Led light fuse/circiut breaker

Kris:

While you're looking at Mouser, check out PTC resettable fuses. They can be placed into your circuit but you'll have to size them according to the voltage and load that you expect to use. Keep in mind the hold voltage and the trip voltage plus be aware of the trip times involved.

Neil

For LED lighting, the PTC you'll need is a very low value one.  Here's a likely one, PTC 50ma hold, 100ma trip.

Hi Neil and Gunrunnerjohn.

Thanks for your help. As Lt. Columbo said "one more question" . I have a MTH O-27 Streamlined Observation Car New York Central - Dreyfuss Product Number: 30-6023 that I would like to place led on the lens. Will the  PTC 50ma hold, 100ma trip fuse work on this as well or do I need something else? There will be a total of 9 LED, 6 Led on the roof and one led for each lens.

Again thnks.

Kris

Why would a derailment cause a short, a circuit amperage overload, in the passenger cars?  The short would be in the track or in an internal wire directly connecting the rollers in each truck.

If your passenger car derails and sets one roller on the outside track, it can cook the wire between the rollers.  I've seen this is a few passenger cars I've worked on, and even in one of mine.  I put the PTC between the two rollers and I'm assured that won't happen.

Kris, it should work fine.

If it's the same on-again, off-again discussion about fuse/circuit breakers I'm thinking of, it has nothing to do with "LED lighting" per se.  As GRJ says it protects the wire that connects the two center-rail power rollers from cooking on a derailment where the rollers end up bridging the center and outer rails.

So this cooking can/does happen on passenger cars with original incandescent bulbs.  The thought is if you're opening up the car anyway to do an LED conversion, why not install a low-cost protection device.  But it protects the wire, not the LED circuitry.

Are you using GRJ's new LED lighting board?  If not, what kind of circuit are you using?  That is, if you operate low-voltage conventional-control and plan to hook up all 9 LEDs in a "parallel" configuration with each LED pulling, say, 10 mA each, then you have 90mA and I'd look at a different PTC.  But if you're using GRJ's board with the 12V LED strips, you're good to go.

Truthfully, the only real reason I see for a PTC in the passenger car is to protect the wire between the pickups.  I don't figure that I need protection for a choke and a bridge rectifier, that's probably overkill.

Dear Stan

I am using GRJ's new design and was think of running the Led series not parallel. Sorry not making clear in the question. Does anyone have a picture or diagram of how the hook would look like once having the PTC installed? Since this a problem will car in this design I might as well wire up the 1950's Lionel Morris and Essex passenger cars.

Thanks for the help.

Kris

Dear Gunrunnerjohn

Thanks for the insight and under the impress that it protected Led lighting and the circuit. 

Kris

GRJ, I concur with your 2 posts just above.  The connector wire is the risk.

There was a recent thread on DCC Specialties electronic circuit breakers.  It looks like it will protect every thing on the track.

Jan

You just put the PTC in the wire between the two roller pickups.  You can wire the power to the LED module from either side of the PTC.

This is not a replacement for what we're discussing.  Besides, what happens if you run something on a different layout, even if that were true?  The wire protection is for a higher resistance short where you don't draw enough to trip the breaker, but you do draw enough to cook the wire.  Many cars have pretty small wiring for the lighting.

Adding to GRJ's scenario, the risk to the thin (22 or 20 gauge?) wiring between car rollers occurs not only possibly in a derailment, but if the car is bridging two power districts and there is a short on one.  I've had that happen, and the heat weakened the roller spring to the point it had to be replaced

Right you are, I forgot about that scenario.  We were just shooting one of those the other day.

GRJ

We have a problem with Ross #8 switches with relays on them. When you run against the switch position we create a short and burn up the relay leads controlling power to the lead rails. We are using 3 amp fuses to prevent this but after reading this post about PTC's would they work in this situation so we wouldn't have to replace the fuse?

I'd probably try one of the PTC units on a switch and see how it works before making a wholesale change.  I'd recommend one with a trip of around 1.5 amps.  There is a noticeable delay even above the trip current before they trip, so I'm thinking those would be about the right value. 

I'm running a couple of locomotives around now with a 1.3A trip PTC in the motor leads, and so far they've never even noticed they're there.  Even with a load I don't see any issue.

GRJ

would you have the part number of the 1.3amp PTC you are using? Digikey search isn't getting me there. Thanks.

Here you go: Bourns MF-R065.  They're a .65A unit, the trip is at 1.3A.  Given the delay in tripping, they need considerably more than 1.3A to trip at all quickly.

Dear All

Thank you all for your help and insight on the above matter. Thank you again and hopeful I will be able to return the knowledge I have gained back one day.

Kris