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I'm using an MRC Pure Power Dual transformer to provide track power to my TMCC controlled locomotives. This transformer has a circuit breaker for each side but I'm thinking I need a faster acting circuit breaker to protect the electronics in my TMCC locomotives.
Can anyone recommend a good piece of equipment to do this? The Lionel 6-1478 lock-on isn't rated for the amount of power the MRC transformer is capable of supplying. Could I still use that item to protect my trains? Thanks in advance for anyone's input on these questions.
 

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You should also use a TVS Protection diode across the track feed. This is the one I use.

1.5KE36CA at Digikey

I'm pretty surprised that the TMCC Direct Lockon doesn't have one, but I looked and it's not there.

I personally don't like the TMCC Direct Lockon, it doesn't keep the power off, keeps banging it back on until you turn it off yourself. When I have a power trip, I want it to stay off until I fix things!
 

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Gunrunnerjohn:

The part you recommended is for over voltage protection. It is a Zener diode that clips AC at high voltage. How does that help when the track is shorted and the power source is trying to deliver max current?

I would think a fast acting circuit breaker or FastBlow fuse would be better than relying on the circuit breaker in the power source.

Bob B.:

I know nothing of the MRC Pure Power Dual transformer circuit breaker but if it doesn't trip immediately from a derailment a person needs better protection. I offered a discussion here several months ago on what I found for a fast acting circuit breaker (that works!) in a post about the MTH 100 watt Power Brick whose circuit breaker was so slow the 20 amp TIU fuses would blow instead. Do a search on my posts to see the details.

LDBennett
 

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Lynn, it's not a Zener diode exactly, and it's for a different type of protection. The TVS doesn't eliminate the need for over-current circuit protection. Fuses and/or circuit breakers do not offer any protection against high-voltage spikes, that's what the TVS is for. Some additional information...

What Are TVS Diodes
 

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John:

Yes, it's not a zener in the traditional sense but a protection device for high voltage transients.

I thought the poster was after protection for high current. Or are you just saying that in addition to fast action current protection you need this transient protection too?

I'm not up to speed on what can be expected in the way of transients on the rails of a toy train layout but my first reaction is that transient suppression is not necessary and only nice to have. With the exception of a lightning strike to the power lines (not very likely in my location, the High Desert of So Cal) I can not imagine what would cause the transients. It may be my lack of experience in this area that makes me think these devices are not necessary (???). Can you offer some experience on this? Do the tracks end up as a transient magnets?

I'm not arguing for or against but just want some enlightenment.

Lynn
 

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Lynn, high voltage transients can be generated any time power is removed from an inductor. That can be a motor, switch coil, operating accessory coil, and even your locomotive motors. Obviously, transformers are a good place to generate them as well.

This is a very common damage issue with solid state logic. I spent many years designing avionics for the commercial and military aircraft, and we were a major user of TVS protection as well as many other EMI measures.

If it has semiconductor logic, it's not a bad idea to use TVS protection. Of note, the MTH TIU includes a TVS diode in each output channel as a standard feature.
 

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John:

OK...you are correct. My aerospace experience did not include electromagnet devices or inductor components. My stuff was pure digital electronics. I did not think about the control of motors, etc. for a toy train layout.

About 6 months ago I finished a digital control system for my point to point wall HO trolley layout. It included three Arduino micro controllers. It randomly stops and starts the trolley at three stations for random stop intervals and includes momentum for stops and starts, all digitally done. The speed control is pure pulse width modulation. The final output was a simple analog switching amplifier that feeds the track and runs the trolleys one at a time. I have no transient protection on this layout. I have not suffered any losses to that final stage yet. Maybe there is a failure in my future(???).

With my use of MTH DCS TIU/AIU I'm protected, apparently. Good. The poster was after one of the Lionel digital control systems I believe which needs transient protection in your opinion, I presume.

Lynn......
 

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Wire them across the output of transformer, or at the tracks? I just wired one across the transformer output, or should say the Powermaster.
 

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OK...you are correct. My aerospace experience did not include electromagnet devices or inductor components. My stuff was pure digital electronics. I did not think about the control of motors, etc. for a toy train layout.
While some of my designs interfaced with electromagnetic devices, the TVS protection was primarily for lightning/Induced EMI protection. The lightning tests for Level A equipment that is exposed to the environment is non-trivial!
 

