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Modelling Tips, Links & Guides for Model Railways

Lumsdonia Railway

A web page for my indulgence and sharing ideas and irregular updates on my Model railway

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To run your layout you will need a power pack, to just run a basic set, all you need is the power pack supplied by Hornby/Bachmann consisting of the controller and wall plug in transformer.

But if you want to do more, you will need further power. Older DC controllers sometimes have an “Auxiliary” output of 12VDC and/or 16VAC. This is useful but cheaper DC and DCC controllers don't tend to have it.

Plan what you want, work out what voltage is needed and the current required.

Some items (“accessories”) you might like are:-

Lights, solenoid point motors, slow action point motors, motorised bridge/conveyor/tipper/level crossing, etc

Most lights are a nominal 12VDC, LED’s are about 2V but with a resistor in series can be fed from 12VDC, “Grain of wheat” bulbs can be had in 6V and either need a special supply or can be paired in series and fed from 12V, but unless you already have them, best not to buy them. They are available in 12V and LED’s are more commonly used now.

Of course if you want to keep it simple to begin with, a large number of LED’s can easily be run from a simple battery!

Point motors fall into two categories

Solenoid or snap type use two coils (3 wire device) and need to have a pulse of electricity to drive one way and a second pulse to a different terminal to drive the other way, although needed for a short duration, they need a lot of power. This is usual at least 12VDC, but as they can accept AC as well, most use a 16VAC supply, but a 17-22VDC is also acceptable. The pulse needs to be very high power, so a large transformer is needed (>1Amp) or a CDU can be fitted which is a better option anyway and means a much smaller PSU can be used.

Slow action or “stall motors” (2 wire type) use a motor and need 12VDC (DCC Concepts Cobalt prefers 9VDC), to change direction, the voltage needs to be reversed. They either have internal switches to stop at the end of travel or the motor hits an end stop and the motor stalls but with little current, so does not burn out. They only consume about 20mA each, but it may be constant.

0n the good 'ole days there was little choice, actually just two, use the aux 16VAC from your DC controller, or make y'er own from a transformer (and if you wanted DC, go to night school to learn electronics!)
These days there is a bewildering choice!
So here is a bit of guidance. There are two basic needs, general power for accessories like lights, etc, and heavy power for point motors.
For general, 12VDC is the most common and will be suitable for most accessories. There are many that advocate 16VAC for solenoid point motors (Hornby, Seep, H&M, etc) and they are not wrong, as it will supply twice the umf of 12VDC! However, using a CDU is the real answer and its power supply is not so critical, 12VDC works just as well.

Making your own is still an option (assuming your competent to mess with 230v mains AC!), can be cheap and can get you a high power supply, but is realistically only a few pence cheaper than hunting down a cheap ready made! (And have some electronics and construction skill!)
The cheapest option is a "wallmart" wall mounted (plug-in) "Adapter". look for 12VDC, 300 to 700mA types are OK for lighting etc, but you need at least 1Amp (1000mA) for point motors. Available as fixed voltage but some have variable voltage (3,4.5,6,7.5,9 &12) and are equally suitable.
Dichromic lamps and now LED lighting both demand a regulated 12VDC, so make an ideal choice, readily available from electrical wholesalers and comparatively cheap but have some high outputs (50VA=4Amps!)
The ultimate cheap option is "open frame", these are still safe to use, but require you make up the mains lead and terminate it,. The advantage is that you wont find cheaper for high power. They come in all sizes and go up beyond 12 Amps!
Another option is CCTV PSU's, they also tend to be 12VDC, and hunting around can find a nice size for a good price, made up with UK plug, ready to go.
Last option are "PC" PSU's types, tend to come with a "Euro connector" and lead for the mains and are ideal, though can be pricey. The choice is yours, but as a guide (2014 prices) expect to pay circa £10 for a 1 Amp wall adapter, circa £20 for a 3-4 Amp PSU, though open framed, can be had at the same price but can supply 6-12 Amps!
I can’t vouch for the supplier, but this supplier could be used for a guide
Example and if your prepared to wait, Ebay Far East suppliers are even cheaper!

A word of warning. A small layout will only need a small PSU (or 2), but if you have a high power demand and therefor want a high power PSU, it comes at a price, as high current will blow things up if you get a short! You must divide accessory types into groups and fuse them accordingly. (Example 5Amp PSU, with fused circuits for lights at 500mA, Points at 2A, turntable at 1A, etc, etc)[i.e. will involve some extra wiring/soldering and components] and the wiring between the PSU and fuses needs to be correctly sized for the PSU.

If you really want your points on 16VAC and a CDU, go for it, you just need to buy a separate transformer/PSU for them.
And finally, if you have slow motion point motors (Cobalt, tortoise) then a 9VDC supply is needed, meaning you need a separate supply, as you don't need anything above 1 Amp, nor a CDU.

Be warned, having several PSU’s for different items (controller, 12VDC, 16VDC, 9VDC, etc) will get complicated and different supplies should never be connected to each other! Each power supply must be treated as a seperate circuit/group and wiring should never be connected between them! A colour code for each type is highly recommended.

Even two power supplies of the same voltage should never be connected (to “double the power”) to each other.

If in doubt, always ask a competent person first! Mains electricity KILLS! Low voltage electricity can cause fires, injury and damage in the wrong hands.

Do not attempt to wire with 230v Mains (create your own PSU or even use the open frame type) unless you have had training or are an experienced electrician!

Some guides to help you with the Electrical side of your hobby

Low voltage Power Supply Unit Guide


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