DC buses for various layout devices.

[Specter3]

So I am going to run wiring for a DC bus for various accessories. In research I stumbled across this conversation on another board:

http://cs.trains.com/mrr/f/744/t/260455.aspx

They talk of two basic DC bus schemes. One seems to be a 12-14v single bus with taps and step down circuitry at the point of use. They talk of multiple components that do this that sound fairly inexpensive. The other scheme is a single device(such as a PC power supply, which is very interesting to me as I have some) that provides 3.3v 5v and 12v and run separate buses for each voltage all around the layout. Before I put down foam I would like to get this closer to firmed up.

[John]

Other than the DCC bus, I have an 18volt 1 amp laptop transformer that I use to power a DC bus all the way around the layout.  On average, I measure 14-15 volts all around the layout on this bus ..

Something like this should supply all the "juice" you need. Most of the accessory decoders work in the 12-15 volt range .. for everything else, such as LED lights, I just use some resistors to bring the voltage to the level I need it .. 

https://ohmslawcalculator.com/ohms-law-calculator

https://ohmslawcalculator.com/voltage-divider-calculator

https://ohmslawcalculator.com/voltage-divider-calculator


I'm sure those other folks are pretty smart fellows over on that other forum .. but why over engineer something and spend money when you don't have to.  Model railroaders should always apply the KISS rule in addition to rule #1

[C855B]

Yeah, what John said. Plus that way you avoid the voltage drop issue if you put too small wire or too long a run with the lower voltages. 1V drop on 12-14V? No big deal. 1V drop on 3.3V? Oops.

[peteski]

Except for some computer chips (on computer motherboards), what uses 3.3V?  I have never seen anybody using that voltage on a model train layout.  I hope the answer is not "white LEDs"!   Even 5V is not that common.  As others have said, lower voltages can be derived easily and cheaply from a 12-14V bus, with plenty of voltage to spare to keep the lower voltages within specs.

[Specter3]

Thanks guys. I was wondering if I was overthinking it after reading the thread.

[CodyO]

Except for some computer chips (on computer motherboards), what uses 3.3V?  I have never seen anybody using that voltage on a model train layout.  I hope the answer is not "white LEDs"!   Even 5V is not that common.  As others have said, lower voltages can be derived easily and cheaply from a 12-14V bus, with plenty of voltage to spare to keep the lower voltages within specs.

I do use the 3.3v from a PC power Supply for my Cobalt switch machines, No real issues with voltage drop with about 20' of run.

[peteski]

I do use the 3.3v from a PC power Supply for my Cobalt switch machines, No real issues with voltage drop with about 20' of run.

Cool, we have one use.  Are those designed specifically for 3.3V, or you are using them at a reduced voltage to slow them down?

[CodyO]

Cool, we have one use.  Are those designed specifically for 3.3V, or you are using them at a reduced voltage to slow them down?

The can use 7-18v but I cut it down to 3.3 so they really crawl

[peteski]

The can use 7-18v but I cut it down to 3.3 so they really crawl

Ok, so 3.3V was not by design, but totally by your choice.  Sounds like you found a prefect application for a computer power supply that provides 3.3V (usually at fairly high amperage).

[John]

http://www.circuitous.ca/ATpsu.html

[MK]

Even easier, a no brainer easier.

https://www.amazon.com/XH-M229-Desktop-Computer-Transfer-Terminal/dp/B07SV4KZ4B/ref=mp_s_a_1_3?dchild=1&keywords=atx+power+supply+adapter+board&qid=1609098936&sprefix=atx+power+supply+ada&sr=8-3

[John]

Even easier, a no brainer easier.

https://www.amazon.com/XH-M229-Desktop-Computer-Transfer-Terminal/dp/B07SV4KZ4B/ref=mp_s_a_1_3?dchild=1&keywords=atx+power+supply+adapter+board&qid=1609098936&sprefix=atx+power+supply+ada&sr=8-3

I like that ..