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SteveH ... appreciate the research and insights of your series of posts.  I run Lionel Legacy Command locomotives.  I have been using ATO Smart Glow Blade Fuses for the past couple of years between my Z4000 transformer and Gargraves track ... https://www.mouser.com/datashe...datasheet-461533.pdf   My consists typically draw ~2 amps on the inner loop and ~2 amps on the outer loop.  Two years ago I opted to go with 5 amp ATO Smart Glow Blade Fuses.  The vendor rates them as "Medium/Normal Blow".  At the time I figured going with 5 amps would give me some margin for track short circuits.  I also have TVS's about every 7 feet around my two track ovals on a 15ft x 10ft track layout.  Have had probably 15-20  trips of my 5 amp ATO fuses in the past 2 years ... and ... so far, no known damage to loco electronics.

However, after reading through your post, I became a believer in the Airpax Snapac for a fairly reasonable cost.  I just went online to the site you identified and ordered the 5 amp Airpax Snapac circuit breakers     Having now compared the 5 amp ATO Smart Glow Blade Fuse datasheet time-current characteristics (in above pdf) to the very fast Airpax Snapacs, I expect the 5 amp Airpax Snapac will trip before the 5 amp ATOs for my normal track short circuit snafus.    I also bought a couple of 7.5 amp Airpax Snapac in case I start getting nuisance trips with the speedy-tripping 5 amp Airpax Snapacs. 

I will wire them up in series with my 5 amp ATO Smart Glow Blade Fuses.  I'll post my anecdotal experience with these Airpax Snapacs vs my ATOs upon receiving them and running my layout for a month or so.  We will see.

Thanks again for a well-done analysis.

Regards,

Tom

SteveH:

Thanks so much for all of this information. I am replacing my "fast blow fuses" with the Airpax Snapac instant trip units you identified.

So far I replaced 5 fuses and when testing found them to be very fast! My (brick) transformers are the Lionel 135 Watt units which is why I installed the quick blow fuses.

I considered replacing the 135 Watt bricks with 180 Watt bricks to have the faster breaker as many have attested to here on the Forum. Since I didn't need the extra power it made perfect sense to install the Airpax Snapac instant trip breakers for less hassle and cost.

To say the least, it has been quite annoying to replace a blown fuse after a derailment, particularly when guests were visiting. Now, re-setting a breaker is really a "snap"!

Best regards,

Stan

Last edited by stangtrain

I just finished installing another 4 of these nice very fast breakers. Now all circuits are well protected together with a TVS on each:

356E38A0-3973-45BB-A300-7E38D8861DBA

Here is the power distribution center prior to the upgrade to the circuit breakers. It was a little tricky making the small panel for the breakers fit in the small space above where the fuses were, but wiring was pretty easy:

IMG_4189

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Last edited by stangtrain

Steve, I have a question.  I'm building a small portable conventional layout with one loop of track and one siding.  It is broken into 4 blocks so that you can switch from the running engine to one parked on the siding, so basically I'll only have one train running at a time.  Would one circuit breaker be enough protection for all of the track or should I put one on each block?  Oh, this is being built on a hollow core door, so it's a really small layout.

Thanks!

I agree with John that one breaker for your layout should be sufficient, unless you're providing power with more than one source.  If you're using more than one transformer or multiple outputs (ie. one for trains and another for accessories), then I'd suggest one breaker per output, especially if you're using a post-war transformer.  What transformer(s) are you using?

The whole layout is designed to be powered by one transformer, either a PW KW, ZW, or an MRC Pure Power Dual.  The layout is designed so that they are all interchangeable.

Below are a couple of pictures so you can have a visual.  I hope I'm doing this right, it's my first time posting photos here.  The first one is an earlier picture and the second one is after I finished the frame and control panel.  The transformer just sits on the control panel when in use and is removed before the control panel gets folded up for transport.  I was just starting the wiring when I read about TVS diodes and circuit breaker protection here on the forum.  My last layout was about 25 years ago and all I used then was what ever my transformer came with.  And yes, I do think I have a thing about toggle switches.

