Transformer Fuse/Circuit Breaker

[Anonymous]

I'm involved in a discussion with a reseller of magnetic circuit breakers (Snapak). My intent is to order "instant trip" vs. fast acting. The reseller says that orders for instant trip are very rare and most applications use fast acting breakers that tolerate input surge currents.

Accoding to the Snapak data sheet delay curves, the response time of instant trip is a max of 1/10 second at 150% load.

The fast acting will trip at 1/2 sec to 5 seconds at 150% load. Depending on manufacturing tolerences and other variables, the fast acting could allow 15 amps for five seconds before tripping.

I have experienced expensive repairs relying on the manufacturer's in-the-box breakers and my instinct is to use instant trip breakers. Before I order a quantity of the breakers, I would like to hear your comments on what you feel is the appropriate option (instant vs. fast) based on your experience with fuses and the more common thermal circuit breakers.

Thanks,
John

[dbaker48]

Last Results -

Responding to some email requests as to what was my final outcome.........

1. We have our circuit breaker box built, installed and operational. Everything seams fine.

Conclusion:
I purchased a DVD, that had a circuit breaker project, among other things for about $20, the DVD was worth it in my situation, had multiple benefits.

- The parts identified within the dvd are available to anyone, but actually are a bit expensive. Ended up with about $65 spent on one box. (Scotts Odds-n-Ends offers the same completed unit for about $20)

- I believe the common question comes up regarding what size fuse/circuit breaker is needed. Their is a real good Ohm's Law calculator available at www.the12volt.com/ohm/page2.asp (Since their are many variables, transformer rating, loop requirements the calcualtor really makes it easy) Overall 10 amp seems pretty good for large transformers.

- Biggest problem was related to Volt/Amp gauge I purchased to fit on the rear of the transformer for constant monitoring. The gauge unit fits over the lugs coming off the xfmr. Provided with the gauge are four bushings which connect onto the ground lugs, and grounds the meter as well as providing the ground for the 4 new ground terminals on the back of the meter. Unfortunately these bushings are not quite long enough, creating an intermittent connection and an unstable ground, which baffled me for a while until I determined what the problem was.

The circuit breaker box was a little tight with all the hardware mounted, especially the long profile banana plugs. Short profile would have been much better.

But, overall this was a fun project for both myson and myself, and he got to solder drill, and buld. That's what it is all about.



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[Anonymous]

The Potter-Brumfield breakers used in the "Breaker Box" are rated at 2-15 seconds trip time. I built a couple and ended up giving them to other O-gaugers so I could return to using a fuse block with fast-acting fuses. Scott's Odd 'n Ends sells a 4 position fuse block or you can pick old autolite fuse blocks by the handfull at many flea markets.

On a pw ZW a 4-position block is handy for protecting binding posts A,B,C&D. The maxium output of the pw ZW is 180-90 watts{nominally 10 amps] so if ,for example, you were using only one throttle for railpower in a single power district a 10 amp fast-acting fuse would be appropriate. If using multiple throttles rate your fuse on each throttle according to the expected load on that track,oval or power district [the engine motors + lighted cars,etc.].

[dbaker48]

THREE WEEKS LATER........

After all the input, got a little confused regarding the tranzorb. (Certainly didn't feel comfortable inserting a device internally to the engine/tender and pc boards.) So I put together the circuit breaker box. (Simple 4 channel 10amp junction box using banana plugs)

Now a little confused....

This box required 10 amp circuit breakers. Seems like a awful lot? But built it as defined anyway. Upon completiion wanted to test the box. Connected it to a LW xformer and set the voltage up to 17 volts. Shorted the ouput coming off the circuit breaker box, and the circuit breaker IN the transformer opened, NOT the on in the circuit breaker box.

Is this due to the fact I was using the LW as oppossed to the ZW for the test? (Lower power rating?) And the LW is a smaller transformer?

[dbaker48]

I just want to thank everyone for the comments, I am continuing to monitor and will advise of my success once I have it installed

Don

[lionelsoni]

The circuit breaker or fuse (you don't need both) goes in series with the transformer. The TVS goes in parallel with the load. So
Transformer---circuit breaker or fuse---TVS---track---locomotive---locomotive circuits
or, if you want,
Transformer---circuit breaker or fuse---track---locomotive---TVS---locomotive circuits

[cheech]

As a practical matter, what is the order in which you connect this protection?

Is the order......Transformer ==>circuit breaker==>fuse===>Diode===>track connection

or is there a different sequence for connection.

Is soldering the only way to connect this protection?

[lionelsoni]

Notice that the MTH site is recommending this protection for their TIU unit, not for the locomotive specifically. There are actually two things to protect here: everything between the transformer and the locomotive against overcurrent, and the locomotive itself against overvoltage. I recommend circuit breakers or fuses for the first purpose and TVSs for the second (for modern locomotives with delicate electronics).

[jefelectric]

MTH recomends a 15 A fuse on their site.

Go to this link and click on the first item for details.

http://www.protosound2.com/

John F

[Anonymous]

As I mentioned on a previous post:

The part number is 1.5KE36CA or 1v5KE36CA. This is a bidirectional transient voltage suppressor and is good for clamping voltage spikes. This particular diode has a minimum breakdown voltage of 34.2V (corresponds to 24V rms AC) and a maximum clamping voltage of 50V at 30A. This is a good choice for most transformers (up to 23V output). If you are using a fixed 18V brick, you could use a 1.5KE33CA. Likewise, if your transformer can exceed 23V output, you should use a 1.5KE39CA for up to 25V .

The body of the diode is about 0.2" diameter by 0.375" long.

