that different accessories have or may have different voltage requirements.  ie led lighting

i am not sure what an ATX is but assume it is a low cost multi voltage plug in power supply. I will check it out on youtube.

With respect to controlling my point motors. I have purchased a power cab controller (still in box unopened) which will control accessories, however, as I understand it, you can not control the loco while you are in accessory control mode. Thus while you are trying to locate and switch a particular point the loco could have travelled 2 or 3 metres or more which seems to me to make the whole thing quite complex compared with flicking a switch. I would be interested in you comments on this along with your thoughts on what type of switch would work for this application. Thank you once again,

Porkster

[Chrissaf]

ATX is an industry standard specification for PC power supply units. Go back in history and IBM (the first to make the XT desktop PC) created a PC termed the AT for Advanced Technology. The AT power supply morphed later into the ATX (Advanced Technology eXtended). Although the original IBM XT PC hails from the 1980's, somehow the ATX power supply (1990's) has survived the last 30 odd years of PC development. Being based upon a common standard means the manufacturers compete on price, making the ATX power supply one of the cheapest ways to get a quality high current switch mode power supply unit. Also, being based on a standard, means worldwide availability with the mains input spec being appropriate to the country being distributed in. For example 220-240V (UK) 110V (US) etc.

.

https://en.wikipedia.org/wiki/ATX

.

/media/tinymce_upload/280a9ee48e0e9acc0bd44a46b1f86ee1.jpg

.

Note the Yellow, Red and Black wires (multiple duplicates) in the photo above. The ATX also has a 3.3 volt output as well, but I don't use that output myself.

.

Point of clarity. LEDs can run off a 12 volt supply just as easily as a 5 volt supply, or any other voltage for that matter as long as the resistor value is carefully chosen to suit (hence my comment relating to 1,800 ohms for 12 volts in first reply). I just run my LED lighting off 5 volts because the ATX has the dual voltage capability and it allows me to switch the layout lighting 'on' and 'off' independently from the other permanently powered accessories.

.

It is true that in DCC you can only control one item at a time and you have to select each item to control 'as and when' required. It is also true that doing that via a physical controller, means doing multiple tasks quickly needs a lot of practice and requires concentration. That is why I use Hornby RailMaster, the mouse 'point and click' support makes doing this a lot easier (with RailMaster you can even automate track routes that can be set up at the click of a single screen icon).There are many here (not using RailMaster) that for the very reason you highlighted, relegate their DCC controller to just controlling locos and use alternative traditional methods for controlling their points. For solenoid based points, this could be via non locking centre off change-over toggle switches, stud and probe or sometimes 'Wire In Tube' (WIT doesn't require any solenoid motors or electrical wiring as the point operation is purely mechanical).

.

Some on here have created, to their own design, a more complex point wiring scheme that allows manual switching arrangements to function in parallel with their DCC Accessory Decoders. This gives them the flexibility to use either DCC OR manual switching to throw their points concurrently in real time.

.

The following comment needs a bit more research to confirm, but I believe that the Power Cab (NCE?) although not compatible with RailMaster may be compatible with other PC Railway control software such as 'Big Bear' and JMRI (Java Model Railway Interface). JMRI is an open source (free) application. Big Bear, looks very similar in appearance and operation to RailMaster, but doesn't do CV reading and writing, only controlling devices. In other words, 'Big Bear' is just a Graphical User Interface (GUI) for the supported controller. A list of the supported controllers is on the Big Bear web site.

.

 

[Porkster]

Thank you for the information on the ATX. I have done some searching over here (NZ) and found I can purchase a "Enermax ENP500 AST psu" . I see it's a uk manufactured unit. i think this is what you are refering to? Would this be suitable? Regards Porkster.

[2e0dtoeric]

Just about any (or all) desktop pc's have an ATX supply! Just find a scrap pc, remove it (four screws, usually) and away you go!

The 'mains in' is via the screened three pin plug - bottom right in Chrissaf's pic, In the UK the are referred to as kettle leads, because the electric kettle has a similar fitting!

[Chrissaf]

As Eric says, it shouldn't really be necessary to buy a brand new ATX specification power supply. The PC churn rate (replacement rate) is so high, that you should be able to obtain a secondhand recycled one for minimal expense. You could try a PC repair shop, they must have a stock room full of recovered units. Even brand new ones sell here in the UK for about £12 to £16, so secondhand should be under £10. If for convenience, you just want to purchase a new one, try Amazon and eBay for cheap prices.

.

Again here in the UK we have 'Freecycle'. A web based 'free recycling' web site that shows what is on offer for personal collection 'free of charge' in ones local area. I have in the past given away old obsolete PC's with good power supplies still in them using Freecycle. According to the website, Freecycle does operate in NZ, there may be a branch in your locality.........use the search function on the above Internet link. There may be other similar recycling services operating in your local NZ area too.

[Hairy]

Another avenue to explore is IT departments where you work, I asked mine if they had any ATX power supplies from dead PCs and hey presto one appeared.

[Porkster]

I asked my wife if she new anyone with an old pc. She looked at me with a smile on her face said yes, us!!  It turns out that a second pc we had that she did the accounts on was no longer needed and not used anymore, so looks like I have myself a ATX. I will attack the pic at some stage soon and extract the goodies. Thank you all very much for your guidance,It's very much appreciated. The money I will save can go toward a good quality CDU, circuit breakers and a couple of RLM's. Cheers Porkster

[robcat]

Hi Porkster

 

I am also in NZ. Maybe we are near to each other. I don't know how we can make contact perhaps Hornby site administrator  can help here if you ae interested , sounds like we may be learning DCC  at the same time. I am in Waikato, any use to you?

cheers

[Porkster]

Hi mate, thanks for your message. Yes I am going through the huge learning curve trying to get a basic understanding of this very fascinating hobby. I am in the process of building a layout which most experienced modellers have told me is very ambitious for s novice and I can now see where they are coming from. Every decision we ( my wife is very interested too ) make takes hours so progress is steady but slow. The guys on here are fantastic, so knowledgeable and so willing to pass on their experience and knowhow. Each day I learn something new. I know it won't run smoothly but we will get there in the end. Cheers Porkster

 

[Porkster]

Just by way of a footnote to this topic I managed to buy an old PC on NZ Trademe for $11.50. I have moved the ATX power supply, followed all the advice and now have a working power supply with 12v and 5v. So thank you all very much for your help and advice. Regards Porkster