Variac and filtered DC control

If you place the Variac ahead of the stepdown, you can use a much smaller Variac.  I would have to look, but I think mine are around two amps, but when stepped down the output is more like ten amps.  Keeps the size down and maybe the cost.

I agree on the Pi filter, but your motors have a reactive component, so just a giant can gives you an L-filter, and ripple is minimal, so you still have the smoothness.  But plenty of room for extra filtration.

I shall endeavor to get a photo.  Bear in mind that I do know how to Leroy Letter a panel, but for these I just use a Sharpie.  I will post one of my aircraft panels to show you how nice it really could look.

Yes, I agree the Variac can be much smaller.  I used what I could find.

Average locomotive uses 12-18 VA (W). A Variac with as little 1 amp 132 V rating can supply 132 VA (W).

Did not know really consider that the motor can be a filtering reactor, but that makes sense. Thanks for the insight, bob2.

Rob

Darned if I can find the latest photos of my beautiful aircraft radio panels, but here are my ugly ancient train power packs.  The first photo is of spare parts - a variac, and a rheostat (potentiometer).  I wonder if I should capitalize those; they are proprietary names.  The Rheostat actually says O Gauge Universal Motors 10 Ohms 3.3 Amp.  The face says "Speed".

I think you can read what the Variac is.  I wonder if anybody has simply used a light dimmer in front of a step-down transformer - might be a lot cheaper.

The photo insert process re-arranged the order - top is my  portable trouble-shooting pack, and the bottom controls my four test loops.  Both have seen lots of wear and tear over three decades.  Parts are for a fourth, should I ever need one.

@bob2 posted:

I wonder if anybody has simply used a light dimmer in front of a step-down transformer - might be a lot cheaper.

Bob,

Very nice old school solutions.  To use a more recent phrase I like the "Look and Feel".

Regarding dimmer for control, common light dimmers are only intended for resistive loads.  A step-down transformer is an inductive load.

You would need a dimmer that can handle inductive loads.  They are available but are not necessarily lower cost items.

Mike

Best to use a pure sine wave into another transformer. Dimmers put out chopped AC with sharp spikes that can overheat inductive loads. Also good advice to use the variac before the step down transformer. I am using a 1000 watt variac to feed a 500:watt transformer which, as wired, is rated for 25 amps. Wired the other way the limit would be ten amps. Two of these actually. One I use for my resistive soldering tools.

Pete

All who have replied so far, thank you.  I have learned a few things.

Rob

Just to make sure you know I can do better panels, here are two of my Cubs - lettered in my kitchen!  Older decals were done by Jim Wilhite - he really helped my hobby!

bob2,

Nice looking aircraft paneling.