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For my layout I use these 7 amp panel mount breakers.

http://www.digikey.com/product-detail/en/W28-XQ1A-7/PB188-ND/45068

I install them into the side of my control panel as shown below in series with the feed to the block. You could just as easily mount them to the side of the layout. There is a companion locking washer that goes with them for securing them to wood panels.

I also use 3 amp breakesr on the layout for protection on lighting and accessory shorts.

 

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The trick with Circuit Breakers (CB) is they must be fast acting. Most run of the mill Circuit Breakers are not. If CB's are not fast acting then, in the case of the MTH DCS TIU, the 20 amp breakers inside the TIU blow. That was the problem I had when I relied on the CB in the MTH 100 watt Power Brick. What a pain to have to pull the TIU off the layout and remove a bunch of screws just to change one blown 20 amp fuse. After doing it about a half dozen times (from common derailments suffered in the early stages of my layout build) I installed a fast acting CB (magnetic trip instead of heat trip internal design). I also went to Passive Mode for the wiring to keep the heavy current of a derailment out of the TIU.

Better CB's have speed curves in their specifications. The ones I chose trips in about one second at the specified rating. Mine is an AirPax CB. To find a fast acting one I had to buy one surplus. It works as desired.

LDBennett
 

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John:

Looks can be deceiving!

Without the specs you really have no idea of how "Fast" the CB is. In searching for the one I bought, most that I found readily available had a 10 sec or slower response time whereas the one I found surplus was a one second response CB. It appears these fast response time ones are not that popular and not always in stock at electronic supply houses. They are cataloged so they can be had. But they might be (??) special order. The key, I think, is that they are magnetically operated and not heat operated. The inductance of the magnetic coil seems not to effect the DCS signal as most of my layout is a "10" when I run the test using the appropriate signal strength commands in the remote DCS controller.

LDBennett
 

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If the thermal breaker in a MTH 100 watt Power Brick is too slow then adding another thermal CB in series seems to me to be futile and no help.

But a lot of money can be saved by having just one expensive magnetic CB vs. a whole bunch of potential ineffective cheap thermal ones.

Of course it depends on the usage. In my case I use the fast CB to protect the fast 20 amp fuses inside the MTH DCS TIU because the MTH 100 watt Power Brick CB is waaay too slow acting.

Just saying!

LDBennett
 

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Surges are part of the game of running PW trains. That's why the breakers I use are not fast acting nor do I want them to be or they would be constantly tripping. They are thermal and there is a cool down time before they can be reset. According to the specs they trip within 4 seconds at 100% current.

They work great and have protected my layout for years without a catastrophic failure.
 

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Here's the problem and why I say for my case (and that of anyone using the MTH DCS TIU/AIU system) that a fast acting CB is absolutely necessary.

If you rely on the MTH 100 watt Power Brick CB to protect your TIU then it won't. It is so slow the 20 Amp (!!!) TIU internal fuse blows before the MTH Power Brick CB heats up enough to click the power off. Several reason that is bad:

1) Allowing 20 amps to pass through the TIU channel might eventually damage it. It is solid state and excessive current is the demise of most solid state devices.

2) To replace the fuses you have to remove the whole TIU from its mount point on the layout in order to remove all the screws.

3) There are MANY screws to remove and replace to get to one of the four fuses. I did this about six times (!!) from simple derailments before "fixing the problem" with the fast acting CB

Please note that if you have the Lionel 180 watt Power Brick I am told (by gunrunner john) that the CB is fast enough by itself. But they have been out of stock new for months and months. The last time I asked Lionel for a due date for sale, they could not give one. They are on the used market for almost the new price, in some cases.

If your layout is powered and controlled in some other way with a different system from my MTH solution then you may or may not need the fast acting CB. Also note that I said the response time was about one second (according to the specs for my CB). A one second "transient" is not transient at all but some kind of a problem.

We all have different experiences and get to choose how we do things. The above is my solution based on my needs and may not reflect your needs at all.

LDBennett
 
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