Lionel TW and DCS

According to http://www.tandem-associates.c..._tw_transformer.htm, the Lionel TW Transformer was produced from 1953 until 1960.  I would not trust the internal breaker of a transfomrer from that era.  Do note that that transformer has separate seconday windings for train controls and fized voltage outputs, meaning a single breaker couldn't handle all outputs. I would strongly recommend using external breakers/fuses on all the outputs.  Sorry, I can't recommend a size since I don't know how the 175-watt output rating was calculated--on a per secondary basis or on an aggregate.

Back in October, Barry had recommended a 10-amp.  Given that maximum output of a TW is 25 volts (per picture at above URL), I'd be reluctant to go above 7 amps for continuous use

Thanks!

I got curious about the innards of a TW, wondering just how it was set up, having 2 secondary windings.  In mucking around the internet, I came across:

1. If anyone out there in OPGRforumland wants to learn how transformers work, here's a good, albeit overdeatiled,  description:  http://css.wsu.edu/people/facu...330/Transformers.pdf

2. A schematic for the TW can be found at http://pictures.olsenstoy.com/...ansfmr%5Cpstw54a.pdf.

Studying the latter, I find several combinations of posts for which the internal breakers provide absolutely no protection.  For example:  D-F (12 volts), A-E (12 volts), C-U (24 volts).  Also, note that the A terminal, not U, appears to be the common that would be tied to the U of a ZW or Z4000 and the outside rail.  Based on this, I'd put a fuse on avery output terminal I used.

Do you know if a fuse rated at 10 amps and 250 volts would work?

In my opinion, 10 amps is too large.  I'd max at 7.

My practice is to take the max voltage a transformer can produce, divide by the wattage rating (amps time volts equal watts) and that gives the maximum amperage that is safe in the wire gauge with which the secondary is wound.  You don't want more than that amperage flowing in any portion of the coil; in other words, if you have a 175 watt transformer capable of 25 volts, that's 7 amps.  If you pull 14 amps with output set at 12.5 volts, you're only pulling 175 watts, but through a portion of the coil you're running 14 amps.  Another factor is that Lionel, in its early 1950's "Model Railroading" Bantam book, recommended not continuously .drawing more than 75% of the wattage rating.

The voltage rating of a fuse is not an issue, so long as you don't exceed its rated voltage.  Notwithstanding what some people say, a 10 amp fuse nominally* blows at 10 amps, regardless of whether it's rated 32 volts or 250 volts.  (*I say nominally because if you look at the fuse blow time charts, slight overloads take a long time to cause a fuse to blow.)

So would you think one 5 amp fuse would do the job for the variable channel (which I'd leave set at 18 volts) and the 14 v channel (with one fuse each)?

Do you know if a fuse rated at 10 amps and 250 volts would work?

If it's a fast-blow fuse it should be fine as long as it's wired in the Hot wire between the transformer output and the TIU's channel input.

Doug, Fuses are fine for accessory circuits where shorts are (hopewfully) rare.  But over time, using fuses for tracks is too expensive compared to breakers, since derailments are frequent.  5 amp will run 2 MTH locos easily.  Although I have much larger transformers (275-watt postwar ZWs & a Z4000), I use 5-amp breakers on tracks because I want them to blow fast on a derailment and I do not use smoke.  I can run 3 freight trains without it opening.

10-amps is adequate to protect a TIU, but I think it would not adequately protect your TW & your house.