Combining or Reducing Power Supplies

Posted by Alan on 28th January 2024 in Digital Command Control, Loco Testing Station, Model Railways with Comments closed |

I have a Kitwood Hill Models Test Track Box into which I’ll be fitting the Digitrax Zephyr DCS50 it was designed for plus a Sprog II USB interface and I’d like to put one combined power supply into my Loco Testing Station, for use by both devices separately, not simultanseously.

The intention is to be able to switch between the two devices, so only one is live at a time – either one or other but never both. So I purchased from RS Components a 870-3271 C14 Panel Mount IEC Connector with 5 x 30mm Fuse Block and a 161-8280 RS PRO Switching Power Supply 15VDC 51W. I haven’t purchased switches yet as I haven’t decided on the aesthetic requirements – there’s no shortage of suitable options.

If you dig deep enough on the Digitrax website, you find:

Digitrax recommends the use of a dedicated PS315 power supply or equivalent for use with the DCS50. PS315 output is rated at 15VAC RMS 60Hz and allows up to 3Amps to enable correct operation of the unit. A DC supply of 18VDC and 3Amps will ensure correct track voltage.

Similarly, on the Sprog DCC website, you find:

Recommended Input Voltage 12-15V DC Regulated

As I’m a member of the Model Electronics Railway Group, I asked on their forum:

Will that RS PRO power supply comfortably and reliably but separately power both devices, do I need to do something a bit cleverer or am I attempting something that is impractical, inadvisable or impossible?

Without copying the entire thread, responses from various obviously knowledgeable people including Andrew Crosland of Sprog-DCC suggested that I was over-enginering the solution. I was focused on the desired outcome rather than examining my starting points. It would be better and safer to use the DC input capability of the DCS50 to see what the output at the track was if the input voltage was safe for the Sprog.

I found among my Stash of Oneday Useful Random Stuff (SOURS) a universal laptop power supply that is variable between 15 and 24 Volts DC which ticks two important boxes in the forum discussion; no mains voltage inside the test box and supply the voltage that best suits the Sprog or DCS50, as neither would be in use at the same time. Power into this supply is a standard IEC C13 “kettle” lead.

As suggested, I connected the power supply to the DCS50 and tested the track voltage with a multimeter at various input voltages, starting at 15VDC. Per the clear instructions on the transformer, I unplugged the mains supply before changing the voltage setting each time. What I found was:

DC InDCC* Out
15.0V12.3V
16.0V12.6V
18.0V13.7V
20.0V13.7V
22.0V13.7V
Note: I’ve deliberately stated DCC (Voltage) Out as it’s neither DC nor AC. It is an alternating current but it’s not sinusoidal. It’s closer to a square wave but isn’t truly that either. So I’ve not called it AC.

Above 18.0VDC input, which was confirmed to be within the capability of the Sprog but probably undesirable, the output from the DCS50 did not increase at the track.

Conclusion? There’s no need for more than 18VDC, which would not adversely affect the Sprog, though it’s preferable to turn it down to the recommended 15VDC. Or use 16VDC as a happy (and safe) medium!

The next step is to return the original power supply and C14 socket to RS Components, or try at least as I’ve had them some months, and purchase a suitable panel mount 12VDC socket to plug that variable power supply into, installed on the end of the test box.

Then, from that power socket to a centre off two-way rocker switch to choose between the Sprog and the DCS50. On the DCS50 side, a second such switch to choose between programming and controlling. All of that running at no more than 18VDC inside the box, so red and black cables.

A Garden Tool Store

Posted by Alan on 3rd September 2017 in Garden Tool Store, Wood Butchery with Comments closed |

Our garden shed was the same as most, a dumping ground with no proper place for anything that was supposed to be in there and a lot of space being taken up by stuff that wasn’t supposed to be in there. Read more…

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Assembly jigs for legs

Posted by Alan on 16th June 2016 in Wood Butchery, Woodworking Jigs with Comments closed |

Although the output from this post benefits my model railway stuff, the subject is actually the jig. The Frem0n30 UK group require legs to hold the modules up at the same height and the easiest way of ensuring that happens is to supply them. Read more…

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Modules finally named and ballasted

Posted by Alan on 30th April 2016 in 0n30 Modules, Model Railways with Comments closed |

In other news, the dry weather today was exploited and my boards have received ballast! Davidson Crossing, Sunstone Creek, Balfern Curve and Inworth Curve are now drying in the shed. Read more…

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Modules depths reduced to 100mm

Posted by Alan on 30th April 2016 in 0n30 Modules, Model Railways, Wood Butchery, Woodworking Jigs with Comments closed |

Using a jig that I constructed last night from bits of wood in the shed, we have this afternoon reduced the depth of all the Tim Horn board kits in stock to 4″ from 6″, or 100mm from 150mm in modern money. Read more…

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Autumn Modelling Day 2015

Posted by Alan on 19th November 2015 in Model Railways with Comments closed |

At the 7mm NGA‘s Surrey Area Group Autumn Modelling Day, I took my four module boards to set up in the hall with Brian’s, partly to show other people the concept but also to try out other operating methods. Read more…

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Why the sporadic updates?

Posted by Alan on 27th October 2015 in 0n30 Modules, Model Railways with Comments closed |

Ask any woman and the one thing that no man can do is multi-task. Who am I to argue with that apparent fact? Railway modelling comes way down the priority list when you have a family and updating a blog about railway modelling below that! Read more…

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Painting the module boards

Posted by Alan on 24th October 2015 in 0n30 Modules, Model Railways with Comments closed |

Another hiatus, another school holiday! Having put my Dear Lady Wife and Son / Heir on a plane to Slovakia for half-term, I was able to take the module boards out of the loft and treat them to a coat of paint. Read more…

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Making stock boxes

Posted by Alan on 6th September 2015 in Model Railways with Comments closed |

For years, in fact forever, my rolling stock has lived in the boxes it arrived in, regardless of whether I bought it new or used. In the case of Bachmann stock, that means either large or larger green boxes with a great deal of dead space inside. When you put it all in the cupboard, a lot of space is used up.

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Laying more cork

Posted by Alan on 5th September 2015 in Model Railways with Comments closed |

In starting the middle board, we decided that we really would get it started and that involved laying some cork to bring the track bed up to the height of the other boards. This is just 3mm cork tile from the DIY superstore. It’s also something that Erik could do, under supervision.

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