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Ivar

Common rail

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Hi!

 

I have a question of how to connect several power units to my tracks.

 

I have 4, 24V 15A regulated power supplies, that will power 4 different parts of track. Could I just isolate 1 track (positive) and use the other as a common rail, or will this make a short.

On my DCC, H0 rr I have done this (4 boosters), and it goes fine, but wonder if the regulated power unit will do the same.

 

The power packs will be placed on 2 different places.

I have used two tool boxes with 2, 24V, 1, 5V and 1, 12V regulated power units. I use trailer contacts for connecting them to the rr (see the end of the box).

 

Ivar

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It depends mostly on the construction of the power supplies.

 

If the Norwegian mains principle is anything like the Danish (and it looks like it is), you have a ground/earth wire (the yellow/green) in the mains cable. This means that you must ensure that the DC outputs are floating and isolated from the mains or you risk ground loops which can carry substantial currents. With the supplies disconnected from mains, measure the resistance from each DC output terminal to each of mains input terminals. There must be no short circuit anywhere.

 

Assuming the outputs are floating, you can safely tie one track together on all four supplies. When a train passes the boundary between power domains, you will have a short on the second track, and now the construction of the power supply will be the deciding factor for what happens.

 

Imagine a two-truck diesel with power pickup on both trucks / all wheels. What happens when:

  • One truck is spanning two power domains ...
  • The engine has one truck in each domain ...

In particular, consider the above if the voltages in the two domains are not exactly matched. Your engine will act as a short, and you can have up to 15A passing through the internal wiring.

 

I have two regulated 24V DC supplies that may be coupled in parallel just like that. When they power up, they argue about the world for a bit, and then they agree on the output voltage and settle down, providing twice the current. They are designed for it.

I have other regulated supplies where this is not possible. They are designed to assume they are alone in the world.

 

So basically the answer to your question is that it's a matter of design. I would at least make sure that my rolling stock could cope with whatever happens when passing domain borders. Ohm's law applies here. I'm not sure what I would do. Other people here may be more experienced with practical MR use - I'm just an electrics/electronics guy.

 

Jens

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Thanks for the answer. Youre right, the Norwegian and Danish system are the same.

I will check as you say, and if they float, I will try, and see what happend.

 

On my HO DCC system I have 4 booster, all 5 amp and 14V. 2 of the boosters are regulated power without a transformer. The other 2 has a transformer each.

Goes without a flaw. Can park over the isolated track with one truck on each side, nothing happen.

No short or smoke. When driving over you cant see anything one the engines. They glide trough.

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The outputs are floating.

First, I have got me a device that cut the power line if there are any leak to ground, that all my power packs will use.

To overcome the other problem, I have find som 45mm plastic track that looks ok. I wil put 3 lenght of those, every place I have where the power packs meet.

That will isolate the powerpacks to the one power district it power and with no way to short them.

The plastic track will be longer than my longest engines, the RDC. Cant get any short then.

I have a system called Train UPS, with 24V in the track and batteries in the engines.

They got charged as soon as they stopped, and when run, they will use either track power or battery power.

Works fine, never had any problem with dirty track. I have a parking track for engines, where they got charged.

 

Ivar

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I say that the Danish and Norwegian powerline system are the same. Thats not true.

Norway are one of very few countries that not have a earth (ground) line in from the power station. In Norway all ground connection are local. The ground are tied to a big copper wire in my house concrete floor, in the basement. All buildings in Norway have a ground that come from the earth around or in the buildings ground floor. Old buildings have a big copper pole driven down in the geound, and get electrical ground from there.

 

Ivar

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