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Airpax Large

DISCLAIMER: This topic is for discussing these types of breakers.  The 10A "Instant trip" example pictured above might not be right for your application.  Choosing the right Amperage rating and Time delay should be based on several factors and less than or equal to the nominal output rating of the transformer to which they are connected.  If you think you may want to use a breaker of this style and you are unsure of the correct model, please ask for help here in the Electrical Forum  in choosing the right one for your application.



Airpax Snapac Hydraulic-Magnetic Circuit Breaker Internal Mechanisms - Updated 12/4/2021

Introduction:  These very fast acting circuit breakers are ideally suited for use in helping protect the sensitive electronics within modern Locomotives (TMCC/Legacy, Lion Chief (all versions), DCS, ERR and others especially when power is supplied from postwar transformers. These Airpax breakers are ideally suited to use on a layout when a mix of Command and Conventional Locomotives are run.

The Airpax "Instant" models presented here will trip in 1/10th of a second when their rated current (in Amps) is exceeded.  They are faster than fast blow fuses and much faster than the original internal Thermal breakers that came stock inside postwar transformers.

The other part of helping protect locomotives' electronics is combining fast acting breakers with TVS (Transient Voltage Suppression) diodes located strategically around the layout.  Since there are numerous other references on this Forum, I will not go into detail about those here.

When I first read about these products here on OGR in early 2021, I decided to learn more about them. This series of hydraulic-magnetic breakers is called AirPax Snapac and is made by Sensata/Airpax.

Their data sheet is attached below.

There is more information on the web about their larger cousins (for example https://www.youtube.com/watch?v=sJU2pTdUyY0 ) used for higher voltage and amperage circuits, how they work and cut-away animations, but I was unable to find details on the inner workings of these smaller Airpax Snapac hydraulic-magnetic versions.

I decided to cut open one of the Airpax Snapac 10A “Instant” trip breakers. They are very similar, in that they have an Arc Chute (for dissipating the arc created by the opening contacts when they trip). They also have what appears to be a gas filled piston inside a coil, but there is one subtle difference in the way it activates the trip linkage. As the current in its stationary coil rises towards a set value, the resulting increase in the magnetic field overcomes the spring tension on the disconnect mechanism and pulls on a lever and disengages the contacts.

AirPax Cutaway3AirPax1

Airpax Snapac hydraulic-magnetic breakers are available with different time delays before tripping at the rated current (Amps). They come in Instant                       ( 100 millisecond delay), Fast (slower than the Instant and the delay time varies by how much above the rated current the actual current flow through them is for a variable period of time), and Slow (which has delay characteristics similar to a Slow Blow fuse).

Choosing the right type of breaker is dependent upon many factors and choosing correctly can mean the difference between experiencing nuisance tripping before the the optimal current flow is reached in the protected circuits, to just right protection, to being either to slow or overrated and not providing adequate protection to prevent damage to the transformer and what's connected to it.



Here are links to the Airpax Snapac "Instant" trip Series Breakers



5 Amp   PP11-0-5.00A-OB-V   https://www.onlinecomponents.c...00aobv-10090638.html



7.5 Amp   PP11-0-7.50A-OC-V   https://www.onlinecomponents.c...50aocv-10090644.html   Link to Alternative overseas Distributor



10 Amp   PP11-0-10.0A-OB-V   https://www.onlinecomponents.c...00aobv-10090622.html



12.5 Amp (no button markings)   PR11-0-12.5A-XX   https://www.onlinecomponents.c...125axx-43802931.html



Links to the Fast and Slow varieties are not included here, but can be found on the same website. Their part numbers differ by having a PP11 -1 - xxxx(Current rating) for Fast, and PP11 -2 - xxxxx(Current rating) for Slow.



Here is some basic information on choosing the correct Amperage rating for a breaker:

There are a few electrical fundamentals in addition to the trip delay time one should understand when choosing a breaker. The transformer Output ratings are a good place to start.  Here's what they mean:

Volts - (electrical energy potential) in Conventional operation this sets the train speed.
Amps (current flow) - More Locos, cars and such (and shorts) pull more current through the circuit from the transformer.  The transformer only delivers as much current as required by the load, up to a point.  This point is it's Output rating.

AC Transformer Output ratings are usually given in either Watts or VoltAmps, both of which have essentially the same meaning when choosing breaker size.

