Tehachapi, BC

[Ed Kapuscinski]

Ahh, I knew the PSX has the adjustability, but I didn't know the scenarios where you'd need it.

The one thing that keeps me leaning towards the PSXes is that one of my local friends uses them, and is a big fan, and much like which system you use, I think there's a benefit to using stuff that has a local support network, especially since the price difference only seems to be $5-$10.

[basementcalling]

Stealing and learning, as my DCC experience could fit on a z scale GE44 tonner decoder with plenty of room left over.

Gary, your layout is as impressive under the benchwork as above.

[bdennis]

A DC bus like this is definitely on the list!  Just haven't had the time yet.  I'd be curious to know more about your step-down circuit because I too have a range of voltage requirements from 5-15 V and I'd prefer not to run separate busses for each.

Gary,
Here is the circuit diagram for the Voltage regulator.



It was available as a small kit from a local electronics store here in Australia. It looks like it is no longer available.

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You could make it by only using a few of the components if you know what voltage you need.
I have about 10 of these around the layout that drops the voltage from 16v to the desired voltage. Mostly 12v.
I have the booklet that comes with the kit. So if you want a full scan of it then PM me with a email address and I will scan and send.

[rodsup9000]

You could come off your 16 volt buss and add voltage regulators where you need them.  They have 3 legs, negative, Positive in and positive out. They are simple to use and solder up for your various power needs.  Voltage regulators are 7805 is 5 volts, 7812 is 12 volts and 7815 is 15 volts. For 9 volts, I use 7808's and they work. Also 79XX's are negative regulators, but I doubt you'll ever need them. 
 

 Your rr is very nice and I like how neat you have keep all the wiring.

[bdennis]

Rodney,
Yep I agree. I could also just use a regulator to suit the voltage I need. The advantage of this small circuit is that it is adjustable.

[GaryHinshaw]

Thanks for the feedback gents, that is very helpful.  I did a bit of reading on the 78xx's and I assume from Rodney's description that I may use them, for example, to tap off a main bus something like this, correct?



Further, suppose I am drawing 100 mA off each tap, then the 7812 regulator would internally dissipate 100 mA * (15−12) V = 0.3 W, while the 7805 would dissipate 100 mA * (15−5) V = 1 W, correct?  In that case I would probably not need to heat sink them.  Would you agree?  Thanks again.

 

[bdennis]

Gary,
Nice work.
I found with the LM317's that once the current approached 0.5A then a heat sink was needed.
Are you going to drive the RRCirkits boards from them and if so if any have tortoise machines then the current may increase.

[GaryHinshaw]

Thanks.  The boards themselves are powered by the 15V serial bus that comes off their Loconet adapter.  Powering the adapter sets the need for a 15 V bus in the first place.  Their Motorman board provides pass-through power for the switch machines and I was planning to use the 12 V taps to supply that.  Given that my boards are distributed around the layout, a single 12V tap would serve 1-2 boards or 8-16 Tortoises, so up to ~250 mA per tap.  That seems pretty manageable.

[C855B]

Thanks for the feedback gents, that is very helpful.  I did a bit of reading on the 78xx's and I assume from Rodney's description that I may use them, for example, to tap off a main bus something like this, correct?



Further, suppose I am drawing 100 mA off each tap, then the 7812 regulator would internally dissipate 100 mA * (15−12) V = 0.3 W, while the 7805 would dissipate 100 mA * (15−5) V = 1 W, correct?  In that case I would probably not need to heat sink them.  Would you agree?  Thanks again.

Ah, if it were only that easy. You need a couple of capacitors on the front and back of each one. Here's a "how to": http://www.electronicshub.org/understanding-7805-ic-voltage-regulator/. I would not use them without a little bit of a heat sink, even at low draws. 78xx/79xx are very inefficient and you will be surprised at how much "ouch!" they can generate.

My plan is commercial power supplies similar to computer types, supplying separate 12V and 5V buses of twisted #12. Many years of wiring 2-way radio transmitters taught me the hard way about shortcuts or cobbled taps.

[railnerd]

There will be quite a bit of heat generated by the 78xx linear regulator chips.  Without a good heat sink, most of the 78xx chips will be limited to about 100-150mA before they hit thermal shutdown as well.  Whenever I am putting regulators near things like wood or foam, that tends to make me nervous as well.

If you are interested in driving higher currents around 500mA and even higher (for more LEDs, Arduinos, etc.) with a lot less heat, there are also "reasonable" switching power supply modules.

I've had a great deal of luck with boards from Pololu like these:

https://www.pololu.com/category/131/step-down-voltage-regulators

Price varies by the amount of current it can supply, and the input voltage limits.

I've been really happy with these: https://www.pololu.com/product/2843

-Dave

[C855B]

Exactly. Start pricing those per tap, and watch your costs grow. Five taps buy you a real standalone regulated power supply from 110VAC from a non-discounted supplier like Mouser. That's why I advocate regulated buses on bigger supplies with beefy conductors to mitigate transmission drop.

Don't forget the necessity of fusing each tap. An engineer friend doing a "quick fix" for a test project burned-up his new Prius by being careless with fusing, "Oh, it's just a small tap... no problem!".

[GaryHinshaw]

Interesting.  This is making me think that a single 12V bus will be simpler and that I'll stick with the in-hand 15V wall warts for the serial bus adapters.

The idea for the 5V bus is still half-baked.  I was thinking it would be handy to have a USB charging bus for the tablets that I'm using as fascia-mounted control panels.  These tablets seem to have no trouble running through a session on a single charge, so it's not strictly necessary, but it seems like it would be nice to have.  The alternative is that I just charge them offline between sessions.  Has anyone here made a 5V bus with USB sockets along it (just for charging, not data)?

[bdennis]

Garry,
You could run your 12V bus and then modify 12v car chargers for the ipads. So the car charger does the 12v to 5V conversion.
Just be careful that Ipads need up to 2A to charge.

[parkrrrr]

The car charger idea is probably your best bet. To get full charging current, the iPad either needs to negotiate with a host controller or find a certain specific arrangement of resistors on the data lines of the USB port. Other manufacturers use a different arrangement, so most decent chargers these days have enough intelligence to emulate a host controller instead. (And the really good ones have resettable circuit breakers for that inevitable moment when someone plugs in a shorted charging cable.)

[GaryHinshaw]

Thank you, that's good to know about the USB specs.  Until I demonstrate that I need more than a single charge during a session, I'll just stick with battery power and an offline charging station.  Meanwhile, back above ground, the ballasting crews have returned to the Hill and are making their way towards Tunnel 9 and Walong:



I have also started brushing up on gimp so I can generate some finished photo back drops.  Now that the supplementary bus wires are run for block detection, ballasting and finished back drops are the only tasks standing in the way of finally laying down land forms.