The parts are available from:
http://www.alliedelec.com/
http://www.digikey.com/
http://www.mouser.com/
http://www.newark.com/
Currently, Allied has the best price on the 1.5KE36CA ($0.43 in quantities of 25).

Daniel Lang

[Big_Boy_4005]

Thanks Bob, next question is which one or ones would be appropriate for this task? I'm not very good at understanding those data sheets. I didn't see a diagram of the device showing its size. Do you think Digi-Key carries them or a similar device?

[lionelsoni]

It's a transient voltage suppressor (TVS). It simply conducts above its rated voltage--no capacitors. Transzorb is the brand made by Vishay:

http://www.vishay.com/diodes/protection-tvs-esd/trans-zorb/

[Big_Boy_4005]

QUOTE: Originally posted by lionelsoni

Let me quibble with you a little, Elliot.

The ZW breaker protects the transformer, but only partially. There is no protection for fault currents between output terminals. It also can protect the wires if they are heavy enough to carry the 15 amperes that the ZW's circuit breaker is supposed to trip at, that is 14AWG, but again only partially, with no protection for faults between terminals.

When a short circuit develops, it is almost always at the track, upstream of the locomotive. So there is not much chance that a breaker in the locomotive would ever see a fault current. It's likely that a locomotive will be damaged not by overcurrent but by overvoltage that is a side effect of overcurrent drawn outside the locomotive, that is a short circuit probably caused by a derailment. So the locomotive would be a good place to put, not overcurrent protection, but overvoltage protection--like a transzorb.

No problem with the quibbling Bob, you're the one with the formal education.[;)]

So what exactly is this transzorb? My guess is that it involves a capacitor, and some other electronic components. It would need to be placed between the roller and the board, inside the loco. Anything would be better than throwing away $150 each time you have a major derailment.

I would love lose "my fear of frying".[swg]

[dbaker48]

Thank you for all the responses, I already ordered the dvd, and doing additional research on these transzorb things. Makes sense to me. Thanks a group !!!
[:D]

[lionelsoni]

Let me quibble with you a little, Elliot.

The ZW breaker protects the transformer, but only partially. There is no protection for fault currents between output terminals. It also can protect the wires if they are heavy enough to carry the 15 amperes that the ZW's circuit breaker is supposed to trip at, that is 14AWG, but again only partially, with no protection for faults between terminals.

When a short circuit develops, it is almost always at the track, upstream of the locomotive. So there is not much chance that a breaker in the locomotive would ever see a fault current. It's likely that a locomotive will be damaged not by overcurrent but by overvoltage that is a side effect of overcurrent drawn outside the locomotive, that is a short circuit probably caused by a derailment. So the locomotive would be a good place to put, not overcurrent protection, but overvoltage protection--like a transzorb.

[Big_Boy_4005]

I've actually considered putting self resetting overload protection in the locomotives themselves. Any other location for overload protection may not save the electronics. I have a 6 amp limit to the rails, and I still managed to fry one of my favorite engines.

In the case of the ZW, it's breaker protects the transformer itself. Breakers placed between the supply and the rails protect the wires, but nothing necessarily protects the locomotives.

[wrmcclellan]

The 10 ampere breakers from Scott's are excellent. They trip when you expect them to.

[spankybird]

If you are looking to circuit breakers between your transformer and track try Scotts Odds-n-ends at

http://www.scottsodds-n-ends.com/circuit_breakers.htm

[lionelsoni]

When you consider that a short circuit results in zero track voltage, it is hard to see why a fuse or circuit breaker would have anything to do with protecting a locomotive, rather than the transformer. However, it is likely that a short circuit will begin with numerous and rapid repeated shortings and openings across the track. The stray inductance of the transformer secondary would be likely during that time to put out spikes much higher than the normal voltage, which could then damage the electronics in modern locomotives. (Traditional locomotives are pretty much bulletproof.)

A fast-acting fuse or circuit breaker can help by opening the circuit before the fatal spike occurs; but it would be more direct to use a transient suppressor, like a TransZorb, to eliminate all the spikes entirely. For a ZW, this should be rated a little above the normal peak voltage of 30.

This is not to say that you shouldn't add fuses or circuit breakers. Do put them in series with the A, B, C, and D outputs. The built-in 15-ampere circuit breaker is in series with the U terminal. This leaves the transformer completely unprotected when any of the outputs are connected together, particularly when using the ill-advised but popular practice of running from a block powered by one control to a block powered by another. I like automatically-resetting automotive circuit breakers for this purpose. They are small, easy to find, electrically appropriate, and cheap.

[ChiefEagles]

Go to this site. http://ogaugerr.com/ Scroll down and see 11 Great Backshop videos. Click on it. Order Number 8. Build you a fast acting circuit breaker box. I did and it is easy. If you have a short [mainly derailments], it will trip. Clear the short, reset it and keeep on training.

[willpick]

If you have a Postwar ZW, a fuse is a must have to at least attempt protecting the electronics in your modern engines.The circuit breaker on the ZW can take up to 15 seconds to trip(and that's brand new!). I would reccomend using 32V 10 amp "fast blow"fuses or you can use the auto blade fuses. For accessories, a 5 A max would be my choice. The fuse should be attached to the A,B,C,D terminals.
HTH1

[dbaker48]

I've read various comments regarding installling a fuse on the ZW, especially when using TMCC. I asked our local train shop and the owner said it was not necessary. However, I don't ever know of a situation where a fuse/ckt brkr created a problem. Pretty cheap insurance! Can anyone give me an idea of what rating is should use, and is it best placed on the U or common connection or should one be placed on each A, B, C, D terminals.

Thanks for any information ![:)]