Transformer damage from whistle diode???

@dogdoc after reading many threads on the subject and asking questions here on the forum, I recently purchased 4x NTE 5991 diodes to replace the original silicon rectifier discs in my two ZWs.

After reading this post, I've searched unsuccessfully trying to find any information about these replacement rectifiers damaging the whistle switch contacts.

I'm very interested in the answer to your question. In the meanwhile, would you please post any links you may have found that discuss this issue?

It is true. I have replaced the original rectifier discs with a diode and if you watch the action with the cover off, you will see a fairly large spark when the contact is broken. This will eventually eat away the contact. The new replacement repo disc's don't have the spark problem.  I know there will be nay sayers, but this has been my experience.

@Chuck Sartor Thank you for the report.  Are you referring to a new replacement disc like this one Lionel 1041-13C Copper Transformer Rectifier Disc or something else?

No, not the original copper oxide one, but the Aluminum oxide repo's now available. They have a solid coating on the front and work better than the original discs. I get mine from Train Tender.

Like this one on ebay?  It looks like aluminum but it's not identified as such.

Also, do these require the fiber spacer to be installed underneath?

Yes, those are the preferred replacements. They won't pit the control contacts. Yes you still need to use the original mounting hardware.

Thank you very much for the advice Chuck!  I think I'll get in touch with Jeff at Train Tender about these.  I appreciate the recommendations.

I will check it out with the case off the transformer but even with the spark is the destruction to the contacts enough to cause problems? With all the diodes out there for many years, you would think there would be reports of actual damage resulting in failure if significant?

I too can echo @Chuck Sartor's observations with the diodes that I install, and those that know me know that I'm pretty true to factory in my work and so I do still install the rectifier discs quite a bit of the time as well. However, I don't think diodes are imminently destroying our transformers any faster than sparks on our pickup rollers, within our mechanical switch machines (O22), or everywhere else traditional operators accept them. I think it boils down to one of those things where in theory, sure, microscopic damage is being done, but in reality, it is insignificant overall and can be minimized with use of CRC 2-26 or 846 Carbon infused Silicone grease.

No question in my experience, the diodes work better. I think I will worry about something else since in the real world they do not result in failure and performance is improved. Classic academic issue

The selenium rectifiers had quite a bit of resistance in series with the diode action. The copper ones, I don't know about, but the silicon diodes don't. The resistance limits the current for an arc.

Has anyone tried installing a TVS across the contacts?

@gunrunnerjohn posted:

Has anyone tried installing a TVS across the contacts?

I easily could use a 1.5KE36CA for an experiment today as this has me intrigued, but I'd like to understand your thinking -  Which contacts in particular were you thinking, and why a TVS and not say a resistor to make up for the silicon disparity?

Not sure where you're installing the resistor, but putting it across the contact would provide a leakage current, that probably wouldn't be good.

Everyone is entitled to what they prefer. But the large arc when the contacts are broken can't be good for the electronics in our engines if you run conventional.  Use what you like.

@gunrunnerjohn posted:

Not sure where you're installing the resistor, but putting it across the contact would provide a leakage current, that probably wouldn't be good.

I was thinking a resistor in series with the diode to make up for the lack of resistance in the silicon diode (when compared to the original disc, or would this actually increase arcing due to more load?). But I did not mean for my resistor comment to overshadow the clarifying ask with regards to TVS theory and placement within the whistle control circuitry.

@gunrunnerjohn

Is something like this what you have in mind for adding a TVS diode?

A resister in series would be easy to do just Have to experiment with the rating. Interesting idea.

@SteveH posted:

@gunrunnerjohn

Is something like this what you have in mind for adding a TVS diode?

Yep, and maybe even a low value resistor in series with it, say 10-15 ohms.   I'd probably experiment if it were me, but I don't really do conventional other than testing repairs, so it's never been a big issue for me.

Maybe Gunrunner could do a test for us with his oscilloscope and check a transformer with a stock or replacement disc and then check one with a temporary silicone diode in place and see if there is a significant voltage spike to the track?

@Chuck Sartor, while TVS diodes usually are recommended and used across track power for transient protections (and I support that use), I see this as a completely separate discussion here specifically around reducing the arcing in the switch contacts.

I did the experiment of adding a TVS as @gunrunnerjohn proposed and @SteveH clarified and saw no improvement with the sparking at the whistle switch.

@bmoran4 posted:

I did the experiment of adding a TVS as @gunrunnerjohn proposed and @SteveH clarified and saw no improvement with the sparking at the whistle switch.

Thanks, I was curious if that would have an effect, I guess not.   I really don't have a dog in this fight as I don't use the whistle switch on transformers, I can't even find it on mine!

@gunrunnerjohn I see that you had a busy day yesterday entertaining (nice video!)

With all you had going on, maybe you missed these questions above.  Your opinions would be welcome.

Well, my resistor idea was just an experiment to see if that in conjunction with the TVS might make a difference in the arcing.  Typically, an RC network is employed to minimize contact arcing.  Tons of information about contact arcing, no need to reinvent the wheel.

Inductive Load Arc Suppression.pdf

Prevent Relay Arcing using RC Snubber Circuits

How to Reduce EMI, Voltage Spiking and Arcing

John thanks for this information.  I was wondering about an RC circuit for this purpose and why no one mentioned it before now, but not being an EE, this is a bit outside my comfort zone of making recommendations.  I was also concerned about the possibility of inadvertently introducing a potential oscillator and/or unintended currents from the RC network.

Do you have any specific RC recommendations for this application that wouldn't potentially lead to other issues, or would it be better to just leave well enough alone?

The solutions are obviously somewhat dependent on the exact scenario.  For the contact arcing in the transformer, I'd consider starting with fairly low value resistors in the 5 to 20 ohm range and .1 or larger caps with a fairly high voltage rating, 400 volts or more.  It'll probably take some tinkering to come up with the right values.

It seems like no one has actually observed any real damage or malfunction from the diodes in the transformer which was my original concern.? I see the arcing but it seems like it does not happen all the time when look activate the whistle with the cover off. How long has this mod been done 20 plus years?

Update on some testing I did on this matter of whistle contact damage from use of a diode to replace original rectifier disk in a zw transformer(as was done on one of my zw). Initially with dry contacts I could see an arc when the whistle contact was released( disengaged ). I purchased some carbon black conductive grease as recommended and applied it to the contact surfaces in the whistle activation mechanism. NO VISIBLE ARC AFTER CONDUCTIVE GREASE APPLIED!! So while any concern was like minimal to begin with, it is even less now. Considering that likely hundreds of transformers have been so modified, this is a simple solution compared to TVS and resistors . The carbon grease is nasty stuff if you get it on you. I applied with a tooth pick as it will get everywhere if not careful and it is a ***** to wash off. Gloves are not a bad idea. Fabulous whistle control and sound with no slowing of train!

@dogdoc thank you for updating us on your testing results.  I'm glad to hear the 846 Carbon infused Silicone grease recommended by @bmoran4 is working well.