Recommended Protection for Post War KW/ZW Transformers

Here is the diagram to connect the 5906 whistle & bell buttons for the ZW & KW. Omit the whistle button for Bell only.

With regard to "protection", you want to keep your electronics from being hit by high voltage spikes by clamping them with strategically placed bidirectional  TVS diodes. This is highly recommended for all new and old transformers regardless of their circuit over-current protection built in as the transients occur even in the absence of a breaker-tripping short circuit. There has been a lot of coverage on this HERE.

Here are some relevant threads:

https://ogrforum.com/...al-mechanisms?page=1

https://ogrforum.com/...8#177257758429315528

This one specifically addresses the use of postwar transformers such as your KW and ZW - https://ogrforum.com/...3#177257758380982153

Lots of others.  Search for "circuit breaker" and TVS.

Fast-acting circuit breakers can be found very inexpensively (under $10) - insert it inline between the transformer and track.  TVS diodes are really inexpensive (under $1 in quantity) - can be placed across the lockon connection.  For maximum protection, they can be added to each engine - minimal cost, but a bit of work.

I tried using these bell buttons on my postwar KW and ZW and they worked, ONCE I rewired them to put all track power through them.  I have track power going to my turnouts and they act like a source of track power.   I had the bell button wired just like the diagram and it would not work until I rewired to get all track power through it.  Just FYI if you have such a layout.

I believe Rob led me to that fix.  Thanks again.

Bob

Thanks guys for the replies.  I am not being lazy just confused, had looked at those threads, but was hoping for a recommendation for a specific fast acting curcuit breaker and diode to use.  Breaker on all feeds (U,A,B) correct?  Diode polarity when installing across U/A?  I am confused, that's why I asked for a diagram.  Really am hoping for a "simple" answer.

The circuit breaker rating will need to be selected by you, the bidirectional TVS diodes do not have polarity but should be in the 33-36 volt range. Here is a sample basic TVS/breaker diagram for ZW or KW A-U... repeat for the other throttles as needed.

@MainLine Steam posted:

Thanks guys for the replies.  I am not being lazy just confused, had looked at those threads, but was hoping for a recommendation for a specific fast acting curcuit breaker and diode to use.  Breaker on all feeds (U,A,B) correct?  Diode polarity when installing across U/A?  I am confused, that's why I asked for a diagram.  Really am hoping for a "simple" answer.

#1 TVS while called diodes, are specifically bi-directional used in this case, and thus not polarized- so no, there is no direction. It's this simple of a concept. A TVS diode in the way we use it, measures the voltage, and anything over the trip voltage, it shorts out- preventing the voltage spike from traveling into something else and damaging it.

So, a TVS goes in PARALLEL to any output or load you are trying to protect. U-A, U-B, U-C, U-D.

#2 From @SteveH, who made this super easy concept drawing for one channel. The breaker goes in series, to the track, BEFORE the TVS.

https://ogrforum.com/...1#157829273661640961

Again, here is the sound logic and reasoning:

#1 your transformer is the power source. In and of itself it is not generating spikes or other problems. It simply makes voltage and has current capacity. One note- in  the ZW- U is common across all 4 U terminals.

#2 You put circuit breakers or fuses in series with the output "hots" (A, B, C, D) as close to the transformer since it is the current source. This protects the wiring and everything downstream from shorts. Again, the transformer is treated like an unlimited (for the purpose of discussion) source of current. We put individual breakers on the output of each output "hot" terminal (A,B,C,D).

#3 TVS diodes are specifically chosen to be bi-directional types when used with AC, so they are not directional when installing. They simply go across or "parallel" to the load. We put them after the fuse or breaker- because they can fail and cause a short. So, we protect  the wiring and everything again, by putting the breaker closest to the transformer, BEFORE the TVS or load.

Thanks @ADCX Rob, I often try to reference that nice drawing that I think @CAPPilot posted in the forum in one of these discussions.

Just trying to give credit to all the folks who contributed and we keep using their work over and over because it was very good info.

Again, top notch info in this topic!!

A company called Ott Machine Services used to make a nice Sound Controller that had two heavy-duty pushbuttons for whistle and bell respectively, as well as a fast-acting resettable circuit breaker.  They came in 8-amp- and 10-amp versions.

The whistle and bell circuitry was better than the ones in Lionel transformers, because it didn't cause the loco to slow down or speed up appreciably when the buttons were pushed.  You would need TWO of these Ott sound controllers, one for each side of your KW.  They are no longer made, but can sometimes be found at train shows or online auctions for reasonable prices.

The OMS sound controllers don't provide any Transient Voltage suppression (TVS).  For that you'll have to add the diodes as shown in ^^Rob's graphic, above.

Thank you VERY MUCH to all, for the clarifications, I understand now.  Maybe it is just me, but in reading through all the links "I couldn't see the forest for all the trees."

I am going to search for those Ott Sound controllers.  I actually was wondering why no such device existed.  What is the best way to determine the current rating I need?  Should I run my largest passenger consist, then see how much current it draws and multiple by some specific factor? (to avoid random tripping)

If I can't find the Ott, is there a specific fast acting breaker that you guys would recommended? Do you consider the Airpax the best?

