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Mean Well 15V 5A

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Alan:
Okay, I get it now. There are multiple power supplies but they are isolated from each other as each power supply feeds only its respective DB150. The power supplies are essentially "hidden" from each other behind the DB150s. That being the case there is no concern about power supplies interfering with each other.

The DB150 appears to have over-current protection built in. The manual says the DB150 will chirp and shut down during a quarter across the rails test. I can't find at what amperage the shut down occurs but I assume it is 5A since that is the advertised rating for the DB150. Nonetheless, it means the DB150 limits the current on the rails, not the power supply. You could wire your single 20A power supply to feed all your DB150s and rely on the DB150s to protect against shorts.

My own setup works similarly. The layout is divided into over 30 different power districts but they are all powered by a single 7A power supply. The trip current for any one district is set based on the expected load. For instance, a 20' stretch of main track is set for 4A because there may be a power hungry consist running across it while a short industry spur may be set for only 1A because all it will ever see is a single engine under light load. I did it this way to reduce short circuit sparking to the lowest possible level. My breakers are adjustable so I can change the trip point without much fuss if need be. Another RP advantage - if in the future I need more than 7A to run my layout all I have to do is swap out the power supply for one with more beef. Done.

20A is a lot of power. Sure you need that much? That is like 60 locomotives running at full load. Must be one heck of a Free-mo arrangement.

TwinStar:
Is 20 amps too much? Maybe, I'm not sure. My module set is 46' across with 110' of mainline. There's the potential of having six freight trains, six passenger trains (with or without lighting), and two local switchers with one working each end of the passenger platforms. The passenger tracks will have kill switches for noise abatement but I can't guarantee they'll all be off. I was planning to split the mains and divide the passenger platforms in half giving each 5a a piece.

TwinStar:
Would this be better?

https://tinyurl.com/ydhvj9ew

G8B4Life:
In a general sense, you can't have too much power, only too little  :)

If we pretend that each DB-150 will only ever be pulling 4A max at the same time you could run 4 DB-150's from the 20A PS at the same time (it's not a good idea to run a PS at it's full rated capacity for extended periods so 4 DB-150's at 4A gives us a nice margin).

If you had a 10A PS you could run 2 DB-150's. If you then needed to add another DB-150 you'd have to get another power supply, either a separate one for the new DB-150 by itself or a larger capacity one to power all of them.

As the power supply is behind the DB-150, ie the DB-150 is between the track (the source of shorts) and the power supply you shouldn't have any worries of putting 20A into a short, the DB-150 should limit that to the rating of the DB-150. I'd still put in circuit breakers anyway so it would look like this (I'll do a better drawing)

Power supply -> DB-150 -> breaker -> Track.

- Tim

Alan:

--- Quote from: TwinStar on January 03, 2018, 08:33:10 PM ---Would this be better?

https://tinyurl.com/ydhvj9ew

--- End quote ---

That power supply is a constant current type. You don't want that. It is made for use with devices that require controlled voltage and controlled current. A conventional general purpose power supply is what you need. MeanWell SE series is the right choice for your application.

It doesn't really matter how many DB150s there are or how long your mainline is. The sole determining factor is the expected electrical load. Add up the current draw of everything that may be running at the same time then add 25% for headroom. That is how many amps you need. Bigger power supplies cost more, take up more space, and make more heat. If those attributes are not important then buy the highest amperage unit you can afford.

Let's add up your example:

* Six freight trains - let's say 4 locos each train = 24 locos @ 300mA ea (under heavy load) = 7.2A
* Six passenger trains - let's say 2 locos each train = 12 locos @ 300mA ea (at high speed) = 3.6A
* Lighted passenger cars - let's say 6 trains with 6 cars per train @ 4 LEDs per car = 144 LEDs @ 20mA per LED = 2.9A
* Two switchers @ 300mA each = 0.6ASubtotal 14.3A
+ 25% headroom = 3.6A
Required power supply = 17.9A

I believe the above estimates are overly generous and represent an absolute worst case use. The actual in use current draw is likely to be much, much less than the above figures. Additionally, each DB150 is limited to 5A so the trains can't all be within one, two, or even three DB150 districts at the same time. They would have to be spread out across at least 4 DB150 districts to stay within the DB150 operating range. Again, not likely a problem as I highly doubt your trains will all be at maximum load at the same time.

If all else fails there is always the MeanWell SE-1500 @ 100 amps. http://www.meanwell.com/productPdf.aspx?i=476 At what point do we stop calling it a power supply and start calling it a welder!

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