Mean Well 15V 5A

[TwinStar]

Our group is still a mix of DCC and RailPro. As such, I still need to provide DCC at the railhead. I have a Digitrax DB150 but I really don't want to pay $50 for their PS-14 power supply. Would the following work or is there something that I'm missing?

https://tinyurl.com/yb77rd7v

[G8B4Life]

Meanwell is a good brand of power supply.

These are the full specs of the unit offered on eBay (note, the picture in the eBay ad is not of the RS-75-15, but of a higher powered model with dual rails, the RS-75-15 has a single output rail): http://www.meanwell.com/webapp/product/search.aspx?prod=RS-75

From what I can tell it should be just fine, the voltage is well within range of the DB-150 and the current rating just as good as the PS-514 Digitrax recommended for the DB-150. I can't tell exactly what protection mechanisms the PS-514 had so the Meanwell RS-75-15 may have less built in protection. You'll have to wire the input and output side yourself so you'll need to take precautions on the exposed live 115v input.

- Tim

[Alan]

I have a combination of eBay China and genuine MeanWell power supplies in use on my railroad. All have been trouble free.



It matters how and where you mount the power supply. Non-fan cooled SPS should be mounted horizontally with free air space above and around the enclosure. The amperage rating is reduced 50% when mounted vertically. I overcame the vertical mount restriction on a 7 amp version of the supply you are considering by adding a fan. The fan is 24V so it runs ultra quiet on the 15V supply.



Noise caused me to add external fans to my fan cooled units too. The internal fans are quite noisy and the constant cycling on/off drew attention to their presence. The external fans run continuously and are quieter than the original power supply fans. They keep the units at temperatures below the internal fan cut-in point.

[TwinStar]

Thanks guys. This will be for a Free-mo modular layout. Is there a way to make this safe and portable?

[Alan]

Are there multiple power supplies on a Free-mo setup? If so, I would bail. Switch mode power supplies generally do not play well together especially if the output voltages are slightly different. They don't load share like batteries. There are SMPS that are meant to be ganged together but they are specialized and pricey.

If your power supply is the sole source of power then I can see no reason why it won't work well and be safe. Give it air space to shed heat. Make sure it is well grounded - use a grounded plug and outlet. Securely cover the electrical connections on the unit. Perhaps put an inline fuse on the output side just in case the internal over-current protection fails.

[TwinStar]

Alan,

There are. The layout is broken down into power districts. Each district is powered by it's own DB-150. I have a DB-150 (I'll need four eventually) and will have PSX circuit breaks (http://www.dccspecialties.com/products/pdf/man_psx1.pdf) between each booster and each of the four power districts that I'll have on my module set.

I had considered a PS2012 (http://www.digitrax.com/products/power-supplies/ps2012e/) but was just looking for a cheaper way to be DCC compliant and power the rails.

[Alan]

If I am reading the DB-150 datasheet correctly, it is not in itself a power supply. There is a separate power supply that provides 12-20VAC or 12-28VDC to the DB-150(s).

What is currently used on your Free-mo setup to provide power to the DB-150s? A single power supply such as PS2012?

[TwinStar]

You are correct. The DB-150 merely boosts the DCC signal from the DCS (Digitrax command station). The DB-150 requires a 15V+/- 5-6A power supply. We typically use the PS514 from Digitrax which runs $50-60. DCC is still the standard for Free-mo and it's also cheaper to just install DCC current detectors instead of dual DC/DCC detectors for our signal system. As much as I loathe DCC it isn't going anywhere soon. I have a PC wall brick for testing but it's only putting out 8-9V resulting in a Low Voltage warning.

[Alan]

Then there is but a single power supply on the Free-mo setup. In that case a generic 15VDC switch mode power supply should work fine. Depending on how many trains run at the same time and given the number of DB-150s you have then perhaps a little more oomph is called for.

Here is a Mean Well 10A unit for $22.00: https://www.ebay.com/itm/new-Out-of-Box-MEAN-WELL-MW-SP-150-15-150w-15V-10A-SWITCHING-POWER-SUPPLY-w-PFC/222425472352?epid=662498749&hash=item33c9975d60:g:MIoAAOSw3v5YtlXN

[TwinStar]

Actually, each DB-150 has it's own power supply which is typically a PS514. These are scattered around the layout with a power supply and booster for each district. One of our module sets is that of Wichita Union Station and it has its own 8a DB-200 power supply and booster. My set is more expansive and I was thinking that 20 amps total would be required. I am buying the DB-150's cheap off ebay and guys buy the upgraded Digitrax boosters. But, these DB-150's don't come with a power supply. If I were to buy a 20 amp power supply how would it 'divide' the power? I'd hate to short 20 amps across the rail.

[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]

Would this be better?

https://tinyurl.com/ydhvj9ew

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 = 0.6A

Subtotal 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!