Watts = Volts x Amps = VA
or

Watts/Volts = Amps



An often asked question is how to connect a Circuit Breaker and TVS Diodes.  Here is a very basic example of a simple loop connected to one transformer:

Track Connections2a

I hope this helps.

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  • Airpax Large
  • AirPax Cutaway3
  • AirPax1
  • Track Connections2a
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Last edited by SteveH
Original Post

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Arthur,

Your post couldn't possibly be farther from helpful given the OP's question.  It adds zero value to this discussion, except to imply that we're all wasting our time because the real answer to the that question is trivial and obvious.

Are you suggesting that he, the rest of us here on the forum, and all model railroaders in general, should walk away from safety because you've been very lucky ignoring it for 65 years?

M.H.M.

Last edited by Mellow Hudson Mike
@Lehigh74 posted:

I can’t answer your questions, but I will say that those 10A breakers might be too slow.  I got some Airpax Snapak breakers a few years ago.  They were too slow.  Mine are PP11-2, so your PP11-0 breakers may be faster.  I ended up replacing them with Eaton-FAZ-B breakers (3, 4 and 5 amp) and I’m happy with them.

Thanks for that insight and a good point. The second part of the model number indicates the trip delay.  The -0 is supposed to be "instant".

airpax delay

The time delay plots are on page 65 of the data sheet.

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Last edited by SteveH

It was offered as a rebuttal to the notion that we need to immerse ourselves in never-ending hand-wringing over trying to make the electric toy train hobby resemble NASA projects.  If electronic components of toy trains are not robust enough in their design or applications, then we need to rethink the design and applications, not fret over multi-dollar protection devices that the manufacturers apparently didn't seem to feel necessary.

As has been explained many times by the electronic experts here, there are only a few things we can do to protect the fragile electronics inside a locomotive, should a fault occur outside the locomotive. The cure to the perceived or real volatility in the electronic components is to source them and design their circuitry so as not to be susceptible to external faults.

My remarks were offered, as are most here, in the spirit of getting a conversation going. They were not made to deride "modern electronics" whatever that means. They were, however, made to try to poke the manufacturers into getting their act together.  My favorite "fix" has been the "add a light bulb and see if that helps" mentality.

Last edited by Arthur P. Bloom

@Arthur P. Bloom I want to thank you for your opinion.  You are certainly welcome to manage your model train layout in the way that you'd prefer.  There is no intent on my part here to tell you or anyone else otherwise, and I respect everyone's decisions even if I may not agree.  I'm not trying to tell anyone to over-complicate the way they might desire to wire their layout.  I'm also not trying to convince you or anyone to change their way of thinking about this.  I am trying to learn specifically about how these breakers function.

Rather than continue debating your points of view on this thread, would you please consider starting your own topic to discuss your grievances about your opinions on complexity?

For the sake of any newbies who may be following this thread:

(1) Fuses and circuit breakers are neither new nor novel.  In particular they have not been introduced in recent years as "band aids", and have never been considered such at any time.  They are a fundamental part of electrical safety and have been so since electricity was first harnessed in the 1800's.  This is very, very mature technology and is depended upon every day in thousands of applications, in industry, transportation, offices, homes, and yes even toys. 

(2) Safety does not concern only whether your locomotive or accessory quits.  Your electric train has the capacity to, and very likely has in at least one case in the past, burn(ed) down a house, or at least started a significant fire.  (If it hasn't, or couldn't, why would a safety organization like Underwriter's Laboratories (UL) be so involved with toy train transformers for all of these years?)

My apologies for elevating the discussion.  This is not a political rant.  These are hard-and-fast technical facts.  (This forum has proven to be very helpful in disseminating the important technical facts if you just let it.)

M.H.M.

As has been explained many times by the electronic experts here, there are only a few things we can do to protect the fragile electronics inside a locomotive, should a fault occur outside the locomotive. The cure to the perceived or real volatility in the electronic components is to source them and design their circuitry so as not to be susceptible to external faults.

The Lionel PowerHouse 180 has a fast acting (maybe instantaneous?) breaker.  However, none of the postwar transformers have these, nor do many other modern transformers. There have been multiple discussions about this these Sensata/Airpax magnetic and magnetic-hydraulic breakers, as well as similar ones from Carling Technology.  The goal, as I see it, is to add a comparable level of protection to these older transformers. 

