LED strips in RK cars, polyfuses?

 I guess I need to ask where to install the fuses on my two rail cars as well? Seems like the best way would be to use four of them?

You only need one or none if you use 2 diodes. some diagrams here

LINK

Dale H

Maybe I'm wrong, but I would just use one polyfuse per car. Take the two leads from the pickups (2 or 3 rail) bring them together then put the polyfuse between them and voltage regulator circuit.

Now there is another thing to consider, if you have multiple power districts. That would be the possible bridging of two districts. This could allow double your max current to pass through those small wires in the car between the pickups. In that case it might be wise to use one per pickup, but only on one side of the circuit. You should never need 4.

on the two rail cars, shouldn't there be at least one on each wire connecting each side then? Remember there are no center rollers.

  I guess I'm overthinking this?

The fuse just protects the connecting wire then right?

Sorry Joe, I edited my previous post behind you, check out the second paragraph (which I added).

Nah, the circuit only has + and -, and the protection only needs to be on one side. That power district bridging business opens up a second can of worms. It is very easy to fry wires doing that if an accident happens in the right spot. Just ask one of my locomotives that split a switch.

Although I can understand your point, what if one set of the two rail car's negative wheels touch the positive on one side during a derail maybe on a set of switches?

 I guess I'm struggling to see where to put the fuses because I need to know what they protect. If it's the circuit, I can see where the hot lead would need a fuse between both + wheel sets, and the circuit.

 As shown in diagrams, it seems more to be protecting the wire itself, as it's just in between the roller's. Either way I could see a need for more unless I'm just not getting it??

I normally put them between the two rollers.  I can see your point that technically you'd need more for total protection, point taken. 

My personal experience has been usually one roller ends up on an outside track and cooks the wire between them.  Usually the wheels will trip the breaker before it gets the wire.

I am by no means an electronics expert. I have a basic understanding at best, but if you "think like an electron" and always seek the path of least resistance, it should tell you where you need over current protection.

In your example, where the wheels short between the rails, the path of least resistance is through the wheel, not through the electronics on the car. The breaker that should trip, is the one back at your power supply.

On my layout, I use 6 Amp polyfuses for over current protection on each power district. Unfortunately, they are a little slow to react, and I have literally welded wheels to the rails.

My big concern these days is the bridging of two of those 6 Amp power districts. That's a potential exposure to 12 Amps! I was thinking 2 amp polyfuses inside engines with can motors (bigger for open frame motors) and something as small as 1/4 amp for LED lights in a passenger car.

I use 1/4A PTC's in my passenger cars, and I use a 1A unit on the motor for anything I put the Cruise Commander Lite into.  That was after one of the early prototypes went up in smoke because the locomotive stalled on a switch, obviously exceeding the 4A rating of the drivers.  I use a 2A unit when I put a power tether between a locomotive and a tender, this is my fix for small steamers stalling on switches.

Thank you for the replies.

I'm just thinking that on a two rail car, it could be any wire, anywhere. Remember the car can be turned around so really, the only way to protect the wires, especially across districts, would be to fuse each connection. Probably gets into different types of protection?

 I guess what worries me, is Murphy's Law. I always get a special version that happens just to me!!

Joe, you're throwing a curve ball, I wasn't thinking 2-rail!   You're right, it's probably a bit different, so you may want to consider all the paths that current might flow in a derailment.

Yeah, see how I did that! I post about RK 3 rail and draw U over to two rail (the dark side).   

I have three locomotives to be upgraded to PS/2 and 2-rail behind me, so I've already been dragged, kicking and screaming, to the dark side.  However, I always find my way back to the friendly confines of 3-rail.