The buttons should go after the circuit breaker but before the TVS correct?

One last question, when you push the whistle or bell button what actually happens (electrically).  Please don't tell me it's magic, that's what I will tell the grandkids.  LOL

Thanks again!

@Vernon Barry posted:

#1 TVS while called diodes, are specifically bi-directional used in this case, and thus not polarized- so no, there is no direction. It's this simple of a concept. A TVS diode in the way we use it, measures the voltage, and anything over the trip voltage, it shorts out- preventing the voltage spike from traveling into something else and damaging it.

So, a TVS goes in PARALLEL to any output or load you are trying to protect. U-A, U-B, U-C, U-D.

#2 From @SteveH, who made this super easy concept drawing for one channel. The breaker goes in series, to the track, BEFORE the TVS.

https://ogrforum.com/...1#157829273661640961

Again, here is the sound logic and reasoning:

#1 your transformer is the power source. In and of itself it is not generating spikes or other problems. It simply makes voltage and has current capacity. One note- in  the ZW- U is common across all 4 U terminals.

#2 You put circuit breakers or fuses in series with the output "hots" (A, B, C, D) as close to the transformer since it is the current source. This protects the wiring and everything downstream from shorts. Again, the transformer is treated like an unlimited (for the purpose of discussion) source of current. We put individual breakers on the output of each output "hot" terminal (A,B,C,D).

#3 TVS diodes are specifically chosen to be bi-directional types when used with AC, so they are not directional when installing. They simply go across or "parallel" to the load. We put them after the fuse or breaker- because they can fail and cause a short. So, we protect  the wiring and everything again, by putting the breaker closest to the transformer, BEFORE the TVS or load.

The TVS on the far side of the layout, how should they be spaced, or are they only at each Power Feed point on Larger Layouts?  Thanks.

Most of this is over my head, so pass the grain of salt on my comments. I bought fast breakers based on this forum's advice and have bypassed them with jumpers, because no trains ran. Steam loco drivers, lighted cabooses, etc. tripped them at switches and crossings.

I am in process of installing TVS diodes, but something that didn't jump out to me on this thread is that people say it's better to have them close to the boards they are protecting. So better in the tender with the boards than in the loco, better in the loco than at the transformer.

@MainLine Steam posted:

..when you push the whistle or bell button what actually happens (electrically)...

Through a simple diode array, wired for horn/whistle the 5906 puts a +DC bias on the rails(center rail positive), wired for bell puts -DC to the rails(center rail negative).

@ADCX Rob posted:

Through a simple diode array, wired for horn/whistle the 5906 puts a +DC bias on the rails(center rail positive), wired for bell puts -DC to the rails(center rail negative).

Thanks Rob - Simple enough.  The weird results I get with the whistle lever on the KW is probably because it isn't sending the proper "jump", often the train speeds up and/or doesn't tigger the horn.

@Ken Wing posted:

Most of this is over my head, so pass the grain of salt on my comments. I bought fast breakers based on this forum's advice and have bypassed them with jumpers, because no trains ran. Steam loco drivers, lighted cabooses, etc. tripped them at switches and crossings.

I am in process of installing TVS diodes, but something that didn't jump out to me on this thread is that people say it's better to have them close to the boards they are protecting. So better in the tender with the boards than in the loco, better in the loco than at the transformer.

Comment noted, thank you.

I bought a refurbished KW at a train show and the diode was installed backward. The "whistle" is now a bell control. For older locos with whistling tenders and no bell, it does nothing.  On this forum, I was told the vendor who sells the replacement diode provides instructions to install it backward so it does not work the whistle.

@Ken Wing posted:

I bought a refurbished KW at a train show and the diode was installed backward. The "whistle" is now a bell control.

This is because the installer followed the schematic from Lionel which shows the wrong polarity. It really didn't matter until 1972 when the electronic whistle was released(& somewhat later with the bell function introduction), but now it's a problem if the installer does not know about this error. They should have tested it before buttoning up with a modern piece of equipment which would have been revealing.

@Ken Wing posted:

Most of this is over my head, so pass the grain of salt on my comments. I bought fast breakers based on this forum's advice and have bypassed them with jumpers, because no trains ran. Steam loco drivers, lighted cabooses, etc. tripped them at switches and crossings.

This is a limitation of the "external breaker" movement & why I have always said TVS mandatory, breakers optional(they can be convenient).

But imagine those folks who went with fuses instead - "sorry kids, no trains today, Poppy is out of fuses"!

@Ken Wing posted:

I am in process of installing TVS diodes, but something that didn't jump out to me on this thread is that people say it's better to have them close to the boards they are protecting. So better in the tender with the boards than in the loco, better in the loco than at the transformer.

Anywhere is better than none, but it would be ideal to have them as close as possible to the components to be protected. On-board would be great, then you don't have to worry about running trains on your Christmas layout or a friend's or club's layout. They are certainly inexpensive enough.