While TVS diodes are a good idea, and highly recommended, in the case of a short circuit, the safest and surest way to avoid damage is to remove the electrical current as quickly as possible.  That is the purpose of these circuit breakers.

Why toss/junk a perfectly good transformer, and spend $100+ when a $20 breaker can remedy this?

Steve, I had a link for octaport.com but I’ve lost it, ....lots of data on that page........I too found them too slow, but have not tried the -0 TBT,....I’ve tried these in the automotive world for different applications and found the release too slow holding voltage on the consumer as it tripped,....didn’t like that, especially with sensitive components that don’t react well to voltage drops,....hope that helps,..

Pat

@SteveH posted:

@harmonyards Pat, thanks for the tip about Octopart.com.  It looks like a good resource for finding who has what parts.  I'll look at it some more to see if I might be able to find a link to a cut-away for the Airpax.

For your notes, on the flip side, we found the reset to be very clean, zero lag, leap years ahead of any thermal breaker,...( normally used in our world) it’s the release we had issues with.....holding voltage on sensitive, and expensive fuel pumps in the performance world.......we were looking for alternatives to ATO’s and fast blows that don’t always react at their “advertised load rating” ........we’ve settled on Eaton breakers and found them a lot faster on the release side, .......I believe another fella mentioned them above as well,....

Pat

Arthur... I'm not speaking for you OR your wise observations.  However, electronics has grown since the early days of RADIOSHACK. So have the complexity of our trains.

I know there are many, a lot of my friends, that wish to go back to those early days where the most advanced electronic gadget was a door-bell circuit. Once again, those days are over and done.

To advance the hobby, a few of us not all, need to get our heads out of the sand.

@harmonyards posted:

For your notes, on the flip side, we found the reset to be very clean, zero lag, leap years ahead of any thermal breaker,...( normally used in our world) it’s the release we had issues with.....holding voltage on sensitive, and expensive fuel pumps in the performance world.......we were looking for alternatives to ATO’s and fast blows that don’t always react at their “advertised load rating” ........we’ve settled on Eaton breakers and found them a lot faster on the release side, .......I believe another fella mentioned them above as well,....

Pat

Pat, unless I'm misunderstanding your meaning, I think we might be talking apples, oranges, and bananas here on the time delay.  The other mention above was for a slow trip time Airpax with the number 2 in the second part of the model number ( PP11 - 2 - **** ).

There's also the "fast" delay option ( PP11 - 1 - **** ) with a trip curve that sounds like what you could be describing.

If you look closely at the picture in the original post, its a PP11 - 0 - 10.0 - OB -  V which is the instant fruit (I mean delay) . The  - 0 = "instant" PN designation Airpax breaker is supposed to disconnect the load in less than 0.001 second ( 1 millisecond ) if current flow to the load rises above its rating.

Instant Delay Air Pax

Do you think the ones you were using might have been the ( PP11 - 1 - **** ) "fast" that has a curve like this?

Fast Delay Air Pax

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  • Fast Delay Air Pax
  • Instant Delay Air Pax
Last edited by SteveH
@SteveH posted:

Pat, unless I'm misunderstanding your meaning, I think we might be talking apples, oranges, and bananas here on the time delay.  The other mention above was for a slow trip time Airpax with the number 2 in the second part of the model number ( PP11 - 2 - **** ).

There's also the "fast" delay option ( PP11 - 1 - **** ) with a trip curve that sounds like what you could be describing.

If you look closely at the picture in the original post, its a PP11 - 0 - 10.0 - OB -  V which is the instant fruit (I mean delay) . The  - 1 = "instant" PN designation Airpax breaker is supposed to disconnect the load in less than 0.1 second if current flow to the load rises to above about 135% of its rating.

Do you think the ones you were using might have been the "fast" that has a curve like this?

Fast Delay Air Pax

The -1 is the one we tried on a 12-14V circuit, ( 13.90 running ) on a 20 amp service,.... ....I believe you’re correct, we’re probably comparing apples to oranges,....when we forced a trip, and observed the drop out, it was not instant, almost as if the arc was holding load as it moved away from the contacts,.....we bought them since they were cheap, and  I could certainly cut one open if that’s the exercise of the thread,......  

Pat

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