TVS Diodes: Sources

You could also get a better price by buying this one at Digikey, 44 cents quantity 10.

1.5KE39CA-TPMSCT-ND

I like both Mouser and Digikey.  Digikey is great for small orders as they will ship First Class for a couple of bucks, Mouser's shipping starts at around $6.

John,

I'm definitely considering putting these on my Legacy engines. Where do I want to place them?

Picture/diagram would be helpful if possible.

How do you use these?

You wire them directly across the locomotive pickups, center rail pickup to frame ground.  For steamers, you'll likely want one in the tender as well, since they have their own power pickup for most Legacy stuff.

You can also wire them across the track output terminals of your transformer, although doing as John recommends probably affords more protection.  I do the former because my locos have no fancy electronics, just electronic reverse units.

Pete

Pete,

Could they also be wired at the track lock-ons.

George

You can wire them between any Hot and Common. You can wire them between the center and outer rail for example.

The reason for putting them in the actual rolling equipment is when the derailment, or other transient happens, it's the best protection.  Take the instance where the train derails and arcs, as the short is removed during the derailment, the TVS that is across the track or transformer no longer protects the locomotive electronics from transients generated as the connection opens.  That's the reason for the TVS inside the actual equipment.

The more I read about these TVS diodes the more I think...Why not just slow the train down?

I rarely run more than 30 smph and have had only a few derailments, mostly all caused by not throwing a switch.

My second thought is...Why doesn't the manufacturer put them in each engine?  Wouldn't that save them some headaches as well?

Other possible reasons for putting a TVS diode inside the locomotive or tender or whatever (in addition to the one (s) on the transformer, lockons or track) are:

1. To to protect the spike-sensitive electronics from static electricity generated by handling, repairing, storing for the "next season," etc. How many of you wear a ground strap when working on your electronic train components?

How many use things like non-static bubble wrap * or make sure to discharge any static electricity before touching your equipment after walking across a carpet, especially under conditions of very low humidity?

2. How many run your equipment on other people's layouts? Are these alternate  venues protected against spikes?

How many of you have put a perfectly-working component away for storage only to find it dead when you next tried it? What might cause this?

* For example: http://www.uline.com/cls_21/Anti-Static

wolverine

John, your suggested TVS has somewhat different specs than mine. Could that make any difference?

wolverine

The differences are insignificant for the most part.  They're both 1500 watt parts, I actually prefer the 33/36 volt parts, but either will work just fine for this application.  The spikes we're trying to kill are a lot more than the clamping voltages on either of these parts.