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@31charlie posted:

The whole layout is designed to be powered by one transformer, either a PW KW, ZW, or an MRC Pure Power Dual.  The layout is designed so that they are all interchangeable.

Below are a couple of pictures so you can have a visual.  I hope I'm doing this right, it's my first time posting photos here.  The first one is an earlier picture and the second one is after I finished the frame and control panel.  The transformer just sits on the control panel when in use and is removed before the control panel gets folded up for transport.  I was just starting the wiring when I read about TVS diodes and circuit breaker protection here on the forum.  My last layout was about 25 years ago and all I used then was what ever my transformer came with.  And yes, I do think I have a thing about toggle switches.

Charlie,  while not necessary, you could power the uncouplers from another (Aux) source than the one controlling the trains.  That would allow you to supply the optimal 10-12 volts to the uncouplers while providing independent speed control the the train either conventionally or 18v for TMCC/DCS/LionChief.  In any case, a second breaker could optionally be used for the Aux power.

Hi SteveH,  Thanks for the idea.  I've thought about powering some things on the layout from another source but since I want this to be portable I think I'll just use one transformer to power it all.  With my KW I'll have 190watts available, and more with the others if I use one of those, I don't think I'll over tax any of them with what I have.  Everything I'll be running will be in conventional transformer control except for when I use a LionChief engine which I can still power with any of the transformers I'll be using.

Please let me know if you have any more thoughts or ideas for me.  I'm at the point where I'm ready to start wiring things up.

@31charlie, I don't want to belabor the point, just trying to ensure sure you understand your options.  You could use any single one of the 3 transformers you mentioned to provide power separately for the trains and for auxiliary devices.  Each one of those (ZW, KW, and MRC-Dual) transformers has multiple outputs.  Each output could use its own external breaker if you don't want to rely on the breaker built into the transformer.  My thinking was that I'd pay about as much for shipping as one breaker costs, so I bought a few more than I thought I'd need.

But, again the choice is entirely up to your personal preference.

@31charlie posted:

Hi SteveH, So your saying to put a breaker on every feed from source to the load?  Even for accessories?  I must admit that I didn't really think of this before, I was only thing about a train derailing or some thing like that.

I'm not saying you should.  Rather, that I would since there is a chance that a misaligned pick-up shoe or roller could catch the accessory power from one of the auxiliary rails on an operating track.  If that happened, the only thing to cut the power would be the transformer's internal breaker. The PW ZW and KW are slow to trip, and take long enough to melt the insulation on small wires in modern locos and accessories.  I'm not sure about the speed of the MRC's breaker.

In other words, adding additional breakers (one per connected output) is cheap insurance if you're already planning to buy/install one breaker anyway.

Thanks SteveH and GRJ!  I never thought of about the accessories causing a problem.  I'll be adding breakers to all the circuits on the layout.  It looks like the Airpax breakers will perfect for my needs.

I'm really glad I ask about this before I started the wiring, this has the potential to save me a lot of problems in the future.  Thanks again to the OGF, this really is the best resource for information on O gauge trains!

I would just like to add that I use two PC power supplies to power almost all my accessories. I can't attest to the exact type, but they have electronic circuit protection. I can short a 30 awg wire and it trips instantly. I use a 3 amp thermal breaker to protect small wiring, but it has never tripped. I use the 12v and 5v taps for all relays, signals, and lighting (90% led).

For anyone looking for fast circuit protection this time of year, I've added a few updates to the original Topic including the diagram below showing a simple example for how to connect a circuit breaker and TVS diodes.

Track Connections2a

For convenience, here is a link back to the beginning of this thread.  Airpax Snapac "Instant" Hydraulic-Magnetic Circuit Breaker Internal Mechanisms




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